Seroprevalence of Antibodies Against T. solium Cysticerci
Refugees who apply for resettlement to the United States are required to undergo a predeparture medical screening examination that includes collection of a peripheral blood sample from persons >15 years of age. The Migrant Serum Bank, established by the Division of Global Migration and Quarantine at the Centers for Disease Control and Prevention (CDC, Atlanta, GA, USA) in 2002, retains a convenience sample of de-identified serum samples from these examinations. Each sample has associated demographic information, including refugee group, age, birth country, refugee camp, and site and date of specimen collection. At the time of this study, ≈31,000 serum samples were available that represented resettled refugee populations from the Middle East, Southeast Asia, and Africa. We identified refugee populations represented in the Migrant Serum Bank in which cases of human cysticercosis or NCC have been reported in the countries of origin. We then randomly selected serum samples from each of these identified populations to test by EITB LLGP for antibodies against T. solium cysts. Populations with limited numbers of samples were excluded because lack of statistical power could impede prevalence estimations. Our final sample comprised 2,001 serum samples from resettled refugees from Laos, Burma (renamed Myanmar in 1989), Bhutan, and Burundi (Figure 1). The institutional review boards at CDC and at Oregon Health & Science University reviewed and approved this study.
(Enlarge Image)
Figure 1.
Geographic location and background of refugee populations sampled for antibodies against Taenia solium cysticerci by using the classic enzyme-linked immunoelectrotransfer blot for lentil-lectin purifi ed glycoprotein. Countries of origin are shaded dark grey (Burundi, Bhutan, Burma [Myanmar], Laos). Host countries are shaded light grey (Tanzania, Nepal, Thailand). Burundi: ≈14,000 Burundian refugees who lived in camps in Tanzania since 1972 were resettled during 2006– 2008. Resettled refugees were primarily ethnic Hutu. Bhutan: ethnic Lhotshampa Bhutanese refugees arrived in Nepal ≈1990. Resettlement began in 2008 and is ongoing, with ≈40,000 resettled thus far. Burma: there has been intermittent infl ux of refugees into Thailand from Burma since 1984. Resettlement began in 2004 and is ongoing, with ≈90,000 resettled thus far. Resettled refugees in this group are primarily ethnic Karen and Karenni. Laos: refugees from Laos arrived in Thailand as early as 1975, and many resettled soon thereafter. The most recent round of resettlement from the Wat Tham Krabok camp occurred during 2004–2006 with resettlement of ≈16,000 ethnic Hmong refugees.
Individual 100-μL aliquots of each sample were separated at the CDC Central Repository, stored in microtubes, and shipped on dry ice to the CNS Parasitic Diseases Research Unit, Universidad Peruana Cayetano Heredia (Lima, Peru), for processing. Serum samples were analyzed by EITB for the presence of antibodies against T. solium cysts (EITB LLGP) as described. The EITB LLGP uses a semipurified fraction of homogenized T. solium cysts containing 7 T. solium glycoprotein antigens named after the Kda molecular weights of the corresponding reactive bands (GP50, GP42, GP24, GP21, GP18, GP14, GP13). Reaction to any of these 7 glycoprotein antigens is considered positive. When applied in community settings, the EITB LLGP provides an estimate of population exposure to T. solium cyst antigens. A positive EITB LLGP result alone does not definitely establish active infection because antibodies can persist even after parasite clearance. The clinical significance of specific glycoprotein bands or combinations of bands in community studies has not been described. Although a highly sensitive and specific EITB is available to detect serum antibodies against adult T. solium intestinal infection, the unknown duration of antibody persistence after parasite clearance and the large sample size required for reasonable confidence intervals precluded our use of this assay in this study.
Methods
Study Populations
Refugees who apply for resettlement to the United States are required to undergo a predeparture medical screening examination that includes collection of a peripheral blood sample from persons >15 years of age. The Migrant Serum Bank, established by the Division of Global Migration and Quarantine at the Centers for Disease Control and Prevention (CDC, Atlanta, GA, USA) in 2002, retains a convenience sample of de-identified serum samples from these examinations. Each sample has associated demographic information, including refugee group, age, birth country, refugee camp, and site and date of specimen collection. At the time of this study, ≈31,000 serum samples were available that represented resettled refugee populations from the Middle East, Southeast Asia, and Africa. We identified refugee populations represented in the Migrant Serum Bank in which cases of human cysticercosis or NCC have been reported in the countries of origin. We then randomly selected serum samples from each of these identified populations to test by EITB LLGP for antibodies against T. solium cysts. Populations with limited numbers of samples were excluded because lack of statistical power could impede prevalence estimations. Our final sample comprised 2,001 serum samples from resettled refugees from Laos, Burma (renamed Myanmar in 1989), Bhutan, and Burundi (Figure 1). The institutional review boards at CDC and at Oregon Health & Science University reviewed and approved this study.
(Enlarge Image)
Figure 1.
Geographic location and background of refugee populations sampled for antibodies against Taenia solium cysticerci by using the classic enzyme-linked immunoelectrotransfer blot for lentil-lectin purifi ed glycoprotein. Countries of origin are shaded dark grey (Burundi, Bhutan, Burma [Myanmar], Laos). Host countries are shaded light grey (Tanzania, Nepal, Thailand). Burundi: ≈14,000 Burundian refugees who lived in camps in Tanzania since 1972 were resettled during 2006– 2008. Resettled refugees were primarily ethnic Hutu. Bhutan: ethnic Lhotshampa Bhutanese refugees arrived in Nepal ≈1990. Resettlement began in 2008 and is ongoing, with ≈40,000 resettled thus far. Burma: there has been intermittent infl ux of refugees into Thailand from Burma since 1984. Resettlement began in 2004 and is ongoing, with ≈90,000 resettled thus far. Resettled refugees in this group are primarily ethnic Karen and Karenni. Laos: refugees from Laos arrived in Thailand as early as 1975, and many resettled soon thereafter. The most recent round of resettlement from the Wat Tham Krabok camp occurred during 2004–2006 with resettlement of ≈16,000 ethnic Hmong refugees.
Laboratory Methods
Individual 100-μL aliquots of each sample were separated at the CDC Central Repository, stored in microtubes, and shipped on dry ice to the CNS Parasitic Diseases Research Unit, Universidad Peruana Cayetano Heredia (Lima, Peru), for processing. Serum samples were analyzed by EITB for the presence of antibodies against T. solium cysts (EITB LLGP) as described. The EITB LLGP uses a semipurified fraction of homogenized T. solium cysts containing 7 T. solium glycoprotein antigens named after the Kda molecular weights of the corresponding reactive bands (GP50, GP42, GP24, GP21, GP18, GP14, GP13). Reaction to any of these 7 glycoprotein antigens is considered positive. When applied in community settings, the EITB LLGP provides an estimate of population exposure to T. solium cyst antigens. A positive EITB LLGP result alone does not definitely establish active infection because antibodies can persist even after parasite clearance. The clinical significance of specific glycoprotein bands or combinations of bands in community studies has not been described. Although a highly sensitive and specific EITB is available to detect serum antibodies against adult T. solium intestinal infection, the unknown duration of antibody persistence after parasite clearance and the large sample size required for reasonable confidence intervals precluded our use of this assay in this study.
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