Efficient method of extracting off-host stages of Tunga penetrans (sand flea) for the identification of transmission hotspots

Abstract text

Introduction

Tunga penetrans, (sand flea) is the cause of a severely neglected parasitic skin disease in the tropics and received little attention from entomologists to understand the transmission ecology.

Objective

Like all fleas, T. penetrans has environmental off-host stages and we used the Berlese-Tullgren funnel method to extract these off-host stages from soil samples to identify the disease transmission hotspots within rural households in Uganda and Kenya.

Material and Methods

The Berlese-Tullgren Funnel extractor was developed from locally available material in a small size with several units to fit the purpose of our work. We calibrated the apparatus by investigating the influence of different bulb powers as heat source and two extraction times. Field surveys were conducted in 50 tungiasis affected households. A total of 65 outdoor samples and 160 indoor samples were collected and extracted. The odds ratios or rate ratios and their 95% confidence intervals were calculated using generalized models in R software.

Results

The impact of heat (bulb wattage) and time (hours) on the efficiency of extraction was demonstrated and through a stepwise approach standard operating conditions defined for parallel extraction of 80% (95% CI 71-87%) of all present off-host stages from any given soil sample alive. The odds of finding off-host stages from indoor samples associated with infected individuals sleeping places was 7-fold higher (95% CI 2.4-21.5) than finding them from outdoor samples and for every larva found in the outdoor environment, 29 larvae were found indoors (95% CI 7.7-110.2).

Conclusions

Our findings highlight that the indoor sleeping areas are the transmission hotspots for tungiasis and can be targeted for disease control and prevention measures.