Malaria Sporozoite Detection by Dissection and Elisa to Assess Infectivity of Afrotropical Anopheles (Diptera: Culicidae)

Abstract

Malaria infection rates determined by dissection and Plasmodium falciparum enzyme-linked immunosorbent assay (ELISA) were compared for 26,935 Anopheles gambiae Giles sensu lato and 17,739 Anopheles funestus Giles collected during 20 mo in western Kenya. ELISA infection rates were about 43% higher than dissection sporozoite rates. In dissection-negative Anopheles, circumsporozoite (CS) protein was detected by ELISA in 5.2% of 10,017 salivary gland samples and in 12.2% of 237 thorax samples. The accuracy of dissection and ELISA techniques was compared by the following tests on a group of 352 field-collected Anopheles (held 10 d to ensure sporogonic development): salivary gland dissection, examination of Giemsa-stained dissection slides, ELISA tests on salivary gland and thorax body parts, and microscopic techniques for determining sporozoite loads. Respective infection rates were 9.9%, 10.8%, and 15.6% for dissection, stained slides, and ELISA. Sporozoite loads were associated significantly with ELISA absorbance values (r = 0.76). Compared with Giemsa-stained dissection slide results, the sensitivity of sporozoite detection was 92.1% for dissection compared with 78.9% for ELISA; specificity was 100.0% for dissection versus 92.0% for ELISA. Immunological detection of CS protein in head-thorax samples of Afrotropical vectors overestimated the proportion of infective Anopheles because the comparison of techniques indicated that 45.4% of the ELISA positive Anopheles did not contain salivary gland sporozoites.

Malaria vectors in a traditional dry zone village in Sri Lanka.

“…However, this may not always be the case since CS proteins in the thorax may be detected even when sporozoite infections abort before reaching the salivary glands. 22 Thus ELISA-based indices could overestimate true infectivity and may also incriminate species that are, in fact, not transmitters in the field. This could well be a factor in Sri Lanka, where in a situation of unstable malaria and low transmission rates, ELISA studies have incriminated a large number of anopheline species.…”

<span>Sporozoite Infection Rate and Identification of the Infective and Refractory Species of <i>Anopheles gambiae</i> (Giles) Complex</span>

“…Macdonald (1952) defined sporozoite rate as the proportion of mosquitoes with sporozoites in their salivary glands. The parameter has been used as an epidemiological index to determine the infectivity of the species of Anopheles (Beier et al, 1990). Sporozoite rate can be determined by dissection and ELISA (Adungo et al, 1991;Beier et al, 1990).…”

“…The parameter has been used as an epidemiological index to determine the infectivity of the species of Anopheles (Beier et al, 1990). Sporozoite rate can be determined by dissection and ELISA (Adungo et al, 1991;Beier et al, 1990). Determination of sporozoite rate by dissection has been found to be more accurate and sensitive than the ELISA method.…”

“…Determination of sporozoite rate by dissection has been found to be more accurate and sensitive than the ELISA method. ELISA is limited by overestimation (Adungo et al, 1991;Beier et al, 1990;Sanofi, 2013) and it cannot distinguish between infected and infectious mosquitoes.…”

ELISA study of oocyst-sporozoite transition in malaria vectors

“…We assumed that the detection of CSP in the head/ thorax and abdomen reflected effective infections of the salivary glands by sporozoites and of the midgut by oocysts, respectively. It has been suggested that the detection of free soluble CSP or sporozoites within the hemocoel overestimates the frequency of salivary gland infection Beier et al, 1990). If this was the case here, then most insects in which CSP was detected in the salivary glands by ELISA would be expected to have CSP throughout the entire body.…”