Browsing by Author "U.S. Naval Medical Research Unit No. 2, Jakarta"

Filter results by typing the first few letters
Now showing 1 - 4 of 4
  • No Thumbnail Available
    PublicationMetadata only
    Biochemical detection of pyrethroid resistance mechanisms in Anopheles minimus in Thailand
    (2003-06-01) Theeraphap Chareonviriyaphap; Pompimol Rongnoparut; Piyanuch Chantarumpom; Michael J. Bangs; Kasetsart University; Mahidol University; Prince of Songkla University; U.S. Naval Medical Research Unit No. 2, Jakarta
    Enzyme-based metabolic mechanisms of insecticide resistance were investigated, comparing a deltamethrin-susceptible parent stock and resistant colonies of Anopheles minimus species A using biochemical assays. The control parent colony was determined susceptible to the diagnostic lethal concentration of deltamethrin (0.05%), whereas the 6 resistant test populations at selected 4, 8, 12, 14, 16, and 18 filial generations (F4, F8, F12, F14, F16: and F18) demonstrated varying levels of tolerance/resistance to deltamcthrin. Expression of levels of non-specific esterases, monooxygenases, and glutathione S-transferases (GSTs) were measured. Results indicated that monooxygenase activity was consistently elevated in resistant-selected test populations compared to the parent colony and increased as resistance intensified from F8to F18. There was a 5-fold increase in monooxygenase in the F18generation compared to the parental stock. Fluctuations in alpha and beta-esterase activity, measured by hydrolysis of alpha and beta-naphthylpropionate, provided no conclusive evidence of an association with pyrethroid resistance in this mosquito species. GSTs were not elevated in the 6 resistant test populations. Based on our results, it appears likely that the development of physiological resistance to deltamethrin in laboratory, resistant-selected generations of An. minimus is primarily associated with increased detoxification by over-expression of monooxygenases. The oxidases are the major contributors to pyrethroid resistance and the importance of kdr has yet to be convincingly determined. This finding represents the first report from Thailand of this metabolic mechanism of resistance in anophelines.
  • No Thumbnail Available
    PublicationMetadata only
    Cytochrome P450 genes: Molecular cloning and overexpression in a pyrethroid-resistant strain of Anopheles minimus mosquito
    (2005-03-01) Prinyada Rodpradit; Soamrutai Boonsuepsakul; Theeraphap Chareonviriyaphap; Michael J. Bangs; Pornpimol Rongnoparut; Mahidol University; Kasetsart University; U.S. Naval Medical Research Unit No. 2, Jakarta
    We previously determined that physiological resistance in a laboratory-selected pyrethroid-resistant Anopheles minimus species A Theobald mosquito is associated with increased detoxification via a P450-mediated mechanism. A CYP6 gene, CYP6AA3, was subsequently cloned and found overexpressed in 2 resistant mosquito generations (F13 and F19). We report herein the cloning of CYP6P7 and CYP6P8 genes with full coding sequences from the same An. minimus mosquito colony strain. CYP6P7 and CYP6P8 encode proteins, each with 509 amino acids. CYP6P7 had the closest (81%) amino acid identity with Anopheles gambiae CYP6P2. CYP6P8 genes had 79% identity with An. gambiae CYP6P1. Using semiquantitative reverse transcription-polymerase chain reaction analysis, the mRNA expression level of CYP6P7 presented ∼2- and 4-fold increases in F19 and F25 deltamethrin-resistant populations, respectively, compared with the parent susceptible strain. CYP6P8 mRNA expression levels were not significantly different between the 3 filial generations. The overexpression of CYP6AA3 mRNA was greater than that of CYP6P7 in F19 and F25 resistant populations. The relative increase of both CYP6AA3 and CYP6P7 mRNA was correlated with increased resistance to deltamethrin in An. minimus. Copyright © 2005 by the American Mosquito Control Association, Inc.
  • No Thumbnail Available
    PublicationMetadata only
    Effects of nutritional and physiological status on behavioral avoidance of Anopheles minimus (Diptera: Culicidae) to DDT, deltamethrin and lambdacyhalothrin
    (2001-12-01) Sungsit Sungvornyothin; Theeraphap Chareonviriyaphap; Atchariya Prabaripai; Vacarobon Thirakhupt; Supaporn Ratanatham; Michael J. Bangs; Mahidol University; Kasetsart University; U.S. Naval Medical Research Unit No. 2, Jakarta
    The monitoring of behavioral responses of mosquitoes to insecticides are critical to the understanding of how chemicals function in the control of disease transmission. The excito-repellency avoidance responses of laboratory-reared Anopheles minimus females exposed to diagnostic concentrations of DDT (2 g/m2), deltamethrin (0.0625 g/m2), and lambdacyhalothrin (0.0369 g/m2) were observed using an excito-repellency escape chamber. Insecticide contact (measuring irritancy) and non-contact (measuring repellency) behavioral assays were conducted on non-blood-fed (unfed), sugar-fed, early blood-fed (recently engorged) and late blood-fed mosquitoes. Rates of escape from the contact and non-contact chambers, regardless of chemical compounds, were most dramatic in unfed mosquitoes compared to other nutritional states (P< 0.05). In general, across all 3 chemicals, slower escape response was observed in sugar-fed and early blood-fed specimens, whereas late blood-fed showed an intermediate response. Relative suppression of escape flight response in comparison to matched non-insecticide treated controls and the unfed condition is likely the result of normal reduced flight activity among recent blood and sugar-engorged mosquitoes. We conclude that nutritional states and physiological conditions of mosquitoes as a result of blood feeding can dramatically influence excito-repellency test results. Therefore, for interpretive purposes, studies on chemical irritancy and repellency must account and control for the inherent variability of avoidance responses to insecticides influenced by nutritional and physiological conditions of the mosquitoes at the time of test.
  • No Thumbnail Available
    PublicationMetadata only
    Status of malaria in THAILAND
    (2000-06-01) Theeraphap Chareonviriyaphap; Michael J. Bangs; Supaporn Ratanatham; Kasetsart University; U.S. Naval Medical Research Unit No. 2, Jakarta; Mahidol University
    Despite decades of control success and a competent network of country-wide health infrastructure, malaria remains an important health threat in rural Thailand. All 4 known human malaria parasites have been reported present, with Plasmodium falciparum and Plasmodium vivax predominant. The expansion and intensity of multi-drug resistant Plasmodium falciparum is the most serious development to occur the last several decades. Members of 3 anopheline species complexes, Anopheles dirus, Anopheles minimus, and Anopheles maculatus, are considered to be primary malaria vectors in the country. Representatives within all 3 taxa are difficult or impossible to separate morphologically from one another, and insufficient information exists about population genetics between sibling species and vector status. Vector control in Thailand has been the primary means of malaria control, mainly by the use of routine residual insecticide spray inside houses. The use of DDT in vector control has resulted in measurable successes to interrupt malaria transmission in many parts of the country. Since 1949, DDT has been the predominant compound used; however, its public health use has continued to decline as a result of perceived operational difficulties, political issues and environmental concerns. The increased use of pyrethroids to impregnate bednets and for intradomiciliary spraying are generally more accepted by rural populations and are rapidly replacing the use of DDT. Organized malaria control activities have reduced malaria morbidity from 286/1,000 population in 1947 to 1.5/1,000 population by 1996. Despite encouraging trends in dramatically reducing malaria, the rates of disease may be re-emerging in the country as evidence from an increased annual parasite index from 1.78/1,000 in 1997 to 2.21 in 1998. The possible reasons for the apparent increase in incidence are discussed in terms of the technical, operational and social obstacles in malaria control in Thailand.