on 21-Aug-2023 (Mon)

Many immigrants are susceptible to vaccine-preventable diseases upon arrival in Canada. For example, 30%–50% of new immigrants are susceptible to tetanus,³⁷ 32%–54% are susceptible to either measles, mumps or rubella,³⁸ and immigrants from tropical countries are 5–10 times more susceptible to varicella,³⁹ which has serious implications for adult immigrants

Immigrants from countries where chronic hepatitis B virus infection is prevalent (affecting 2% or more of the population) can benefit from screening and treatment to prevent hepatitis and hepatocellular carcinoma

Foreign-born people account for 65% of all active tuberculosis in Canada,⁴¹ and screening and treatment for latent tuberculosis remain priorities for immigrants from countries in sub-Saharan Africa, Asia, and Central and South America.⁴²

Subclinical strongyloidiasis and schistosomiasis can persist for decades after immigration and, if left untreated, can lead to serious morbidity or death through disseminated disease.⁴⁷ Serologic tests for these intestinal parasites, rather than traditional stool testing, are recommended.⁴⁸

Measles, mumps and rubella

Vaccinate all adult immigrants without immunization records using one dose of measles–mumps–rubella vaccine.

Vaccinate all immigrant children with missing or uncertain vaccination records using age-appropriate vaccination for measles, mumps and rubella.

Diphtheria, pertussis, tetanus and polio

Vaccinate all adult immigrants without immunization records using a primary series of tetanus, diphtheria and inactivated polio vaccine (three doses), the first of which should include acellular pertussis vaccine.

Vaccinate all immigrant children with missing or uncertain vaccination records using age-appropriate vaccination for diphtheria, pertussis, tetanus and polio.

Varicella

Vaccinate all immigrant children < 13 years of age with varicella vaccine without prior serologic testing.

Screen all immigrants and refugees from tropical countries ≥ 13 years of age for serum varicella antibodies, and vaccinate those found to be susceptible.

Hepatitis B

Screen adults and children from countries where the seroprevalence of chronic hepatitis B virus infection is moderate or high (i.e., ≥ 2% positive for hepatitis B surface antigen), such as Africa, Asia and Eastern Europe, for hepatitis B surface antigen, anti-hepatitis B core antibody and anti-hepatitis B surface antibody.

Tuberculosis

Screen children, adolescents < 20 years of age and refugees between 20 and 50 years of age from countries with a high incidence of tuberculosis as soon as possible after their arrival in Canada with a tuberculin skin test.

If test results are positive, rule out active tuberculosis and then treat latent tuberculosis infection.

HIV

Screen for HIV, with informed consent, all adolescents and adults from countries where HIV prevalence is greater than 1% (sub-Saharan Africa, parts of the Caribbean and Thailand).

Link HIV-positive individuals to HIV treatment programs and post-test counselling.

Hepatitis C

Screen for antibody to hepatitis C virus in all immigrants and refugees from regions with prevalence of disease ≥ 3% (this excludes South Asia, Western Europe, North America, Central America and South America).

Refer to a hepatologist if test result is positive.

Intestinal parasites

Strongyloides: Screen refugees newly arriving from Southeast Asia and Africa with serologic tests for Strongyloides, and treat, if positive, with ivermectin.

Schistosoma: Screen refugees newly arriving from Africa with serologic tests for Schistosoma, and treat, if positive, with praziquantel.

Malaria

Do not conduct routine screening for malaria.

Be alert for symptomatic malaria in migrants who have lived or travelled in malaria-endemic regions within the previous three months (suspect malaria if fever is present or person migrated from sub-Saharan Africa). Perform rapid diagnostic testing and thick and thin malaria smears.

About one-third of the world’s population is infected with intestinal parasites,⁴⁷ and most of these infections are sustained through cycles of repeated exposure from the environment.

When populations emigrate from parts of the world where intestinal parasites are endemic and resettle in countries where they do not exist, most infections will clear without treatment within a few years after immigration.

Two intestinal parasites — Strongyloides and Schistosoma — are notable exceptions in that they may persist for decades as subclinical infections or as low-grade disease with nonspecific clinical manifestations.

Strongyloides is estimated to infect 100 million people worldwide. Among immigrant populations, refugees from Southeast Asia and Africa appear to have the highest risk of infection

Treatment with ivermectin is of short duration, is highly effective (number needed to treat [NNT] 2, 95% confidence interval [CI] ~1 to 3) and has a favourable adverse-effect profile.

Schistosoma is estimated to infect 200 million people worldwide, of whom approximately 85% live in Africa. Among immigrant populations, refugees from Africa have the highest risk of infection.

