The parasitological and serological prevalence of tsetse-transmitted bovine trypanosomosis in the Eastern Caprivi (Caprivi District, Namibia).

Between August 1995 and June 1997 a survey to determine the distribution of tsetse-transmitted trypanosomosis was conducted in the Eastern Caprivi (Caprivi District, Namibia). A total of 1,481 adult cattle was examined at 33 sampling sites. Direct parasitological diagnostic tests were used and eluted blood spots were screened for the presence of anti-trypanosomal antibodies. Tsetse-transmitted trypanosomal infections were detected in 66 animals (4.5%) from 14 different locations. The parasitological and serological prevalence of trypanosomosis was highest in the Mamili area. Trypanosomosis was virtually absent in the Linyanti/Chobe area and the target barrier along the Kwando River had significantly reduced the prevalence of trypanosomosis in cattle grazing to the east of it. This suggests that anti-trypanosomal antibody prevalence data can be used to evaluate and monitor the effectiveness of tsetse control measures. Survey results suggest that in the Katima Mulilo area, trypanosomal infections were being acquired when cattle grazed along the Zambezi River. Moreover, survey results indicate that tsetse have not been able to establish themselves in the Katima Mulilo area. The parasitological prevalence in a herd and the respective prevalence of anti-trypanosomal antibodies was significantly correlated to the percentage of anaemic animals in that herd. Furthermore, the parasitological prevalence in a herd was positively correlated with the prevalence of anti-trypanosomal antibodies of that herd. It is concluded that the prevalence of anti-trypanosomal antibodies in a herd can be used as an additional indicator of the extent of infection in that particular herd.

The effect of short-interval deltamethrin applications to control tsetse on the seroprevalence of babesiosis in cattle.

For the past decade, treatment of cattle with 0.00375% deltamethrin (Decatix, Coopers) at two-weekly intervals has been part of an integrated approach to counteract continuous invasion of Zimbabwe by tsetse from the Mozambique fly-belt. To determine the effect of these regular deltamethrin treatments on the epidemiology of babesiosis, a survey was conducted to estimate the prevalence of antibodies against Babesia bigemina in adult communal cattle. The seroprevalence of antibodies against B. bigemina in adjacent areas, where cattle are treated with short-residual acaricides, was also determined for comparison. The prevalence of antibodies to B. bigemina was much higher in areas where dipping with a non-pyrethroid acaricide was conducted. This was attributed to the successful control of Boophilus spp. and hence a very low level of B. bigemina transmission in the 'deltamethrin treatment zone'. This low level of disease transmission was confirmed by the low prevalence of antibodies against B. bigemina in sentinel cattle that were introduced to the 'deltamethrin treatment zone'. The potential adverse effects of severely reducing the tick population should be taken into consideration at the onset of tsetse control operations in which cattle are to be treated with deltamethrin at short treatment intervals.

Evaluation of insecticide-treated cattle as a barrier to re-invasion of tsetse to cleared areas in northeastern Zimbabwe.

A field trial in Zimbabwe investigated the efficacy of insecticide-treated cattle as a barrier to prevent the re-invasion of tsetse, Glossina morsitans and G. pallidipes (Diptera: Glossinidae), into cleared areas. The original tsetse barrier consisted of insecticide-treated odour-baited targets, at an operational density of four to five targets per km2, supported by insecticide-treatments of cattle with either deltamethrin dip (Decatix, Coopers) at two-weekly intervals, or deltamethrin pouron (Spoton, Coopers) at monthly intervals, in a band approximately 20 km wide from the re-invasion front. Tsetse catch, and trypanosomiasis incidence in nine sentinel herds was recorded for 7-8 months, respectively, before the targets were removed, leaving only the insecticide treatment of the local cattle to stem the re-invasion of tsetse. After the removal of the target barrier, the tsetse readily invaded the trial area and the incidence of trypanosomiasis in sentinel herds increased, while their PCVs decreased. After seven months without the targets in place, trypanosomiasis prevalence in the local stock had reached alarmingly high levels; the trial was terminated prematurely and the target barrier re-deployed. Immediately after the re-deployment of the target barrier, the tsetse catch in the trial area reverted to acceptable levels along the re-invasion front, and trypanosomiasis incidence in the sentinel cattle decreased. It is concluded that, under the conditions of the field trial, the insecticidal treatment of local cattle did not in itself form an effective barrier to tsetse re-invasion. By contrast, the target barrier performed as was predicted by mathematical and experimental analysis, and readily cleared the tsetse infestation and reduced trypanosomosis incidence in the trial area.

Detection of bovine-virus-diarrhoea-virus antibodies in cattle with an enzyme-linked immunosorbent assay.

The serum-neutralization (SN) and the indirect-immunofluorescence (IIF) assays have invariably been used for detecting antibodies against bovine virus diarrhoea virus (BVDV) in cattle sera. An enzyme-linked immunosorbent assay (ELISA) was applied which has a sensitivity comparable with the SN and IIF in detecting antibody to BVDV. A total of 472 bovine sera were assayed and a high prevalence of 79.2% was recorded. Positive correlations between the ELISA and the SN were found when certain sera were assayed, implying that the former test could then be used for routine diagnosis of BVDV.