Seroepidemiology of Strongyloides stercoralis in Dhaka, Bangladesh YASMIN SULTANA 1,2 *, GWENDOLYN L. GILBERT 1,2 , BE-NAZIR AHMED 3 and ROGAN LEE 1,2 1 Centre for Infectious Diseases and Microbiology Laboratory Services, ICPMR, Westmead Hospital, Westmead, NSW, Australia 2 Discipline of Medicine, Sydney Medical School, University of Sydney, Camperdown, NSW, Australia 3 Institute of Epidemiology Disease Control and Research, Mohakhali, Dhaka, Bangladesh (Received 1 February 2012; revised 3 April 2012; accepted 3 April 2012; first published online 20 July 2012) SUMMARY Human strongyloidiasis is a neglected tropical disease with global distribution and this infection is caused by the parasitic nematode Strongyloides stercoralis. The aim of this study was to determine the prevalence of strongyloidiasis in Dhaka, Bangladesh. Sera from 1004 residents from a slum (group A) and 299 from city dwellers (group B) were tested for total IgG and IgG subclasses to Strongyloides antigen. There was a significant difference (P < 0·001) in IgG seroprevalence between group A (22%) and group B (5%). Reactive IgG subclasses (IgG1 and IgG4) were also higher in group A (P < 0·05). The seroprevalence of strongyloidiasis in group A increased with age but was unrelated to sex. The presence of reactive IgG to Strongyloides antigen had no correlation with either socio-economic or personal hygiene factors. However, a history of diarrhoea in a family member, in the past 6 months, but not in the respondents was associated with detection of antibodies to S. stercoralis (P <0·01). None of the sera from either group had an HTLV-I reaction. This study demonstrates that strongyloidiasis is prevalent in Dhaka, especially among slum dwellers, but concurrent infection with HTLV-I was not found. Future epidemiological studies should identify individual risk factors and other communities at risk so that appropriate interventions can be planned. Key words: Strongyloides stercoralis, slum, prevalence, HTLV-I, seroepidemiology, Bangladesh. INTRODUCTION Strongyloidiasis is an infection caused by the parasitic nematode Strongyloides stercoralis. This parasitic infection is found in tropical and subtropical regions and also in temperate areas where migrants travel from impoverished regions to more affluent countries (Genta et al. 1987; Olsen et al. 2009; Gonzalez et al. 2010). It has been estimated that 30–100 million people are infected globally (Bethony et al. 2006). The prevalence of strongyloidiasis in temperate regions is estimated to be below 1%, while prevalences up to 25% and above, have been found in tropical areas (Pawlowski, 1989; Yelifari et al. 2005; Steinmann et al. 2007; Olsen et al. 2009; Gonzalez et al. 2010). The true prevalence of strongyloidiasis in a community is difficult to determine because of the chronic subclinical nature, non-specific clinical features of this parasitic infection and the low sen- sitivity of current laboratory diagnosis (Genta et al. 1987; Dreyer et al. 1996; Uparanukraw et al. 1999; Steinmann et al. 2007; Stothard et al. 2008; Agrawal et al. 2009; Knopp et al. 2009; Olsen et al. 2009). Diagnosis of S. stercoralis relies basically on stool examination, which is less sensitive in chronic cases with low larval output (Gill and Bell, 1979; Pelletier, 1984). The detection of serum antibodies may faci- litate a diagnosis, although serology is highly sen- sitive but specificity can be low. A false positive result may occur due to either past infection or cross reaction with other helminth infections especially filariasis (Gam et al. 1987; Conway et al. 1993; Lindo et al. 1994; Olsen et al. 2009); this is reported to be up to 8–16% of cases (Ganesh and Cruz, 2011). Strongyloides stercoralis, unlike other nematodes, can remain in its host for decades with successive prolonged periods of active infection after the origi- nal exposure due to the internal autoinfection pheno- menon. This may eventually lead to hyperinfection syndrome (HS) or disseminated infection where high worm burdens invade major organs, causing sepsis and death (Igra-Siegman et al. 1981; Hakim and Genta, 1986; Siddiqui and Berk, 2001; Carvalho and Da Fonseca Porto, 2004; Vadlamudi et al. 2006; Marcos et al. 2008). The epidemiological association of concurrent S. stercoralis infection in patients infected with human T lymphotrophic virus type I (HTLV-I) has been documented in Japan, Jamaica and in Australia (Nakada et al. 1984; Robinson et al. * Corresponding author: Centre for Infectious Diseases and Microbiology Laboratory Services, ICPMR, Westmead Hospital, Westmead, NSW 2145, Australia. Tel: + 61 2 98457662. Fax: + 61 2 98938659. E-mail: ysul7258@uni.sydney.edu.au 1513 Parasitology (2012), 139, 1513–1520. © Cambridge University Press 2012 doi:10.1017/S0031182012000753