DISEASES CARRIED BY FLIES 283 



Another group of protozoan parasites are called tryp'anosomes. 

 These are parasitic in insects, fish, reptiles, birds, and mammals 

 in various parts of the world. They cause several diseases of 

 cattle and other domestic animals, being carried to the animal in 

 most cases by flies. One of this family is believed to live in the 

 blood of native African zebras and antelopes. Seemingly it 

 does them no harm, but if one of these parasites is transferred by 

 the dreaded tsetse (tse'tse) fly to one of the domesticated horses 

 or cattle of that region, death of the animal results. 



Another fly carries to the natives of Central Africa a species of 

 trypanosome which causes " the dreaded and incurable sleeping 

 sickness." This disease has carried off more than fifty thousand 

 natives yearly, and many Europeans have succumbed to it. Its 

 ravages are largely confined to an area near the large Central Afri- 

 can lakes and the upper Nile, for the fly which carries the disease 

 lives near water, seldom going more than 150 feet from the banks 

 of streams or lakes. The British government has attempted 

 to control the disease in Uganda by moving all the villages at 

 least two miles from the lakes and rivers. Among other diseases 

 that may be due to protozoa is kala-agar, a fever in hot Asiatic 

 countries which is probably carried by the bedbug, and African 

 tick fever, carried by a small insect called the tick. The body 

 louse carries the dreaded typhus fever, which has played great 

 havoc in Russia and the near East since the World War. Bubonic 

 plague, one of the most dreaded of all bacterial diseases, is carried 

 to man by fleas from rats or ground squirrels. In this country 

 many fatal diseases of cattle, as '' tick fever," or Texas cattle 

 fever, are caused by protozoa. 



The House Fly. — We have already seen that mosquitoes of 

 different species carry malaria and yellow fever. Another addition 

 to the black list is the house fly or typhoid fly. The development 

 of the house fly is extremely rapid. A female may lay from one 

 hundred to two hundred eggs. These are usually deposited in 

 filth or manure. Dung heaps about stables, privy vaults, ash 

 heaps, uncared-for garbage cans, and fermenting vegetable refuse 

 form the best breeding places for flies. In warm weather, the 

 eggs hatch a day or so after they are laid and the larvae or maggots 

 crawl out. After about one week of active feeding these wormlike 



