Stolk, W.A.

Health seeking behaviour and utilization of health facilities for schistosomiasis-related symptoms in ghana (Article)

2010-11-01T00:00:00Z

Background: Schistosomiasis causes long-term illness and significant economic burden. Morbidity control through integration within existing health care delivery systems is considered a potentially sustainable and cost-effective approach, but there is paucity of information about health-seeking behaviour. Methods: A questionnaire-based study involving 2,002 subjects was conducted in three regions of Ghana to investigate health-seeking behaviour and utilization of health facilities for symptoms related to urinary (blood in urine and painful urination) and intestinal schistosomiasis (diarrhea, blood in stool, swollen abdomen and abdominal pain). Fever (for malaria) was included for comparison. Results: Only 40% of patients with urinary symptoms sought care compared to.70% with intestinal symptoms and.90% with fever. Overall, about 20% of schistosomiasis-related symptoms were reported to a health facility (hospital or clinic), compared to about 30% for fever. Allopathic self-medication was commonly practiced as alternative action. Health-care seeking was relatively lower for patients with chronic symptoms, but if they took action, they were more likely to visit a health facility. In a multivariate logistic regression analysis, perceived severity was the main predictor for seeking health care or visiting a health facility. Age, socio-economic status, somebody else paying for health care, and time for hospital visit occasionally showed a significant impact, but no clear trend. The effect of geographic location was less marked, although people in the central region, and to a lesser extent the north, were usually less inclined to seek health care than people in the south. Perceived quality of health facility did not demonstrate impact. Conclusion: Perceived severity of the disease is the most important determinant of seeking health care or visiting a health facility in Ghana. Schistosomiasis control by passive case-finding within the regular health care delivery looks promising, but the number not visiting a health facility is large and calls for supplementary control options.

The role of monitoring mosquito infection in the Global Programme to Eliminate Lymphatic Filariasis (Article)

2009-07-01T00:00:00Z

In addition to monitoring infection in the human host, there is also a need to assess larval infection in the vector mosquito population to evaluate the success of interventions for eliminating lymphatic filariasis transmission from endemic communities. Here, we review the current status of the available tools for quantifying vector infection and existing knowledge and evidence regarding potential infection thresholds for determining transmission interruption, to assess the potential for using vector infection monitoring as a tool for evaluating the success of filariasis treatment programmes.

LYMFASIM, a simulation model for predicting the impact of lymphatic filariasis control: quantification for African villages. (Article)

2008-11-23T00:00:00Z

LYMFASIM is a simulation model for lymphatic filariasis transmission and control. We quantified its parameters to simulate Wuchereria bancrofti transmission by Anopheles mosquitoes in African villages, using a wide variety of reported data. The developed model captures the general epidemiological patterns, but also the differences between communities. It was calibrated to represent the relationship between mosquito biting rate and the prevalence of microfilariae (mf) in the human population, the age-pattern in mf prevalence, and the relation between mf prevalence and geometric mean mf intensity. Explorative simulations suggest that the impact of mass treatment depends strongly on the mosquito biting rate and on the assumed coverage, compliance and efficacy. Our sensitivity analysis showed that some biological parameters strongly influence the predicted equilibrium pre-treatment mf prevalence (e.g. the lifespan of adult worms and mf). Other parameters primarily affect the post-treatment trends (e.g. severity of density dependence in the mosquito uptake of infection from the human blood, between-person variability in exposure to mosquito bites). The longitudinal data, which are being collected for evaluation of ongoing elimination programmes, can help to further validate the model. The model can help to assess when ongoing elimination activities in African populations can be stopped and to design surveillance schemes. It can be a valuable tool for decision making in the Global Programme to Eliminate Lymphatic Filariasis.

Advances and challenges in predicting the impact of lymphatic filariasis elimination programmes by mathematical modelling. (Article)

2006-03-28T00:00:00Z

Mathematical simulation models for transmission and control of lymphatic filariasis are useful tools for studying the prospects of lymphatic filariasis elimination. Two simulation models are currently being used. The first, EPIFIL, is a population-based, deterministic model that simulates average trends in infection intensity over time. The second, LYMFASIM, is an individual-based, stochastic model that simulates acquisition and loss of infection for each individual in the simulated population, taking account of individual characteristics. For settings like Pondicherry (India), where Wuchereria bancrofti infection is transmitted by Culex quinquefasciatus, the models give similar predictions of the coverage and number of treatment rounds required to bring microfilaraemia prevalence below a level of 0.5%. Nevertheless, published estimates of the duration of mass treatment required for elimination differed, due to the use of different indicators for elimination (EPIFIL: microfilaraemia prevalence < 0.5% after the last treatment; LYMFASIM: reduction of microfilaraemia prevalence to zero, within 40 years after the start of mass treatment). The two main challenges for future modelling work are: 1) quantification and validation of the models for other regions, for investigation of elimination prospects in situations with other vector-parasite combinations and endemicity levels than in Pondicherry; 2) application of the models to address a range of programmatic issues related to the monitoring and evaluation of ongoing control programmes. The models' usefulness could be enhanced by several extensions; inclusion of different diagnostic tests and natural history of disease in the models is of particular relevance.

Lymphatic Filariasis: Transmission, Treatment and Elimination (Doctoral Thesis)

2005-11-25T00:00:00Z

Lymphatic filariasis (LF) is a mosquito-borne, tropical disease caused by filarial worms. Infection can lead to disabling chronic disease, characterized by swelling of extremities or external genitalia (lymphoedema, elephantiasis and hydrocele). Mass treatment with antifilarial drugs is used to reduce the parasite load in the population, in order to reduce transmission and prevent disease. This is so effective that elimination of LF seems possible. Using a mathematical for lymphatic filariasis transmission in Pondicherry, India, we predicted how long yearly mass treatment would have to be continued to achieve elimination. Six annual treatments with the recommended combination of diethylcarbamazine (DEC) and albendazole would be sufficient if population coverage is 65% per round. Only four rounds would do if coverage is 80%. The required duration of mass treatment increases with endemicity level. In a comparison of transmission efficiency for different mosquito species, we found that the relationship between infection intensity in humans and the number of infective larvae developing in mosquitoes differed markedly. Mosquito characteristics may largely influence elimination prospects and predictions for Pondicherry cannot be generalized. A further study concentrated on the role of acquired immunity. We found that existing models for such immunity, which predict a decline in infection intensity in older humans, are not valid for lymphatic filariasis. We also quantified the effects of drugs treatment on different parasite stages: DEC and ivermectin were found to affect a very large proportion of microfilariae and adult worms; these drugs were even more effective when given in combination with albendazole. In conclusion, prospects for LF elimination by mass treatment are good if population coverage is sufficiently high, but the required duration depends on local transmission dynamics, endemicity level, and the efficacy of employed treatment regimens.