By Philip R. Fischer, MD, DTM&H

Professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN

Dr. Fischer reports no financial relationships relevant to this field of study.

SYNOPSIS: Screening and potential treatment of refugees prior to travel to the United States effectively reduces the burden of infection.

SOURCE: Mitchell T, Lee D, Weinberg M, et al. Impact of enhanced health interventions for United States-bound refugees: Evaluating best practices in migration health. Am J Trop Med Hyg 2018; in press, doi: 10.4269/ajtmh.17-0725. [Epub ahead of print].

In the past four decades, approximately 3 million refugees have settled in the United States, with 85,000 arriving in 2016. Refugees typically undergo three steps in screening for infectious illnesses. First, two to six months prior to expected arrival in the United States, refugees undergo a history and physical exam review with some focused testing for tuberculosis and sexually transmitted infections. Then, three to five days before travel, refugees undergo a “fitness-to-travel” evaluation along with presumptive treatment for some parasitic infections. Finally, there are voluntary domestic evaluations within 90 days of arrival, but the implementation of Centers for Disease Control and Prevention (CDC) recommendations at those post-arrival exams varies from state to state. With the U.S. Department of State and the International Organization for Migration, the CDC has developed supplemental overseas health programs to improve the health of refugees and to reduce risks to public health in the United States. Mitchell and colleagues reported on the usefulness of enhanced, additional screening and treatment interventions as evaluated in Asian refugees.

Voluntary screening (and treatment, as indicated) was offered to refugees living in three camps along the Thailand-Burma border. Screening included tests for anemia, hepatitis B infection, and intestinal parasites. Hepatitis B surface antigen-positive individuals were counseled and evaluated; those who were negative were offered a series of hepatitis B vaccines.

Typically, United States-bound refugees in Thailand receive albendazole (to presumptively treat soil-transmitted helminths) and ivermectin (to presumptively treat Strongyloides infection) at their fitness-to-travel visit a few days before leaving for the United States. During this study, stool and blood testing followed by albendazole and ivermectin treatment were included during the initial pre-departure visit. Then, follow-up testing was conducted at the fitness-to-travel visit.

From July 2012 to November 2013, 2,004 refugees participated in this study; 42% were younger than 18 years of age. Comparative data were available for 89% at the pre-departure time (median 167 days from the initial evaluation/treatment) and for 39% following arrival in the United States (median 35 days after the pre-departure evaluation). Overall, 10% of travelers were hepatitis B surface antigen-positive, and 98% of the positive individuals were 12 years of age or older. Males were more at risk of hepatitis B infection; having tattoos was not a risk factor.

Overall, 73% of refugees had at least one pathogenic stool parasite, and 40% had multiple pathogens. Ascaris, Trichuris, hookworm, and Giardia were the most common; only 4% had Strongyloides infection. Three different hookworm infections were identified: Necator americanus, Ancylostoma duodenale, and Ancylostoma ceylanicum. Overall, 28% of refugees were anemic, with 61% of children aged 6 months to 2 years being anemic. Iron deficiency accounted for most (72%) of the anemia, with thalassemia accounting for most of the rest; hookworm likely contributed to just some of the iron deficiency.

With treatment, the rates of infection dropped; only 12% had stool positive for parasite at the U.S. evaluation, and some of those were new infections since the initial visit prior to departure. Overall, eosinophil counts dropped with the use of initial visit anti-parasitic treatment.

The authors concluded that enhanced screening and treatment were feasible. And, there was health benefit to refugees with early treatment as well as less risk of transmission of parasites following arrival in the United States.


It is estimated that there are currently 65 million people (approximately 1% of the planet’s population) who have been forcibly displaced from their homes by violence and persecution, and about one-third of those have fled to a different country (and are, thus, refugees).1,2 Half of refugees are children.2 Currently, most refugees are from Syria, Afghanistan, South Sudan, Somalia, Sudan, Democratic Republic of Congo, Central African Republic, and Myanmar.2 Turkey, Pakistan, and Lebanon are hosting more refugees than are other countries.2 There are three options for refugees: return home when the threat of violence and persecution seems to have resolved; integrate into the host country; or resettle elsewhere. Refugees may spend many, many years in “temporary” refugee camps, such as that in Dadaab, Kenya, with a population that at one point had reached 500,000.3 By the time refugees are resettled in the United States, they typically have been living as refugees for more than a decade.

Mitchell’s study is useful in demonstrating both the feasibility and value of enhanced screening and treatment programs for refugees. Providing such care prior to departure from the temporary host country is more likely to reach more refugees with systematic care and allows for better health at the time of arrival in the United States. Of course, the specifics of screening and treatment will vary with the specific site and population in question. United States-bound refugees have been subject to pre-departure treatment of parasitic infections since 1999, and antimalarials are included for refugees from sub-Saharan Africa. These programs have proven cost-effectiveness.4

Those of us trained when there were just two human hookworm species can learn from the experience of refugees. Previously thought to be an animal parasite that was an uncommon cause of human infection, Ancylostoma ceylanicum recently has emerged as an important human pathogen and now is known to be even more prevalent than A. duodenale in parts of Asia.5,6 This parasite also has been identified in domestic pets and tourist resort soil in northern Australia.7 Relevant to many Asian refugees, A. ceylanicum recently was identified in rural communities in Myanmar,8 not surprising since it similarly had been found in refugees studied by Mitchell and colleagues. A. ceylanicum eggs are similar to other Ancylostoma eggs, as seen under the microscope, so molecular characterization is helpful.5,8 In addition, it is thought that A. ceylanicum leads to more blood loss and more iron deficiency than does Necator.5

Whatever the geographic origin of refugees, whatever the local hookworm species, and whatever the pre-arrival treatment, the data in this study remind us that there is still risk that newly arrived refugees in the United States will be harboring intestinal parasites (12% with helminths and 23% with protozoa in Mitchell’s study). Some of these infections apparently were new since the pre-departure testing. One way or another, physicians seeing newly arrived refugees should consider the possibility of intestinal parasite infection.


  1. United Nations High Commission for Refugees. Figures at a glance. Available at: Accessed March 5, 2018.
  2. United Nations High Commission for Refugees. Global trends. Available at: Accessed March 5, 2018.
  3. Rawlence B. City of Thorns: Nine Lives in the World’s Largest Refugee Camp. Picador; New York: 2016.
  4. Maskery B, Coleman MS, Weinberg M, et al. Economic analysis of the impact of overseas and domestic treatment and screening options for intestinal helminth infection among US-bound refugees from Asia. PLOS Negl Trop Dis 2016;10:e0004910.
  5. Papaiakovou M, Pilotte N, Grant JR, et al. A novel, species-specific real-time PCR assay for the detection of the emerging zoonotic parasite Ancylostoma ceylanicum in human stool. PLOS Negl Trop Dis 2017;11:e0005734.
  6. Bradbury RS, Hii SF, Harrington H, et al. Ancylostoma ceylanicum hookworm in the Solomon Islands. Emerg Infect Dis 2017;23:252-257.
  7. Smout FA, Skerratt LF, Butler JRA, et al. The hookworm Ancylostoma ceylanicum: An emerging public health risk in Australian tropical rainforests and Indigenous communities. One Health 2017;3:66-69.
  8. Pa Pa Aung W, Htoon TT, Tin HH, et al. First molecular identifications of Necator americanus and Ancylostoma ceylanicum infecting rural communities in Lower Myanmar. Am J Trop Med Hyg 2017;96:214-216.