Biomedical subjects

Apiwat Tawatsin

Publications and source records attributed to Apiwat Tawatsin.

12 recordsLinked to original sources

PubMed2006

Field evaluation of deet, Repel Care, and three plant based essential oil repellents against mosquitoes, black flies (Diptera: Simuliidae) and land leeches (Arhynchobdellida: Haemadipsidae) in Thailand.

Diethyl methyl benzamide, or deet, a commercial plant-based repellent (Repel Care), and essential ils from 3 species of plants (finger root rhizomes, guava leaves, and turmeric rhizomes), steam distillated and formulated as insect repellents, were evaluated in the field on human volunteers against hematophagous mosquitoes, black flies, and land leeches in Thailand. Field trials were conducted against wild mosquitoes in Bang Bua Thong District, Nonthaburi Province, and in the Thap Lan National Park Headquarters, Nadee District, Pranchinburi Province; anthroophilic black flies (Diptera: Simuliidae) at the Forestry Fire Control Station in Doi Inthanon National Park, Chomthong district, Chiang Mai Province; and land leeches (Arhynchobdellida: Haemadipsidae) in the Khao Yai National Park, Pak Chong District, Nakhon Ratchasima Province. The 3 experimental plant-based essential oil formulations as well as Repel Care and deet provided complete protection from mosquito landing and biting for up to 9 h (duration of the experiment). Similar results were obtained with the 5 products against black flies, providing 100% protection for 9 h but 96-82% protection after 10 and 11 h posttreatment. The 5 repellent products also provided 100% protection against land leeches for at least 8 h. Thi is the 1st report of repellency of plant-based repellents against black flies and land leeches in Thailand. The identification and availability of inexpensive sources of plant-based oils, i.e., finger root rhizomes, guava leaves, and turmeric rhizomes providing long-lasting repellency against blood-sucking organisms are promising leads into commercial production of relatively safe and effective repellents.

Aedes↗

PubMed2006

Laboratory and semi-field evaluation of Mosquito Dunks against Aedes aegypti and Aedes albopictus larvae (Diptera: Culicidae).

Laboratory bioassays and semi-field studies were conducted on the efficacy and longevity of Mosquito Dunks (7,000 ITU/mg Bti) in order to determine the concentration-response relationship and the effectiveness on the potency of the Bti product against Aedes mosquito species based on the WHO protocol standard methods and to determine the longevity of release for this product against Ae. aegypti mosquito larvae in water storage containers. This bio-potency study with the late 3rd instar larvae of Ae. aegypti and Ae. albopictus was carried out according to WHO standard protocols. The six concentrations of the Bti product used in each test were replicated 4 times with 25 mosquito larvae. Probit analysis was then used to determine the LC50 and LC95 which was equated with dosages of 1.02 and 1.86 ppm for Ae. aegypti; and 0.39 and 0.84 ppm for Ae. albopictus, which reveals a potency of 382.95 and 303.74 ITU/mg, respectively. The semi-field evaluation of this product in 200-liter earthen jars against 3rd instar larvae of Ae. aegypti showed satisfactory control of greater than 80% at 11 weeks post-treatment.

Aedes↗

PubMed2006

Double infection of heteroserotypes of dengue viruses in field populations of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) and serological features of dengue viruses found in patients in southern Thailand.

In order to understand more about the epidemiology of DHF, a study of the type of dengue viruses and vectors under natural conditions was carried out. Mosquito vectors in the field and the serum of DHF patients in southern Thailand were examined. The two mosquito species are abundant and DHF incidence remains high in this region. Dengue viruses were examined in field-caught mosquitoes by RT-PCR technique. The mosquitoes were caught in 4 provinces: Krabi, Phuket, Phang-Nga and Surat Thani during the late dry season until the early rainy season in 2005. Three dengue serotypes (DEN-2, DEN-3, DEN-4) were detected in Ae. aegypti males and females, and 2 (DEN-2, DEN-3) were detected in Ae. albopictus females. Double infection with 2 serotypes of dengue viruses (DEN-2 and DEN-3) were detected in Ae. aegypti males and females and Ae. albopictus females. DEN-2 and DEN-1 were the most prevalent serotypes found in the serum of the patients in this area, followed by DEN-4 and DEN-3. The prevalence of the predominant dengue serotype varied from province to province. Detection of viruses in adult male mosquitoes reveals the role of transovarial transmission of dengue viruses in field populations of DHF vectors and elucidates circulation of dengue viruses in vectors in the natural environment of endemic areas. The incidence of multiple serotypes of dengue virus in Ae. aegypti and Ae. albopictus in the same area points toward a high risk for an epidemic of DHF. These findings provide greater understanding of the relationship among mosquito vectors, virus transmission and DHF epidemiology in endemic areas.

