ELISA study of oocyst-sporozoite transition in malaria vectors

C Czeher,R Labbo,J.B Duchemin,L Here,I Arzika,A Djibrilla

doi:10.1051/parasite/2006133257

C Czeher, R Labbo + Show 4 more

Open Access

https://doi.org/10.1051/parasite/2006133257

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Abstract

Intrinsic vector characteristics and environmental factors affect the sporogonic development of P. falciparum in Anopheles mosquitoes. We tested for the presence of the circumsporozoite protein, as a marker of the oocyst to sporozoite transition in naturally infected Anopheles gambiae s.l. and Anopheles funestus. Malaria vectors were collected in a village in the Sahel of Niger during the rainy and dry seasons. ELISA-CSP was carried out on abdomen and head/thorax portions from more than 2000 samples. No significant difference was found in the overall rates of infection of An. gambiae s.l. (4.13%) and An. funestus (3.58%). Given the differences in duration of the two parasite stages, P. falciparum CSP antigen prevalence was nearly as high in the abdomen as in the head/thorax, and did not differ significantly between An. gambiae s.l. and An. funestus. These preliminary results suggest that development from oocysts to salivary gland sporozoites is similar in the two vectors. However, these developmental indices varied as a function of the season in which samples were collected, particularly for An. gambiae s.l. This simple method may be useful for field studies assessing the effect of environmental and genetic factors on parasite survival.

Highlights

We used enzyme-linked immunosorbent assay (ELISA) to test for the presence of P. falciparum circumsporozoite protein (CSP) in: 1) the head and third anterior portion of the thorax; and 2) the abdomen portion
We used ELISA to assess the levels of abdomen and head/thorax infection separately for 920 An. gambiae s.l. and 1,172 An. funestus collected over the study period (Table I)
As late oocysts are present for only a short, determinate period of time, whereas sporozoites may persist throughout the life of the mosquito, we would expect to obtain a high sporozoite to oocyst ratio, consistent with our results

Summary

Methods

This study was conducted in Zindarou (13° 26’ N, 2° 55’ E), a village in the Nigerien Sahel region, classically defined as a meso-endemic malaria transmission zone with a rainy season between July and October and a rainfall peak during August and September. We used ELISA to test for the presence of P. falciparum CSP in: 1) the head and third anterior portion of the thorax (salivary gland sporozoites); and 2) the abdomen portion (late-stage oocysts). Sporozoite indices (i.e. salivary gland infection rates) were estimated for all specimens for which at least the head/thorax portion tested positive, whereas oocyst prevalences were estimated for all specimens in which at least the abdomen portion tested positive. We studied a subset of An. gambiae s.l. specimens in the two main periods (rainy/dry), with An. gambiae s.s. and An. arabiensis identified on the basis of direct PCR (Scott et al, 1993) on legs, without prior extraction of DNA. We clustered the sampling series into two periods: rainy season (August and October) and dry season (June December, February and April) and carried out chisquared tests

Results

Discussion

Conclusion