An epidemiological study of human tapeworm infections in the Eastern Province of Zambia

Abstract

Neurocysticercosis is an important neglected parasitic zoonoses caused by the metacestode stage of Taenia solium. The infection is endemic in most developing countries of Africa, Asia and Latin America. Most studies on the parasite in endemic regions of sub-Saharan Africa have been carried out in pigs with little or no data available on human taeniosis/cysticercosis. The aim of this thesis was to provide an understanding of the epidemiology of human taeniosis/cysticercosis in the Eastern province of Zambia where porcine cysticercosis is endemic, and to assess the performance of the existing diagnostic tests under field conditions. Community-based cross sectional and longitudinal studies (Chapters 3 and 4 respectively) were carried out in two rural communities of Eastern Zambia to obtain the prevalence of taeniosis/cysticercosis and incidence of cysticercosis respectively as well as to study related risk factors. Given the constraints associated with blood collection in epidemiological studies, the use of urine, which is better accepted by communities, as a diagnostic specimen for human cysticercosis in field conditions, was evaluated (Chapter 6). Furthermore, three techniques, coproscopy, copro-Ag ELISA and copro-PCR, for the detection of taeniosis in stool samples were compared (Chapter 7). Prevalences of 6.3% (45/718) and 5.8% (41/708) were determined for taeniosis based on copro-Ag ELISA and cysticercosis using Ag-ELISA assays, respectively in the study area in Petauke district with an increased frequency of cysticercosis positive individuals from the age of 30 onwards. In a neighbouring district, Katete, higher prevalences of 12.0% (27/227) and 14.5% (155/1069) were determined for taeniosis and cysticercosis using the same tests, respectively, but no significant relationship with age could be identified. A higher prevalence rate of cysticercosis based on sero-Ab analysis (EITB) ranging between 33.5 (54/161) and 38.5% (62/161) was recorded in the Katete study. The overall incidence rate for cysticercosis in Katete was determined to be 6.2% after 12 months. The longitudinal study revealed that even though many people were exposed to the infection as indicated by the antibody and antigen presence, few actually established active infections. This highlighted the importance of a multitude of factors, and not just exposure, that play a role in the establishment of infection and/or symptomatology. Classification and regression analyses (CART) revealed that older individuals and those that came from households with many inhabitants were associated with higher prevalence rates of infection, listing these disease determinants as being very important for infection, and as such potential focus points of control programmes. Moreover, the CART highlighted differences in important disease determinants in neighbouring endemic areas, indicating the complexity of identifying optimal control measures. Evaluation of the urine Ag-ELISA revealed a lower specificity as compared to the serum Ag-ELISA which was more pronounced testing the Zambian samples (78.6%) than the Ecuadorian samples (88.4%). Therefore, aspects of specificity have to be addressed for urine to be used as a sample in field conditions. Comparison of three different diagnostic tests for taeniosis showed coproscopy to be the least sensitive (52.5%) and the copro-PCR the most specific (99.6%). Given the findings of this study, control of the tapeworm remains a challenge. It is proposed that, as there is a lack of knowledge of the parasite at all levels; health education should always be included in control programmes. It would be the best option in the long term, and would also determine the success of other more short term control measures as the more people get to know about the importance of the parasite the more they will accept control measures such as improved sanitation, vaccination and/or treatment of pigs and treatment of adult tapeworm carriers. Chapters 3, 4 and 5 of this thesis demonstrated that human T. solium taeniosis/cysticercosis is endemic in the study area. It also indicated the need for further studies on transmission dynamics and burden of disease on the local people, as well as further improvement of diagnostic techniques. Finally, given the complexity of the disease determinants, as highlighted in chapter 5, the control of T. solium in our study area depends on multi-sectoral collaboration including the medical, veterinary and other relevant sectors as well as effective engagement of the affected communities.