Patchara Sriwichai

Infectivity of symptomatic and asymptomatic Plasmodium vivax infections to a Southeast Asian vector, Anopheles dirus

Plasmodium vivax is now the predominant species causing malarial infection and disease in most non-African areas, but little is known about its transmission efficiency from human to mosquitoes. Because the majority of Plasmodium infections in endemic areas are low density and asymptomatic, it is important to evaluate how well these infections transmit. Using membrane feeding apparatus, Anopheles dirus were fed with blood samples from 94 individuals who had natural P. vivax infections with parasitemias spanning four orders of magnitude. We found that the mosquito infection rate was positively correlated with blood parasitemia and that infection began to rise when parasitemia was >10parasites/μl. Below this threshold, mosquito infection is rare and associated with very few oocysts. These findings provide useful information for assessing the human reservoir of transmission and for establishing diagnostic sensitivity required to identify individuals who are most infective to mosquitoes.

DNA barcoding and wing morphometrics to distinguish three Aedes vectors in Thailand

Aedes aegypti (Diptera: Culicidae) (L.), Ae. albopictus (Skuse), and Ae. scutellaris (Walker) are important mosquito vectors of dengue and chikungunya viruses. They are morphologically similar and sympatric in some parts of their distribution; therefore, there is a risk of incorrect morphological identification. Any confusion could have a negative impact on epidemiological studies or control strategies. Therefore, we explored two modern tools to supplement current morphological identification: DNA barcoding and geometric morphometric analyses. Field larvae were reared to adults and carefully classified based on morphological traits. The genetic analysis was based on the 658bp each of 30COI sequences. Some Culex spp., Mansonia bonneae, were included as outgroups, and inclusion of a few other Aedes spp. facilitated phylogenetic inference of the relationship between Ae. albopictus and Ae. scutellaris. The two species were separated by an average interspecific divergence of 0.123 (0.119-0.127). Morphometric examination included landmark- (392 specimens) and outline-based (317 specimens) techniques. The shape of the wing showed different discriminating power based on sex and digitizing technique. This is the first time that Ae. scutellaris and Ae. albopictus have been compared using these two techniques. We confirm that these morphologically close species are valid, and that geometric morphometrics can considerably increase the reliability of morphological identification.

CLONING OF A TRYPSIN‐LIKE SERINE PROTEASE AND EXPRESSION PATTERNS DURING PLASMODIUM FALCIPARUM INVASION IN THE MOSQUITO, ANOPHELES DIRUS (PEYTON AND HARRISON)

Understanding specific gene regulation during responses to malaria infection is key to dissecting the mosquito defense mechanisms and host/parasite interactions. A full-length serine protease cDNA was isolated from the fat body of female Anopheles dirus, a major malaria vector in Thailand. The predicted amino acid sequence of SERF4 identifies it as a member of the serine protease family containing a single trypsin-like protease domain. Digestive trypsins function in the female mosquito midgut and are inducible in two phases in this tissue upon blood intake. However, the gene was highly upregulated in the midgut at day 3 postinfection by Plasmodium falciparum. In situ hybridization confirmed that SERF4 transcripts were located in the midgut epithelial cells rather than hemocytes or other tissues associated with the midgut. SERF4 was also strongly downregulated in the whole insects at day 16 after infection in comparison with the blood-fed control. Changes in the expression of the SERF4 gene in response to infection with this human malaria parasite suggest a role in parasite-specific innate immunity.

Expression of three serine protease genes from the South East Asian malaria vector, Anopheles dirus, in relation to blood feeding and parasite infection.

Three serine protease cDNA clones were isolated from Anopheles dirus, a major vector of malaria in Southeast Asia. Transcript abundance was examined following infection by Plasmodium falciparum by RT-PCR analysis. SerF3 exhibited increased transcript abundance in the whole body at 10 days post-infection with P. falciparum. All three genes are candidates for further investigation to determine their roles in mosquito immune responses.

