[Music] we're going to take a look at infectious diseases what they are some terms used to describe them and take a look at a few different types of infectious diseases first of all what is an infectious disease an infectious disease is a disease caused by an infectious agent like viruses bacteria parasites or fungi infectious diseases are a global problem and in the past used to be the leading cause of death there were large epidemics of small poox TB syphilis chalera and plague that caused millions of deaths around the world the 1918 influenza pandemic alone was responsible for the death of around 40 million people globally thankfully advances in nutrition antibiotics immunization food safety housing and sanitation has led to a massive reduction in infectious diseases however even now they're a problem in 2012 infectious diseases were responsible for three of the top 10 causes of death in the world these three were lower respiratory tract infections HIV AIDS and diarrheal diseases in addition to this malaria and tuberculosis continue to affect millions of people new diseases like Ebola and M kov have sprung up causing deadly outbreaks and killing thousands of people let's have a look at what happens when a person gets infected and talk about some terms that are used to describe infectious diseases when an organism enters the body some people fight it off with their immune system while other others can go on to develop disease people are likely to develop disease if they have weakened immune systems this could be due to drugs age or other disease they're also more likely to develop the disease if they're not immune to it for example if they haven't had the disease before or if they haven't been vaccinated the time from when someone gets infected to when symptoms start is called the incubation period the clinical stage of the disease is marked by the onset of symptoms there can be considerable variation in the clinical stage ranging from very mild symptoms to very severe symptoms the disease lasts until the infection has resolved or the person dies now for some important terms that you'll hear when describing infectious diseases the Infectious period is the time during which the infected person can spread the disease and infect others sometimes people may not have any symptoms but still be able to infect others these people are called carriers case fatality is a measure of the severity of a disease it is the proportion of people that die from being infected for example if 6 out of 10 people with the disease die from it the case fatality is 60% the basic reproductive rate is a term that describes how infectious a disease is it is the average number of secondary cases that occurs as a result of one infected individual for example measles can have a basic reproductive rate of up to 15 this means that one case of measles can cause up to 15 other cases of measles another way to measure infectiousness and the spread of disease is the secondary attack rate this is the proportion of people who are exposed to the disease that develop an infection for seasonal influenza it's about 10% meaning one out of every 10 susceptible people exposed to an influenza case will develop the infection now let's have a look at some important categories of infectious diseases zonic diseases are diseases of animals which when transmitted to humans can cause disease it is estimated that over 60% of human infectious diseases are xonotic examples of zoonotic diseases include diseases like leptospirosis toxoplasmosis ciloa and rabies an emerging infectious disease is a disease that has appeared in the population for the first time or one that may have existed previously but is rapidly increasing in incidence or geographical range examples of emerging infectious diseases include mov Ebola Hendra and new influenza strains neglected tropical diseases are a group of tropical diseases that affect the poorest countries of the world traditionally they have not received much Global attention but continue to cause illness in the most vulnerable groups of people in the world they include diseases like leishmaniasis troma sleeping sickness and schistosomiasis Vector born diseases are diseases that are transmitted from an infected animal or human to another person through the bite of a vector the most common Vector is the mosquito others include ticks flies fleas or snails example of vector born diseases are malaria D sleeping sickness and schistosomiasis Vector born diseases are responsible for over 17% of all infectious diseases and cause more than 1 million deaths each year so that's a quick introduction to infectious diseases what they are some terms to describe them and a few different types