High Prevaience of Bancroftian Filariasis in Myanmar- Migrant Workers: A Study in Mae Sot District, Tak Province, Thailandt

Although the prevalence of lymphatic filariasis in the Thai population is low, migration of Myanmar labor into Thailand may increase the incidence of bancroftian filariasis. Epidemiology of filariasis in Myanmars has not been precisely determined. By using microscopic examination, we found that the microfilarial rate in 654 Myanmar migrants working in Mae Sot, Tak province, was 4.4 per cent. The highest microfilarial rate was found in males aged 21-30 years (6.8%). History of mosquito bites was significantly correlated with microfilaremia. The majority of Myanmar migrants (55.5%) have been staying in Thailand 1-6 years; most (82.0%) have never been back to Myanmar. Seventy-nine per cent of infected Myanmars were from Moulmein (Maulamyine) city. Since these migrants carry the parasite with high infected rate and the mosquito vector Culex quinquefasciatus is also prevalent in Thailand, Thai people are at high risk of acquiring this disease if good control and prevention strategies are not implemented. Key word: Bancroftian Filariasis, Myanmar Migrant, Thailand ~ Lymphatic filariasis is caused by filarial nematode parasites, mainly Wuchereriabancrofti and Brugia ma/ayi. It is estimated that 120 million persons are infected with these parasites and 1.1 bil!ion people are at risk of acquiring infectionO,2). The infection begins when the third infective stage larvae enter the skin from the labium of mosquito vectors at time of blood feeding. After entering the-skip.,. they migrate to the lymphatics and develop into adult worms. The females, after mating, will produce * Department of Parasitology, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, ** Vector-borne Disease Control Center 18, Mae Sot, Tak 63110, Thailand. t Part of this work was presented at the 6th annual Chula10ngkorn Universtiy Asahi Glass (CU-AG) seminar on "Medical Science towards the Year 2000"; jointly organised by the Asahi Glass Foundation, Faculty of Engineering and Faculty of Medicine, Chu1alongkornUniversity at Chulalongkorn Universtiy on February 5. 1998. Vol. 82 No.7 HIGH PREVALENCE OF BANCROFTIAN FILARIASIS IN MYANMAR-MIGRANT WORKERS microfilariae into the blood circulation. Microfilariae will be taken by mosquito vectors during the next blood feeding. The host-parasite interactions are established that will eventuaUy lead to the chronic infections that are associated with pathology of the disease, including lymphedema, hydrocele and elephantiasis. The disease seriously affects socio~ec()~nomic status of the endemic areas. In Thailand, lymphatic filariasis has been well coritroUed and endemic areas are limited to only 5 provinces: Tak, KanchanabUl~,;,:~.:. ::'::"'6~0n, Surat Thani and Narathiwat, with the low prevalence rate of 3.7 per 100,000 population(3). The strain of W. bancrofti among Thai people is the nocturnal subperiodic (rural) type and the main mosquito vectors are the Aedes niveus group, whose habitats are in the rural areas. Recently, however, the migration of hundreds of thousands of workers from Myanmar to Thailand for better jobs and income has had a significant impact on public health of Thailand. These Myanmars not only come with their labor but also with many infectious organisms. Out of many infections they carry, lymphatic filariasis needs considerable attention. Myanmar migrants are infected with W. bancrofti, nocturnal periodic (urban) type, which has CuLex quinquefasciatus as the main mosquito vector. Though the number may be underestimated, the microfilarial rates among Myanmar migrants is as high as 2 per cent to 5 per cent(3). Such a high infection rate obviously deserves Thai public health concern. Tak province is located at the Thai-Myanmar border. Tens of thousands of Myanmars have migrated to work here for years. We report here the survey of microfilarial rate in the Myanmar migrants -working in Mae Sot District, Tak province, Thailand. MATERIAL AND METHOD Study area Mae Sot District, Tak Province, is located about 500 km northwest of Bangkok, near to the Thai-Myanmar border. Therefore, it is one of the most common places where Myanmars come to work for b~tter income." Study population In cooperation with local health workers and health officers from the Filari2.~is Division, CDC Department, the Ministry of Public Health, 654 Myanmar workers in 6 industrial plants at Mae Sot, Tak province were interviewed and examined 735 for microfilaremia. The interview process was performed through a translator. Verbal informed consent was obtained from each individual or child's parent or guardian. All subjects were well informed about the dangers of filariasis and the disease's consequences. Individuals who were microfilaremic were treated with standard treatment (diethylcarbamazine, DEC). Individuals who had Iymphedema, elephantiasis, and/or hydrocele were classified as clinical filariasis.