gering problem. As recently as 1949 about a fourth 

 of Africa was still completely denied to man. 



The African disease in man begins with anemia 

 and fever as the flagellates begin to multiply, and 

 then manifests itself as swollen lymph glands, ex- 

 treme lethargy, and finally coma as they invade the 

 lymph glands and then enter the fluids surrounding 

 the spinal cord and the brain. After this last stage 

 death may ensue. Two closely related forms of the 

 human disease are known: one caused by Trypano- 

 soma gambiense, and another more acute form of 

 the disease caused by Trypanosoma rhodiense. 

 Whether these are really separate species of Trypa- 

 nosoma, or whether both are only variant strains of 

 Trypanosoma hrucei, which causes nagana in cattle, 

 is not yet settled. If we examine the blood of a vic- 

 tim we see long, slender flagellates propelled about 

 among the red corpuscles by a delicate ruffled mem- 

 brane along one side of the body. The single long 

 flagellum is attached along the outer border of this 

 undulating membrane, and it may extend free like a 

 little tail at the front end of the animal, the end that 

 goes first as it swims. Many years of patient investi- 

 gation have shown that the flagellates in human 

 blood are injected into the blood stream with the sa- 

 liva from the bite of the tsetse fly (Glossina). The 

 same flagellates are also found in the blood of almost 

 all the large wild game of Africa. In the wild hosts, 

 such as antelopes, however, there are no obvious 

 signs of disease. And we can only conclude that an 

 amicable relationship has been worked out between 

 antelope and flagellate, who were introduced to each 

 other a very long time ago. They have had ample 

 time to adjust, apparently by a steady elimination of 

 the most susceptible hosts and also of those trypano- 

 somes that abused their hosts too severely and so 

 were killed when their hosts died. Where unbalance 

 occurs, such that a parasite kills its host, it is likely 

 that host and guest have been very recently intro- 

 duced and have not yet worked out the biological 

 amenities. 



Trypanosomes probably infested only inverte- 

 brates at first, and many still do, but in their long 

 history some have come to use their invertebrate 

 hosts as a means of gaining entrance to the bodies of 

 vertebrates. In the Western Hemisphere, where there 

 are no tsetse flies, Trypanosoma cruzi, of South 

 America, can be transmitted to man from its natural 

 hosts (armadillos, opossums, rodents) and also from 

 cats, dogs, monkeys, and other mammals, by the 

 bite of triatomid bugs that regularly live in houses, 

 like bedbugs, and suck blood from the human inhab- 

 itants. Having gained entrance to human tissues, 

 Trypanosoma cruzi causes the anemia and the nerv- 

 ous symptoms of Chagas's disease in scattered areas 

 from northern Argentina to Mexico. In some parts 

 of Brazil, Bolivia, Chile, and Argentina. 10 to 20 



per cent of the population is infected. The same 

 flagellate is found in many species of triatomid bugs 

 in the scrub woods and farms of Texas and in the 

 deserts and canyons of Arizona and California; but 

 natural infections, if they occur, must be rare. Some 

 trypanosomes have dispensed with the invertebrate 

 host altogether and can be transmitted directly; for 

 example, Trypanosoma eqiiiperdiim. which is passed 

 from horse to horse in coitus, and causes dourine 

 disease. It is found in all regions except Australasia. 

 The family Trypanosomidae also includes such 

 forms as Herpetomonas, parasitic in the intestine of 

 invertebrates, and Leishmania, which causes kala 

 azar and Oriental sore in people living in warm parts 

 of the world. Phytomonas, from the milky latex of 

 many plants, can be found abundantly in our com- 

 mon milkweeds, and infection is carried from one 

 plant to another by sucking bugs that visit the plants. 

 For the amateur wishing to see trypanosomes, an 

 easily obtained form is in the blood of frogs and of 

 crimson-spotted newts. The transmitting agent for 

 flagellates that live in such aquatic hosts is often a 

 pond leech. Fortunately, flagellates parasitic in the 

 lower vertebrates do not infect man. Details about 

 such disease-causing protozoans are best sought in 

 the specialized books on human parasitology or on 

 the parasitology of domestic animals, as listed in the 

 bibliography. Information on the protozoan parasites 

 of animals other than man or his pets and flocks will 

 be found in books on protozoology. 



The most highly organized of the flagellates are 

 the polymastiginads, which usually have more than 

 three flagella, often many. The trichomonads are 

 common in the digestive tracts of vertebrates, and 

 also in the urinogenital passages. They are pear- 



Trypanosomcs among red blood cells in a stained 

 blood smear. Those shown here, Trypanosoma gam- 

 biense, cause .African sleeping sickness. ( General 

 Biological Supply House, Chicago ) 



