A retrospective study of wildlife rabies in Zimbabwe, between 1992 and 2003.

To assess the epidemiological features of wildlife rabies in Zimbabwe, a retrospective study covering a period of 12 years (1992-2003) was conducted using rabies records of the Central Veterinary Laboratories (CVL), Department of Veterinary Technical Services at Harare. Records of monthly and annual wildlife rabies were perused with regard to total samples submitted to the CVL and corresponding positive cases. Positive cases were analyzed in relation to the animal species involved, seasonal trends, and land-use categories. A total of 2107 samples were submitted and 1 540 (73.1%) were positive. Jackals (Canis mesomelas and C. adustus), with a peak occurrence of rabies between January and March were the major maintenance host, representing approximately 91% of the total rabies cases confirmed. The Canidae family recorded the highest number of cases followed by the Viverridae, Mustelidae, Felidae, Herpestidae and Hyaenidae families in that order. During the present study rabies cases were confirmed in 7 additional wild animals. The majority of the positive cases (83.7%) were recorded in commercial farming areas in the northeast parts of the country.

Observations on the use of Anaplasma centrale for immunization of cattle against anaplasmosis in Zimbabwe.

A total of 93 Bos taurus cattle was used in pen trials to compare vaccine stocks of Anaplasma centrale from South Africa and Australia (which stock came from South Africa in 1934) in protecting against three virulent field isolates from clinical Anaplasma marginale infections. In addition, field observations were made on the use of a vaccine, prepared from the Australian stock, in over 9553 cattle of mixed age and breeds on 16 co-operator farms and at one communal dip. The results of the pen trials indicated that the two vaccine stocks were comparable and that neither provided adequate protection against two of the three isolates of A. marginale. The field observations indicated that the vaccine was highly infective and produced mild reactions in most recipient cattle, and that users were generally satisfied with the vaccine. These somewhat conflicting results are discussed in the context of observations in Australia and future vaccination against anaplasmosis in Zimbabwe.

Isometamidium concentrations in the sera of cattle maintained under a chemoprophylactic regime in a tsetse-infested area of Zimbabwe.

An experiment was carried out to determine the concentrations of the trypanocidal drug isometamidium chloride in the sera of cattle maintained under a chemoprophylactic regimen at Rekomitjie, Zimbabwe, an area of high tsetse challenge in the Zimbabwe valley. In February 1993, 24 cattle at this site were treated intramuscularly with isometamidium chloride at a dose of 1.0 mg/kg body weight. Thereafter all animals were monitored regularly for 6 months for the presence of trypanosomes and sera were collected to determine the concentrations of isometamidium using an ELISA. Isometamidium treated cattle appeared to be protected against trypanosome infections for at least 18 weeks following treatment. Thereafter, three trypanosome infections were detected, between 20 and 22 weeks following treatment. In contrast, in 18 untreated control cattle at the same site, 9 trypanosome infections were detected over the first 18 weeks of the experiment. Quantification of the isometamidium concentration in sera from the drug treated cattle indicated that the apparent half-life of isometamidium in these animals was 23 days. This was similar to the half-life observed previously in cattle treated under laboratory conditions. The isometamidium ELISA was shown to be capable of quantifying drug levels in 20 out of 23 cattle for at least 70 days after treatment. There was no evidence of drug resistant trypanosomes at this site.

Correlation between antibodies to Cowdria ruminantium (rickettsiales) in cattle and the distribution of Amblyomma vector ticks in Zimbabwe.

Cowdriosis, caused by Cowdria ruminantium, is transmitted by Amblyomma ticks, which are widely distributed in Zimbabwe. To assess the distribution of this disease in Zimbabwe, cattle either exposed to Amblyomma ticks or maintained in areas free from these ticks were tested for antibodies to Cowdria. A total of 324 sera were tested using competitive ELISA and the indirect fluorescent antibody test (IFAT). At diptanks in Amblyomma-infested areas 52% (n = 95) and 26% (n = 47) of sera were positive by cELISA and IFAT, respectively. At diptanks in Amblyomma-free areas 11% (n = 125) and 10% (n = 134) of sera were positive by cELISA and IFAT, respectively. The results were significantly different between Amblyomma-infested and tick-free areas (chi 2 = 24.73, P < or = 0.005 for IFAT and chi 2 = 57.53, P < or = 0.005 for cELISA). High background readings in field sera, possibly due to cross-reactive antibodies to Ehrlichia spp., complicated the determination of a realistic cut-off point, especially in cELISA. On the basis of the distribution of Amblyomma ticks, currently a large part of Zimbabwe can be considered endemic for the disease.