okay so chapter 17 now next group of diseases is the nervous system so starting off with a little background the nervous system overall is broken down to two main parts the central nervous system and the peripheral nervous system the central nervous system basically entails the brain and the spinal cord or essentially anything in the very center of the body and then the peripheral nervous system is all the nerves going out from the brain and spinal cord going to like the limbs and other areas of the body so now let's look at some defenses so the biggest defenses that the nervous system has is all of it is encased in bones especially that central nervous system the brain and spinal cord are protected from most injuries i mean crushing injuries things like that of course things that would break bone it's not protected from but most injuries we try and encase those important parts of our body in those hard bony structures additionally we have this fluid known as cerebrospinal fluid inside those bones that kind of creates a little cushioning effect so you don't have your brain like smacking against the inside of your skull because that's a hard surface also so we kind of have that internal protection as well we also have a pathogen protection system known as the blood brain barrier and this is basically kind of a separation between the blood vessels and the brain itself that allows only very few things to actually get through or pass through to the brain so this stops things like viruses hopefully or bacteria from getting into the brain and causing damage it also stops some good things from entering like antibiotics and other drugs we do have some things that get through as well as some microbes that can get through but for the most part most things do not get into our nervous system we also have the meninges so these are several layers around the brain and spinal cord that are again going to add that extra layer of protection so the meninges overall there are going to be three different parts we have the dura mater the arachnoid mater and the pia mater and you can see those on the left hand side in those little brackets they go around the brain and then they move down the spinal cord so they're technically called cranial meninges when they're around the brain and spinal meninges when they're around the spinal cord but overall i would just call them meninges because they're the same structures so another thing that is good in some cases and bad for in others about the central nervous system the brain and the spinal cord is that it's considered immunologically privileged which means that it has a different type of immune response generally than the rest of our body so if bacteria or viruses do get in there's sometimes only a partial immune response or just a completely different immune response because normal immune responses like sorry heat um swelling things like that we don't want those around our brain or our spinal cord because then we're impinging on nerves and things like that and every once these things do happen and generally they're associated with the disease because it causes its own set of issues so generally the central nervous system is that immunologically privileged it has this different set of responses now microbes of course do sometimes get in we have all these defenses we have these immune responses but sometimes things happen sometimes you get in through skull or spinal fractures sometimes medical procedures that go into the brain or spinal cord or the nerves sometimes along the peripheral nerves where a microbe can enter a nerve somewhere else in the body that's less protected and then travel up the nerve to the spinal cord in the brain and then sometimes it gets in through that blood and lymph tissue even with that blood-brain barrier particularly viruses for this one they're small enough that sometimes they can get through that barrier regardless but again most things are kept out so the nervous system is one of those sterile environments in our body which means they do not have normal biota so when you do find microbes there it generally relates to some kind of disease some departure from health there are some viruses for example that can hide in the central nervous system in that dormant or latent state but they're not supposed to be there so they are not considered normal biota and examples of those would be herpes simplex virus that causes chickenpox hides and then later becomes shingles it hides in the nervous system in the meantime so now we're going to start getting into the diseases most of the diseases of the nervous system are going to fall into one of two categories there's some other ones as well but the two big categories are going to be some type of meningitis or some kind of encephalitis meningitis means you're going to have some kind of inflammation of those meninges that dura mater arachnoid mater and that pia mater and these we'll see are caused by lots of different microbes and they all generally have the same basic symptoms and for the most part you can treat those with antibiotics and then we'll get back to encephalitis later and that's where you can have actual inflammation of the brain so starting with bacterial meningitis so again this is a big category of meningitis it's caused by several different microbes we'll look at some specific ones here in a second overall symptoms are all going to be the same for this you'll have fever headache and a stiff neck to start with followed by nausea and vomiting you can also have photophobia which means like a sensitivity to light it can cause things like migraines and just kind of um nausea uh just general like sensitivity sorry you can also get this progressing far enough that it could start causing convulsions that photophobia could eventually lead to things like seizures and eventually coma virulence factors for these are generally the microbes that causes have capsules which hinders that phagocytosis so they're hard to get rid of once they're in and then a lot of them produce endo or exotoxins which are typically the parts that can cause those kind of worse symptoms the shock and death and convulsions coma things like that seventy percent of all the cases are going to be caused by three different bacteria but there are a couple other ones as well so now getting to the specific strains of meningitis starting with meningococcal meningitis this is caused again by bacteria we're starting with our bacterial category specifically by nyseria meningitidis this is a reservoir only in humans and it's transmitted mostly by respiratory droplets but sometimes also just close contact with secretions it's not a very contagious disease except in places where people are packed really tight together things like dorms things like army barracks places like that you'll start seeing outbreaks now and then there are lots of different strains for these i wouldn't worry about them the