Aedes↗

PubMed2005

Sequential release and residual activity of temephos applied as sand granules to water-storage jars for the control of Aedes aegypti larvae (Diptera: Culicidae).

Two long-term experiments were carried out on the release profile and efficacy of temephos 1% GR (sand granules) against Aedes aegypti larvae in water-storage containers. In the first experiment, the efficacy of temephos 1% GR enclosed and tied in a muslin cloth and placed in water at the bottom of 200 L earthen water-storage jars was studied by exposing the packets for four to nine wk in one set ofjars and then transferring them sequentially to new sets ofjars four times successively. Temephos released slowly from the granules, the magnitude of release being adequate in the initial period of two to three wk after treatment. Following this period, the efficacy of the granules increased substantially where 92-100% inhibition of emergence even at the lowest dosage of 1 g/100 L (0.05 mg/L AI) was obtained for about another five mo or longer. On removal of the packets from a given set of jars, the released residues remaining in the jars and water lasted a maximum of one to six wk post-removal depending on the magnitude of prior release into the jars. This experiment provided clear evidence that temephos is released slowly over a long period of time in water-storage jars. In the second experiment, we compared the efficacy of temephos 1% GR at 1 and 10 g (0.05 and 0.5 mg/L AI) per 200-L water in jars painted and unpainted on the inside. The efficacy in the painted jars, although high, was consistently lower than that in the unpainted jars, where 99-100% control of larvae was achieved at both rates for a minimum of five mo after treatment. On the basis of this experimental evidence, it is desirable to study the efficacy of lower dosages of temephos than those currently used in Ae. aegypti control programs. The use of controlled release formulations or sachets that are retrievable during cleaning and washing will be more practical and desirable. Both of these interventions will make the program more cost effective.

Aedes↗

PubMed2005

Decrease of mosquito salivary gland proteins after a blood meal: an implication for pathogenesis of mosquito bite allergy.

Salivary gland protein profiles ofAedes aegypti (L.) and Culex quinquefasciatus (Say) pre- and post-blood feeding were analyzed. SDS-PAGE studies before blood feeding of Ae. aegypti demonstrated 8 major polypeptide bands of 20, 35, 37, 42, 45, 47, 70 kDa and a high molecular weight band >118 kDa, whereas those of Cx. quinquefasciatus demonstrated 9 major polypeptide bands of 20, 26, 36, 38, 45, 47, 49 kDa and 2 high molecular weight bands >118 kDa. After a blood feeding, salivary gland polypeptides of Ae. aegypti at 35, 37, 45, 47, 70 kDa and high molecular weight band >118 kDa were depleted, while the polypeptide bands of 20, 26, 36, 38 kDa were depleted in Cx. quinquefasciatus. The presented study suggests that these major polypeptides were introduced into vertebrate hosts when a mosquito took a blood meal. Further investigation in molecular, biochemical and immunological aspects of these salivary gland polypeptides may provide information for better understanding in the role of these proteins in mosquito bite allergy.

Aedes↗

PubMed2004

Procedures for the evaluation of field efficacy of slow-release formulations of larvicides against Aedes aegypti in water-storage containers.

In Thailand, water-storage jars, barrels, drums, pails, and tanks constitute vast developmental sites for Aedes aegypti in urban, semiurban, and rural areas. Earthen water jars, cement jars, and concrete tanks constitute the greatest proportion of artificial containers where Ae. aegypti breed. This species is a major vector of the causal agents of dengue and dengue hemorrhagic fever, and vector control by larviciding is one of the main approaches to disease control. At present, temephos sand granules (SG) (1%) are used in large-scale community-based larviciding programs. Because of the use of this larvicide over the past 30 years, the likelihood exists that Ae. aegypti already has become resistant to this larvicide. To develop more options for control and make them available for use, we evaluated VectoBac tablets (Bacillus thuringiensis var. israelensis [Bti] 5%) and a new formulation of zeolite granules (ZG) of temephos (1%) and compared these formulations for efficacy with temephos SG (1%) in water-storage jars. In these tests, we used 48 identical glazed earthen water-storage jars (200-liter capacity) and developed quantitative sampling procedures for larvae, pupae, and pupal skins. Pupal skins were the easiest to count and this technique was used for the 1st time for assessing emergence of adults in water-storage containers. Three water regimens were used: full jars, half-full jars, and full jars emptied half way and refilled weekly. The 3 formulations with 3 regimens of water were assessed over a period of 6 months. VectoBac tablets at the dosage of 1 tablet or 0.37 g per 50 liters of water provided excellent control for about 112 days in full water jars. In the other 2 water regimens, VectoBac gave excellent control for 90 days. The 2 temephos formulations at the operational rate of 5 g per 50 liters of water were equal in efficacy, yielding almost 100% control for more than 6 months. Unlike temephos SG, the temephos ZG had no objectionable odor. Both the temephos ZG and Bti tablets increased clarity of the water, a feature desired by the users. Lack of odor and depression of turbidity are important attributes of Bti tablets and temephos ZG.

