Prevalence of Taenia solium porcine cysticercosis in the Eastern, Southern and Western provinces of Zambia

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Abstract

Tongue examination and detection of circulating antigen (Ag-ELISA) were used to establish the prevalence of Taenia solium porcine cysticercosis in free-range pigs in selected districts of Eastern, Southern and Western provinces of Zambia, and to determine if prevalence of porcine cysticercosis was associated with age, breed and sex. Households with pigs were identified using the snowballing technique. A total of 1691 pigs were examined out of which 183 (10.8%) were positive on tongue examination. Ag-ELISA gave a sero-prevalence of 23.3%. When considering the factors in a logistic regression analysis, only breed type was significantly associated with porcine cysticercosis (OR = 0.72; 95%CI = 0.63–0.81). The crossbred pigs were 72% more likely to have had cysticercosis than the Nsenga (dwarf local) breed as determined by Ag-ELISA. The result that crossbred pigs had a higher prevalence of T. solium cysticercosis suggests that pig breeds may display different susceptibility to cysticercosis. The limited use of latrines in these areas implies that people use the nearby bush for defecation, resulting in pigs having access to human faeces. Therefore, investigation of taeniosis and cysticercosis in humans is warranted to better comprehend the local epidemiology and transmission risks. This should then be followed by extension programs to communities so that the control plans that could be instituted are more sustainable.

Introduction

Taenia solium cysticercosis is a serious public health problem in endemic regions (Garcia-Garcia et al., 1999, Geerts et al., 2002). Humans are the only definitive hosts while pigs act as intermediate hosts. Pigs are the source of human taeniasis, an intestinal tapeworm infection acquired by eating undercooked pork contaminated with Cysticercus cellulosae (cysticerci) the larval stage of the cestode. The pig is infected by ingestion of parasite eggs or proglottids in human faeces and acquires cysticercosis. Thus, porcine infection with T. solium is limited to areas where animal husbandry practices are such that pigs come into contact with human faeces (Toledo et al., 2001). Cysticercosis may also occur in humans if eggs are conveyed to the mouth by unclean fingers after defaecation (Flisser, 1994), but the swallowing of T. solium egg-contaminated soil, water or vegetation are the most likely causes of the human condition (Schantz et al., 1992).

Garcia et al. (1999) suggested that determining the percentage of the porcine population that is infected is a better epidemiological indicator of T. solium infection pressure than measuring the infection in the human population. These authors listed the following reasons for their proposal: firstly, porcine infection is much more common than the human infection; secondly, the life span of pigs in field conditions is much shorter than that of humans; and thirdly, the bleeding of pigs for diagnostic purposes is more easily accepted by pig owners compared to obtaining blood and/or stool specimens from humans.

Surveys in pigs have contributed to an increased awareness of this zoonotic infection in many developing countries, including Eastern and Southern Africa (Phiri et al., 2003). A pilot field study conducted by Phiri et al. (2002) suggested that porcine cysticercosis was prevalent in the rural areas of the Southern and Eastern provinces of Zambia and they recommended that an extensive study covering more districts and larger areas be conducted in order to explore the extent of T. solium infection in these areas.

The present survey, therefore, was conducted with the aim of establishing the prevalence of T. solium porcine cysticercosis in rural free-range pigs in selected districts of Eastern, Southern and Western provinces of Zambia and to establish if the prevalence of porcine cysticercosis was associated with age, breed and sex.

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Study areas

The study was done in five districts; Katete and Petauke in the Eastern province, Gwembe and Monze in the Southern province, and Mongu in the Western province (Fig. 1). With the exception of Gwembe, Monze and Mongu, these districts were selected following a preliminary survey that was conducted by Phiri et al. (2002), which indicated the presence of free-ranging pigs.

Study design and animals

A cross sectional study was conducted between June 2002 and September 2003. Sample size estimation was calculated using the

Study population

A total of 1691 pigs were examined comprising 769, 772 and 150 from the Eastern, Southern and Western provinces, respectively. Pigs were sampled from a total of 856 households.

Prevalence of T. solium porcine cysticercosis by district

Of the 1691 pigs examined, 182 (10.8%) were found to be positive on tongue examination. Ag-ELISA detected an overall sero-prevalence of 23.3%. Pigs in the Southern province had a higher prevalence of cysticercosis 15.2% (P < 0.001) on tongue examination than pigs in the Eastern and Western provinces, which had 7.0% and 7.3%

Discussion

We have conducted an extensive study in order to explore the endemicity of T. solium cysticercosis in pigs in Zambia, as recommended by Phiri et al. (2002) using two of the available diagnostic methods used in detection of T. solium cysticercosis infection in pigs, namely tongue examination and antigen-ELISA. The high prevalence of porcine cysticercosis observed in the Southern province on both tongue examination and Ag-ELISA, confirmed the findings of a preliminary field survey conducted by

Acknowledgements

The Danish International Development Agency (DANIDA) through the Enhancement in Research Capacity (ENRECA) Helminths Research Project in Eastern and Southern Africa is greatly thanked for funding this study. The authors would also like to thank the VLIR-UNZA IUC project for providing laboratory equipment used in this study. We are indebted to Mr. A.R. Mwanza for his cartographic assistance in drawing the map of study areas. The authors are grateful to the District Veterinary Officers,

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