most common one is serotype b meningo mening meningococcal meningitis sorry in the united states but serotypes a b and c are kind of the overall majority of cases signs and symptoms again for the most part you have those same general symptoms for meningitis overall fever nausea stiff neck could eventually lead to convulsions coma things like that this one is kind of weird though because it's very sudden and it gets bad really really quickly typically starts with a throat infection that travels to the blood and then you get those kind of characteristic meningitis symptoms this one also have has one specific set of signs and symptoms that's pretty unique to meningitis it causes bleeding under the skin and this creates these pink rashes that eventually will turn like a dark purple when it gets to this point for this type of meningitis it's almost always a death sentence because it means it's traveled so far and is so prevalent that there's really not much you can do and at that point is where it's already traveled to the meninges and it's causing that swelling of those meninges around the brain what's interesting is that not all people actually get the disease we do have carriers that about 10 percent of people are healthy they carry the bacteria in their nose and throat reason region in that nasopharyngeal region so they have no symptoms but they can pass the disease luckily there is a vaccine for this mcv4 vaccine typically you get this about ages 11 or 12 and then you usually get a booster as you're like in the middle of high school kind of going through high school eventually into college if you go that route so this is showing that characteristic rash i was mentioning and you can see there's some areas that are pretty pink but most of them have turned that really dark purple shade now this is a very advanced stage it usually starts small and then starts spreading but again by the time it gets to this point it's pretty late in the game generally okay another type of bacterial meningitis is pneumococcal meningitis this is again caused by a bacterium this time streptococcus pneumoniae this is also the bacteria that causes most pneumonians which we'll talk about in the respiratory chapter again about 25 of patients that get this type of meningitis also get pneumonia on top of it it's pretty common with people that have some kind of underlying susceptibility they have some kind of weakened immune system for one reason or another the reservoir again is humans this is actually a normal microflora for a lot of people it's found normally in the nasopharynx region in the nose and the upper throat region not usually a ton but there generally are some of these bacteria already in the body transmission is solely respiratory droplets in this case and this is actually the most common form of meningitis in the us at this moment and so he said this is a common microflora for some people about 70 of people have this normally and they're considered those healthy carriers most common in children actually get this type of meningitis where the immune system is not kind of strong enough to keep that normal microflora at bay so typically between one month to four years old is where you really see this disease kind of take hold and then again in the elderly as well mortality rate unfortunately is pretty high it's about eight percent in children and then gets worse and worse twenty percent adults eighty percent in the elderly and that's just because again the immune system start breaking down again as you get older typically the 22 percent in adults those are again usually people that are some kind of immuno like susceptible reason they have some other disease they have some underlying cause something like that for prevention and treatment there are vaccines available one for kids and one for adults and then if you get the disease you can treat it with antibiotics but there are some cases of antibiotic resistance that we're seeing now but for the most part we're still treating this with antibiotics our next type of bacterial meningitis is hemophilia meningitis caused by haemophilus influenzae reservoir again humans respiratory droplets are again the transmission this type of meningitis is very very severe before the vaccine that was made in the late 80s it was a common cause of meningitis that led to death now because we have this vaccine there's less than 50 cases in the u.s a year and then our last type of bacterial meningitis is listeria meningitis caused by listeria monocytogenes this is found instead of mostly in humans as the reservoir it's primarily found in water and animals and then moves on as a secondary source or secondary reservoir into animals and plants and of course that includes humans as well transmission for this then is usually ingestion by some kind of contaminated product usually contaminated like dairy products poultry or meat so it usually gets into those animals first and then when humans ingest that secondary source that's when we get the bacteria but sometimes we get it straight from soil and water as well usually for like normal healthy adults this type of meningitis isn't a big deal typically fever diarrhea sore throat usually people just think kind of like a general cold or even flu symptoms overall but in the again people with weakened immune systems the very young the elderly and immunocompromised that's when it gets really bad and it causes those meninges to swell so much that it can sometimes result in septicemia with bacteria in the blood and 20 percent of cases at that point result in death and so this is just a little graph you don't need to know numbers or anything like that but just kind of showing the more common bacterial meningitis cases so again we see that meningococcal and the yellow there and then the pneumococcal those are the two most common with that hemophilia influenzae is the third most it's just kind of grouped in with some other ones as that as well we do have several unknown meningitis cases as well we know they're bacteria because we can get bacteria in the blood but it's sometimes hard to distinguish which type of microbe it is so they're just grouped all together as just some kind of bacterial meningitis so now moving on to another category of meningitis with fungal meningitis so these are going to be caused by two groups of fungi that we'll look at cryptococcus neoformings and then coccidio species um these are more commonly called valley fever so starting with cryptococcus neoformans so this one again has those pretty standard meningitis symptoms of headaches stiff neck nausea but these are generally a chronic form so they last a really long time in patients reservoir is mostly in bird populations and this is because uh it likes to grow in the feces of birds the fungus grows on their droppings and we see this a lot especially here in the us with like pigeons um just because there's a lot of them in urban areas