Theileriasis
Johanna L. Watson • Gary P. Carlson
Theileriasis is caused by a small hemoparasite of the genus Theileria that infects lymphocytes and erythrocytes of ruminants and is most common in tropical and subtropical climates.
The organism is spread by bloodsucking arthropods, particularly ticks of the Ixodidae family. Theileria parva is the cause of East Coast Fever, a highly fatal disease of cattle in Africa. Other members of the genus Theileria (spp. annulata, mutans,hirci, and ovis) tend to be less pathogenic and produce diseases with a wider geographic distribution.2 Theileria cervi has been seen in North American deer. Theileria mutans has been seen in erythrocytes of both cattle and deer in North America. Theileriosis due to an agent indistinguishable from Theileria buffeli has been described in cattle from Texas and North Carolina with parasitemia, but clinical signs were not reported.3 T. buffeli was reported as the cause of hemolytic anemia in a 6-month-old Simmental calf.4 There was serologic evidence of a high herd prevalence of Theileria infection, and the agent was transmitted to splenectomized calves that developed mild anemia. The organism produces a brief illness characterized by mild fever, anorexia, and modest anemia, followed by rapid recovery.
Trypanosomiasis
Johanna L. Watson • Gary P. Carlson
Trypanosomes are flagellated protozoal organisms that can produce a variety of serious diseases of humans and animals, although many are nonpathogenic. Nagana, a disease of cattle in Africa, is caused by Trypanosoma congolensi. Trypanosoma evansi is the cause of Surra, a disease of cattle in India, and Trypanosoma equiperdium is the cause of Dourine in horses. In North America, Trypanosoma theileri (Trypanosoma americanum) is the only agent reported and is principally of academic interest because it is relatively nonpathogenic. On stained blood films from cattle, small numbers of the organism can occasionally be seen free in plasma, appearing as large flagellated protozoa with undulating membranes. Trypanosoma is best visualized in buffy coat smears, which tend to concentrate it. T. theileri rarely produces clinical signs, but occasionally a fulminating parasitemia may develop, resulting in fever, depression, and decreased milk production.