Schistosomiasis and Strongyloidiasis in African Refugees

Abstract & Commentary

By Brian Blackburn, MD Clinical Assistant Professor of Medicine, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine Dr. Blackburn reports no financial relationships relevant to this field of study. This article originally appeared in the February 2008 issue of Infectious Disease Alert. It was edited by Stan Deresinski, MD, FACP, and peer reviewed by Connie Price, MD. Dr. Deresinski is Clinical Professor of Medicine, Stanford University; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, and Dr. Price is Assistant Professor, University of Colorado School of Medicine. Dr. Deresinski is on the speaker's bureau for Merck, Pharmacia, GlaxoSmithKline, Pfizer, Bayer, and Wyeth, and does research for Merck. Dr. Price reports no financial relationship relevant to this field of study.

Synopsis: Schistosomiasis and strongyloidiasis were highly prevalent in two cohorts of African refugees resettled to the United States; presumptive treatment for parasitic diseases in such groups should include coverage for these parasitoses.

Source: Posey DL, et al. High prevalence and presumptive treatment of schistosomiasis and strongyloidiasis among African refugees. Clin Infect Dis. 2007;45:1310-1315.

Refugees resettling to the United States and other developed countries frequently suffer from infectious diseases, and can pose diagnostic or therapeutic dilemmas for health care providers in their new homes. Posey and colleagues examined two cohorts of African refugees that had resettled to the United States over the 5 years preceding the study, focusing on serologic testing for schistosomiasis and strongyloidiasis. Among 462 Lost Boys of Sudan refugees, schistosoma seroprevalence was 44% (predominantly S. mansoni), and strongyloides seroprevalence was 46%. Among 100 Somali Bantu refugees, schistosoma seroprevalence was 73% (predominantly S. haematobium), and strongyloides seroprevalence was 23%. Sixty-eight percent of Lost Boys had at least one of the two infections, as did 75% of the Somali Bantu. Although the inciting reason for the study was investigation of chronic abdominal pain in the Lost Boys, no association was found between these infections and abdominal pain, which was attributed to multifactorial causes.


Although several studies have assessed the prevalence of various infectious diseases in refugees and immigrants from the developing world, few have specifically evaluated these parasitic diseases, and fewer still have utilized serology to this end. Although stool testing provides an estimate of schistosoma or strongyloides prevalence, the low sensitivity of this methodology for both of these infections likely leads to substantial underestimates in most studies. Although serology can be less specific (particularly for strongyloides), Posey et al provide rationale (based on the life cycle of the parasites, epidemiological factors in these refugee groups, antigenemia rates for schistosomiasis, and the chronic nature of strongyloidiasis) in favor of active infection in most of the persons seropositive for these parasites in this study.

The high seroprevalence rates, while not entirely surprising in such a cohort, re-emphasize the high risk of parasitic infections in such persons. The importance of these particular diseases lies in the potential long-term morbidity associated with untreated schistosomiasis, as well as the strongyloides hyperinfection syndrome, which can develop in persons infected with this parasite who are immunosuppressed or co-infected with HTLV-1. Strongyloides is typically a lifelong infection in untreated patients because of the autoinfection cycle of S. stercoralis, meaning that persons who have been subject to poor sanitary conditions in endemic areas during any period of their life are at risk of harboring the parasite indefinitely. In fact, screening or presumptive treatment for strongyloides should be considered in any person who has spent a substantial period of time in an endemic area that is about to undergo immunosuppressive therapy because of the subsequent risk of the hyperinfection syndrome.

Previous work has demonstrated that predeparture treatment of African refugees with albendazole effectively decreases the parasitic burden in these populations and is cost-effective in many situations.1-4 In part, because of this work, the existing policy for US-bound African refugees has been presumptive treatment with a single 600 mg dose of albendazole, as well as a dose of an antimalarial; however, this is not effective for treatment of schistosomiasis or most strongyloides infections.

As a result of these data, Posey et al issued recommendations regarding empirical treatment of these two refugee groups with drugs that include coverage for these parasites.5,6 Given the data presented in this study, it may be incumbent upon policymakers involved with refugee resettlement to change predeparture regimens to include coverage for schistosomiasis and strongyloidiasis for African refugees (regimens should include praziquantel plus ivermectin [with additional albendazole to cover geohelminths] or praziquantel plus albendazole, depending upon whether risk exists epidemiologically for Loa loa infection) and other refugees from highly endemic areas.

In lieu of such policy changes, extending the data to other refugee groups seems reasonable at this point. Health care providers of refugees from endemic areas should gather data regarding whether their patients have received presumptive treatment for parasitic infections. If they have not, empirical treatment should be considered, with a regimen that includes coverage for schistosomiasis and strongyloidiasis. If this is not done, at minimum these infections should be addressed by a screen-and-treat approach. Extension of this to non-refugee immigrants that have been exposed to conditions that place them at substantial risk for infection should also be considered. Physicians who care for such patients should remember that immigrants from the developing world should trigger a high index of suspicion for infectious diseases, and that these two parasitic infections in particular pose unique threats that are not easily addressed by existing refugee and immigration policies.

Note: Dr. Blackburn, the author of this article, is also one of the authors of the paper discussed in this article.


1. Miller JM, et al. Malaria, intestinal parasites, and schistosomiasis among Barawan Somali refugees resettling to the United States: A strategy to reduce morbidity and decrease the risk of imported infections. Am J Trop Med Hyg. 2000;62:115-121.

2. Muennig P, et al. The cost effectiveness of strategies for the treatment of intestinal parasites in immigrants. N Engl J Med. 1999;340:773-779.

3. Muennig P, et al. The cost-effectiveness of ivermectin vs. albendazole in the presumptive treatment of strongyloidiasis in immigrants to the United States. Epidemiol Infect. 2004;132:1055-1063.

4. Geltman PL, et al. Intestinal parasites among African refugees resettled in Massachusetts and the impact of an overseas pre-departure treatment program. Am J Trop Med Hyg. 2003;69:657-662.

5. Centers for Disease Control and Prevention. Recommendations for presumptive treatment of schistosomiasis and strongyloidiasis among the Lost Boys and Girls of Sudan. Atlanta: Division of Global Migration and Quarantine, 2005. Available at: Accessed 12 Dec 2007.

6. Centers for Disease Control and Prevention. Recommendations for presumptive treatment of schistosomiasis and strongyloidiasis among the Somali Bantu refugees. Atlanta: Division of Global Migration and Quarantine, 2005. Available at: Accessed 12 Dec 2007.