52 



THE HEMOFLAGELLATES 



Hosts : Camels, horse, donkey, ox, 

 zebu, goat, pig, dog, water buffalo, ele- 

 phants, capybara, tapir, and (in Mauri- 

 tius) deer. 



Location : Blood, lymph. 



Geographic Distribution : Northern 

 Africa (north of 15 N latitude in the west 

 and central part of the continent, but ex- 

 tending almost to the equator in the east), 

 Asia Minor, U.S.S.R. from the Volga 

 River east into Middle Asia, India, Burma, 

 Malaya, Indochina, parts of southern 

 China, Indonesia, Philippines, Central 

 America, South America. Hoare (1956) 

 has shown how the original distribution of 

 T. evansi coincided with that of the camel. 

 In Africa, its southern boundary coincides 

 roughly with the northern boundary of 

 tsetse fly distribution. It now extends far 

 to the east of the camel's range in the Old 

 World. It is often associated with arid 

 deserts and semi-arid steppes, but may 

 occur in other types of climate as well. 

 In India, it is most common in the Punjab, 

 which is mostly in the northwestern dry 

 region (Basu, 1945; Basu, Menon and Sen 

 Gupta, 1952). It was probably introduced 

 into the New World in infected horses by 

 the Spanish conquerors during the 16th 

 century. 



Prevalence : T. evansi is an impor- 

 tant cause of disease over a large part of 

 its range. 



Morphology : The morphology of the 

 Old World strains of T. evansi has been 

 studied intensively by Hoare (1956). The 

 mean length of different host and geo- 

 graphic strains varies considerably. How- 

 ever, the typical forms are 15 to 34 ji 

 long, with a mean of 24 |i. Most are slen- 

 der or intermediate in shape, but stumpy 

 forms occur sporadically. All forms are 

 morphologically indistinguishable from 

 the corresponding ones of T. briicei. 

 Strains which lack a kinetoplast have oc- 

 casionally arisen spontaneously or can be 

 produced by treatment with certain dyes 

 (Hoare, 1954). 



Life Cycle : T. evansi is transmitted 

 mechanically by biting flies. No cyclic 



development takes place in the vectors, 

 the trypanosomes remaining in the pro- 

 boscis. The usual vectors are horseflies 

 of the genus Tabanus, but Stomoxys, 

 Haematopola and Lyperosia can also trans- 

 mit it. In Central and South America, the 

 vampire bat is a vector, the disease in 

 this case being known as murrina. 



Pathogenesis : Surra is nearly always 

 fatal in horses in the absence of treatment; 

 death occurs in a week to six months. The 

 disease is also severe in dogs and elephants. 

 It is less severe in cattle and water buffalo. 

 Cattle may carry the parasites without 

 showing signs of disease for months. How- 

 ever, occasional outbreaks of acute disease 

 occur in cattle and water buffalo. Surra in 

 camels is similar to the disease in horses 

 but more chronic. In dogs, T. evansi 

 causes a chronic disease with a high mor- 

 tality rate; untreated dogs usually die in 1 

 to 2 months (Gomez Rodriguez, 1956). 



The signs of surra include intermittent 

 fever, urticaria, anemia, edema of the legs 

 and lower parts of the body, loss of hair, 

 progressive weakness, loss of condition 

 and inappetence. Conjunctivitis may occur, 

 and abortion is common in camels. 



The lesions include splenomegaly, en- 

 largement of the lymph glands and kidneys, 

 leucocytic infiltration of the liver paren- 

 chyma, and petechial hemorrhages and 

 parenchymatous inflammation of the kidneys. 



Diagnosis: Same as for T. brucei. 



Cultivation : Same as for T. brucei. 



Treatment : Treatment of T. evansi 

 is similar to that of T. brucei. Antrycide 

 methyl sulfate is less toxic than suramin 

 for horses; a single subcutaneous dose of 

 5 mg/kg or even less is effective. A dose 

 of 3 mg/kg has given good results in cattle. 

 A single injection of 2 g is effective in 

 camels. 



The dose of suramin for horses is 4 g 

 per 1000 lb body weight intravenously. 

 Camels tolerate suramin well, and a single 

 intravenous injection of 4 to 5 g is effective 

 against surra in these animals. Tartar 