so they kind of focus on those populations as far as how it gets into humans but essentially what happens is bird droppings have this fungus in them fungus starts growing on their droppings and then transmission is that dust starts blowing air starts picking up the dust from the feces from the fungus on those bird droppings and then humans inhale those fungal cells usually healthy people aren't affected by this specific type of meningitis but again people that are immunocompromised for whatever reasons um especially in like aids patients where the immune system is almost non-existent at that point this is almost always fatal and then our last fungal one is valley fever for the most people this is again a pretty mild disease with just some general respiratory symptoms most people generally think they just have a cold but in some people it causes decimated disease which is essentially a wasting disease so you get meningitis but then you also other parts of the body affected like osteomyelitis causes like a almost like a bone infection or bone breakdown and skin granulomas where your skin cells start clumping together as they grow transmission is still inhalation just like the last one where air gets picked up and moves the dust and the cell particles around and humans inhale them it's very common in southwest u.s about 60 of cases are in arizona specifically but that region is generally where we see valley fever another category for meningitis is viral meningitis we're not going to know any specific types of viral meningitis we're just going to lump them all together these are sometimes known as just aseptic meningitis because essentially what happens is we can't find any bacteria we can't find any fungal cells in the central nervous system so we're just assuming that it's viral meningitis sometimes of course that just means we didn't find those cells but most commonly it's viral meningitis most of these cases do occur in children about 90 percent of them are caused by enteroviruses generally viral meningitis is a much kind of weaker type of disease it's more mild than bacterial or fungal infections they usually resolve themselves within two weeks less than one percent of them end up in death so in most cases no treatment is actually needed a lot of times it's not even really considered meningitis because people don't even go to the doctor they just think oh my kid has like the flu or a cold or something and then the last category we'll look at with meningitis is neonatal meningitis this is always a result of infection that's transmitted by the mother in utero or during the birthing process so it can either cross the placenta or happen during the actual birth canal movement typically this is seen with premature babies because they have an already weakened immune system there are three causes that we'll look at streptococcus algalecte estricia coli more commonly just called e coli and then chronobacter starting with that escalator so this is again a bacterium this is the most common type of neonatal meningitis because it's commonly found in a lot of females genital tracts already about 10 to 30 percent of females already have this so during the birthing process it's fairly simple for that to kind of jump ship and go to the infant reservoir then of course is humans transmission is that direct contact during the birthing process generally for prevention treatment women that are seen as like a high risk they are known to have it or they have maybe had previous issues with things like that in prior deliveries they're given antibiotics through an iv if they find the bacterium so it's just kind of like a preventative thing for the infant then for e coli another another bacterial meningitis same reservoir and transmission here and same prevention treatment if we find it in the birthing canal we'll use that intravenous antibiotics and then the last type is that chronobacter this is still a bacterium but the reservoir transmission are different in this case reservoir now is environment transmission is usually ingestion of some kind of contaminated infant formula the bacterium gets into the powdered formula so prevention is making sure you're using fda approved formula if you you know are making your own things like that even if you're using fda approved formula make sure to keep things clean wash your hands when you're making the formula always use fresh formula for each feeding don't keep leftovers things like that cases of this are pretty rare because most people are using you know store-bought formula but unfortunately when it does happen mortality rates are pretty high about 40 percent of in death next we're going to look at zika this is caused by the zika virus mostly this is transmitted through mosquito bites but there are a couple other ways as well the two other most common are passing vertically from mother to fetus or mother to infant and then through sexual intercourse as well but again mosquito bites most common prevention unfortunately there is no vaccine for this yet um so for right now it's just avoiding mosquito bites in areas that have zika as an endemic illness where it's constantly around especially pregnant women symptoms vary significantly between adults and fetuses for adults it's really not terrible usually there are some that are pretty bad but it's more rare for adults to have the worse symptoms usually it's something like a skin rash conjunctivitis which remember is just an infection of the eye similar to pink eye muscle and joint pain or no symptoms at all sometimes it can also trigger julian barr syndrome which is a neurological condition where immune cells start attacking those peripheral nerves and the limbs causing pain and sometimes even paralysis for a short time usually those effects kind of resolve themselves but sometimes it can cause death because it can also attack the respiratory muscles which means you can't breathe which of course will lead to death and fetuses though it's always bad typically it causes microcephaly which means they have abnormally small heads which in itself doesn't seem like that bad of a thing except it typically alters then the brain the eyes and all the nerves coming out of the head as well so you have vision problems anywhere from just blurry vision to blindness involuntary muscle movements like seizures and tremors things like that and also nerve irritability where things hurt that normally wouldn't hurt a person next we have polio more commonly just called polio this is caused by the poliovirus reservoir is just in humans and transmission is typically ingestion of some kind of contaminated food or water sometimes fomites like touching something with your hands and then putting your hands near your mouth or your face and then also some mechanical vectors as well prevention and treatment vaccine right now is the only treatment but it is high or sorry only prevention but it is highly effective