Abstract
BackgroundA stenogamous colony of Anopheles cracens (A. dirus B) established 20 years ago in a Thai insectary proved susceptible to Plasmodium vivax. However, routine sporozoite production by feeding on field-collected blood samples has not been described. The setting-up of an A. cracens colony in an insectary on the Thai-Myanmar border and the process of using P. vivax field samples for the production of infectious sporozoites are described.MethodsThe colony was started in 2012 from egg batches that were sent from the Department of Parasitology, Faculty of Medicine, University of Chiang Mai, to the Shoklo Malaria Research Unit (SMRU), on wet filter paper in sealed Petri dishes. From May 2013 to December 2014, P. vivax-infected blood samples collected from patients seeking care at SMRU clinics were used for membrane feeding assays and sporozoite production.ResultsMosquitoes were fed on blood samples from 55 patients, and for 38 (69 %) this led to the production sporozoites. The average number of sporozoites obtained per mosquito was 26,112 (range 328–79,310). Gametocytaemia was not correlated with mosquito infectiousness (p = 0.82), or with the number of the sporozoites produced (Spearman’s ρ = −0.016, p = 0.905). Infectiousness did not vary with the date of collection or the age of the patient. Mosquito survival was not correlated with sporozoite load (Spearman’s ρ = 0.179, p = 0.282).ConclusionConsistent and routine P. vivax sporozoites production confirms that A. cracens is highly susceptible to P. vivax infection. Laboratory-bred colonies of this vector are suitable for experimental transmission protocols and thus constitute a valuable resource.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0830-0) contains supplementary material, which is available to authorized users.
Highlights
A stenogamous colony of Anopheles cracens (A. dirus B) established 20 years ago in a Thai insectary proved susceptible to Plasmodium vivax
A regular supply of P. vivax infectious sporozoites is needed in order to develop and exploit hepatic stages in vitro cultivation protocols
Assessment of infectivity to Plasmodium vivax field strains From May 2013 to December 2014, a total of 55 P. vivaxinfected patients with microscopically detectable circulating gametocytes were identified
Summary
A stenogamous colony of Anopheles cracens (A. dirus B) established 20 years ago in a Thai insectary proved susceptible to Plasmodium vivax. Plasmodium vivax is the most widely distributed of the Plasmodium species infecting humans outside of Africa, with 80 million cases recorded yearly [1] This species, characterized by a dormant liver stage, the hypnozoite, can resume its development and lead to relapses over the months or years following the initial infectious bite. The recent development of a protocol for the in vitro cultivation of P. cynomolgi hypnozoites opens the way to higher throughput screening [6, 7], as well as conducting investigations on the biology of the liver stages of relapsing parasite species. A regular supply of P. vivax infectious sporozoites is needed in order to develop and exploit hepatic stages in vitro cultivation protocols This would rely on the simultaneous availability of susceptible anopheline mosquitoes and a supply of gametocyte-carrying infected blood. For P. vivax, a parasite that cannot at present be propagated in vitro, this implies the proximity of infected patient donors to a suitable anopheline colony
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