Animals↗

PubMed2004

Efficacy and longevity of a new formulation of temephos larvicide tested in village-scale trials against larval Aedes aegypti in water-storage containers.

Field trials on the initial and long-term efficacy of a new formulation of temephos granules (1% on zeolite) applied at 1 ppm active ingredient (AI) were conducted in water-storage containers against Aedes aegypti in 3 villages in the Kanchanaburi Province in Thailand. A total of 316 water-storage containers of various types and sizes were included in the study. In the initial survey, we found that some containers were positive for larval Ae. aegypti, whereas others were devoid of larvae before the initiation of treatments. The containers all were numbered with paint and divided into 4 groups: with larvae and treated, without larvae and treated, with larvae untreated, and without larvae and untreated. Assessment of larval abundance was made 48 h after treatment and monthly thereafter for 5 months. Containers with larvae and that were treated exhibited almost complete absence of larval Ae. aegypti for 2 months, but a small proportion became positive after 3 months. Most of these positive containers were devoid of zeolite granules, which are visible in the containers. The number of positive containers increased in months 4 and 5, despite the fact that residues of temephos granules were present in some of the larvae-positive containers. The containers initially without larvae and treated with temephos essentially were devoid of larvae for 2 months. After 3, 4, and 5 months, about 6-23% of the containers became positive despite the fact that some had visible amounts of temephos granules. In the 2 control groups initially with and without larvae, sustained and consistent production of larvae occurred. Even in the group initially without a larval population, the containers became positive for larvae 1 month after the start of the experiment and the positivity rate increased as the trial progressed. From these studies, the conclusion can be made that a single application of temephos zeolite granules at 1 ppm AI can provide highly satisfactory control of larval Ae. aegypti in water-storage containers for at least 3 months in the field under normal water-use practices.

Aedes↗

PubMed2004

Evaluation of attractants and egg-laying substrate preference for oviposition by Aedes albopictus (Diptera: Culicidae).

Evaluation of oviposition attractants and substrate preferences of Aedes albopictus was carried out under laboratory and field conditions. To obtain candidate oviposition substances we used a water rinse of 3 mollusk species: blood cockle (Anadara granosa), carpet shell (Paphia undulata), and sea mussel (Mytilus smaragdinus), and the giant tiger prawn (Penaeus monodon). The rinse water of carpet shell and giant tiger prawn showed higher attractiveness for ovipostion than the other candidate attractants. The filter paper substrate received fewer eggs than the other two substrates. There was no significant difference between the mean number of eggs laid on hardboard paddles and sponge sheets. The hatching rate of Ae. albopictus eggs laid on hardboard paddles was higher than those from the filter papers and sponge sheets. The sponge had lethal effects on Ae. albopictus eggs, and very few eggs laid on sponge hatched. In field experiments, evaluation of attractiveness of carpet shell rinse in ovitraps lined with sponge sheet as egg-laying substrate was carried out in various habitats and different areas of Thailand. The mean number of eggs in traps containing carpet shell rinse was significantly higher than those laid in rainwater traps. These studies reveal that the carpet shell and giant tiger prawn rinses are sources of oviposition attractant for Ae. albopictus under both laboratory and field conditions and could possibly be used as an attractant in surveillance and control.

Aedes↗

PubMed2004

Cockroach surveys in the Northern region of Thailand and Guangxi Province of China.

Cockroach surveys were carried out in three provinces of the Northern region of Thailand: Chiang Mai, Chiang Rai, and Mae Hong Son, and three cities of Guangxi Province of the People's Republic of China: Nanning, Huangjiang, and Hechi. Sticky traps were used for cockroach sampling in these surveys. At least 30 houses in each province or city were randomly sampled. Traps were placed in kitchen areas for 2 nights. In Thailand, a total of 214 cockroaches was caught in 65 of 112 houses (59.4%) with an average of 1.9 cockroaches/ house. There were 5 species of cockroach caught: Periplaneta americana (32.7%), Pycnoscelis surinamensis (29%), Periplaneta australasiae (18.2%), Periplaneta brunnea (17.3%), and Periplaneta fuliginosa (2.8%). In China, a total of 198 cockroaches was caught in 67 of 99 houses (67.5%) with an average of 2 cockroaches/ house. There were 6 species of cockroaches caught: P. americana (53%), Py. surinamensis (12.6%), P. brunnea (12.1%), P. australasiae (12.1%), P. fuliginosa (9.6%), and Neostylopyga rhombifolia (0.6%). According to the surveys in this study, there were no significant differences among the number of cockroaches caught in the six locations of the two countries (p > 0.05). P. americana was the most abundant cockroach species in both countries.

