Authors

R J Reimer¹; T D Hollinsworth²; M A Irvine²;  ¹ Liverpool School of Tropical Medicine;  ² University of Warwick

Discussion

Lymphatic Filariasis is a neglected tropical disease caused by mosquito-borne filarial nematodes that infect the lymphatic system. Approximately 1 billion people are at risk and there are currently ongoing efforts towards the elimination of the disease. This international programme has had a great number of successes, although open questions remain. One such question is how the origin of heterogeneity in the number of mature parasites and consequently the number of microfilariae (mf) in the blood. We test the hypothesis that this is derived primarily from the distribution from the number of infective bites received by an individual over their lifetime. We employed a dataset from five villages where moderate transmission of LF is present. These included spatially resolved bite counts along with mf blood counts and antigenic status of individuals. We calculated the heterogeneity of bites and mf by the fitting of a negative binomial distribution at both village-level and at the level of individuals. We found that the heterogeneity of bites at the village level is a very poor indicator of heterogeneity in the mf count (correlation less than 0.1). At the individual level, the number of bites was a stronger indicator of mf burden, although there was a significant variation in the distribution unaccounted for. This readdresses the need for further investigation and modelling effort in understanding how the population-level distribution of parasites arises from environmental, geographic and individual factors.