Phylogenetic Complexity of Morphologically Identified Anopheles squamosus in Southern Zambia

Despite dramatic reductions in malaria cases in the catchment area of Macha Hospital, Choma District, Southern Province in Zambia, prevalence has remained near 1–2% by RDT for the past several years. To investigate residual malaria transmission in the area, this study focuses on the relative abundance, foraging behavior, and phylogenetic relationships of Anopheles squamosus specimens. In 2011, higher than expected rates of anthropophily were observed among “zoophilic” An. squamosus, a species that had sporadically been found to contain Plasmodium falciparum sporozoites. The importance of An. squamosus in the region was reaffirmed in 2016 when P. falciparum sporozoites were detected in numerous An. squamosus specimens. This study analyzed Centers for Disease Control (CDC) light trap collections of adult mosquitoes from two collection schemes: one performed as part of a reactive-test-and-treat program and the second performed along a geographical transect. Morphological identification, molecular verification of anopheline species, and blood meal source were determined on individual samples. Data from these collections supported earlier studies demonstrating An. squamosus to be primarily exophagic and zoophilic, allowing them to evade current control measures. The phylogenetic relationships generated from the specimens in this study illustrate the existence of well supported clade structure among An. squamosus specimens, which further emphasizes the importance of molecular identification of vectors. The primarily exophagic behavior of An. squamosus in these collections also highlights that indoor vector control strategies will not be sufficient for elimination of malaria in southern Zambia.

Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

Anopheles stephensi, an efficient Asian malaria vector, recently spread into the Horn of Africa and may increase malaria receptivity in African urban areas. We assessed occurrence, genetic complexity, blood meal source and infection status of An. stephensi in Awash Sebat Kilo town, Ethiopia. We used membrane feeding assays to assess competence of local An. stephensi to P. vivax and P. falciparum isolates from clinical patients. 75.3% of the examined waterbodies were infested with An. stephensi developmental stages that were genetically closely related to isolates from Djibouti and Pakistan. Both P. vivax and P. falciparum were detected in wild-caught adult An. stephensi. Local An. stephensi was more receptive to P. vivax compared to a colony of An. arabiensis. We conclude that An. stephensi is an established vector in this part of Ethiopia, highly permissive for local P. vivax and P. falciparum isolates and presents an important new challenge for malaria control.Summary of the articleAn. stephensi, a metropolitan malaria vector that recently expanded to the Horn of African, was highly susceptible to local P. falciparum and P. vivax isolates from Ethiopia and may increase malariogenic potential of rapidly expanding urban settings in Africa.

Effects of Host Blood on Fecundity and Longevity of Female Anopheles Mosquitoes

Aim: The effect of Host blood on the fecundity of female Anopheles gambiae sensu lato mosquitoes was studied under normal conditions of 64±2% Relative Humidity and 27±2ºC Temperature. Methods: Three-five day old (F1) female Anopheles mosquitoes were transferred into wooden cages (40x40x40 cm) and fed blood from the following sources: man, cattle, chicken, goat, pig and sheep through an artificial feeding membrane. Engorged females were observed and fecundity recorded. The entire experiment was replicated five (5) times. Results: From the 1st to 4th gonotropic cycle, mosquitoes fed human blood produced significantly greater (p<0.05) number of eggs (Mean=121.90±1.18, 101.36±1.56, 64.12±1.54 and 29.66±1.69 respectively) than mosquitoes fed other blood meal sources. Across the six (6) blood meal trials (excluding that of sheep), there was a significant reduction (p<0.05) in fecundity from the 1st to 4th gonotropic cycles (1st>2nd>3rd>4th). There was no significant difference (p>0.05) in fecundity between pigs, chicken and sheep. Total mean longevity and total mean fecundity was significantly greater (p<0.05) in mosquitoes fed human and cattle blood than in mosquitoes fed the other blood sources. Conclusion: The results showed that blood meal source affects fecundity and longevity of female Anopheles gambiae s. l mosquitoes reared under laboratory conditions and that blood from humans as well as from other domestic animals is suitable for sustaining vectorial capacity in Anopheles gambiae s. l mosquitoes.