most countries are now polio free treatment unfortunately is really not much of a thing there's no curing the disease it's mostly just kind of an easing of pain and suffering at this point so this is just a nice image kind of showing how far we've come with polio so on the left you have um countries that had or did not have polio in 1988 the red ones have polio the white ones do not and then in 2014 is on the right there and you can see most countries have eliminated polio at this point there's still a couple out there that are dealing with it regularly but for the most part most countries are dealing with it like a couple of cases here and there for most infections of polio symptoms are actually short-term and pretty mild pretty non-specific symptoms of just general like aches and pains fever type things sore throat nausea headache fever things of that nature but in some cases the virus persists in the body and it eventually gets into the blood where it can then make its way into the central nervous system and start attacking nerve cells usually it attacks motor neurons which are the ones that control all of our muscle responses which means if we break down those motor neurons eventually it will cause paralysis this can also affect again the respiratory muscles similar to zika virus which causes breathing problems this then creates a need for mechanical respirators originally called ir iron lung but now we have ventilators and things like that so usually the iron lung isn't needed until it's like pretty dire but it's just kind of where we're at at the moment in children especially this attacking of the motor neurons can be especially damning because their muscles aren't strong enough yet to support their body and so if those muscles are weakened it's going to cause the bones that are still growing to eventually deform and so this is showing just some images here so on the far left we have those iron lungs so those are breathing machines this is a children's hospital in i believe berlin back in the day but i might be wrong in the country um but each one of those has a child in it and it's forcing their breathing muscles to breathe for them and then you can see uh the two images there on the right are showing some of those deformities it's very common in the legs because those are the ones that support most of the body weight but you can also have deformities in the back like you see in that bonded image there and then that very top right image that's actually the vaccine currently the most common form of vaccine is something that children can just swallow so it's really easy to administer for the moment which is part of the reason why it's worked so well in most countries so next we have meningoencephalitis which is going to be a combination of meningitis and encephalitis that we'll see here in a second this is caused by a protozoan specifically amoebas which remember is one type of protozoan specifically by two species nigleria fowlery and acanth amoeba both of these are found in in warm fresh water sources usually and then also in some humans they are common as normal biota in some people not all people but some people transmission of these is in accidental inoculation of the nasal passage so getting them into the nose for fowlery for acanthamoeba it's a little more a little more common because it has more modes of entry so it can get in through broken skin it can get in through the eyes and everyone smile can get into the urogenital tract although that one is much more rare prevention and treatment because this has found a lot of fresh water sources even in like tap water sometimes so it's important to make sure things like pools are kept clean especially here in the us it's very common when we see this disease it's from public pools that weren't maintained properly so keeping pools clean also making sure you don't ingest the contaminated water so try not to breathe in water i mean that's always the goal when you're swimming but things like that especially if you're not a good swimmer plug your nose if you need wear goggles especially don't open your eyes under water if you're not wearing goggles because both of them are very common typically you only get the disease if you have that accidental entry occur if you get it in through the nose or if you go swimming and you have like cuts on and then that acanthamoeba can get into the broken skin or you don't wear goggles things like that treatment unfortunately is almost always futile because the disease progresses very very quickly and it's usually too fast to be managed so almost all cases end in death symptoms for this we said is a combination of meningitis encephalitis so the amoebas regardless of which species we're looking at will make their way to the brain and basically cause this kind of rupturing or this just destruction of both the meninges and the brain tissue itself and this is called pam primary amiibo meningoencephalitis so it's just this rapid destruction of brain and spinal tissue eventually it will cause hemorrhaging in the brain and the spinal upper spinal cord which will lead to a coma and death usually within a week so again very serious so make sure you're going to clean pools not going in with cuts you know wearing your goggles don't breathe water i mean ideally again that's always the goal but things like that all right so now we're moving into groups of diseases known as encephalitis encephalitis itself is just inflammation of the brain so we're going to start with acute encephalitis acute encephalitis is always serious encephalitis in general is always serious anything involving your brain is pretty damning because your brain is very sensitive because it controls everything else and then on top of that remember we mentioned that the inflammatory process the immune system response can also be damaging so our body trying to stop these things once they start in the brain can also cause some of these symptoms but it's just because it's trying to get ahead of this disease and it ends up hurting us in the long run as well some pretty common symptoms you see with any kind of encephalitis are behavioral changes because again you're affecting the brain especially the frontal lobe is in in charge of like your personality and your judgment so if that's near the area of inflammation that's affected confusion decreased consciousness seizures all pretty common almost always these are caused by viruses that are carried by insects and so the common name for these is arboviruses some we'll see more examples but some examples are herpes virus and west nile virus you do have some bacterial causes of encephalitis but usually that's the meninges that are affected when you have bacteria and viruses get straight to the brain not always but usually so a little brief look at those arboviral encephalitis cases or those arbor viruses so again these are carried by some kind of insect or an arthropod