Parasite survey of eight wild animals in the Ruma National Park.

Eight game animals representing seven species in the Ruma National Park in South Nyanza, Kenya, were examined for the presence of blood protozoa, ectoparasites, and helminthic and coccidian endoparasites using standard parasite-identification methods. Haematological parameters were also determined. The oribi was positive for Trypanosoma brucei ssp. and the reedbuck for T. congolense. No other blood protozoans were found. Strongyle eggs were found in the faeces of all species except the water buck. Five of eight animals harboured liver flukes and five were parasitized by ticks of the genus Amblyomma. One roan antelope was anaemic, but the other animals had haemoglobin levels within the normal range and appeared to be in a good state of health.

Experimental infection of cattle with Trypanosoma brucei rhodesiense.

Infection of cattle with various stocks of Trypanosoma brucei rhodesiense indicated that 49% developed a fatal CNS disease comparable to that found in man. Duration of disease ranged from 85 to 1613 days post infection. All eight stocks of T. b. rhodesiense tested, including those from Ethiopia and Tanzania, induced CNS disease. Blood became positive three to five days after inoculation, and after an initial peak of parasitaemia remained positive for three to five months. Subinoculation of blood into rodents subsequently became negative, although trypanosomes persisted in the lymph nodes for at least 56 to 1613 days. Only animals with CNS disease had detectable parasites in the CSF, usually after the animals had undergone severe deterioration. At post mortem examination trypanosomes could usually be found in the lymph nodes and CSF, and occasionally in the blood. Clinical signs included fever, hyperkinesia, weight loss, cerebellar ataxia, tremor, salivation and hyperaesthesia. A mild to moderate anaemia accompanied a transient thrombocytopenia and leucopenia. Animals subsequently developed leucocytosis. A pleocytosis and elevated total protein in the CSF was found, which persisted in some animals for long periods. Histopathological examination of the brain showed prominent generalized perivascular infiltrates consisting mainly of lymphocytes and plasma cells. Mott's cells were regularly observed. Vascular changes were characterized by swollen endothelium, infiltration of the vascular wall by inflammatory cells, and in some instances perivascular oedema. In the most severe cases evidence of ischaemia consisted of large numbers of astrocytes, rarefaction of the parenchyma, and areas of necrosis with loss of normal architecture. Demyelination was limited to perivascular areas. Occasionally a moderate to severe pancarditis was found.

Cerebral trypanosomiasis in naturally-infected cattle in the Lambwe Valley, south Nyanza, Kenya.

Surveys in Zebu cattle in the Lambwe Valley in 1980 indicated that many (up to 70%) were infected with trypanosomes. The predominant parasite was Trypanosoma brucei sspl followed by T. congolense. Cerebrospinal fluid (CSF) analysis showed a high proportion of animals with pleocytosis and elevated total CSF protein. Trypanosomes were detected in CSF and signs of a central nervous system (CNS) disease were observed. Histopathological lesions in the CNS were identical to those found in experimentally-infected cattle and consisted of perivascular infiltrations, swollen endothelium of vessels, infiltration of the vascular wall, and perivascular oedema. The severest cases showed rarefaction, astrocytosis and areas of necrosis. Infected cattle transported to the Veterinary Research Laboratory were studied for up to four years. Absence of trypanosomes from the peripheral blood was common, and even subinoculation of lymph node aspirates and CSF were usually negative. Death was preceded by a period of weight loss and the development of severe CNS signs. An attempt to cure animals with Mel-B treatment failed. Serum from naturally-infected cattle neutralized T. b. rhodesiense stocks collected in the same area.

Effects of splenectomy on Trypanosoma congolense infection in cattle.

The role of the spleen in cattle infected with Trypanosoma congolense was studied by comparing levels of parasitaemia, blood cell values, and body weights of intact and splenectomized cattle. A total of 28 Zebu x Hereford steers were used in two separate experiments. Seven animals were splenectomized at least four weeks prior to infection and two others were splenectomized 128 days after infection. Splenectomized animals were compared to 12 intact infected animals and seven intact uninfected controls. The splenectomized animals suffered no less severe anemia and no higher parasitaemia than the intact, infected cattle. Splenectomy in two animals during infection had no effect on packed cell volumes, parasitaemia or survival. Splenectomized cattle have lower levels of circulating lymphocytes following treatment than intact animals; also, the splenectomized steers lost more weight during the active infection.