Imported bancroftian filariasis: diethylcarbamazine response and benzimidazole susceptibility of Wuchereria bancrofti in dynamic cross-border migrant population targeted by the National Program to Eliminate Lymphatic Filariasis in South Thailand.

The implementation on the Thailand-Myanmar border of annual mass drug administration (MDA) of a single 6 mg/kg dose of diethylcarbamazine (DEC) plus 400mg albendazole, part of the National Program to Eliminate Lymphatic Filariasis (PELF), has been challenging. In particular, chain migration of cross-border Myanmar workers at risk for nocturnally periodic Wuchereria bancrofti infection can lead to imported bancroftian filariasis (IBF) in Thailand. IBF is targeted for multiple-dose MDA with 300 mg DEC, in addition to what is recommended by the World Health Organization (WHO). The dynamic Myanmar migrants in Phang-nga, southern Thailand were sampled to test whether the responsible W. bancrofti has a genetic predisposition of benzimidazole exposure, and IBF exhibits DEC susceptibility. The long-term migrants had more access to DEC. IBF in W. bancrofti antigenemic (microfilaremic vs. amicrofilaremic) short-term migrants exhibited susceptibility to a 300-mg single-dose DEC treatment. During the course of a 3-month follow-up, antigenemia was significantly reduced, but microfilaremia was fluctuated. Surprisingly, a newly recognized Mansonella infection co-existing among W. bancrofti-affected Myanmar migrants elicited microfilaremia clearance within a month after treatment. As a result of the presence of genetically stable W. bancrofti beta-tubulin (Wbtubb) gene responsible for benzimidazole susceptibility, IBF did not possess a genetic predisposition for benzimidazole exposure. Point mutations at positions Phe167Tyr and Phe200Tyr were not detected by Wbtubb locus-specific nested PCR and sequencing. This study has the potential to help guide not only the Thai/Myanmar PELF surveillance and monitoring of mass treatment impacts on W. bancrofti, but also the other endemic countries allied with the Global Program to Eliminate Lymphatic Filariasis (GPELF).

Field trial of the ICT filariasis for diagnosis of Wuchereria bancrofti infections in an endemic population of Thailand.

The ICT Filariasis, a rapid card test format, which is based on qualitative detection by monoclonal antibody of the circulating antigen of Wuchereria bancrofti adult worm, is a new diagnostic test of choice for determining the infections under field conditions. By using clinical and recall techniques and microscopy (thick smear and capillary tube technique) as reference, we assessed the efficiency of the ICT card test in sera from 225 subjects living in W. bancrofti-endemic villages of Tak Province, Thailand, who were recruited during a cross-sectional community survey. The ICT card test gave a 20% antigen positive rate, while other tests gave lower positive rates of the same 5.8% by clinical and recall techniques and thick smear, and 5.3% by capillary tube technique, respectively. The ICT card test had a specificity of 100% when sera from microfilaremic subjects were positive, as when sera from W. bancrofti non-endemic subjects either with Brugia malayi microfilaremia or with other parasites, and those from normal controls were all negative by the test. When done in W. bancrofti microfilaremia sera, the ICT card test had a sensitivity of 100% using a microscopy as reference, and 84.6% when using clinical and recall techniques. However, the ICT card test was more sensitive than the others when done in endemic normal sera (14% positive). Such findings compared well with findings in endemic area of South America, suggested its usefulness to detect W. bancrofti infections in endemic area, especially on the Thai-Myanmar border.