In an attempt to discover the cause of malaria, a deadly infectious disease common in tropical areas, early European settlers in Hong Kong attributed the malady to poisonous gases supposed to be emanating from lowlying swampland. Malaria, in fact, translates from the Italian as "bad air." In the 1880s, however, doctors determined that Anopheles mosquitoes were responsible for transmitting the disease to humans. The female of the species can carry a parasitic protozoa that is passed on to unsuspecting humans when a mosquito feasts on a person's blood.