Infectious Diseases - An Introduction


we're gonna 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 smallpox TB syphilis

cholera 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 there a

problem in 2012 infectious diseases were

responsible for three of the top ten

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


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 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 - and 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

percent meaning one out of every ten

susceptible people exposed to an

influenza case will develop the

infection now let's have a look at some

important categories of infectious

diseases zone onic diseases are diseases

of animals which when transmitted to

humans can cause disease it is estimated

that over 60% of human infectious

diseases are zoonotic examples of

zoonotic diseases include diseases like

leptospirosis toxoplasmosis

Campylobacter 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 an

incidence or geographical range examples

of emerging infectious diseases include

murska v ebola Hendra and new influenza


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 the

include diseases like leishmaniasis

trachoma sleeping sickness and

schistosomiasis vector-borne 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 borne diseases

are malaria dengue sleeping sickness and

schistosomiasis vector borne diseases

are responsible for over 17% of all

infectious diseases and caused 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