Abstract
The relationship between mosquito vectors and lymphatic filariasis (LF) parasites can result in a range of transmission outcomes. Anophelines are generally characterized as poor vectors due to an inability to support development at low densities. However, it is important to understand the potential for transmission in natural vectors to maximize the success of elimination efforts. Primary vectors in Papua New Guinea (n = 1209) were dissected following exposure to microfilaremic blood (range 8–233 mf/20 µl). We examined density dependent and species-specific parasite prevalence, intensity and yield, barriers to parasite development as well as impacts on mosquito survival. We observed strikingly different parasite prevalence and yield among closely related species. Prevalence of infective stage larvae (L3s) ranged from 4.2% to 23.7% in An. punctulatus, 24.5% to 68.6% in An. farauti s.s. and 61.9% to 100% in An. hinesorum at low and high density exposures, respectively. Injection experiments revealed the greatest barrier to parasite development involved passage from the midgut into the hemocoel. The ratio of L3 to ingested mf at low densities was higher in An. hinesorum (yield = 1.0) and An. farauti s.s. (yield = 0.5) than has been reported in other anopheline vectors. There was a negative relationship between mosquito survival and bloodmeal mf density. In An. farauti s.s., increased parasite yield and survival at low densities suggest greater competence at low microfilaremias. In Papua New Guinea the likelihood of transmission will be strongly influenced by vector composition and changes in the mf reservoir as a result of elimination efforts. Global elimination efforts will be strengthened by the knowledge of transmission potential in the context of current control measures.
Highlights
Human lymphatic filariasis (LF) is a mosquito-borne disease that is a leading cause of morbidity worldwide. 1.4 billion people in 81 countries are at risk of infection with the nematode parasites Wuchereria bancrofti, Brugia malayi or B. timori
If the adults were reared from wild-caught larvae, morphological characteristics were observed with a stereomicroscope and used to classify individuals into the three major An. punctulatus morpho groups (An. punctulatus, An. farauti s.l. and An. koliensis) prior to dissection
There was no significant difference in the mean number of mf ingested between An. punctulatus and An. farauti s.s. (ANCOVA p = 0.6)
Summary
Human lymphatic filariasis (LF) is a mosquito-borne disease that is a leading cause of morbidity worldwide. 1.4 billion people in 81 countries are at risk of infection with the nematode parasites Wuchereria bancrofti, Brugia malayi or B. timori. Human lymphatic filariasis (LF) is a mosquito-borne disease that is a leading cause of morbidity worldwide. 1.4 billion people in 81 countries are at risk of infection with the nematode parasites Wuchereria bancrofti, Brugia malayi or B. timori. Clinical manifestations, including acute fevers, chronic lymphedema, elephantiasis and hydrocele, result in the loss of 5.9 million disability-adjusted life-years [1]. Even individuals with mild manifestations are stigmatized in their societies and suffer psychological impacts [2]. W. bancrofti parasites, which account for 90% of the global disease burden, dwell in the lymphatic system, where the adult female worms release microfilariae (mf) into the blood. Mf are taken up in the blood meal of a mosquito, and go through several developmental stages within permissive vector species. Infectivestage larvae (L3s) actively escape from the mosquito mouthparts during a bloodfeeding event and enter a new vertebrate host through skin
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