Impact of dogs with deltamethrin-impregnated collars on prevalence of visceral leishmaniasis

Leishmaniasis is a vector borne zoonosis which is classified as a neglected tropical disease. Among the three most common forms of the disease, Visceral Leishmaniasis (VL) is the most threatening to human health, causing 20,000 to 30,000 deaths worldwide each year. Areas where VL is mostly endemic have unprotected dogs in community and houses. The presence of dogs usually increases VL risk for humans since dogs are the principal reservoir host for the parasite of the disease. Based on this fact, most earlier studies consider culling dogs as a control measure for the spread of VL. A more recent control measure has been the use of deltamethrin-impregnated dog collars (DIDCs) to protect both humans and dogs by putting DIDCs on dogs neck. The presence of dogs helps to grow the sandfly population faster by offering a more suitable blood-meal source. On the other hand, the presence of DIDCs on dogs helps to reduce sandfly population by the lethality of deltamethrin insecticide. This study brings an ecological perspective to this public health concern, aiming to understand the impact of an additional host (here, protected dogs) on disease risk to a primary host (here, humans). To answer this question, we compare two different settings: a community without dogs, and a community with dogs protected with DIDC. Our analysis shows the presence of protected dogs can reduce VL infection risk in humans. However, this disease risk reduction depends on dogs’ tolerance for sandfly bites.

Advantageous Feeding on Different Blood Meal Sources by the Chagas Disease Vector Triatoma barberi (Hemiptera: Reduviidae)

Triatominae bugs (Hemiptera: Reduviidae) are usually associated with different vertebrate species, upon which many of them feed. Yet how these different blood meal sources influence key biological parameters is rarely investigated for triatomines. To fill this knowledge gap, this study sought to determine the effect of a domestic rat species (Rattus norvegicus Berkenhout (Rodentia: Muridae)), a domestic mice species (Mus musculus L. (Rodentia: Muridae)), and chickens (Gallus gallus domesticus L. (Galliformes: Phasianidae)), as blood meal sources upon several biological parameters (development time, number of required blood meals to moult and feeding and defecation behaviors) of the Mexican major vector Triatoma barberi Usinger. The three studied cohorts’ development times were similar (325–338 d), but the number of required blood meals to moult (21), as well as the total mortality rate (26%), were both the highest in the cohort that fed on chickens. The longevity of females (186–190 d) was similar among the three studied cohorts, as was that of males. The median time elapsed between the presentation of a blood meal source and onset of feeding (10 min) was similar among the three studied cohorts, as were their feeding times and defecation patterns. Most of our studied parameters demonstrate how T. barberi can effectively take advantage of feeding on rodents as much as it does on hens. Those parameter results also show that T. barberi should be considered as a potential yet underappreciated vector in some areas, thus warranting a surveillance program of its current distribution area in Mexico.

Blood meal identification in the cryptic species Anopheles gambiae and Anopheles coluzzii using MALDI-TOF MS

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has recently emerged in entomology as a technique to identify arthropods and their blood meal source. In this study, female Anopheles gambiae were fed on five host blood sources: ocelot (Leopardus pardalis), binturong (Arctictis binturong), springbok (Antidorcas marsupialis), jaguar (Panthera onca) and Hamadryas baboon (Papio hamadryas), while Anopheles coluzzii were fed on three hosts: dromedary (Camelus dromedarius), Barbary sheep (Ammotragus lervia) and pig (Sus scrofa). We obtained the MS spectra from 240 engorged mosquito abdomens and selected high quality ones from 72 mosquito abdomens to upgrade our home-made database. We excluded from the analysis any spectra of low quality (n = 80), and the remaining 88 specimens were subjected to a blind test analysis against the home-made database. We obtained 100% correct identification of the blood meal source for the specimens collected, 1, 12 and 24 h post-feeding, whereas for the specimens collected 36 h post-feeding, the correct identification rate decreased dramatically. We confirm here that MALDI-TOF MS can be used to identify the blood meal origin of freshly engorged mosquitoes, which opens new perspectives for further studies, including the impact of the mosquito species on blood meal identification.