Abstract
BackgroundLymphatic filariasis (LF) is a mosquito-borne disease caused by mosquito-transmitted filarial nematodes, including Wuchereria bancrofti and Brugia malayi. The Lymphatic Filariasis Elimination Program in Thailand has reduced the prevalence of nocturnally subperiodic W. bancrofti (Thai strain), mainly transmitted by the Ochlerotatus (Aedes) niveus group in Thailand to 0.57/100,000 population. However, it is estimated that more than one million Myanmar migrants with high prevalence of bancroftian filariasis have settled in the large urban cities of Thailand. These infected migrants carry the nocturnally periodic W. bancrofti (Myanmar strain) which has Culex quinquefasciatus as the main mosquito vector. Although transmissions of the Myanmar strain of W. bancrofti by the Thai Cx. quinquefasciatus has never been reported, previous study showed that Cx. quinquefasciatus could nurture the Myanmar strain of W. bancrofti to the infective stage. Thus, the potential now exists for a re-emergence of bancroftian filariasis in Thailand. The present study was undertaken in an attempt to differentiate between the Thai and Myanmar strains of W. bancrofti.MethodsThe microfilarial periodicity of Thai and the Myanmar strains of W. bancrofti were determined. Comparative morphology and morphometry of microfilariae and a study of random amplified polymorphic DNA (RAPD) was performed. The Nei's genetic distance was calculated, and a phylogenetic tree was constructed using the Unweighted Pair Group Method with Arithmetic mean (UPGMA).ResultsThe Thai strain of W. bancrofti was nocturnally subperiodic, and the Myanmar strain of W. bancrofti was nocturnally periodic. The body length, cephalic space length, and cephalic space width of the Thai strain of W. bancrofti were significantly larger than those of the Myanmar strain of W. bancrofti (p < 0.05). However, an overlapping mean of these parameters made it impractical for field application. RAPD-PCR profiles showed specific bands characteristic for the Myanmar strain of W. bancrofti. The phylogenetic tree indicated two genetically distinct clusters of the Thai and Myanmar strains of W. bancrofti.DiscussionThis study was the first report on the genetic polymorphism of the Thai and Myanmar strains of W. bancrofti. Differentiation between the Thai and Myanmar strains of W. bancrofti could not rely on morphological criteria alone. However, RAPD profiles revealed a significant diversity between the two strains. The RAPD-PCR technique was suitable for differentiating Thai and Myanmar strains of W. bancrofti. The RAPD marker could be used for epidemiological assessment of the Myanmar strains of W. bancrofti in Thailand.
Highlights
Lymphatic filariasis (LF) is a mosquito-borne disease caused by mosquito-transmitted filarial nematodes, including Wuchereria bancrofti and Brugia malayi
We developed the random amplified polymorphic DNA (RAPD)-PCR technique to differentiate between the Thai and Myanmar strains of W. bancrofti
Microfilarial periodicity The periodicity profiles of the Thai and Myanmar strains of W. bancrofti were determined (Figure 2)
Summary
Lymphatic filariasis (LF) is a mosquito-borne disease caused by mosquito-transmitted filarial nematodes, including Wuchereria bancrofti and Brugia malayi. These infected migrants carry the nocturnally periodic W. bancrofti (Myanmar strain) which has Culex quinquefasciatus as the main mosquito vector. It has been reported that Myanmar migrant workers in Thailand carry W. bancrofti at a prevalence of 2–8% [4] These infected Myanmar migrants carry the nocturnally periodic W. bancrofti (urban strain; Myanmar strain) which has Culex quinquefasciatus as the main mosquito vector [7]. The Thai strain of Cx. quinquefasciatus could nurture the Myanmar strain of W. bancrofti to the infective stage in a recent laboratory study [5] This means that the urban Thai population is at risk of the infection. The high prevalence of W. bancrofti infection in Myanmar migrant workers has prompted concern that a re-emergence of bancroftian filariasis in Thailand is impending
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