Clinical and haematological responses of domestic dogs and free-living jackals (canis mesomelas) to ehrlichia canis infection

Abstract

A high incidence of clinical and subclinical canine ehrlichiosis was found in dogs from Nairobi and the surrounding area, using a modification of an established blood mononuclear cell culture test. Clinical signs observed included pyrexia, depression, selective appetite, weight loss, splenomegaly, lymphadenopathy, epistaxis, haematemesis, haematuria, blood in faeces and haemorrhages in the skin and mucous membranes. Bleeding into joints and the spinal column, reduced conception rates and abortions also appeared to be associated with the presence of Ehrlichia canis. The frequency of these signs and corresponding changes in the blood were studied in 373 domestic dogs and 16 silver-backed jackals. The cases were grouped according to the major presenting signs and individual clinical cases representing the characteristics of most groups have been described. There was no difference in the clinical disease seen in pure-bred dogs~ German Shepherd dogs or cross-bred dogs. Eight cross-bred puppies were experimentally infected with E. canis and the disease reactions were studied. The clinical and haematological changes were mild and transient in all but one of these dogs. These changes, though mild, were similar to *(exluding German Shepherd dogs) those presented by naturally occurring cases seen at the clinic. One of these eight dogs however, died after becoming severely pancytopenic. On post-mortem examination, extensive haemorrhages were found throughout the carcase and histologically plasma cell infiltration was evident in most organs. These findings were typical of the disease as described elsewhere in the world. Tetracycline hydrochloride, doxycycline and imidocarb dipropionate were evaluated for their efficacy in the treatment of the clinical disease and for their ability in the elimination of the causative organism from the peripheral blood. All three drugs were effective in treating the clinical disease, but imidocarb dipropionate was the most efficient in eliminating the organism from the peripheral blood. The use of imidocarb dipropionate was associated with a number of undesirable side effects which have been documented. The responses of 153 of these clinical cases to treatment with these compounds were followed in detail. Free-living jackals were shown to harbour E. canis using the blood mononuclear test. Ehrlichia canis from jackals was cultured and subinoculated into young cross-bred puppies. Clinical and haematological changes in these puppies indicated a disease process that was similar to that seen in the experimentally infected puppies and in many of the naturally occurring cases. Rhipicephalus sanguineus and Haemaphysalis leachii, which are common ticks on domestic dogs, were among the tick species carried by these infected jackals and R. sanguine us is the known vector of ehrlichiosis. Tick-sharing could occur where dogs and jackals intermingle and it is likely that free-living jackals could act as a natural reservoir for ehrlichiosis in Kenya.