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Thanispong K.,Kasetsart University | Achee N.L.,Uniformed Services University of the Health Sciences | Grieco J.P.,Uniformed Services University of the Health Sciences | Bangs M.J.,Public Health and Malaria Control | And 4 more authors.
Journal of Medical Entomology | Year: 2010

Chemicals can protect humans from the bites of hemophagous arthropods through three different primary actions: irritancy (excitation), repellency, or toxicity, actions that can be evaluated using a laboratory-based assay system, In this study, the deterrent and toxic actions of three synthetic pyrethroids and DDT were characterized on six field strains of Aedes aegypti from Thailand under laboratory-controlled conditions using the high throughput screening system. All six strains showed significant contact irritant responses to the three synthetic pyrethroids, but significantly weaker irritant responses to DDT, Marked repellency responses were seen in all six Ae. aegypti test strains exposed to DDT, whereas the synthetic pyrethroids resulted in greater toxicity than DDT under similar test conditions. Although significantly different in actions, irritancy and repellency may reflect and be influenced by the background insecticide susceptibility status of a particular mosquito population. Results from this study can be used to guide decision making regarding more effective Ae. aegypti adult control in Thailand. © 2010 Entomological Society of America.

Kinzer M.H.,Us Naval Medical Research Unit No2 | Chand K.,Us Naval Medical Research Unit No2 | Basri H.,Us Naval Medical Research Unit No2 | Lederman E.R.,Us Naval Medical Research Unit No2 | And 6 more authors.
Malaria Journal | Year: 2010

Abstract. Background. Chloroquine-resistant Plasmodium falciparum was first described in the Republic of Vanuatu in the early 1980s. In 1991, the Vanuatu Ministry of Health instituted new treatment guidelines for uncomplicated P. falciparum infection consisting of chloroquine/sulphadoxine-pyrimethamine combination therapy. Chloroquine remains the recommended treatment for Plasmodium vivax. Methods. In 2005, cross-sectional blood surveys at 45 sites on Malo Island were conducted and 4,060 adults and children screened for malaria. Of those screened, 203 volunteer study subjects without malaria at the time of screening were followed for 13 weeks to observe peak seasonal incidence of infection. Another 54 subjects with malaria were followed over a 28-day period to determine efficacy of anti-malarial therapy; chloroquine alone for P. vivax and chloroquine/sulphadoxine-pyrimethamine for P. falciparum infections. Results. The overall prevalence of parasitaemia by mass blood screening was 6%, equally divided between P. falciparum and P. vivax. Twenty percent and 23% of participants with patent P. vivax and P. falciparum parasitaemia, respectively, were febrile at the time of screening. In the incidence study cohort, after 2,303 person-weeks of follow-up, the incidence density of malaria was 1.3 cases per person-year with P. vivax predominating. Among individuals participating in the clinical trial, the 28-day chloroquine P. vivax cure rate was 100%. The 28-day chloroquine/sulphadoxine-pyrimethamine P. falciparum cure rate was 97%. The single treatment failure, confirmed by merozoite surface protein-2 genotyping, was classified as a day 28 late parasitological treatment failure. All P. falciparum isolates carried the Thr-76 pfcrt mutant allele and the double Asn-108 + Arg-59 dhfr mutant alleles. Dhps mutant alleles were not detected in the study sample. Conclusion. Peak seasonal malaria prevalence on Malo Island reached hypoendemic levels during the study observation period. The only in vivo malaria drug efficacy trial thus far published from the Republic of Vanuatu showed chloroquine/sulphadoxine-pyrimethamine combination therapy for P. falciparum and chloroquine alone for P. vivax to be highly efficacious. Although the chloroquine-resistant pfcrt allele was present in all P. falciparum isolates, mutant alleles in the dhfr and dhps genes do not yet occur to the extent required to confer sulphadoxine-pyrimethamine resistance in this population. © 2010 Kinzer et al; licensee BioMed Central Ltd.

