Infectious diseases

While many infectious diseases have been successfully controlled in some parts of the world, many people worldwide are still at risk of these diseases.

1. Define the term disease and explain the difference between an infectious disease and a non-infectious disease

• A disease is an illness or disorder of the body or the mind that leads to poor health and each disease is associated with a set of signs and symptoms
• An infectious disease is a disease that is caused by organisms known as pathogens and they are passed from infected people to uninfected people 
• A non-infectious disease is not caused by pathogens but instead is caused by either genetic disorders (sickle cell anemia) or environmental factors (lung cancer which is linked to smoking) and they cannot be passed from infected people to uninfected people

2. State the name and type of causative organism (pathogen) of each of the following diseases: cholera, malaria, tuberculosis (TB), HIV/AIDS, smallpox and measles

• Cholera: Vibrio cholerae, bacterium
• Malaria: Plasmodium sp, protoctist
• Tuberculosis (TB): Mycobacterium tuberculosis and M. bovis, bacterium
• HIV/AIDS: Human immunodeficiency virus, virus
• Smallpox: Morbillivirus, virus
• Measles: Variola virus, virus

3. Explain how cholera, measles, malaria, TB and HIV/AIDS are transmitted

a) Cholera

• Cholera is a water-borne and food-borne disease
• It is transmitted through contaminated sources of water or food
• Most of the infected people do not show any symptoms and they pass out large numbers of the bacteria through their faeces
• The bacteria-containing faeces can contaminate the water supply
• Or when infected people handle food or cooking without washing their hands, the bacteria can be transmitted to uninfected people

b) Measles

• It is an air-borne disease
• When infected people sneeze or cough, the droplets released contain millions of virus particles
• And when these particles are inhaled by uninfected people who have no immunity to the disease, they will also become infected and develop symptoms
• The measles virus is transmitted easily in overcrowded insanitary places and where there is a high birth rate

c) Malaria

• Malaria is transmitted through a vector, which is the female Anopheles mosquitoes
• When the mosquitoes feed on an infected human's blood, they take up some of the pathogen's gametes with the blood meal
• The male and female gametes fuse in the mosquito's gut and develop to form infective stages which then move into the mosquito's salivary glands
• When the mosquito feeds again, she injects an anticoagulant from her salivary glands to prevent blood from clotting
• The infective stages pass into the human's blood together with the anticoagulant
• Then the parasites enter the red blood cells where they multiply
• Malaria may also be transmitted through blood transfusion and when unsterile needles are re-used
• The protoctist can pass across the placenta from mother to fetus

d) TB

• TB (caused by M. tuberculosis) is an air-borne disease
• When infected people with the active form of the disease sneeze or cough, the bacteria are carried in the air in tiny droplets of liquid
• When…