Genetic diversity and gene structure of mitochondrial region of Anopheles minimus (Diptera: Culicidae) - major malaria vector of North east India

Field evaluation of zero vector durable lining to assess its efficacy against malaria vectors and malaria transmission in tribal areas of the Balaghat district of central India

BACKGROUND

Indoor residual spray (IRS) and long-lasting insecticidal nets are the two principal intervention methods of vector control. Zero vector durable lining (ZVDL), a relatively new vector control method, was evaluated to assess its efficacy against malaria vectors in hard to reach areas in the Balaghat district, where malaria transmission is perennial.

METHODS

ZVDL was installed in six experimental villages during November-December 2012. In control villages, IRS was carried out with Alphacypermethrin. Cone bioassays were performed to assess the efficacy and persistence of insecticide-treated ZVDL following WHO bioassays.

RESULTS

The mean per man hour density of Anopheles caught during 2013 was 12.1 in experimental villages and 16.2 in control villages. No sporozoite-positive Anopheles culicifacies were found in experimental villages; however, in control villages, four sporozoite-positive A. culicifacies were found (two Plasmodium vivax and two P. falciparum). The knock-down rate of A. culicifacies was 95-100% with 100% mortality during the 24 h recovery period. Malaria declined sharply in experimental villages showing a slide positivity rate of 22.3% compared with control villages (36.4%) (p<0.05).

CONCLUSIONS

A supplementary vector control intervention such as ZVDL has the potential to become a viable alternative to IRS in malaria endemic areas.

A checklist of the Anopheles mosquito species (Diptera: Culicidae) in Bhutan

The present paper records, for the first time, the Anopheles fauna of Bhutan, determined from surveys conducted from 2007 to early 2018. Adult mosquitoes were collected mainly on cattle bait and occasionally in human landing catches. Collections of immature stages were performed in various aquatic habitats. Larvae were preserved or reared to adults. Identification was based on morphological characters using available keys. A total of 30 species were identified, including nine species of subgenus Anopheles and 21 species of subgenus Cellia. Distribution and collection data are provided with notes on the locations and habitats of the species. Anopheles pseudowillmori is suspected to be a vector of malarial parasites in the plains and hilly forested areas of the country because it is widely distributed and the most common species collected in human landing catches. Notes also include observed morphological variation observed in An. baileyi and An. lindesayi, which differ from the type forms. Corrections are made for previous reports of Anopheles in Bhutan. The need for further surveys and molecular identification of members of species complexes and morphological variants is emphasized.

Genetic Differentiation of Colombian Populations of Anopheles darlingi Root (Diptera: Culicidae)

Anopheles darlingi Root is a primary vector of malaria in the neotropic region, a species not just highly anthropophilic but very efficient in transmitting Plasmodium species and considered the most important vector in the Amazon region. The main goal of this study was to determine the genetic structure of the A. darlingi populations using microsatellites (STR) in western and eastern regions of Colombia. DNA extraction was done with the cited protocol of band using the Genomic Prep™ cell and tissue isolation commercial kits. We used the STR reported by Conn et al (Mol Ecol Notes 1: 223-225, 2001). The analysis with STR proved there was a high genetic diversity and significant alterations of the Hardy-Weinberg equilibrium. The greatest genetic diversity was recorded in Mitu (Vaupes) (Na = 14, Ho = 0.520). The lowest was in Pueblo Nuevo (Cordoba) (Na = 12, Ho = 0.457). The eastern region and the Mitu (Vaupes) populations presented the highest number of primer alleles (Ap = 30; Ap = 13; Ap = 9), with variations between 0.010 and 0.097. The AMOVA revealed that the whole population underwent moderate genetic differentiation (F _ST = 0.063, p < 0.05). The same differentiation was noticed (0.06 < F _ST > 0.06, p < 0.05) with five of the six populations included in this job, and there was a low differentiation in the Las Margaritas (Santander) area (F _ST = 0.02s3, p < 0.05). Our results suggest a slight positive correlation, which does not show a statistical significance between the geographic and genetic distances, probably suggesting that the moderate genetic differentiation found between pairs of populations does not need to be explained for the hypothesis of separation by distance.

Biology, distribution and control of Anopheles (Cellia) minimus in the context of malaria transmission in northeastern India

Among six dominant mosquito vector species involved in malaria transmission in India, Anopheles minimus is a major species in northeast India and held responsible for focal disease outbreaks characterized by high-rise of Plasmodium falciparum infections and attributable death cases. It has been now genetically characterized that among the three-member species of the Minimus Complex spread in Asia, An. minimus (former species A) is prevalent in India including northeastern states and east-central state of Odisha. It is recorded in all seasons and accounts for perennial transmission evidenced by records of sporozoite infections. This species is highly anthropophilic, and largely endophilic and endophagic, recorded breeding throughout the year in slow flowing seepage water streams. The populations of An. minimus in India are reported to be highly diverse indicating population expansion with obvious implications for judicious application of vector control interventions. Given the rapid ecological changes due to deforestation, population migration and expansion and developmental activities, there is scope for further research on the existence of potential additional sibling species within the An. minimus complex and bionomics studies on a large geographical scale for species sanitation. For control of vector populations, DDT continues to be applied on account of retaining susceptibility status even after decades of residual spraying. Anopheles minimus is a highly adaptive species and requires continuous and sustained efforts for its effective control to check transmission and spread of drug-resistant malaria. Anopheles minimus populations are reportedly diminishing in northeastern India whereas it has staged comeback in east-central State of Odisha after decades of disappearance with its eco-biological characteristics intact. It is the high time to siege the opportunity for strengthening interventions against this species for its population diminution to sub-optimal levels for reducing transmission in achieving malaria elimination by target date of 2030.

Malaria elimination in India and regional implications

The malaria situation in India is complex as a result of diverse socio-environmental conditions. India contributes a substantial burden of malaria outside sub-Saharan Africa, with the third highest Plasmodium vivax prevalence in the world. Successful malaria control in India is likely to enhance malaria elimination efforts in the region. Despite modest gains, there are many challenges for malaria elimination in India, including: varied patterns of malaria transmission in different parts of the country demanding area-specific control measures; intense malaria transmission fuelled by favourable climatic and environment factors; varying degrees of insecticide resistance of vectors; antimalarial drug resistance; a weak surveillance system; and poor national coordination of state programmes. Prevention and protection against malaria are low as a result of a weak health-care system, as well as financial and socioeconomic constraints. Additionally, the open borders of India provide a potential route of entry for artesunate-resistant parasites from southeast Asia. This situation calls for urgent dialogue around tackling malaria across borders-between India's states and neighbouring countries-through sharing of information and coordinated control and preventive measures, if we are to achieve the aim of malaria elimination in the region.