examples are mosquitoes flies and fleas are the most common but you also have things like crabs bees spiders those are less common to be carriers though so all of these are vector transmission because remember you have some kind of insect carrying this most arthropods that are vectors are ones that feed on the blood of hosts so things like mosquitoes some of the flies things like that less likely to be a crab or a spider in that case or a b peak infection time generally is when those vectors then have high activity so it's usually late spring early fall but then because the reservoir is vertebrates like humans those viruses are maintained during the cold and dry seasons so it's not like they go away you're just less likely to be infected during those times so again some examples west nile virus the examples of the specific vertebrates for those are birds and then it's actually pretty common to have horses around here as well be those uh reservoirs along with humans of course when humans are infected they are almost always dead end hosts or accidental hosts for example with equine encephalitis those are meant to be reservoirs and horses but humans get bitten by a vector by accident and then the disease progresses sometimes though we do have some diseases like yellow fever that humans are a reservoir where the virus can get passed on so arbor viruses in general is a huge group of different diseases um that all have a huge impact as a whole on humans because millions of people are infected each year and thousands die from all of these diseases a pretty common outcome is at least you have a fast or an acute fever that comes on sometimes with a rash involved as well but transmission and epidemiology between the different vectors varies between which virus we're looking at symptoms on the other hand and management of the encephalitis cases are all very similar for all arbor viruses so the signs and symptoms again we have those overall effects of encephalitis on the previous slides but you can also have things like coma convulsion tremors eventually paralysis loss of coordination you can even have personality and speech changes heart defects memory deficits all of these as kind of those more severe symptoms of encephalitis treatment unfortunately there really is not one for most arbor viruses so prevention instead is the best best method to get ahead of these viruses get ahead of these diseases one way that we do that is trying to lower or eliminate the population vector for example mosquitoes carry a lot of these arbor viruses so we try and remove breeding sites for those mosquitoes like standing water is a common breeding site so think having things like stagnant ponds or bird baths that don't get cleaned or whatever pools that aren't cleaned properly you don't have moving water all of those who try and remove and sites that have those vectors also using things like insecticides to try and knock down those populations we do still have several reservoirs as other vertebrates as well humans and we mentioned like birds and horses as well but very rarely do we have the viruses jump from a reservoir to a human so we mostly focus on the vectors because they're the ones that kind of pass it from reservoir to reservoir and this is just showing some of those examples of those different arbor viral encephalitis cases like western and eastern equine st lewis encephalitis california west nile and it's showing the different reservoirs you don't need to know the mosquito vectors but this is mostly just showing you kind of like where these things affect us so here in illinois for example we're more affected by those bottom three and then kind of the states around us more often are the equine encephalitis all right we have two more types of acute encephalitis the first one being herpes simplex encephalitis this is caused by herpes simplex type 1 and type 2 which are just two strains of the herpes simplex virus both of these cause encephalitis in newborns when the mother is infected or has that hsv positive and unfortunately progno prognosis is pretty poor in these cases if a newborn gets it it's just kind of the end of it so they try and look out for the mothers to get ahead of it but older children and adults are also susceptible specifically from that herpes simplex type one typically though that's a reactivation of a virus that was already there rather than new infections it went dormant at some point or latent at some point and then it kind of pops back up and then our last acute encephalitis is the jc virus this is usually an asymptomatic infection and really only causes symptoms in those immunocompromised patients people with like aids or other underlying conditions when it does cause symptoms in those patients it causes progressive multifocal leukoencephalopathy or pml which is uncommon but almost always fatal again anything involving the brain and meaning the head is pretty damning now moving on to subacute encephalitis so this is the same as encephalitis it's just the difference between acute and subacute is that acute comes on faster so subacute kind of takes a little bit longer to show up and usually it's not as bad usually not always but usually not as bad as acute encephalitis we're just going to look at three causes the most common causes toxoplasma measles virus and prions so starting with toxoplasmosis which again is a type of subacute encephalitis this is caused by a protozoan microbe known as toxoplasma gondii this reservoir is in mammals mostly in cats especially here in the u.s but mostly in cats like house cats but also wild cats like bobcats cougars things like that transmission is inhalation ingestion or transplacental so it can pass from mother to fetus in the u.s though almost all cases involve inhalation or ingestion from litter boxes gross generally what happens is mammals are infected and then the parasite reproduces in the host's intestines and then released again in the feces and then it gets picked up by the next mammal and the process kind of starts all over most cases are asymptomatic for people or have very mild symptoms in fact about 95 percent of the world population is believed to have been infected at some point and were asymptomatic or had again very mild symptoms because we mostly have strong immune systems so at most you might have had sore throat swollen lymph nodes low grade fever something like that it's generally only cases where you have that weakened immune system that the symptoms are more severe and very severe causing that sub-acute encephalitis sometimes chronic encephalitis causing brain lesions disruption of heart and lung function and again usually death transmission for this there's several different ways we saw already um the most common is again going to be that inhalation so you could have ingestion from like raw or undercooked meat of whatever mammal was infected could have unhygienic handling of cat feces or