Seasonality and Prevalence of Leishmania major Infection in Phlebotomus duboscqi Neveu-Lemaire from Two Neighboring Villages in Central Mali

Phlebotomus duboscqi is the principle vector of Leishmania major, the causative agent of cutaneous leishmaniasis (CL), in West Africa and is the suspected vector in Mali. Although found throughout the country the seasonality and infection prevalence of P. duboscqi has not been established in Mali. We conducted a three year study in two neighboring villages, Kemena and Sougoula, in Central Mali, an area with a leishmanin skin test positivity of up to 45%. During the first year, we evaluated the overall diversity of sand flies. Of 18,595 flies collected, 12,952 (69%) belonged to 12 species of Sergentomyia and 5,643 (31%) to two species of the genus Phlebotomus, P. duboscqi and P. rodhaini. Of those, P. duboscqi was the most abundant, representing 99% of the collected Phlebotomus species. P. duboscqi was the primary sand fly collected inside dwellings, mostly by resting site collection. The seasonality and infection prevalence of P. duboscqi was monitored over two consecutive years. P. dubsocqi were collected throughout the year. Using a quasi-Poisson model we observed a significant annual (year 1 to year 2), seasonal (monthly) and village effect (Kemena versus Sougoula) on the number of collected P. duboscqi. The significant seasonal effect of the quasi-Poisson model reflects two seasonal collection peaks in May-July and October-November. The infection status of pooled P. duboscqi females was determined by PCR. The infection prevalence of pooled females, estimated using the maximum likelihood estimate of prevalence, was 2.7% in Kemena and Sougoula. Based on the PCR product size, L. major was identified as the only species found in flies from the two villages. This was confirmed by sequence alignment of a subset of PCR products from infected flies to known Leishmania species, incriminating P. duboscqi as the vector of CL in Mali

Integrated seroprevalence-based assessment of Wuchereria bancrofti and Onchocerca volvulus in two lymphatic filariasis evaluation units of Mali with the SD Bioline Onchocerciasis/LF IgG4 Rapid Test.

BACKGROUND:Mali has become increasingly interested in the evaluation of transmission of both Wuchereria bancrofti and Onchocerca volvulus as prevalences of both infections move toward their respective elimination targets. The SD Bioline Onchocerciasis/LF IgG4 Rapid Test was used in 2 evaluation units (EU) to assess its performance as an integrated surveillance tool for elimination of lymphatic filariasis (LF) and onchocerciasis. METHODOLOGY/PRINCIPAL FINDINGS:A cross sectional survey with SD Bioline Onchocerciasis/LF IgG4 Rapid Test was piggy-backed onto a transmission assessment survey (TAS) (using the immunochromatographic card test (ICT) Binax Filariasis Now test for filarial adult circulating antigen (CFA) detection) for LF in Mali among 6-7 year old children in 2016 as part of the TAS in two EUs namely Kadiolo-Kolondieba in the region of Sikasso and Bafoulabe -Kita-Oussoubidiagna-Yelimane in the region of Kayes. In the EU of Kadiolo- Kolondieba, of the 1,625 children tested, the overall prevalence of W. bancrofti CFA was 0.62% (10/1,625) [CI = 0.31-1.09]; while that of IgG4 to Wb123 was 0.19% (3/1,600) [CI = 0.04-0.50]. The number of positives tested with the two tests were statistically comparable (p = 0.09). In the EU of Bafoulabe-Kita-Oussoubidiagna-Yelimane, an overall prevalence of W. bancrofti CFA was 0% (0/1,700) and that of Wb123 IgG4 antibody was 0.06% (1/1,700), with no statistically significant difference between the two rates (p = 0.99). In the EU of Kadiolo- Kolondieba, the prevalence of Ov16-specific IgG4 was 0.19% (3/1,600) [CI = 0.04-0.50]. All 3 positives were in the previously O. volvulus-hyperendemic district of Kolondieba. In the EU of Bafoulabe-Kita-Oussoubidiagna-Yelimane, an overall prevalence of Ov16-specific IgG4 was 0.18% (3/1,700) [CI = 0.04-0.47]. These 3 Ov16 IgG4 positives were from previously O.volvulus-mesoendemic district of Kita. CONCLUSIONS/SIGNIFICANCE:The SD Bioline Onchocerciasis/LF IgG4 Rapid test appears to be a good tool for integrated exposure measures of LF and onchocerciasis in co-endemic areas

Estimated infection prevalence of <i>Leishmania major</i> in female <i>Phlebotomus duboscqi</i> from July 2006–June 2008.

<p>Estimated infection prevalence of <i>Leishmania major</i> in female <i>Phlebotomus duboscqi</i> from July 2006–June 2008.</p

<i>Leishmania</i> specific PCR products from field collected female <i>Phlebotomus duboscqi.</i>

<p><i>Leishmania</i> specific (A) and tubulin loading control (B) PCR products. N  =  negative control, P  =  positive control (DNA from <i>P. duboscqi</i> experimentally infected with <i>L. major</i>). L  =  100 bp ladder. Predicted band size of the PCR product for (A) <i>L. major</i> (650 bp) and (B) tubulin (325 bp) is indicated.</p

Collection success of female <i>Phlebotomus duboscqi</i> using various trapping methods.

<p>Number of female <i>P. duboscqi</i> collected per trapping method per night during monthly collection from July 2006 to June 2008 in two neighboring villages, Kemena (A) and Sougoula (B), in Central Mali: morning resting site collection (RSC AM)  =  female <i>P. duboscqi</i> (Pd) collected during 2 man hours, evening resting site collection (RSC PM)  =  female <i>P. duboscqi</i> collected during 2 man hours, tree light traps (TLT)  =  female <i>P.duboscqi</i> collected by 10 traps, indoor light traps (ILT)  =  female <i>P duboscqi</i> collected by 20 traps, outdoor light traps (OLT)  =  female <i>P. duboscqi</i> collected by 20 traps.</p

Satellite image of study villages in Central Mali.

<p>Satellite image of the two study villages, Kemena (A) and Sougoula (B) illustrating the sites of monthly sand fly collections (circles) during the study of <i>Phlebotomus duboscqi</i> seasonality, July 2006 to June 2008. Red  =  compounds of indoor/outdoor house light trap collections; green  =  compounds of resting site collections; yellow  =  light trap location near trees. Image collected on May 22, 2006 by the Quickbird Satellite (DigitalGlobe, Inc. Longmont, CO USA).</p

Sand fly species diversity in two neighboring villages, Central Mali, March 2005-June 2006.

<p>Sand fly species diversity in two neighboring villages, Central Mali, March 2005-June 2006.</p

Estimated prevalence of infected sand flies collected from Kemena and Sougoula, two neighboring villages in Central Mali.

<p>Numbers in parenthesis represent the overall number of female <i>P. duboscqi</i> specimens tested in pools of 1–20 flies.</p