Sero-prevalence and zoonotic implication of toxoplasmosis in sheep in South Africa

Abstract

Toxoplasmosis is a zoonotic disease with severe manifestations in HIV-positive human patients. In 1978 the overall sero-prevalence of toxoplasmosis in human patients in South Africa was found to be 20%. Toxoplasmosis in immunocompromised patients is known to be a cause of sometimes fatal complications, such as encephalomyelitis and ocular lesions. According to the literature, mutton infected with the cysts of Toxoplasma gondii is an important route of transmission to humans who ingest under-cooked meat, or eat with unwashed hands after working with meat. There is no data on the sero-prevalence in sheep in South Africa, although this is available for most other countries, including Zimbabwe. The aim of this study was to estimate the sero-prevalence of T.gondii in sheep in South Africa and to discuss the zoonotic aspects related to the prevalence of toxoplasmosis in humans. Three-stage cluster sampling was done where five different provinces randomly chosen from all the provinces in South Africa were the primary units: Gauteng, KwaZulu-Natal, Free State, Eastern Cape and Western Cape. Two sheep abattoirs and one rural location per province, selected randomly from a list supplied by the provincial Departments of Agriculture, were the secondary units. A total of 677 serum samples from these sheep were tested for IgG using the Indirect Fluorescent Antibody (IFA) test (Diagnostic&Technical Services CC, Randburg, South Africa) and the commercial Enzyme-linked Immunosorbent-Assay (ELISA) kit. Informal interviews were conducted with doctors (n=5), doctors regarded as experts (n=17) were selected for an expert opinion survey and National Laboratories (n=3) supplied data on human serum tested for toxoplasmosis in different provinces. The sero-prevalence in sheep, per province, was found to be: Gauteng 6%, Eastern Cape 7.8%, Western Cape 6%, KwaZulu-Natal 6.3% and Free State 2.7% when tested with the IFA test. The results obtained with the ELISA test were: Gauteng 6%, Eastern Cape 5.4%, Western Cape 4%, KwaZulu-Natal 3.6% and Free State 2.7%. Overall prevalences of 5.6% (IFA) and 4.3% (ELISA) were obtained. From the results it appears that toxoplasmosis in sheep has a lower sero-prevalence in South Africa than in other countries. Zimbabwe has an average sero-prevalence in sheep of 67.9%, there is a 80% sero-prevalence in sheep in France and 20-30% in different states in the USA. There was no significant difference between the levels in rural and commercial sheep at the 95% confidence level in South Africa, although there was a significantly higher prevalence in intensively farmed sheep in contrast to those farmed extensively. The informal interviews with the medical doctors indicated that they do not consider toxoplasmosis as an important disease. In contrast to these findings, the experts regard toxoplasmosis as a significant disease and the data obtained from the National Laboratories substantiated this opinion. The seroprevalence in humans was found to be between 14 and 32 % in the three provinces from which data were obtained. It can be concluded that the lower sero-prevalence of toxoplasmosis in sheep in South Africa, as compared with international levels, was probably due to more extensive methods of sheep farming and the relatively low rainfall in southern Africa. It must be noted, however, that comparison of sero- prevalence in different countries is made difficult by the many different tests and end-titres used in both humans and animals. Standardisation is recommended. The presence of toxoplasmosis in sheep in South Africa should be considered as significant because in this country we have a high consumption of mutton. Medical practitioners underestimate the importance of toxoplasmosis in humans. It was recommended that a pamphlet for education of veterinarians, doctors, health workers and patients be produced to increase the knowledge and understanding of this disease and its prevention in South Africa.