Ovitrap surveillance was conducted in a selected urban area and suburban area, ie. Taman Permai Indah(TPI) and Kampung Pasir Gebu (KPG) in Penang for 14 months. It was found that Aedes albopictus was the most abundant Aedes species in both study areas, even though a small percentage of Aedes aegypti and Culex quinquefasciatus were found to breed simultaneously in the same ovitrap. This study indicated that the main dengue vector was Ae. albopictus. A strong correlation was found between rainfall and egg population in both of the study sites (r = 0.982 and r = 0.918).
A semi laboratory experiment using 3 cohorts of Aedes albopictus adults was performed to obtain age-specific mortality and fecundity information and to derive statistical estimates of some population growth parameters. Life expectancy was calculated for both males and females. The following population parameters were estimated: intrinsic rate of increase (rm= 0.21), net reproductive (replacement) rate (Ro= 68.70), age at mean cohort reproduction (To=10.55 days), birth rate (B=0.23), death rate (D=0.02) and generation time (G=20.14 days). The high rm/B (0.91) and B/D (11.50) ratios indicated the high colonizing ability of Ae. albopictus in nature.
The bioefficacy of a commercial formulation of temephos, Creek against Aedes aegypti larvae was studied in the laboratory. Earthen jars were filled with 10 L tap water each. One g of temephos (Creek) sand granule formulation was added into each earthen jar as recommended by the manufacturer. The final test concentration of Creek was 1 mg a.i./L. One earthen jar was filled with 10 L tap water and served as a test control (untreated). Thirty late 3(rd) or early 4(th) instar of lab-bred Ae. aegypti larvae were added into each earthen jar. Mortality of the larvae was recorded after 24 hours and percent mortality was calculated. Test was repeated every week. The results showed that complete larval mortality was achieved after 24 hours. The residual effect lasted 15 weeks (105 days), indicating that Creek is effective at the dosage recommended by the manufacturer which is 1 mg a.i./L.
The mechanism of insecticide resistance is traditionally attributed to detoxification enzymes, target site alteration, decreased penetration of insecticides and behavioural resistance. Other form of mechanisms, such as the role of protein(s) in resistance is unknown. In the present study, the protein profiling of both IMR-PSS strain (permethrin-selected) and IMR-LS strain (laboratory-susceptible) 24 hours post exposure period to permethrin was carried out via 1D-gel electrophoresis and liquid chromatography mass spectrometry (LC-MS/ MS). The bands which appeared in the gel of 1D-electrophoresis revealed an abundance of proteins. The band pattern of both strains looked macroscopically alike and differed only in band intensity. However, LC-MS/MS analysis revealed that the IMR-PSS strain produced extra 388 peptides that were not found in the IMR-LS strain, indicating that IMR-PSS strain reacted differently from IMR-LS strain as a result of persistent exposure to permethrin. Since the complex banding patterns of 1D-gel electrophoresis were difficult to interpret the significance of the protein difference between IMR-PSS and IMR-LS strain, hence LC-MS/MS analysis is ideally suited for better protein resolution and thus will allow more in-depth comparison of the complex pattern. The findings here provide the first preliminary evidence that insecticide resistance in mosquito induces up regulation of proteins that may be protective to mosquitoes against insecticide and proteins could be another mechanism that contributes to development of resistance.
During the past decade outbreaks of a severe haemorrhagic disease caused by dengue viruses of multiple types have been reported in the Philippines, Thailand, Malaysia, Viet-Nam and eastern India. In many of these outbreaks chikungunya virus, a group A arbovirus, was simultaneously the cause of similar but probably milder disease. Both these viruses appear to be able to be able to produce classical dengue fever in some individuals and disease with haemorrhagic manifestations in others. Because of the growing public health importance and the progressive spread of this disease a unified review of its clinical and epidemiological features has been needed. This paper presents the history and salient clinical features of mosquito-borne haemorrhagic fever and summarizes recent epidemiological studies and current diagnostic and control methods.
