Human diseases. Artwork of a male silhouetted figure, surrounded by various disease-causing organisms. The mosquito (Anopheles gambiae, upper left) transmits a parasitic protozoan it bites, causing malaria. A pollen grain is seen at upper centre (orange), which can cause an allergic reaction (hay fever). When the bacterium (Vibrio cholerae) at lower left is ingested from contaminated food or drink, it causes cholera. Cholera is an intestinal disorder with symptoms including sever vomiting and diarrhoea. The virus at centre (red) is transmitted from the bite of certain animals and causes rabies (hydrophobia).