Detection and isolation of chikungunya virus from field collected Aedes albopictus skuse in selected sites, Peninsular Malaysia

Chikungunya fever, an Aedes borne viral disease, is becoming a serious public health concern today since the first reported outbreak in Port Klang in 1998/99. Recently, more outbreaks were reported in Malaysia. Entomological investigations were conducted in Chikungunya virus cases localities in Peninsular Malaysia which cover Johor, Negeri Sembilan, Melaka, Perak, Pahang and Selangor state in order to identify the vector responsible for transmitting the Chikungunya virus. The adult mosquitoes were collected using modified aspirator and sweep net methods, whereas water holding containers were inspected for larvae. Reverse transcriptase polymerase chain reaction (RT-PCR) were used as the detection of the virus. Positive samples were inoculated on the cell to isolate the virus. The most common species collected at the localities was Aedes albopictus followed by Culex quinquefasciatus, Aedes aegypti and Armigeres sp. Five pools (n=78) of female, adult Aedes albopictus collected from Tangkak, Johor were positive for the Chikungunya virus as detected by reverse transcription-polymerase chain reaction. Three isolates were obtained and grouped with Central/East African genotype. The presence of Chikungunya virus in wild Aedes albopictus indicated that this mosquito is the most likely vector responsible for the transmission of virus to humans in Johor during the outbreak

Weekly Variation on Susceptibility Status of Aedes Mosquitoes against Temephos in Selangor, Malaysia

Larvae of Aedes aegypti and Aedes albopictus obtained from 6 consecutive ovitrap surveillance (OS) in Taman Samudera and Kg. Banjar were evaluated for their susceptibility to temephos. Larval bioassays were carried out in accordance with WHO standard methods, with diagnostic dosage (0.012 mg/L) and operational dosage (1 mg/L) of temephos respectively. Aedes aegypti and Ae. albopictus obtained from six OS in Taman Samudera showed resistance to diagnostic dosage of temephos with percentage mortality between 5.3 to 72.0 and 9.3 to 56.0, respectively, while Ae. aegypti and Ae. albopictus obtained from Kg. Banjar showed resistance to temephos with percentage mortality between 16.0 to 72.0 and 0 to 50.6, respectively. Only two strains of Ae. aegypti from Kg. Banjar were susceptible to temephos with 93.3 (OS 2) and 100 (OS 3) mortality. The 50 mortality at lethal time (LT50) for all strains of Ae. aegypti and Ae. albopictus tested against operational dosage of temephos showed range between 36.07 to 75.69 minutes and 58.65 to 112.50 minutes, respectively, and complete mortality was achieved after 24 hours. Our results indicated that there is weekly variations of the resistance status for Ae. aegypti and Ae. albopictus. Aedes susceptibility to temephos is changing from time to time in these two study sites. It is essential to continue monitoring the resistance of this vector to insecticides in order to ensure the efficiency of program aimed at vector control and protection of human health

Susceptibility of Aedes aegypti and Aedes albopictus to temephos in four study sites in Kuala Lumpur City Center and Selangor State, Malaysia

Larvae obtained from Taman Samudera (Gombak, Selangor), Kampung Banjar (Gombak, Selangor), Taman Lembah Maju (Cheras, Kuala Lumpur) and Kampung Baru (City centre, Kuala Lumpur) were bioassayed with diagnostic dosage (0.012 mg/L) and operational dosage (1 mg/L) of temephos. All strains of Aedes aegypti and Aedes albopictus showed percentage mortality in the range of 16.00 to 59.05 and 6.4 to 59.50 respectively, after 24 hours. LT50 values for the 6 strains of Ae. aegypti and Ae. albopictus were between 41.25 to 54.42 minutes and 52.67 to 141.76 minutes respectively, and the resistance ratio for both Aedes species were in the range of 0.68 to 1.82 when tested with operational dosage, 1 mg/L temephos. These results indicate that Aedes mosquitoes have developed some degree of resistance. However, complete mortality for all strains were achieved after 24 hours when tested against 1 mg/L temephos

