Identification of entomopathogenic nematodes and symbiotic bacteria from Nam Nao National Park in Thailand and larvicidal activity of symbiotic bacteria against Aedes aegypti and Aedes albopictus.

Entomopathogenic nematodes (EPNs) that are symbiotically associated with Xenorhabdus and Photorhabdus bacteria can kill target insects via direct infection and toxin action. There are limited reports identifying such organisms in the National Park of Thailand. Therefore, the objectives of this study were to identify EPNs and symbiotic bacteria from Nam Nao National Park, Phetchabun Province, Thailand and to evaluate the larvicidal activity of bacteria against Aedes aegypti and Ae. albopictus. A total of 12 EPN isolates belonging to Steinernema and Heterorhabditis were obtained form 940 soil samples between February 2014 and July 2016. EPNs were molecularly identified as S. websteri (10 isolates) and H. baujardi (2 isolates). Symbiotic bacteria were isolated from EPNs and molecularly identified as P. luminescens subsp. akhurstii (13 isolates), X. stockiae (11 isolates), X. vietnamensis (2 isolates) and X. japonica (1 isolate). For the bioassay, bacterial suspensions were evaluated for toxicity against third to early fourth instar larvae of Aedes spp. The larvae of both Aedes species were orally susceptible to symbiotic bacteria. The highest larval mortality of Ae. aegypti was 99% after exposure to X. stockiae (bNN112.3_TH) at 96 h, and the highest mortality of Ae. albopictus was 98% after exposure to P. luminescens subsp. akhurstii (bNN121.4_TH) at 96 h. In contrast to the control groups (Escherichia coli and distilled water), the mortality rate of both mosquito larvae ranged between 0 and 7% at 72 h. Here, we report the first observation of X. vietnamensis in Thailand. Additionally, we report the first observation of P. luminescens subsp. akhurstii associated with H. baujardi in Thailand. X. stockiae has potential to be a biocontrol agent for mosquitoes. This investigation provides a survey of the basic diversity of EPNs and symbiotic bacteria in the National Park of Thailand, and it is a bacterial resource for further studies of bioactive compounds

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Abstract. Food-borne trematode infections, such as opisthorchiasis, are major causes of morbidity in Asia. This present study was performed to determine the prevalence of infection with Opisthorchis viverrini and other intestinal parasites in five areas of Khukan District, Si Sa Ket Province, Thailand. Data regarding socioeconomic characteristics and the health behavior of the population were thought to be useful in the development of a strategy to control and eradicate parasitic infections in a cost-effective manner. Stool samples were collected from 774 subjects, including all age-groups, from below 10 years of age to more than 60 years. The prevalence of infection varied in the 5 investigated areas and ranged from 7 to 13.6%. The majority of detected parasites (61 cases, 7.9%) were Opisthorchis viverrini. Males were significantly more often infected than females (p=0.03), and the prevalence of infection significantly increased with age (p=0.003) and lower educational level (p=0.03). Hand cleaning behavior was not significantly associated with the prevalence of infection (p=0.44). Subjects who claimed to wash their hands always tended to be even more often infected than subjects who only washed their hands sometimes (10.1 and 7.7%, respectively). These results indicate that opisthorchiasis is still a public health problem in Khukan District is more restricted to populations of lower education. However, hand cleaning behavior and personal hygiene do not seem to play as crucial a role in the transmission of the disease as previously thought. Further studies on social habits are required and might offer the possibility of targeted treatment and education of predisposed groups or communities