81 2 Surra. 



and camels, wliile cattle and dogs are affected less severely. 

 According to some authors (Laveran, Pease and others), Mboire 

 and the El Debab of the camels in North Africa (see p. 838) 

 is supposed to be identical with surra, having been introduced 

 with camels from India. Surra appears to occur also in north- 

 eastern Africa. 



In 1906 the disease was brought to Xew York with an importation of cattle 

 from India, but was suppressed by the slaughter of the infected, and prolonged 

 quarantine of the other animals. Camels have introduced the disease from India 

 to Australia. 



Etiology. The Trypanosoma Evansi is morphologically 

 amiost identical with the producer of nagana. As an only, 

 although not constant difference is given a somewhat more 

 slender form, somewhat longer flagella, a more pointed posterior 

 part of the body, and a smaller proportion of chromatin 

 granules, and finally more active motility. 



The possibility of differentiating surra from nagana consists at 

 the present time principally in the fact that goats and cattle immunized 

 against the usually more virulent nagana virus, are still susceptible to 

 surra (Laveran & Mesnil, Nocard & Vallee), which although a differ- 

 ential sign, is declared by Koch to be not conclusive. 



As Trypanosoma vivax, Ziemann descril^ed in Kamerun a trypanc- 

 some which is characterized by very lively motility and resembles the 

 virus of surra in other particulars. 



Relative to the pathogenicity between the trypanosomes 

 of surra and those of nagana, the only difference is that in 

 artificial infection experiments the nagana trypanosomes are 

 usually slightly more virulent. 



The natural infection is transmitted according to Eogers 

 and Musgrave & Clegg by horse flies, namely, the Tabanus 

 tropicus, the T. lineola and the Stomoxys calcitrans, according 

 to Leese also by the Hamatopa fly. Carnivora may infect them- 

 selves also by the ingestion of blood from affected, or of meat 

 from dead animals, also through losses of substance in the 

 skin and mucous membranes (Lingard; Vrijburg succeeded in 

 infecting a mare by smearing the urethral secretion of an in- 

 fected stallion upon the mucous membrane of the vagina). 



Cattle and zebus are generally considered in the first place 

 as virus carriers (virus reservoirs), although they are only 

 slightly susoepti])le to the disease and usually become affected 

 but mildly ; nevertheless they may harbor tr^T^anosomes in their 

 blood for years. In the second place camels, when recovering 

 from the disease, may likewise carry the parasites in their 

 blood for a long time. Wild animals (foxes, jackals, hyenas) 

 may also supply the virus to stinging flies. 



For all stinging flies which have hitherto been considered as transmitters of 

 the natural infection of surra, it is generally accepted that they transmit the 

 trypanosomes entirely in a mechanical way; at least the experiments carried out 

 failed to .show that the surra trypanosomes pass through any stages of development 