Vector-borne viral diseases pose an urgent public health challenge, particularly in the tropics. Field releases of mosquitoes carrying bacterial symbionts that reduce vector competence are ongoing in Kuala Lumpur, Malaysia. Early results show that wAlbB Wolbachia can persist in mosquitoes in urban settings and decrease dengue incidence in humans.
The present study aims to investigate the susceptibility status of Aedes albopictus (Skuse) collected from residential areas in Sabah, Malaysia towards eight WHO-recommended dosages of larvicides representing the classes of organophosphates and organochlorines. Field and reference strains of Ae. albopictus larvae were bioassayed in accordance to WHO standard methods using diagnostic dosages of bromophos, malathion, fenthion, fenitrothion, temephos, chlorpyrifos, dichlorodiphenyltrichloroethane (DDT), and dieldrin. The results revealed that Ae. albopictus was resistant (mortality < 90%) towards malathion, temephos, and DDT. In addition, most of the Ae. albopictus strains exhibited a wide range of susceptibilities against bromophos, with mortality ranged from 49.33 to 93.33%. On the contrary, only dieldrin was able to induce 100% mortality against all strains of Ae. albopictus. Tolerance to fenitrothion, fenthion, and chlorpyrifos, with mortality ranging from 81.33 to 97.33%, was also observed in this study.
This study was conducted using the glass chamber method to determine the susceptibility status of the dengue vector, Aedes aegypti (L.) from 11 states in Malaysia to commercial mosquito coils containing four different active ingredients, namely metofluthrin, d-allethrin, d-trans allethrin, and prallethrin. Aedes aegypti exhibited various knockdown rates, ranging from 14.44% to 100.00%, 0.00% to 61.67%, 0.00% to 90.00%, and 0.00% to 13.33% for metofluthrin, d-allethrin, d-trans allethrin, and prallethrin, respectively. Overall, mortality rates ranging from 0.00% to 78.33% were also observed among all populations. Additionally, significant associations were detected between the knockdown rates of metofluthrin and d-allethrin, and between metofluthrin and d-trans allethrin, suggesting the occurrence of cross-resistance within pyrethroid insecticides. Overall, this study revealed low insecticidal activity of mosquito coils against Ae. aegypti populations in Malaysia, and consequently may provide minimal personal protection against mosquito bites.
The continued absence of an effective and safe tetravalent dengue vaccine and the lack of specific anti-viral treatment have made mosquito vector control using chemical insecticides as the mainstream for dengue prevention and control. However, the long-term use of chemical insecticides may induce resistance. Hence detection of insecticide resistance in dengue vectors is crucially important in ensuring the insecticide-based intervention in dengue control program is still effective and reliable. In this study, the susceptibility status of Aedes aegypti from five selected dengue hotspots in Klang Valley, Malaysia against pyrethroids was determined by employing the World Health Organization (WHO) protocol of adult bioassay. Four types of pyrethroids were tested against adult female Aedes aegypti to determine the knockdown rate, post 24-h adult mortality and resistance ratio. All field-collected Aedes aegypti strains were resistant to the four pyrethroids tested, except for the Taman Sungai Jelok (TSJ) strain. Permethrin exhibited the lowest knockdown rate against Aedes aegypti, followed by deltamethrin, cyfluthrin and lambda-cyhalothrin. This present study indicated the widespread of pyrethroid resistance in Aedes aegypti in Klang Valley, indicating the needs of implementing alternative measures in vector control program. The data in this study can be utilised as an input for insecticide resistance management of Aedes aegypti in Malaysia.
Buruli ulcer (BU) is a globally recognized, yet largely neglected tropical disease whose etiologic agent is Mycobacterium ulcerans. Although the exact mode of transmission is unclear, epidemiological evidence links BU incidence with slow-moving or stagnant, aquatic habitats, and laboratory-based experiments have shown disease manifestation in animals with dermal punctures. Therefore, hypotheses for transmission include contact with slowmoving aquatic habitats and associated biting aquatic insects, such as mosquitoes. Recent research demonstrated the toxin produced by M. ulcerans, mycolactone, is an attractant for adult mosquitoes seeking a blood-meal as well as oviposition sites. In the study presented here, we examined the impact of mycolactone at different concentrations on immature lifehistory traits of Aedes aegypti, which commonly occurs in the same environment as M. ulcerans. We determined percent egg hatch was not significantly different across treatments. However, concentration impacted the survivorship of larval mosquitoes to the adult stage (p < 0.001). Resulting adults also showed a slight preference, but not significant (p > 0.05), for oviposition in habitats contaminated with mycolactone suggesting a legacy effect.