Salivary gland proteome during adult development and after blood feeding of female anopheles dissidens mosquitoes (Diptera Culicidae)

Understanding changes in mosquito salivary proteins during the time that sporozoite maturation occurs and after blood feeding may give information regarding the roles of salivary proteins during the malarial transmission. Anopheles dissidens (formerly Anopheles barbirostris species A1) is a potential vector of Plasmodium vivax in Thailand. In this study, analyses of the proteomic profiles of female An. dissidens salivary glands during adult development and after blood feeding were carried out using two-dimensional gel electrophoresis coupled with nano-liquid chromatography-mass spectrometry. Results showed at least 17 major salivary gland proteins present from day one to day 21 post emergence at 8 different time points sampled. Although there was variation observed, the patterns of protein expression could be placed into one of four groups. Fifteen protein spots showed significant depletion after blood feeding with the percentages of the amount of depletion ranging from 8.5% to 68.11%. The overall results identified various proteins, including a putative mucin-like protein, an anti-platelet protein, a long form D7 salivary protein, a putative gVAG protein precursor, a D7-related 3.2 protein, gSG7 salivary proteins, and a gSG6 protein. These results allow better understanding of the changes of the salivary proteins during the adult mosquito development. They also provide candidate proteins to investigate any possible link or not between sporozoite maturation, or survival of skin stage sporozoites, and salivary proteins.

Natural Plasmodium vivax infections in Anopheles mosquitoes in a malaria endemic area of northeastern Thailand

There was recently an outbreak of malaria in Ubon Ratchathani Province, northeastern Thailand. In the absence of information on malaria vector transmission dynamics, this study aimed to identify the anopheline vectors and their role in malaria transmission. Adult female Anopheles mosquitoes were collected monthly by human-landing catch in Na Chaluai District of Ubon Ratchathani Province during January 2014−December 2015. Field-captured mosquitoes were identified to species using morphology-based keys and molecular assays (allele-specific polymerase chain reaction, AS-PCR), and analysed for the presence of Plasmodium falciparum and Plasmodium vivax using an enzyme-linked immunosorbent assay (ELISA) for the detection of circumsporozoite proteins (CSP). A total of 1,229 Anopheles females belonging to 13 species were collected. Four anopheline taxa were most abundant: Members of the Anopheles barbirostris complex, comprising 38% of the specimens, species of the Anopheles hyrcanus group (18%), Anopheles nivipes (17%) and Anopheles philippinensis (12%). The other nine species comprised 15% of the collections. Plasmodium infections were detected in two of 668 pooled samples of heads/thoraces, Anopheles dirus (1/29) and An. philippinensis (1/97). The An. dirus pool had a mixed infection of P. vivax-210 and P. vivax-247, whereas the An. philippinensis pool was positive only for the latter protein variant. Both positive ELISA samples were confirmed by nested PCR. This study is the first to incriminate An. dirus and An. philippinensis as natural malaria vectors in the area where the outbreak occurred. This information can assist in designing and implementing a more effective malaria control programme in the province.

Corrigendum to “Wing geometry of Phlebotomus stantoni and Sergentomyia hodgsoni from different geographical locations in Thailand” [C. R. Biologies 340(1) (2017) 37–46]

Comptes Rendus Biologies - In Press.Proof corrected by the author Available online since jeudi 9 fevrier 2017

Ecology of Malaria Vectors and Current (Nongenetic) Methods of Control in the Asia Region

Abstract Approximately 1.4 billion people are at some risk of malaria infection in the South East Asia region, with 352 million at high risk. The most common and effective malaria vector control strategies currently in use are based on insecticides: indoor residual spraying (IRS) and long-lasting insecticide-treated nets. However, these interventions were designed for indoor-biting vectors, and hence are not necessarily effective in all regions. Although there are many nongenetic tools for vector control, a major limitation is the research-based evaluation of efficiency of those tools in many areas. Another limitation for research of malaria vectors in Asia is due to the high complexity of many vector species and the difficulty to maintain most of the important vectors in the laboratory, as it is very labor intensive. Here, we review the ecological and behavioral characteristics of only the most important anthropophilic vectors within this region: Anopheles culicifacies , Anopoheles fluviatilis , and Anopheles stephensi across the Indian subcontinent; and Anopheles dirus and Anopheles minimus within Southeast Asia. The challenges in applying genetic control methods to malaria vectors in Asia will be similar to the other nongenetic tools that have been used to control vectors in this region: species complexity, multiple vectors, and potential vectors in each endemic area and only a few species that can be successfully maintained in the laboratory.