An Outbreak Investigation of Autochthonous Lymphatic Filariasis in Wangchan District, Rayong, Thailand, December 2013 – July 2014

Abstract

Background: Rayong Provincial Health Office had been notified a filariasis in young Thai boy from the Wangchan Hospital. The case’s habitat locates in Wangchan district, Rayong. The Surveillance and Rapid Response Team (SRRT) from national, regional and local conducted outbreak investigation during December 27, 2556 - July 2, 2557 with aim to confirm the diagnosis and outbreak of filariasis, to determine the magnitude of filariasis, to identify the vector and reservoir of filariasis including implementing preventive and control measures in the area.
Methods: The descriptive epidemiological study was conducted. We reviewed the situation of filariasis in Thailand and Rayong and reviewed patient's medical record at the Hospitals. We interviewed with parents and children in the family. Active case finding was done by blood smear in the population at risk and also domestic animals in the community for identifying reservoir. Environmental surveys and entomological studies also were carried out.
Results: We found confirmed case of lymphatic filariasis in 18 months old boy. He lives with his parents in a hut at rubber tree plantation at village number 6 Chumseang Sub-district, Wangchan District. The laboratory testing revealed microfilaria in the case’s blood and physical examination showed inguinal lymph nodes enlargement for both sides. The molecular sequencing of filaria in case’s blood revealed Brugia pahangi. He was treated with Diethylcarbamazine (DEC) from Rayong Hospital. Active case finding among population at risk in the community, both in Thailand and foreign workers, was no case identifying and blood survey among 565 people was all negative filarial. But we found blood microfilaria in 51 dogs and a cat and identified as Brugia pahangi, Dirofilaria immitis and Dirofilaria repens. The vector survey found Mansonia uniformis as main vector of Brugia spp. and the rate of mosquito bites (Biting rate) was 0.37 mosquito/person/night (low density). However, we found the high quantity of Armigeres spp. In the community, there were no filarial identified in these mosquitoes. The environmental survey around the case’s habitat revealed 4 households with 12 people, all are Thai. The backyard around 200 meters has a pond and weed where was suitable for Armigeres mosquito bleeding site.
Conclusion and Discussions: We confirmed autochthonous lymphatic filariasis caused by Brugia pahangi by accidental infection in a boy aged 1 year and 6 months. Brugia pahangi is typically found in animals. The animal reservoirs were dogs and cats in the community. Treatment of Ivermectin in positive microfilaria in pets and use repellent to avoid mosquito bite is a crucial prevention accidental infection.