10.1.2—Examples of infectious diseases

Transmission occurs when a pathogen leaves an infected source, remains viable in a route or medium, and reaches a new host. The route is disease-specific: water/food, an insect vector, droplets or direct exchange of body fluids.

• Cholera — contaminated water or food: infected people egest Vibrio cholerae in faeces; water becomes contaminated, and another person can acquire the bacterium through contaminated water, washing in it or food exposed to it.
• Malaria — vector and blood route: a female Anopheles mosquito takes up Plasmodium with a blood meal from an infected person, then passes the protist into the blood of the next person it feeds on. Blood transfusion, reused unsterile needles and passage across the placenta are also listed routes.
• Tuberculosis — droplets or animal-product route: an infected person with active TB releases droplets containing Mycobacterium tuberculosis when coughing or sneezing; another person inhales them. M. bovis can pass from cattle to humans through contaminated meat or unpasteurised milk.
• HIV/AIDS — direct body-fluid exchange: HIV reaches a new person through exchange of infected body fluids, including sexual intercourse, blood exposure or shared needles, and mother-to-child transfer across the placenta, during birth or through breast milk.

A mosquito is a vector, not the malaria pathogen; a cough-related route for TB is droplet infection, not a generic label for every contact; HIV requires direct body-fluid exchange rather than casual contact. These are transmission chains only: prevention, diagnosis and treatment belong to later cards. No image generated or bound.