The incidence of human cysticercosis in a rural community of Eastern Zambia

Immunology of Taenia solium taeniasis and human cysticercosis

The life cycle of Taenia solium, the pork tapeworm, is continuously closed in many rural settings in developing countries when free roaming pigs ingest human stools containing T. solium eggs and develop cysticercosis, and humans ingest pork infected with cystic larvae and develop intestinal taeniasis, or may also accidentally acquire cysticercosis by faecal-oral contamination. Cysticercosis of the human nervous system, neurocysticercosis, is a major cause of seizures and other neurological morbidity in most of the world. The dynamics of exposure, infection and disease as well as the location of parasites result in a complex interaction which involves immune evasion mechanisms and involutive or progressive disease along time. Moreover, existing data are limited by the relative lack of animal models. This manuscript revises the available information on the immunology of human taeniasis and cysticercosis.

Study and ranking of determinants of Taenia solium infections by classification tree models

Taenia solium taeniasis/cysticercosis is an important public health problem occurring mainly in developing countries. This work aimed to study the determinants of human T. solium infections in the Eastern province of Zambia and rank them in order of importance. A household (HH)-level questionnaire was administered to 680 HHs from 53 villages in two rural districts and the taeniasis and cysticercosis status determined. A classification tree model (CART) was used to define the relative importance and interactions between different predictor variables in their effect on taeniasis and cysticercosis. The Katete study area had a significantly higher taeniasis and cysticercosis prevalence than the Petauke area. The CART analysis for Katete showed that the most important determinant for cysticercosis infections was the number of HH inhabitants (6 to 10) and for taeniasis was the number of HH inhabitants > 6. The most important determinant in Petauke for cysticercosis was the age of head of household > 32 years and for taeniasis it was age < 55 years. The CART analysis showed that the most important determinant for both taeniasis and cysticercosis infections was the number of HH inhabitants (6 to 10) in Katete district and age in Petauke. The results suggest that control measures should target HHs with a high number of inhabitants and older individuals.

Taenia spp. infections in wildlife in the Bangweulu and Kafue flood plains ecosystems of Zambia

Taenia spp. have an indirect life cycle, cycling between a definitive and an intermediate host with zoonotic species causing public health problems in many developing countries. During the course of 2 separate surveys in Zambia (2004 and 2009), the presence of Taenia larval stages (cysticerci) was examined in Kafue lechwe (Kobus leche kafuensis), Black lechwe (Kobus leche smithermani) and other wildlife species from the Kafue and Bangweulu flood plains. Examinations involved post-mortem inspection and serum specific antigen detection. The recovered cysts from seven carcasses were characterised using PCR and DNA sequence analysis. The overall proportion of infection in wildlife on post-mortem examination was 19.0% (95% CI: 9.1-29.0%). The proportion of infected wildlife based on post-mortem examinations in the Kafue flood plains was estimated at 28.6% (95% CI: 13.3-43.9%), while the seroprevalence was estimated at 25.0% (95% CI: 2.9-47.1%). The seroprevalence for cattle in the Kafue flood plains was estimated at 61.5% (95% CI: 42.0-81.0%) while that of Kafue lechwe in the same ecosystem was estimated at 66.6% (95% CI: 45.6-85.7%). Infection rates were higher in Kafue lechwe than in Black lechwe suggesting differences in the exposure patterns. The sequencing results indicated that none of the recovered cysts were either Taenia solium or Taenia saginata. We therefore conclude they most likely belong to a less studied (wildlife) Taenia species that requires further characterisation.

Incidence of human Taenia solium larval Infections in an Ecuadorian endemic area: implications for disease burden assessment and control

BACKGROUND

Human cysticercosis is a zoonotic disease causing severe health disorders and even death. While prevalence data become available worldwide, incidence rate and cumulative incidence figures are lacking, which limits the understanding of the Taenia solium epidemiology.

METHODOLOGY/PRINCIPAL FINDINGS

A seroepidemiological cohort study was conducted in a south-Ecuadorian community to estimate the incidence rate of infection with and the incidence rate of exposure to T. solium based on antigen and antibody detections, respectively. The incidence rate of infection was 333.6 per 100,000 person-years (95% CI: [8.4-1,858] per 100,000 person-years) contrasting with a higher incidence rate of exposure 13,370 per 100,000 person-years (95% CI: [8,730-19,591] per 100,000 person-years). The proportion of infected individuals remained low and stable during the whole study year while more than 25% of the population showed at least one antibody seroconversion/seroreversion during the same time period.

CONCLUSIONS/SIGNIFICANCE

Understanding the transmission of T. solium is essential to develop ad hoc cost-effective prevention and control programs. The estimates generated here may now be incorporated in epidemiological models to simulate the temporal transmission of the parasite and the effects of control interventions on its life cycle. These estimates are also of high importance to assess the disease burden since incidence data are needed to make regional and global projections of morbidity and mortality related to cysticercosis.

Nothing is perfect! Trouble-shooting in immunological and molecular studies of cestode infections

This personal review focuses on ways to approach and overcome some of the more common issues encountered while studying cestode zoonoses. The information presented here is based on the author's own experiences with immunological and molecular approaches for the detection of these parasites. There are many incongruities between immunological and molecular studies due to biased work. Nothing is perfect. Indirect approaches using either immunological, or even molecular tools, are limited without confirmation from direct evidence of infection. The dilemma of whether developing countries should develop their own diagnostic tests or rely on commercially available kits is also discussed.