This parasite is very common in sheep thruout the world. It is non-pathogenic, and infections are so sparse that it can ordinarily be found only by cultivation. The trypanosomes in the blood resemble T. theileri and are 50 to 60 u long.
T. melophagium is transmitted by the sheep ked, Melophagus ovinus, and can readily be found in its intestine. Its life cycle has been described by Hoare (1923). Crithidial forms are abundant in the midgut, and leishmanial forms occur here also. Both multiply by binary fission. The crithidial forms change into small, metacyclic trypanosome forms in the hindgut. Nelson (1956) found that T. melophagium. may kill the ked by blocking the midgut. Sheep are infected when they bite into the keds and the trypanosomes pass thru the intact buccal mucosa. Because infections in sheep are so sparse, it has been suggested that no multiplication occurs in this host.
This non-pathogenic species was found in goats in Palestine. It resembles T. melophagium and has a similar life cycle, except that its intermediate host is another hippoboscid fly, Lipoptena caprina. T. theodori may be a synonym of T. melophagium.
This species occurs in the wild European rabbit, Oryctolagus cuniculus. It has been found sporadically in England, France and other European countries. It is 24 to 28 u long. Its intermediate host is the flea, Spilopsyllus cuniculi, in which it develops in the gut. The metacyclic infective forms occur in the rectum. Infection is presumably by ingestion. Grewal (1956) described its life cycle briefly.
This species occurs quite commonly in the black rat, Norway rat and other members of the genus Rattus thruout the world. It is not normally transmissible to mice. It is 26 to 34 u long. Its vector is the rat flea, Nosopsyllus fasciatus, in which it develops in the gut, and in which the metacyclic, infective forms occur in the rectum. Rats become infected by eating infected fleas or flea feces. T. lewisi is non-pathogenic. A great deal of research has been done on this species, since it is easy to handle and its host is a convenient one.
This species occurs in the house mouse and other species of Mus thruout the world. It is not normally transmissible to rats. It is 28 to 34 u long. Its vector is the flea, Nosopsyllus fasciatus, and its life cycle is the same as that of T. lewisi. It is non-pathogenic.