inhalation of dust contaminated with infected cat droppings that that one is the most common in the us you could also have again the parasite crossing the placenta going from mother to fetus now this next part is mostly just interesting although humans get these um symptoms again not all humans most cases don't have symptoms but the ones that do they're pretty bad cases what we found is the most common reservoir other than humans cats are all asymptomatic they are not affected at all by this protozoan or this microbe and there's actually been research into how this gets passed from mammal to mammal because another pretty common reservoir for this microbe is mice and rats and so what they found is that this protozoa tends to make the infected host braver because what they would find is that the mice or the rats infected with this no longer showed fear for cats and so then the cats were eating infected hosts and then the cats were then infected themselves and then they were able to keep passing it and passing it and passing it and they've started doing research they haven't found anything solid yet but they are now doing research on humans because again they assume that most of the world has been infected at some point and they're noticing that people that are infected are more likely to display thrill seeking behaviors and especially nowadays it seems like more people are doing things like you know bungee jumping and skydiving and you know diving in a shark tank which no way not doing it yep i said it no um but doing all these like you know thrill-seeking behaviors and they're also noticing that some people have slower reaction times now that's more with um other other mammals that have been affected they haven't seen that as much in humans but especially the thrill-seeking behavior thing they're thinking that this might be linked to this toxoplasmosis so that's kind of cool another one of those causes of subacute encephalitis is the measles virus when this occurs when measles virus causes subacute encephalitis it's known as sub-acute sclerosing pan encephalitis this is sometimes called a slow virus infection because generally the symptoms appear years after that very first measles episode that very first inoculation of the patient it seems to be caused by the viral particles getting directly into neural tissue somehow unfortunately there is no effective treatment and it is always fatal but we haven't really figured out why the virus kind of sticks around in some people but not in others and then the last cause of subacute encephalitis are prions so remember we mentioned these in unit 1 chapter 5 with viruses these are little infectious proteins remember they have no genetic material they have no dna no rna these are just little proteins that kind of folded wrong and then cause pretty significant diseases reservoirs for these are in humans and several different animals depending on which type of prion we're looking at transmission then get into humans is ingestion of usually contaminated brain tissue or contaminated surgical surgical equipment that has these uh has this brain matter on it so the types of crayons that specifically cause subacute encephalitis are a specific form of protein called a human glycoprotein and again it's just a little protein that folded incorrectly at some point and then becomes catalytic where it essentially like bumps into another pro a protein that's correct in the body and then causes it to mutate as well causes it to fold incorrectly as well and then it becomes a prion another bad thing about prions is that they are very hard to destroy they're resistant to chemicals they're resistant to radiation they're resistant to heat and they have survived prolonged autoclaving which is a combination of heat and pressure that pretty much has been able to kill everything so far for us except for these prions at the moment there's only one combination that's been found for prions it's a mix of a chemical bath and a significantly long autoclaving process that we've found works but otherwise we don't really know how to kill these things yet so when a prion does cause encephalitis it's known as transmissible spongiform encephalopathies which is just a group of diseases that we'll see affects brain tissue so the most common way that these are going to get out we said is through contaminated meat usually you get infected brain tissue into packaged meat that then goes out to be sold this actually happened relatively recently maybe 10 years ago nowish in england they had bovine spongiform and cephalopathy or mad cow disease where some of the cows that went to the slaughterhouse were infected and then they didn't know how much of it might have gotten into need or well but they basically recalled all of the meat they also slaughtered that entire that entire like year's worth of cattle essentially because there's no way to tell if an organism has a transmission spongiform encephalopathy while the organism is living because you have to do a dissection of the brain and of course you can't do that with a living thing there are other um spongiform diseases like sheep scrapey um crucif jacobs disease and kuru are the more common ones and then of course mad cow disease regardless of which one you get they all have 100 mortality rating and it's pretty quick it's death usually within a year so these spongiform diseases are all neurodegenerative diseases which means that it's going to break down or degenerate the nervous tissue the brain and the spinal cord they do have pretty long incubation periods anywhere from a couple months to even several years before you start to see symptoms once you see symptoms though that's when you have that really rapid progression where you have death usually within a year signs and symptoms typically start with things like altered behavior maybe some memory loss impaired senses maybe some delirium a couple of them like kuru have senality things like that eventually it keeps it evolves and starts affecting muscles so you have uncontrollable muscle contractions and that just basically just gets worse and worse and worse more memory loss more altered behavior more senility more muscle contractions until the patient dies and so this is just showing an example of how this affects brain matter so we have three examples here we have uh kuru sheep scrapie and then chris of jacob's disease on the right and then the bottom left there versus normal brain tissue on the top left and you can see all the little white holes in all three of those spongiform examples are not supposed to be there it's supposed to be a clear tissue or a you know a clear field of brain tissue with no holes in it and that's those prions basically eating away the brain matter in all of those cases next we're looking at rabies and this is caused by the rhabdo virus this is a zoonotic disease because the reservoir is all animals there are some primary