Oil-in-water (o/w) emulsion is utilized as an insecticide delivery system for mosquito control. However, evaporation inhibition adjuvant is needed to prevent fog drift, inhibit release of insecticidal actives and prolong suspension time. In the current study, we evaluated the effect of different short-chain alcohols, namely, propylene glycol, 1,3-propanediol, glycerol and crude glycerol, as adjuvants on the physicochemical properties of d-phenothrin o/w emulsion system. The bioactivity of optimized formulations containing 20 wt% glycerol (D1), 20 wt% propylene glycol (D2) and without added alcohol (negative control) were tested against larvae, pupae and adult Aedes aegypti (Ae. aegypti). It was found that propylene glycol produced smaller droplets at lower concentrations but poor long-term stability at higher concentrations, whereas glycerol had an appreciable effect on initial droplet size and stability with increasing concentration. According to the dose-response bioassays and room size chamber testing, the highest larvicidal, pupicidal and adulticidal activities were observed with D2, followed by D1 and negative control. Overall, the above study demonstrated improved emulsion stabilities and potency against Ae. aegypti larvae, pupae and adults using glycerol as adjuvant for effective mosquito control.
Resistance status of Aedes albopictus (Skuse) from 13 districts in Sarawak State, Malaysia, was evaluated against four major classes of adulticides, namely organochlorine, organophosphate, carbamate, and pyrethroid. Adult bioassays were performed according to the World Health Organization (WHO) standard protocols to assess knockdown and mortality rates of Ae. albopictus. Among the tested pyrethroids, only cyfluthrin was able to exhibit complete knockdown. On the other hand, different susceptibility and resistance patterns were observed in other adulticides. As for mortality rates, the mosquitoes were susceptible to cyfluthrin and dieldrin but exhibited various susceptibilities to other tested adulticides. Cross-resistance was discovered within and between tested insecticide classes. Significant correlations were found within pyrethroid and carbamate classes (i.e., bendiocab and propoxur, P = 0.036; etofenprox and permethrin, P = 0.000; deltamethrin and lambda-cyhalothrin, P = 0.822; deltamethrin and permethrin, P = 0.042). Additionally, insecticides belonging to different groups were also found significantly correlated (i.e., malathion and deltamethin, P = 0.019; malathion and bendiocarb, P = 0.008; malathion and propoxur, P = 0.007; and bendiocarb and deltamethrin, P = 0.031). In conclusion, cyfluthrin was effective for Aedes albopictus control in Sarawak State and these data may assist local authorities to improve future vector control operations.
Susceptibility status of Aedes albopictus (Skuse) sampled from residential areas in Interior, Sandakan and Tawau divisions of Sabah, Malaysia, was evaluated based on the WHOrecommended doses of organochlorine and organophosphate larvicides. To determine susceptibility status, larval bioassays were carried out and post 24-hour mortalities based on WHO resistance classifications were adopted. The results demonstrated that Ae. albopictus larvae were resistant toward 5 out of the 8 larvicides tested. Larvae from all populations were resistant against bromophos, fenitrothion, malathion, temephos and dichlorodiphenyltrichloroethane (DDT), with mortalities ranging from 0.00 to 89.33%. Dieldrin, on the other hand, could induce 100.00% mortalities in all populations, followed by fenthion and chlorpyrifos, with mortalities ranging from 97.33 to 100.00% and 81.33 to 100.00% respectively. Despite most populations exhibiting similitude in their resistance status, larvae from Sandakan exhibited the highest resistance level whereas the lowest level was observed in Keningau. In view of the inadequacy of some larvicides in controlling Ae. albopictus in this study, integrated management such as insecticide rotation or combination of interventions is warranted.