Insecticide Resistance Development in Aedes aegypti upon Selection Pressure with Malathion

Bioassay test against malathion had been carried out with larval and adult stages of Aedes aegypti. The mosquitoes were under selection pressure against malathion for fortyfive consecutive generations. The rate of resistance development was measured by LC 50 and LT 50 values. The larvae and adult females, after subjection to malathion selection for 45 generations, developed high resistance level to malathion, with resistance ratio of 52.7 and 3.24 folds, respectively over control mosquitoes. Cross-resistance towards the same and different groups of insecticides was determined using the F44 and F45 malathion-selected adult females. Insecticides tested were DDT (4.0), permethrin (0.75), propoxur (0.1), fenitrothion (1), λ-cyhalothrin (0.05) and cyfluthrin (0.15). Results indicated that the mosquitoes were highly resistant to DDT and fenitrothion, moderately resistant to propoxur, tolerant to permethrin and λ-cyhalothrin, and very low resistant to cyfluthrin

Bacteria Fauna from the House Fly, Musca domestica (L.)

The house fly, Musca domestica has long been considered a potential agent for disease transmission ever since its existence. The general truth of this assertion remains undisputed till the present day in spite of increasing awareness toward an improved sanitation and better hygiene. The habitual movement of house fly from filthy substrata such as human faeces, animal excreta, carcasses, garbage, etc. makes them ideal candidates for disease transmission such as cholera, shigellosis, salmonellosis and others when settling on food. Fly as a potential mechanical vector of pathogenic bacteria was elucidated in this study by examining flies from various breeding sites such as food courts, dumping ground, food processing areas and poultry farm in Peninsular Malaysia. The flies were baited with 10 sugar solution on a glass slide in the field. All materials used for collection of samples were sterile. Bacteria from fly sample were isolated using the normal isolation technique. Bacillus sp., Coccobacillus sp., Staphylococcus sp., Microccus sp., Streptococcus sp., Acinetobacter sp., Enterobacter sp., Proteus sp., Escherichia sp., Klebsiella sp. and yeast cells were isolated from feaces, vomitus, external surfaces and internal organs of house fly. Newly emerged house fly did not harbour any bacteria

Determination of homozygous susceptible strain in Culex quinquefasciatus (Say), using single raft sib-selection method.

The standard laboratory strain was found to be heterozygous for susceptibility. Hence, an attempt was made to obtain a homozygous susceptible strain in Culex quinquefasciatus (Say) using single raft sib-selection method. Lab-bred females of Cx. quinquefasciatus from insectariums, Unit of Medical Entomology were used in the experiment. After blood feeding Cx. quinquefasciatus mosquitoes laid eggs in raft form, ten rafts selected randomly for the test. Each egg raft was introduced into a plastic tray from number one to number ten. Twenty-five third stage larvae from each tray were exposed to 17.5 microl from 500mg/l malathion in a paper cup label number 1 to number ten. In the bioassay, which had 100% mortality, the respective larva in that particular tray was bred to adult stage for the following generation. Less than 7days old female mosquitoes that emerged from F(0) were used in the test. The F(0) and the subsequent adult and larval stage generations were subjected to adult and larval bioassay. After selection for about 10 generations, a homozygous susceptible strain in Cx. quinquefasciatus was obtained

Resistance development and insecticide susceptibility in Culex quinquefasciatus against selection pressure of malathion and permethrin and its relationship to cross-resistance towards propoxur.