reservoirs like canines like coyotes and dogs things like that but you also see them in like skunks and raccoons cats and bats are all pretty common reservoirs as well essentially like small mammals for the most part transmission for humans to get this is typically through an animal bite or a scratch from an infected animal you can also have droplet inhalation but that's more rare mostly because we're generally not breeding the same air as wild animals at least i don't know what you guys do on your weekends i suppose but it's usually not my go-to move domestic animals can get this and they can transmit it as well so that's typically where we do see that droplet inhalation it's like it's your pet you know signs and symptoms is you usually have an incubation period anywhere from a month to two months depending on where the bite or scratch occurred but essentially during that time the virus is traveling to the brain and so the kind of closer it is to the brain to start with again that shorter that incubation period is once it reaches the brain it'll start with special muscle spasms of the mouth sorry you'll also have the pharynx kind of start clenching up so the throat areas start clenching up you'll also have a kind of weird sensation of hydrophobia you'll have a fear of water that wasn't there originally and we see this especially with animals because things like dogs and stuff they're usually not afraid of water but it's essentially to make sure that animal doesn't die because if they go on water and they're acting weird there's a chance they could drown so this virus keeps them away from water so they can pass the virus on which is interesting but also terrifyingly smart eventually it does end with fatal encephalitis there are two types of rabies furious rabies and paralytic rabies and it basically just depends on how how the animal is affected so animals that have furious rabies tend to be restless and really excitable kind of like going after people um if you ever saw the old movie like cujo that would be a furious rabies case paralytic rabies on the other hand that's where animals are more like unaware of their surroundings they just kind of like stumble around don't really know what they're doing you see videos of those all the time like a raccoon or a skunk out in the middle of broad daylight and just acting strange prevention and treatment you fortunately do have both for these prevention there is a vaccine that you can get for pre-exposure generally it's only recommended for people that are high-risk groups things like if you deal with animals often like vets or animal handle handlers there's three doses that it's recommended that you get but there is a post-exposure treatment and this is a vaccine with an immunoglobulin that basically if you get it within a certain time period you're you're okay so if you ever do get bit by an animal that's like acting strange or scratched just go get checked out better safe than sorry you don't need to know these steps by any means but this is a kind of nice image showing how this virus travels from person to person or i should say host a host because in this case you have i think that's supposed to be a dog but it is the fugliest dog i have ever seen it's fine we'll let it go but you can see the virus is in the animal it bites person and it's going to travel up the nerves to the spinal cord eventually get to the brain once it gets to the brain the virus is going to enter the salivary glands and it's so it's basically going to be in the spit this is part of the reason why especially for furious rabies it passes so easily because that's an organism's like go to move when they're mad is to bite right so that's how it passes from organism to organism so these are a little bit dated at this point but still relevant showing the more common uh organisms that pass these to humans and then also based on location which of those organisms is most likely to pass it so on the right there we'll start with the little pie chart it shows the different organisms that are more likely to be infected both wild and domestic the four most common are wild animals raccoons skunks bats and foxes and then if you jump to the left there based on where we live generally skunks are most common for us in illinois to pass this on but we also do see all of those other three raccoons foxes we do see bats now and then we also see coyotes now and then so but skunk for us more common and then again you don't know this i just think it's interesting but they actually have tracked all of the rabies cases or as many of the rabies cases as they've found um through the past like 30-ish years or so between foxes raccoons skunks and bats because again those are the most common species and you can see huge spikes now and then certain years versus other years drops it's just kind of interesting all right and then our last two diseases are going to be tetanus and botulism which are kind of related to each other so starting with tetanus this is caused by a bacterium known as clostridium tetani this is an endospore little gram-positive bacterium that generally is found in soil uh the way it usually gets into people if you've probably heard the like old wives tale or the um you know the saying like if you step on a rusty nail you're gonna get tetanus and that's kind of true but it's not from the nail generally though if you have if you step on a rusty nail it was probably laying in the dirt somewhere so what happens is that nail if you step on the nail it causes this kind of deep wound like in your foot or wherever you you know got poked and then the soil that was sitting on this nail might have that endospore on it of this bacterium and it gets shoved deep into that wound well these grow best they are obligate anaerobes so they don't like to grow in air so if they get shoved deep in the wound where there's no air then they're going to start growing again so generally you hear the same like stepping on a nail but it can be really anything that deals with soil and then with a wound so you can have like burn skin gets dirt in it or even umbilical stumps that's pretty common especially in some african countries for a long time they would close off like umbilical cords like they'd put a mud like essentially like a mud mask on it for healing to keep flies and things off it as well but if the soil is contaminated then we were seeing these huge bouts of tetanus it's gone down in past couple years luckily though so reservoir for this is environment transmission is direct contact or entering through a wound or some kind of injection point like sort of kind of stepping on a nail it's kind of like injecting it into the body this is a neuromuscular disease and it's sometimes known as lockjaw there's also another type of lockjaw that is not the same so the actual disease of tetanus is caused by this microbe producing a neurotoxin known as tetnospasmin and this is a