Analysis of Variance↗

PubMed2003

Climatic and social risk factors for Aedes infestation in rural Thailand.

An intense epidemic of dengue haemorrhagic fever in 1998 prompted the Thai government to investigate the feasibility of focalized vector (Aedes aegypti) control programmes. We tested for correlations of three indices of Aedes larval abundance (housing index, container index and Breteau index) against 38 socio-economic and four climatic variables. Availability of public water wells, existence of transport services and proportion of tin houses were positively associated with larval indices. Private water wells, health education, health insurance coverage, thatched houses and use of firewood for cooking were negatively associated. These probably represent both direct effects on breeding sites (private vs. public wells decrease necessity to store water, and health education may encourage breeding site removal), and more general effects of health-related attitudes, housing quality and remoteness from urban areas. Indices were positively associated with daily minimum temperature, an increase in precipitation from the previous month (reflecting the onset of the rainy season) and daily maximum temperatures of approximately 33-34 degrees C. The associations were used to derive statistical models to predict the rank order of larval indices within the study area (Spearman's correlation coefficients = 0.525-0.554). The study provides a rational basis for identifying possible social interventions, and for prioritizing previously unsurveyed villages for further monitoring and focalized vector control.

Aedes↗

PubMed2003

Emergence of resistance and resistance management in field populations of tropical Culex quinquefasciatus to the microbial control agent Bacillus sphaericus.

In recent years, highly potent mosquitocidal strains of the microbial agent Bacillus sphaericus (Bsph) have been isolated and developed for the control of mosquito larvae around the world. Laboratory selection experiments with the most active strains and their use in large-scale operational mosquito control programs resulted in the emergence of resistance in larvae of the Culex pipiens complex. This generated great concern among vector control agencies around the world, who feared reduced efficacy of this highly active larvicidal agent. To address this issue, the current studies were started to find practical strategies for controlling resistant mosquitoes and more importantly to develop resistance management strategies that would prevent or delay development of resistance. We initiated field studies in 3 low-income communities in Nonthaburi Province, Thailand. In 1 of the communities, larvae of Culex quinquefasciatus that were highly resistant (>125,000-fold) to Bsph strain 2362 were successfully controlled with applications of Bacillus thuringiensis var. israelensis (Bti) alone or in combination with Bsph. To prevent or delay resistance to Bsph, 2 other sites were selected, 1 treated with Bsph 2362 alone and the other treated with a mixture of Bsph 2362 and Bti. Mosquitoes treated with Bsph 2362 alone showed some resistance by the 9th treatment and almost complete failure of control occurred by the 17th treatment. After 9 treatments with the mixture over a 9-month period at another site, no noticeable change in susceptibility to Bsph was detected. During this period, the site treated with Bsph alone required 19 treatments, whereas the site treated with mixtures took only 9 treatments because of slower resurgence of larvae at the site treated with the mixture than at the site treated with Bsph alone. This is the 1st field evidence for delay or prevention of resistance to microbial agents in larval Cx. quinquefasciatus by using mixtures of Bti and Bsph. Further studies on the use of mixtures for the management of field resistance are warranted.

Animals↗

PubMed2003

Laboratory and field evaluation of novaluron, a new acylurea insect growth regulator, against Aedes aegypti (Diptera: Culicidae).

Novaluron, a new chitin synthesis inhibitor type of insect growth regulator, was evaluated in the laboratory and field against larvae of the mosquito Aedes aegypti (L.). In the laboratory, the technical material showed a high level of activity against 2nd and 4th instar larvae. The inhibition of emergence (IE) was 100% at concentrations of 0.25 to 1.0 microg/L. Second instars were slightly more susceptible than fourth instars. At the high concentration (1 ppb), most of the mortality occurred in the larvae, but at sublethal concentrations (for larvae) mortality also occurred in pupae and adults (incomplete eclosion). An EC10 (emulsifiable concentrate containing 10% active ingredient) formulation of novaluron was evaluated against Ae. aegypti in water-storage containers in the field in Thailand. Two tests at high (0.05 to 1 mg/L) and low (1 to 20 microg/L) concentrations were carried out in clay jars (200 L) and plastic pails (75 L). At high concentrations in clayjars, we obtained 86-96% inhibition of emergence (IE) for about 190 d, but the mortality declined at low concentrations after 190 d. At much lower concentrations, in jars and plastic pails in the second experiment, the IE was 80-100% for 2 mo. The highest concentrations of this series (10 microg/L in jars and 20 microg/L in pails) were active for 75 and 68 d respectively, losing efficacy by 82 d post-treatment. In the experiment using low concentrations, all treatments in jars and plastic pails failed to provide adequate control 90 d after treatment. These studies show that novaluron, even as EC10, has exceptional long-term activity against Ae. aegypti in water-storage containers, with higher concentrations yielding greater long-term control than low concentrations.

Aedes↗