The control of camel trypanosomiasis

Abstract

The control of camel trypanosomiasis (T. evansi type) is most easily effected by diagnosis and cure. In regard to diagnosis, the mercuric chloride test has shown itself to be of high accuracy under laboratory conditions, and although it may lose somewhat in precision under field conditions it is by far the best available method. It has the advantages that it develops in all infected camels, that it develops early in the disease, that it never disappears spontaneously, and that it always disappears following cure. The only faulty diagnoses appear to be due to the existence of a few positively reacting non-infected camels, and to the fact that under field conditions the technique may so suffer from lack of facilities as to permit of apparently positive reactions in healthy camels. Both of these factors have been found in practice to be of little account; healthy camels giving a true positive reaction are extremely rare, and whenever their number is apparently slightly increased owing to the necessity for carrying out tests under bad conditions the only loss is a dose of Naganol. Treatment is universally successful with a single intravenous dose of Naganol. The smallest dose that has been found successful over a long period in the field is 4 grammes, but it is not yet certain that a smaller dose may not suffice. Immunity following cure is for practical purposes non-existent. Camels are certainly resistant to re-infection for a short time after treatment, but the resistance in general practice may be considered as entirely due to residual traces of Naganol, since the resistant period, except possibly in advanced chronic cases, is no greater than that conferred by Naganol alone on healthy camels. For prophylactic treatment Naganol is of some value, but in routine field practice its use in such a manner is not to be recommended, since diagnosis and cure constitute the best control procedure. The period of protection is proportional to the dose administered; with the present routine dose of 4 grammes protection for so short a time as two months is not certain. Circumstances, however, are indicated in which Naganol might profitably be used as a prophylactic. Trypanosome “carriers” among other domestic animals play little part in spreading camel trypanosomiasis. Of the two most closely associated species, the horse in the Sudan is probably never infected, but donkeys may rarely be so, and the infection is of a type that would lead to the establishment of carriers. Suggestions are made for dealing with this situation. In consideration of the foregoing data, it may be simply said that for routine purposes the mercuric chloride test should be freely used, in particular during and at the end of the “fly” season. Any camel showing a positive reaction, either for the first time or at an interval of three months or more after earlier treatment, should be treated. Fortunately for field officers, the seasonal occurrence of camel trypanosomiasis, and the fact that most routine treatments are undertaken towards the end of the “fly” season, ensures that few camels require a second treatment in one year. Regarding the tsetse-borne trypanosomes, camels appear to be susceptible to all species. Infections rarely occur in nature because camels are rarely introduced into tsetse areas. With the exception of Tryp. congolense the infections appear to be comparable with the common one due to trypanosomes of the Tryp. evansi type, and the routine system of control would be applicable. If deliberate exposure of camels to tsetse is ever contemplated an antecedent study of Tryp. congolense infection will be necessary.