neurotoxin that blocks the relaxation pathways and muscles so it forces the muscles to contract and then stay contracted or like tense up so signs and symptoms start with clenching of the jaws which is why it's sometimes called lockjaw but you have like this clenching of the back muscles of the jaw and then it basically just travels through the entire body causing that same effect with all your muscles so you end up having an arching of the back you have flexed arms extension of the legs usually it's most common for patients that have tetanus that goes all the way through to die of suffocation because it clinches down on those respiratory muscles and causes them to be paralyzed like all the other muscles which means you can't breathe sometimes you do die of a broken neck though because it causes your back muscles to and your neck muscles to contract so hard that it will break the neck luckily though there is a vaccine so you don't have to die in arguably one of the most terrifying ways i've ever heard and then if you don't have the vaccine if you do like step on a nail or you know get burned like roll around in the mud or something there is a treatment that you can get called tetanus immunoglobulin or tig that you can get within i think like 72 hours but i would check that um so kind of like make sure if you can't remember the last time you had the vaccine or whatever there is like an after treatment as well and so this is just showing especially that image on the left there when we think of like clenched muscles we don't really get the same view this is what tetanus causes that huge arching of the body you can see the hands and the fists and the jaw all clenched up typically this like bowed figure is because the back muscles are really large muscles so they overpower the front muscles even though those are also clenching that's what caused that like arch back look and you can see how this can very easily like break someone's neck or break someone's back as well pretty terrifying something that's interesting about this i guess interesting historical is they actually think a lot of cases of quote-unquote exorcism were actually cases of tetanus that had gone too far because if you look at this it looks like he is possessed right like a demon's got a hold of him but they actually think now that was probably tetanus and then our last disease is botulism so this is kind of like the crazy cousin of tetanus because we had clostridium tetani for tetanus and then we have clostridium botulinum for botulism which is again a gram-positive bacterium endospore forming obligate anaerobe so they're very similar organisms and they actually cause very similar disease it just kind of works in the opposite way so these are also generally found in the soil transmission is also ingestion entering a wound or intoxication which is just the ingestion of the toxin not the microbe itself there are generally three forms of botulism infant botulism foodborne botulism and wound botulism infant botulism of course is uh specifically associated with infants another name for this one is floppy baby syndrome which sounds funny it's not funny and it's most commonly associated with feeding infants raw honey because the bacterium will get into like um you know i just totally lost what i was going to say oh gets into like honey that's like being sold at like a farmer's market or something that's not going through strict pasteurization measures and then it was pretty common for a while to like dip a binky in honey especially if babies are like teething or something to kind of calm them down give them something to think about other than like the tooth pain and then they were seeing all this botulism and these little babies foodborne this is more commonly with again improper like canning measures things like getting some of this bacteria into a can of like you know peaches or something like that and then again not going through that pasteurization process going to eat those later and then getting botulism and then wound botulism that's more similar to like stepping on a nail signs and symptoms are very similar to tetanus they just have the opposite effect so you have a toxin being released acts as a kind of a block for the muscles it blocks a neurotransmitter that tells the muscles what to do in this case though whereas tetanus causes paralysis or clenching of the muscles botulism causes flaccid process and that's where the muscles are relaxed and they can't contract so either way you end up getting paralysis you end up losing function of the muscles so death and kind of the end result of botulism is the same death almost always occurs from suffocation due to the paralysis of those respiratory muscles because either they're clenched or they're so relaxed they won't work either way you can't breathe so this was a pretty uh frequent and fatal disease up until the last hundred years or so when we got modern food preservation techniques and of course medical treatment has gotten significantly better so those numbers have dropped a lot it's almost exclusively associated at least in places like the us now with improper home canning because again there's no fda regulations there's no pasteurization so that micro could possibly get into that canning process and you just created this perfect environment for that endospore to just kind of go crazy so then if you eat that food it's bad so prevention would be making sure for proper canning for foodborne botulism also making sure to never feed raw honey to infants for that floppy baby syndrome treatment is pretty much there is an anti-toxin you just have to get it very quickly and there is some supportive care something that's interesting about this botulinum toxin the thing that causes all the kind of trouble in the body is that we actually have used that toxin modified it slightly and it's now used as botox because what more human thing is oh this can kill me let's inject into my face because i don't want wrinkles and so this is showing that example for floppy baby syndrome you can see just that limp nature that flaccid paralysis so just like in the previous chapter your textbook has two images that i think are helpful so you have the different infectious diseases not all of them but most of them listed here with what type of microbe they are as well as what disease they cause and then again that deadliness versus communicability image in this case polio and rabies are the two that they really have pop out at you but rabies especially you can see has very high deadliness but pretty low communicability it is pretty hard to pass it because most people aren't going up at least hopefully to animals acting weird or acting you know out of character and getting bit and now we do have again treatments and things like that as well and then polio same thing it has a pretty low deadliness rating but it has a higher communicability okay that's it for chapter 17.