74 



COLLEGE ZOOLOGY 



portant cause of abortion in cattle; while 

 Trichomonas gallinae produces a fatal in- 

 fection in pigeons and other birds. Tricho- 

 monas gallinarum inhabits the lower intes- 

 tine of chickens and turkeys, and, in chronic 

 cases, invades the liver. Giardia infections 

 may cause severe diarrhea in both rabbits 

 and dogs. Blackhead in turkeys is caused by 

 an amoeboid flagellate, Histomonas melea- 

 gridis. 



Balantidium coli is common in pigs and 

 in chimpanzees, both of which probably 

 serve as reservoirs for human infection. 



Trypanosome diseases of animals are com- 

 mon in tropical areas. Horses, camels, cattle, 

 pigs, dogs, and monkeys are susceptible to 

 nagana, an African disease, caused by Try- 

 panosoma brucei and transmitted by tsetse 

 flies. Dourine or horse "syphilis" is also 

 caused by a trypanosome, as is mal de Ca- 

 deras, a South American disease of horses. 

 Trypanosoma evansi is responsible for surra, 

 a serious disease of horses, dogs, elephants, 

 camels, and other species. Trypanosoma 

 lewisi is a parasite almost universally found 

 in rats. Bats, mice, sheep, goats, and other 

 animals also harbor trypanosome infections. 



Malaria is by no means confined to man. 

 Several species of Plasmodium occur in 

 birds; also monkeys, bats, squirrels, buffalo, 

 and antelope become infected. At least thir- 

 teen species occur in reptiles, and two have 

 been reported in amphibians. 



Of particular interest is the malarialike 

 disease, red-water fever of cattle, also called 

 Texas fever; this is caused by a sporozoan, 

 Babesia higemina, which parasitizes the red 

 blood cells. This species is transmitted by 

 a tick, Boophilus (Fig. 167, p. 275). The 

 infection passes from the mother tick into 

 her eggs and is thus present in the larvae 

 which emerge from them. Each new genera- 

 tion is therefore able to transmit the disease 

 to new bovine hosts. This is the first case in 

 which it was shown that an arthropod trans- 

 mitted a protozoan disease agent. The dis- 

 covery of this fact by Smith and Kilbourne 

 in 1893 was an important early contribution 

 to medical entomology. 



Sporozoa are abundantly present in ani- 

 mal hosts. Coccidial infections of the intes- 

 tine are particularly destructive to rabbits 

 and birds; and Nosema bombycis, a sporo- 

 zoan parasite of the silkworm caterpillar, 

 once threatened the silk industry of the 

 entire world. Infested caterpillars that did 

 not succumb gave rise to moths which laid 

 infected eggs, and thus the infection con- 

 tinued. Pasteur studied the problem (1865- 

 1870) and discovered that diseased eggs may 

 be detected by microscopic examination. 

 Such eggs can be destroyed before hatching, 

 and a healthy generation of caterpillars 

 thereby assured. 



Nosema apis is also a destructive parasite 

 of honey bees. Many harmful insects are un- 

 doubtedly held somewhat in check by proto- 

 zoan parasites. 



PROTOZOA IN 

 WATER SUPPLIES 



Water for drinking may not only be con- 

 taminated by Protozoa of fecal origin, but 

 it may also be unpalatable because of the 

 multiplication of various free-living proto- 

 zoans under natural conditions. This is espe- 

 cially likely to occur when the water is con- 

 fined in a quiet open reservoir before being 

 released for use. Uroglenopsis (Fig. 39) 

 forms spherical colonies, the individuals of 

 which are embedded in the periphery of a 

 gelatinous matrix. Dinobryon (Fig. 39) is a 

 branching flagellate, which occurs more 

 commonly in alkaline regions. A colony of 

 Synura (Fig. 39) consists of from two to 

 fifty individuals, arranged in radial fashion. 



Among several protozoans known to make 

 water unfit for drinking, Uroglenopsis is pos- 

 sibly the worst since it imparts a fishy odor 

 like cod-liver oil. Similar odors result from 

 the presence of Eudorina, Pandorina, Vol- 

 vox, and Glenodinium. Both Synura and 

 Pelomyxa produce an odor like ripe cucum- 

 bers. Bursaria gives off an odor like a salt 

 marsh, while a culture of Peridinium smells 

 like clam shells. The fishy odor of Dino- 



