A parasitic malady is a communicable disease caused or transmitted by a parasite. Several parasites don't cause diseases. Parasitic diseases will have an effect on all living organisms, as well as plants and mammals. The study of parasitic diseases is named parasitology.
Contaminated water is one source of infection. Improperly washed or undercooked food is a common means of infection. Transmission from pets is another. Contact with another infected person is also a common route of infection.
WHO estimates there may be 50–100 million dengue infections worldwide every year. Before 1970, only 9 countries had had severe dengue epidemics, but the disease is now endemic in more than 100 countries and territories in 5 WHO regions: Africa, the Americas, the Eastern Mediterranean, South-east Asia and the Western Pacific.