Multiparasitism in Sub-Saharan West African Countries: Don't Forget the Least Important!

Abstract

In a recent issue of Parasitology Today[1xZinsstag, J. et al. Parasitol. Today. 1998; 14: 46–49Abstract | Full Text | Full Text PDF | PubMed | Scopus (15)See all References][1], Jakob Zinsstag et al. gave us a very nice review on the epidemiology and economic weight of gastrointestinal parasites of sheep and cattle in West Africa. This work includes the observations of the efficient young West African researchers network that Pfister and Zinsstag developed. However, some comments have to be made because multiparasitism is often not taken into account.A few years ago, during the WAAVP meeting held in Yokohama, Japan, Peter Hansen (Abstract)1P. Hansen, Tropical livestock industry: parasite control, food security and the environment. Proceedings, 15th International Conference of the World Association for the Advancement of Veterinary Parasitology, Yokohama, Japan, 1995, p. 551 stressed the impact of `secondary' pathogens. The extensive campaigns against Rinderpest, trypanosomiasis, etc. have utilized funds, therefore causing a shortage of money with which to fight against strongyles, flukes, etc. These pests are not often `serial killers', but their pathogenic weight is high. To establish prevalence of some of them, and evaluate their importance, we performed sero-epidemiological surveys in sheep and goats in Africa using indirect haemagglutination assay for Toxoplasma[2xDorchies, P. et al. Revue de Medecine Veterinaire. 1996; 147: 377–378See all References][2]and by a specific ELISA (enzyme-linked immunosorbent assay) for CEstrus ovis (P. Dorchies, Abstract)2P. Dorchies et al. (1997) Proceedings, 16th International Conference of the World Association for the Advancement of Veterinary Parasitology, Sun City, South Africa, 1997, p. 212.Table 1Table 1 (Ref. [2xDorchies, P. et al. Revue de Medecine Veterinaire. 1996; 147: 377–378See all References][2]) shows that toxoplasmosis may be a serious threat in African countries mainly in wet areas. Toxoplasmic ovine abortion is frequent in some countries such as the UK, but the situation in Africa is not well known. Moreover, this infection may be serious for the babies of young women. Some correlation has been observed between human and animal seroprevalence as both are exposed to the same risk.Table 1Seroprevalence of ovine toxoplasmosis in AfricaaCountrySera, NbPositive (%)Burkina Faso6523Ivory Coast6268Djibouti18312.6Ethiopia9425.6Niger7719.5Senegal5211.5 View Table in HTML aData from Ref. [2xDorchies, P. et al. Revue de Medecine Veterinaire. 1996; 147: 377–378See all References][2].Sheep nasal bot is another example of a widespread parasite, and is so frequent that its pathological weight is difficult to evaluate. Sheep or goats mouth-breathing is a common sight during the dry season because nasal discharge cakes with dust on the nostrils. This is known by vets or breeders to be related to pasteurellosis: of course, but the infection is secondary to CEstrus ovis infection. Because the CEstrus ovis infection results in impairment of grazing and rumination, a local but not very pathogenetic parasite can have a serious economic weight.Parasitologists are increasingly aware that one of the most important threats due to helminths and arthropods is related to immunomodulation. The permanent challenge to the immune system increases the susceptibility of the animal to viral and bacterial diseases that finally kill it. If we want sustainable development of breeding in many countries we have to be aware of the weight of these `small' parasites.In their paper, Zinsstag et al.[1xZinsstag, J. et al. Parasitol. Today. 1998; 14: 46–49Abstract | Full Text | Full Text PDF | PubMed | Scopus (15)See all References][1]did not stress the impact of helminth circulation among grazing animals[3xJacquiet, P. et al. Int. J. Parasitol. 1998; 26: 253–261Crossref | Scopus (24)See all References][3]. Some recent papers deal with the importance of host range (sheep, goats, cattle and camels) in the survival of Homonchus spp in Africa. Parasites may survive as adults or as hypobiotic larvae in specific hosts (eg. H. contortus in sheep, H. placei in cattle and H. longistipes in camel), but also in nonspecific hosts (eg. H. longistipes in goats, H. placei in sheep). These facts have to be taken into account when a drenching program is planned.These examples confirm once again the impact of `secondary' pests that, in some cases, may represent serious health threats.