New insights into malaria vector bionomics in Lao PDR: a nationwide entomology survey

Abstract

Background . In Laos, the malaria burden remains high despite a significant reduction of cases during the last decade. In the context of the disease elimination by 2030, a nationwide entomological survey was conducted to better understand the distribution, abundance and behavior of major malaria vectors (Anopheles spp.) in the country. Methods . Mosquito collections were implemented in ten villages from ten provinces during the rainy and dry seasons of 2014 and 2015 by using human landing catch (HLC) and cow bait collection (CBC) methods. After morphological identification in the field, molecular identification of the sibling species of Anopheles mosquitoes from the Funestus, Leucosphyrus, and Maculatus groups were determined using PCR specific alleles. A screening of Plasmodium falciparum and P. vivax infections in in the vectors was carried out by quantitative PCR assays. Results. A total of 14,146 adult mosquitoes representing 25 different Anopheles species were collected and morphologically identified. Molecular identification revealed the presence of 13 sibling species within the main primary vector groups including An. maculatus s.s., An. rampae, An. sawadwongporni, An. pseudowillmori, An. dravidicus, An. willmori, An. minimus s.s., An. aconitus, An. pampanai, An. harrisoni, An. dirus s.s., An. baimaii, An. nemophilous. An. maculatus and An. minimus were predominant during both the dry and rainy seasons, but showed highly zoophilic preferences (Zoophilic index of 98% and 95%, respectively). Overall, solely 22% of the total malaria vectors were collected between 10:00 PM and 5:00 AM indoors when people are sleeping. Twenty-seven percent of primary and secondary vectors were collected outdoors before 10:00 PM or after 5:00 AM, times when people are usually awake and outdoors. Only two specimens were positive for P. falciparum, one Anopheles aconitus from Phongsaly and one An. minimus from Vientiane Province Conclusions. The results indicate that people living in rural areas in Laos are constantly exposed to malaria vectors throughout the year and specifically outdoors. The use of LLINs/IRS remains important but innovative tools and new strategies are needed to address locally, the early and outdoor malaria transmission. Lack of expertise in general entomological methods may further exacerbate the situation.

Anopheles bionomics in a malaria endemic area of southern Thailand

“…pampanai ] [ 33 ]. Previously published protocols [ 31 – 34 ] were used, with the following modifications. The amplification was carried out using total volumes of 25 μl, with the final optimized reaction conditions as follows: (i) 1× GoldStar Best Master mix (GoldStar DNA Polymerase, dNTP, PCR stabilizer and enhancer); (ii) three specific primer cocktails, each containing four or five different primer pairs to discriminate between species with 400 nM for the primers specific for the Funestus group and Maculatus group and 500 nM for the primers specific for the Dirus complex; (iii) 4% dimethyl sulfoxide (DMSO) was included only for Dirus complex reactions; (iv) a universal forward primer, located in the conserved region of the 5.8S gene, and species-specific reverse primers in the ITS2 spacer region were employed to amplify a portion of the mosquito ITS2 region; and (v) 1 μl of genomic DNA was used as template.…”