Trypanosoma simiae

Synonyms: T. ignotum, T. rodhaini, T. porci.

T. simiae was first found in a monkey, but its natural reservoir host is the warthog (Phacophoerus aethiopicus). It is highly pathogenic for the pig and camel, causing a peracute disease with death usually in a few days. This is the most important trypanosome of domestic swine. It is only slightly pathogenic for sheep and goats, and apparently non-pathogenic for cattle, horses or dogs, altho it may infect them. The rabbit appears to be the only susceptible laboratory animal. There is a great deal of variation in pathogenicity between strains, and indeed marked changes can occur in the pathogenicity of a single strain.

T. simiae occurs mostly in East Africa and the Belgian Congo, but it has also been found in other parts of Africa where T. congolense occurs.

T. simiae differs morphologically from T. congolense in being polymorphic instead of monomorphic. It varies in length from 12 to 24 u. About 90% of its forms are long and stout, with a conspicuous undulating membrane, about 7% are long and slender with an inconspicuous undulating membrane, and about 3% are short, with an inconspicuous undulating membrane. A free flagellum is usually absent, but has been reported in from 1 to 4% of different strains.

This species is transmitted in the warthog reservoir host by tsetse flies, including Glossina morsitans and G. brevipalpis, in which it develops in the midgut and proboscis. Tsetse flies also transmit it to swine, but once it has been introduced into a herd, it can apparently be transmitted mechanically by horseflies and other blood-sucking flies (Unsworth, 1952).

T. simiae is more resistant to drugs than the other African trypanosomes. Antrycide methyl sulfate is probably the best drug, but it may not be completely effective. It is injected subcutaneously at the rate of 5 mg/kg; more than one injection is probably necessary.

Control measures are the same as for T. brucei. In addition, horseflies and other biting flies should be controlled.

Trypanosoma dimorphon

This species was once thought to be a synonym of T. congolense, but Hoare (1959) restudied Laver an and Mesnil’s original slides, measuring 1200 individuals and analyzing the data statistically, and showed that it differs in length. T. dimorphon is 11 to 24 u, long with a mean of 16.2 u; the means of different populations ranged from 15.3 to 17.6 u. Despite its name, Hoare (1959) found that it is actually monomorphic. It is slender, without a free flagellum, and its undulating membrane is not pronounced. The posterior end is rounded (chiefly in the shorter forms) or pointed (chiefly in the longer forms). The nucleus is in the middle or posterior part of the body. The kinetoplast is fairly large and typically subterminal and marginal.

T. dimorphon occurs in Gambia, French Guinea, Ivory Coast, Belgian Congo, Sudan, Somalia, Southern Rhodesia, Portuguese East Africa, Zululand and possibly Nigeria, and has been found in the horse, sheep, goat, cattle, pig and dog. It is transmitted by tsetse flies in the same way as T. congolense.