Abstract
BackgroundThe outcomes of insecticide-treated bednet (ITN) interventions for malaria control in Papua New Guinea tend to suggest a differential protective effect against Plasmodium falciparum and Plasmodium vivax. Little is known about the impact of ITNs on the relative abundance of mosquitoes infected with either P. falciparum or P. vivax. This paper describes the biting cycle of P. falciparum and P. vivax-infected mosquitoes and the impact of an ITN intervention on the proportion of mosquitoes infected with either parasite species.MethodsEntomological investigations were performed in East Sepik (ESP) and New Ireland Provinces (NIP) of PNG. Mosquitoes were collected using the all-night (18:00 - 06:00) landing catch and CDC light-trap methods and species specific malaria sporozoite rates were determined by ELISA.Results and discussionThe distribution of sporozoite positive mosquitoes in three four-hour periods (18:00-22:00, 22:00-02:00 & 02:00-06:00) showed that a higher proportion of P. vivax-infected mosquitoes were biting before people retired to bed under the protection of bednets. In the intervention village, the 308 mosquitoes collected before ITNs were introduced included eight (2.0%) P. falciparum-positive and four (1.0%) P. vivax-positive specimens, giving a parasite ratio of 2:1. The sporozoite rate determined from 908 mosquitoes caught after ITNs were introduced showed a significant decrease for P. falciparum (0.7%) and a slight increase for P. vivax (1.3%), resulting in a post intervention parasite ratio of 1:2. In the East Sepik Province, where ITNs were not used, P. falciparum remained the dominant species in 12 monthly mosquito collections and monthly P. falciparum:P. vivax formula varied from 8:1 to 1.2:1.ConclusionThese findings suggest that people sleeping under treated bednets may be more exposed to P. vivax than P. falciparum-infected mosquitoes before going to sleep under the protection of bednets. This difference in the biting behaviour of mosquitoes infected with different malaria parasites may partly explain the change in the P. falciparum:P. vivax formula after the introduction of ITNs.
Highlights
The outcomes of insecticide-treated bednet (ITN) interventions for malaria control in Papua New Guinea tend to suggest a differential protective effect against Plasmodium falciparum and Plasmodium vivax
These findings suggest that people sleeping under treated bednets may be more exposed to P. vivax than P. falciparum-infected mosquitoes before going to sleep under the protection of bednets
This difference in the biting behaviour of mosquitoes infected with different malaria parasites may partly explain the change in the P. falciparum:P. vivax formula after the introduction of ITNs
Summary
The outcomes of insecticide-treated bednet (ITN) interventions for malaria control in Papua New Guinea tend to suggest a differential protective effect against Plasmodium falciparum and Plasmodium vivax. The outcomes of insecticide-treated bednet (ITN) interventions for malaria control in PNG tend to suggest a differential protective effect against P. falciparum and P. vivax. Millen [2] working in the coastal areas of Madang Province showed a significant reduction in the prevalence of P. falciparum among children between one to four years of age, after treated bednets were introduced, but there was no effect on P. vivax prevalence. In the Highlands Region, the P. falciparum:P. vivax ratio in all age-groups changed from 3.8:1, before ITNs were introduced, to 1:1 six months afterwards [4] Other phenomena such as P. vivax relapses may lead to a change in the prevalence of P. vivax in humans independent of ITN interventions. The form and frequency of relapses depend on the infecting strain and occur due to the activation of hypnozoites in liver cells [5]
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