Showing papers by "Shinji Kasai published in 2009"

Widespread distribution of a newly found point mutation in voltage-gated sodium channel in pyrethroid-resistant Aedes aegypti populations in Vietnam.

Abstract: Background: Resistance of Aedes aegypti to photostable pyrethroid insecticides is a major problem for disease-vector control programs. Pyrethroids target the voltage-gated sodium channel on the insects’ neurons. Single amino acid substitutions in this channel associated with pyrethroid resistance are one of the main factors that cause knockdown resistance in insects. Although kdr has been observed in several mosquito species, point mutations in the para gene have not been fully characterized in Ae. aegypti populations in Vietnam. The aim of this study was to determine the types and frequencies of mutations in the para gene in Ae. aegypti collected from used tires in Vietnam. Methods and Findings: Several point mutations were examined that cause insensitivity of the voltage-gated sodium channel in the insect nervous system due to the replacement of the amino acids L1014F, the most commonly found point mutation in several mosquitoes; I1011M (or V) and V1016G (or I), which have been reported to be associated to knockdown resistance in Ae. aegypti located in segment 6, domain II; and a recently found amino acid replacement in F1269 in Ae. aegypti, located in segment 6, domain III. Among 756 larvae from 70 locations, no I1011M or I1011V nor L1014F mutations were found, and only two heterozygous V1016G mosquitoes were detected. However, F1269C mutations on domain III were distributed widely and with high frequency in 269 individuals among 757 larvae (53 collection sites among 70 locations surveyed). F1269C frequencies were low in the middle to north part of Vietnam but were high in the areas neighboring big cities and in the south of Vietnam, with the exception of the southern mountainous areas located at an elevation of 500–1000 m. Conclusions: The overall percentage of homozygous F1269C seems to remain low (7.4%) in the present situation. However, extensive and uncontrolled frequent use of photostable pyrethroids might be a strong selection pressure for this mutation to cause serious problems in the control of dengue fever in Vietnam.

Prevalence of kdr-like mutations associated with pyrethroid resistance in human head louse populations in Japan.

Abstract: Pyrethroid insecticides play very important roles in the control of pediculosis, which is caused by human head louse (Pediculus humanus capitis De Geer) worldwide. The development of head louse resistance to pyrethroid pediculicides has become a global issue during the last two decades. Pyrethroid resistance is associated with amino acid substitutions in the α-subunit of the para-sodium channel gene; these substitutions are termed kdr-like mutations. The frequencies of four mutations (D11E, M815I, T929I, and L932F) in the sodium channel gene were studied in human head louse colonies collected from Japan by using SNaPshot method. A total of 630 head lice collected from 282 infested people were analyzed, and it was found that 55 lice of 19 colonies homozygously or heterozygously possessed kdr-like genes, in which the four mutations existed concomitantly. This suggested that the quadruple mutant haplotype is a common feature of the kdr genes of pandemic head lice. The frequencies of the occurrence o...

Dispersal of a blow fly, Calliphora nigribarbis, in relation to the dissemination of highly pathogenic avian influenza virus.

Abstract: A mark-release-recapture study of the dispersal ability of blow flies, Calliphora nigribarbis, was conducted in Ikumo-Naka, Ato Town, Yamaguchi Prefecture, Japan in December 2004. A location where a fatal avian influenza outbreak had occurred 1 year previously was selected for the present study. A total of 3,884 C. nigribarbis were collected, 1,915 of which were marked and released from 4 different collection sites during 2 successive days. The recapture rate of the released C. nigribarbis ranged from 0.014 to 0.029 among the collection sites, and the overall recapture rate was calculated as 0.022. Based on the distance between the released site and the recaptured site, the dispersal rate of C. nigribarbis was estimated as 256 m/h on the 1st day and 179 m/h on the 2nd day of the experiment, and the maximum dispersal rate observed in this study was estimated as 500 m/h. Taking into account the active period of C. nigribarbis on a fine day (7 h/day), the distance traveled by C. nigribarbis within a day was estimated as 1,789 and 1,250 m/day on average for the 1st and 2nd days, respectively, and the maximum distance was 3,500 m/day. These results suggest that C. nigribarbis could play a role in the mechanical dissemination of avian influenza virus and spread of the outbreak in Japan.

Monitoring of kdr-Mediated Pyrethroid Resistance in Head Louse Colonies in Japan

Abstract: Recently, in Japan, cases of head louse infestation have been gradually increasing and this increase is a social concern. Phenothrin, the only registered active ingredient used as a pediculicide in Japan has been in use since 1981. Development of insecticide resistance within Japanese head lice colonies has been suspected as the main factor in the reemergence of head lice infestations in this country. Therefore, we investigated the current level of insecticide resistance in the head louse population in Japan. We focused on the four resistance-associated amino acid substitution mutations in the para-orthologous sodium channel gene, which is the target site of pyrethroids and 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT). Head lice were collected through the efforts of dermatologists, public health centers, and our departmental website. DNA was extracted from each larva, adult, or nit and the frequency of four mutations were monitored using a genotyping assay. Overall, 282 head louse colonies were collected from 22 prefectures in Japan. Nineteen louse colonies contained knock down resistance (kdr) -like sodium channel mutations and the frequency of occurrence of resistant colonies was 6.7%. Resistant head lice were confirmed in 10 prefectures. We could not determine if development of insecticide resistance is the main factor in the recent increase in head lice infestations in Japan. However, based on results from other countries, the occurrence of kdr-type head louse colonies is expected to increase. Thus, it is necessary to prepare alternative louse control agents.