Changing epidemiology of dengue in South-East Asia.

The burden of dengue and its potential threat to global health are now globally recognized, with 2.5 billion people at risk worldwide. The pathogenesis of severe dengue is particularly intriguing with the involvement of different immune factors. Also, the epidemiology of dengue in South-East Asia is undergoing a change in the human host, the dengue virus and the vector bionomics. Shift in affected age groups, sex differences and expansion to rural areas are evident, while the virulence and genotype of the virus determine the severity and time interval between sequential infections. The Aedes mosquito, a potent and adaptive vector, has evolved in longevity and survival, affected by seasonality and climate variability, socio-cultural and economic factors of human habitation and development. This review provides insights into the changing epidemiology and its factors in South-East Asia, one of the most important epicentres of dengue in the world, highlighting the major factors influencing these rapid changes. Addressing the changes may help mitigate the challenges in the current dengue control and prevention efforts.

Vector control interventions for visceral leishmaniasis elimination initiative in South Asia, 2005-2010.

The Visceral Leishmaniasis (VL) Elimination Initiative in the Indian subcontinent was launched in 2005 as a joint effort between the governments in the Region (India, Nepal and Bangladesh) and the World Health Organization (WHO). The objective is to reduce the annual VL incidence below 1/10,000 inhabitants by 2015 based on detection and treatment of VL cases and vector control. We present here a review of studies published in the period 2005-2010 on the efficacy of different tools to control Phlebotomus argentipes. The review indicates that the current indoor residual spraying (IRS) and novel vector control methods mainly insecticide treated nets (ITN) have low effectiveness for several reasons. Efforts to improve quality of IRS operations and further research on alternative and integrated vector control methods need to be promoted to reach the VL elimination target by 2015.

Mosquito biting activity on humans & detection of Plasmodium falciparum infection in Anopheles stephensi in Goa, India.

Background & objectives: Knowledge of the bionomics of mosquitoes, especially of disease vectors, is essential to plan appropriate vector avoidance and control strategies. Information on biting activity of vectors during the night hours in different seasons is important for choosing personal protection measures. This study was carried out to find out the composition of mosquito fauna biting on humans and seasonal biting trends in Goa, India. Methods: Biting activities of all mosquitoes including vectors were studied from 1800 to 0600 h during 85 nights using human volunteers in 14 different localities of three distinct ecotypes in Goa. Seasonal biting trends of vector species were analysed and compared. Seasonal biting periodicity during different phases of night was also studied using William’s mean. Results: A total of 4,191 mosquitoes of five genera and 23 species were collected. Ten species belonged to Anopheles, eight to Culex, three to Aedes and one each to Mansonia and Armigeres. Eleven vector species had human hosts, including malaria vectors Anopheles stephensi (1.3%), An. fluviatilis (1.8%), and An. culicifacies (0.76%); filariasis vectors Culex quinquefasciatus (40.8%) and Mansonia uniformis (1.8%); Japanese encephalitis vectors Cx. tritaeniorhynchus (17.4%), Cx. vishnui (7.7%), Cx. pseudovishnui (0.1%), and Cx. gelidus (2.4%); and dengue and chikungunya vectors Aedes albopictus (0.9%) and Ae. aegypti (0.6%). Two An. stephensi of the total 831 female anophelines, were found positive for P. falciparum sporozoites. The entomological inoculation rate (EIR) of P. falciparum was 18.1 and 2.35 for Panaji city and Goa, respectively. Interpretation & conclusions: Most of the mosquito vector species were collected in all seasons and throughout the scotophase. Biting rates of different vector species differed during different phases of night and seasons. Personal protection methods could be used to stop vector-host contact.

Evolutionary insights into duffy gene in mammalian taxa with comparative genetic analysis.

Background & objectives: Evolutionary analyses of genes conserved across taxa are keys to understand the complexity of gene and genome variation. Since malaria is a highly infectious human disease and its susceptibility in human is genetically controlled, characterization and evolutionary analyses of such genes are of prime importance to understand genetic mechanisms of disease susceptibility. In the present study we have characterized and performed comparative genomic analyses of the human Duffy gene responsible for malaria pathogenesis in nine different mammalian taxa. Methods: DNA sequences of human duffy gene were downloaded from public domain and have been characterized in detail and compared with eight other different mammalian taxa (Pan troglodytes, Macaca mulatta, Pongo pygmaeus, Rattus norvegicus, Mus musculus, Monodelphis domestica, Bos taurus and Canis familiaris). Comparative and evolutionary analyses were performed using statistical software and tools. Results: We observed that the genetic architecture of this gene was entirely different across all the nine taxa and a close similarity between Homo sapiens and Pan troglodytes (chimpanzee) was evident for several aspects of this gene. Comparisons on several aspects, such as ratio of coding and non-coding regions, total gene length number and size of introns and difference of number of nucleotides in human and chimpanzees have revealed interesting features. Phylogenetic inferences based on the Duffy gene among nine different taxa were found to be different than other genes previously studied. Interpretation & conclusion: Most remarkably, human and chimpanzee were only 0.75% different in this gene. The results were discussed on the similarities between human and chimpanzee and gain of introns in human-chimpanzee clade with an inference on the role of evolutionary forces (mainly natural selection) in maintaining such variations across closely-related mammalian taxa.

Characterization & evolutionary analysis of human CD36 gene.

Background and objectives: Understanding evolutionary genetic details of immune system genes responsible for infectious diseases is of prime importance concerning disease pathogenecity. Considering malaria as a devastating disease in the world including India, detail evolutionary understanding on human immune system gene is essential. The primary aim of this study was to initiate work on one such gene, the human CD36 gene responsible in malaria pathogenesis. Methods: DNA sequences of the human CD36 gene was retrieved from public domain and fifi ne-scale details were characterized. Both comparative and evolutionary analyses were performed with sequences from six other taxa (5 mammalian one avian) where CD36 homologs are present. Different statistical analyses were also performed. Results: Differential distribution in number and length of exons and introns was detected in CD36 gene across seven taxa. The CpG islands were also found to be distributed unevenly across the gene and taxa. Neighbour-joining tree was constructed and it was observed that the chimpanzee and human are diverged at the CD36 gene relatively recently. The chicken, Gallus gallus was found to be diverged from rest of the taxa signifi cantly. Also copy number variation was observed across different taxa. Interpretation & conclusions: Comparative genomic study of a human immune system gene CD36 show relationships among different taxa at the evolutionary level. The information can be of help to study genetic diversity in malaria endemic zones and to correlate it with malaria pathogenecity.