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Human infection patterns and heterogeneous exposure in river blindness
João A N Filipe1, Michel Boussinesq, Alfons Renz
1Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London W2 1PG, United Kingdom. joao.filipe@lshtm.ac.uk
Summary
Infection patterns of Onchocerca volvulus, the cause of river blindness, vary by location. Differences in exposure to infected black flies largely explain these variations in onchocerciasis.
Area of Science:
- Parasitology
- Epidemiology
- Mathematical Modeling
Background:
- Onchocerca volvulus causes river blindness, a significant neglected tropical disease.
- Infection patterns of O. volvulus differ across geographic locations and ecologies.
- Unlike other helminths, O. volvulus infection intensity does not consistently follow a humped pattern with host age.
Purpose of the Study:
- To investigate the reasons behind locale-specific infection patterns of O. volvulus.
- To test the hypothesis that heterogeneous exposure to vector bites influences infection intensity.
- To develop and apply a mathematical model to understand O. volvulus transmission dynamics.
Main Methods:
- Developed an age- and sex-structured mathematical model incorporating parasite regulation in humans and vectors.
- Fitted the model to pre-ivermectin microfilarial data from Cameroon, Guatemala, and Venezuela.
- Compared model estimates of transmission and infection loads with entomological and epidemiological data.
Main Results:
- Host age- and sex-heterogeneous exposure to vector bites significantly explains variations in onchocerciasis infection patterns across different localities.
- The basic reproductive number (R0) for O. volvulus was estimated to range from 5 to 8.
- These findings contrast with explanations involving acquired protective immunity seen in other helminth infections.
Conclusions:
- Heterogeneity in exposure to black fly bites is a primary driver of differing onchocerciasis infection patterns globally.
- Mathematical modeling provides valuable insights into the transmission dynamics of O. volvulus.
- Understanding exposure patterns is crucial for effective control strategies against river blindness.