To determine resistance level and characterize malathion and permethrin resistance in Culex quinquefasciatus, two methods were used namely: WHO procedures of larval bioassay to determine the susceptibility of lethal concentration (LC) and adult bioassay to determine the lethal time (LT) which are resistant to malathion and permethrin. These mosquito strains were bred in the Insectarium, Division of Medical Entomology, IMR. Thousands of late fourth instar larvae which survived the selection pressure to yield 50% mortality of malathion and permethrin were reared and colonies were established from adults that emerged. Larvae from these colonies were then subjected to the subsequent 10 generations in the test undertaken for malathion resistant strain (F61 - F70) and permethrin resistant strain (F54 - F63). Selection pressure at 50% - 70% mortality level was applied to the larvae of each successive generation. The rate of resistance development and resistance ratio (RR) were calculated by LC5 0 for larval bioassay and LT50 value for adult bioassay. The lab bred Cx. quinquefasciatus was used as a susceptible strain for comparison purpose. The adult bioassay test was carried out by using diagnostic dosages of malathion 5.0%, permethrin 0.75% and with propoxur 0.1%. All bioassay results were subjected to probit analysis. The results showed that LC5 0 for both malathion (F61 - F70) and permethrin (F54 - F63) resistant Cx. quinquefasciatus increased steadily to the subsequent 10 generations indicating a marked development of resistance. The adult female malathion resistant strain have developed high resistance level to malathion diagnostic dosage with resistance ratio 9.3 to 9.6 folds of resistance. Permethrin resistance ratio remained as 1.0 folds of resistance at every generation. It was obvious that malathion resistance developing at a higher rate in adult females compared to permethrin. Female adults exposed to 2 hours of exposure period for propoxur 0.1% showed presence of cross-resistance among the both strains of mosquitoes towards propoxur and it was indicated by 70%-100% mortality at 24 hours post-recovery period

Review of forensically important entomological specimens collected from human cadavers in Malaysia (2005-2010)

Forensic entomological specimens collected from human decedents during crime scene investigations in Malaysia in the past 6 years (2005-2010) are reviewed. A total of 80 cases were recorded and 93 specimens were collected. From these specimens, 10 species of cyclorrphagic flies were identified, consisting of Chrysomya rufifacies (Macquart) -38 specimens (40.86), Chrysomya megacephala (Fabricius) -36 specimens (38.70), Chrysomya villeneuvi (Patton) -2 specimens (2.15), Chrysomya nigripes (Aubertin) -2 specimens (2.15), Chrysomya pinguis (Walker) -1 specimen (1.08), Hermetia illucens (Linnaeus) -1 specimen (1.08), Hemipyrellia liguriens (Wiedemann) -5 specimens (537), Synthesiomyia nudiseta (Wulp) -1 specimen (1.08), Megaselia scalaris (Loew)-1 specimen (1.08) and Sarcophaga ruficornis (Fabricius) -4 specimens (4.30). In two specimens (2.15), the maggots were not identifiable. Ch. megacephala and Ch. rufifacies were the commonest species found in human decedents from three different ecological habitats. S. nudiseta is an uncommon species found only on human cadavers from indoors. A total of 75 cases (93.75) had a single fly infestation and 5 cases (6.25) had double fly infestation. In conclusion, although large numbers of fly species were found on human decedents, the predominant species are still those of Chrysomya. (C) 2013 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved

Comparative oviposition preferences of Aedes (Stegomyia) aegypti (L.) to water from storm water drains and seasoned tap water

The comparative oviposition preferences of Aedes aegpti to water from storm-water drains and seasoned tap water were evaluated in the laboratory. The sample was collected from concrete storm-water drains with stagnant clear water in a dengue-endemic site, Taman Samudera, Selangor. Ae. aegypti adults were given a blood meal and released into the caged. Gravid females were given a choice between drain water and seasoned tap water for egg deposition. In a no-choice test, there was no significant difference in the numbers of eggs, larvae, pupae and adults colonized from the drain water and seasoned tap water (p>0.05), indicating that Ae. aegypti oviposit their eggs on a substrate which is readily available. In a choice test, the number of eggs laid by Ae. aegypti in drain water (1630.67 ± 204.26) was significantly more than that in seasoned tap water (221.33 ± 53.18) (p0.05), indicating that water from the drain did not contain high organic content. Significant water conductivity (p<0.05) and the presence of bacteria could have contributed to the site selection for egg laying by Ae. aegypti. The drain water successfully supported the colonization of the immatures, with the emergence of 824.33 ± 13.96 adult mosquitoes. The ratio of male and female mosquitoes was 1:1. This study concluded that the concrete drainage system with clear stagnant water provides a suitable medium for the colonization of dengue vector Ae. aegypti