Malaithong N.,Kasetsart University | Polsomboon S.,Kasetsart University | Poolprasert P.,Kasetsart University | Parbaripai A.,Kasetsart University | And 5 more authors.
Journal of Medical Entomology | Year: 2010

Anopheles dirus females landing on humans inside experimental huts treated with residual applications of DDT or deltamethrin were observed during the wet season in Pu Teuy Village, Kanchanaburi Province, western Thailand. Two identical experimental huts were constructed in the fashion of typical local rural Thai homes. Pretreatment (baseline) human-landing collections (HLC) in both huts showed an early evening peak of activity between 1900 and 2000 h with no significant difference in numbers of mosquitoes captured between huts over a period of 30 collection nights. During posttreatment HLC, female mosquitoes continued to show greater landing activity inside huts fitted with insecticide-treated panels during the first half of the evening compared with the second half. A greater number (proportion) of An. dims females landed on humans in the hut treated with deltamethrin compared with DDT. Comparing pre- and posttreatment HLC, the DDT-treated hut showed a 79.4% decline in attempted blood feeding, whereas exposure to deltamethrin resulted in a 56.3% human-landing reduction. An odds ratio was performed to demonstrate the relative probability (risk) of mosquitoes entering and attempting to blood feed in the two treated huts compared with untreated control huts. Mosquitoes were ≈times less likely to land on humans inside a DDT-treated hut compared with the deltamethrin-treated hut. Although both chemicals exerted strong excitatory responses, DDT appears to have a more pronounced and significant (P = 0.002) effect on behavior than deltamethrin, resulting in greater movement away from the insecticide source and thus potential reduction of blood-feeding activity. © 2010 Entomological Society of America.

Nixon C.P.,University of California at San Francisco | Nixon C.E.,Eijkman Institute of Molecular Biology | Arsyad D.S.,Eijkman Institute of Molecular Biology | Chand K.,Eijkman Institute of Molecular Biology | And 13 more authors.
Pathogens and Global Health | Year: 2014

Background: The decline in intensity of malaria transmission in many areas now emphasizes greater importance of understanding the epidemiology of low to moderate transmission settings. Marked heterogeneity in infection risk within these populations creates opportunities to understand transmission and guide resource allocation to greater impact. Methods: In this study, we examined spatial patterns of malaria transmission in a hypo- to meso-endemic area of eastern Indonesia using malaria prevalence data collected from a cross-sectional sociodemographic and parasitological survey conducted from August to November 2010. An entomological survey performed in parallel, identified, mapped, and monitored local anopheline larval habitats. Results: A single spatial cluster of higher malaria prevalence was detected during the study period (relative risk 5 2.13; log likelihood ratio 5 20.7; P, 0.001). In hierarchical multivariate regression models, risk of parasitemia was inversely correlated with distance to five Anopheles sundaicus known larval habitats [odds ratio (OR) 5 0.21; 95% confidence interval (CI) 5 0.14–0.32; P, 0.001], which were located in a geographically restricted band adjacent to the coastline. Increasing distance from these sites predicted increased hemoglobin level across age strata after adjusting for confounders (OR 5 1.6; 95% CI 5 1.30–1.98; P, 0.001). Conclusion: Significant clustering of malaria parasitemia in close proximity to very specific and relatively few An. sundaicus larval habitats has direct implications for local control strategy, policy, and practice. These findings suggest that larval source management could achieve profound if not complete impact in this region. © W. S. Maney & Son Ltd 2014.

Chuaycharoensuk T.,Kasetsart University | Juntarajumnong W.,Kasetsart University | Boonyuan W.,Kasetsart University | Bangs M.J.,Public Health and Malaria Control | And 5 more authors.
Journal of Vector Ecology | Year: 2011

ABSTRACT:: Thirty-two Aedes aegypti populations collected throughout Thailand and five populations of Aedes albopictus from southern Thailand were subjected to standard WHO contact bioassays to assess susceptibility to three commonly used synthetic pyrethroids: permethrin, deltamethrin, and lambda-cyhalothrin. A wide degree of physiological response to permethrin was detected in Ae. aegypti, ranging from 56.5% survival (Lampang, northern Thailand) to only 4% (Kalasin in northeastern and Phuket in southern Thailand). All 32 populations of Ae. aegypti were found to have evidence of incipient resistance (62.5%) or levels of survival deemed resistant (37.5%) to permethrin. Four populations of Ae. albopictus were found with incipient resistance (97 - 80% mortality) and one with resistance (< 80%) to permethrin. The majority of Ae. aegypti populations (68.7%) was susceptible (> 98% mortality) to deltamethrin, with incipient resistance (observed 97-82% mortality) in other localities. In contrast, all populations of Ae. aegypti were completely susceptible (100% mortality) to the recommended operational dosage of lambda-cyhalothrin. All five populations of Ae. albopictus were found completely susceptible to both deltamethrin and lambda-cyhalothrin. Evidence of defined incipient or resistance to synthetic pyrethroids mandates appropriate response and countermeasures to mitigate further development and spread of resistance. In light of these findings, we conclude that routine and comprehensive susceptibility monitoring of dengue mosquito vectors to synthetic pyrethroids should be a required component of resistance management policies and disease control activities. © 2011 The Society for Vector Ecology.

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