Serologic testing is the most sensitive diagnostic modality currently available. Treatment with praziquantel is of short duration, is highly effective (NNT 4, 95% CI ~1 to 124) and has a favourable adverse-effect profile.

Most estimates of burden have been derived from small observational studies and included primarily refugees from selected countries. Furthermore, a significant number of these studies used stool microscopy, a diagnostic test that is known to have limited sensitivity in the detection of each of these parasites.

In the case of strongyloidiasis, existing data have been derived primarily from refugee populations originating from Southeast Asia and Africa ( Figure 10A ). Studies using stool microscopy have reported prevalence rates between 0.8% and 4.3%,^322–327 the highest burden being identified in refugees from Southeast Asia.^322,327 Studies using serologic enzyme immunoassays have reported significantly higher prevalences of infection (between 9% and 77%),^{107,316,328–333} the highest burden being identified in refugees from Southeast Asia^316,329,330 and Africa.^328,331,334

Figure 10A:

Number of immigrants and refugees screened for strongyloidiasis by birth country, as identified in our review of the medical literature between 1988 and 2010.

Figure 10A:

Number of immigrants and refugees screened for strongyloidiasis by birth country, as identified in our review of the medical literature between 1988 and 2010.

About 85% of the global burden of schistosomiasis is believed to occur in Africa.³³⁵ Studies using stool microscopy to detect Schistosoma in African refugee populations have reported prevalences from 0.4% to 7%.^{323–325,336} In contrast, studies using serologic enzyme immunoassays have reported significantly higher prevalences,^{107,328,329,331–334,337,338} ranging from 2.2% in East African pediatric populations³³² to 64% in Sudanese refugees and 73% in Somalia refugees.^331,334

The scope and analytic horizon of existing studies prevent establishment of a direct link between screening for strongyloidiasis or schistosomiasis and an improvement in health outcomes.

Stool microscopy for ova and parasites is the only definitive way to confirm the presence of intestinal infection with either Strongyloides or Schistosoma, but this diagnostic modality has suboptimal sensitivity. Although overall sensitivity can be improved by increasing the number of stool specimens examined, the costs associated with this approach can be substantial, and many patients are reluctant to provide multiple specimens.

The sensitivity of a single stool examination to detect Strongyloides is estimated at just 30%, but this increases to over 90% when seven specimens are examined.³³⁹

By contrast, serologic testing is the most sensitive diagnostic modality to detect Strongyloides and Schistosoma, making such tests ideal screening tools. Although these tests are also quite specific, serologic positivity cannot definitively distinguish current from remote infection.

The National Reference Centre for Parasitology in Montréal, which performs serologic testing for both parasites in Canada, estimates that its enzyme immunoassays have 100% sensitivity and 88% specificity for Strongyloides stercoralis and 96% sensitivity and 82% specificity for Schistosoma mansoni.

A two-day course of ivermectin (200 μg/kg orally once daily) is the preferred treatment for strongyloidiasis ( Table 10A ); however, among refugees from areas of the world where Loa loa is endemic, a seven-day course of albendazole (400 mg orally twice daily) should be used. This is because cases of encephalopathy have been reported with use of ivermectin during large-scale treatment campaigns in West and Central Africa, where Loa loa is endemic (see the guidelines of the US Centers for Disease Control and Prevention³²¹ for a table of countries where Loa loa is endemic). This rare but potentially serious event may occur in persons who have a high load of Loa loa microfilaria, which are rapidly killed by ivermectin.

Alternatively, because ivermectin is the most effective treatment option available for strongyloidiasis, practitioners may screen refugees at risk for Loa loa infection with a daytime-collected, thin blood smear for microfilaria and treat with ivermectin if high-level microfilaremia is not identified.

For Schistosoma species found in Africa, a one-day course of praziquantel (40 mg/kg divided in two doses) is the preferred treatment strategy ( Table 10B ).

Treatment with ivermectin or praziquantel in patients with underlying neurocysticercosis may lead to an acute inflammatory reaction and could precipitate seizure activity. Therefore, these drugs should not be used in persons with known neurocysticercosis or an unexplained seizure disorder. Otherwise, ivermectin, albendazole and praziquantel each have a generally favourable side-effect profile.³⁴⁴

On the basis of this review, we propose routine serologic screening for all newly arriving refugees at high risk for strongyloidiasis and schistosomiasis.

Practitioners should consider testing foreign-born persons for strongyloidiasis and/or schistosomiasis if they have lived in areas of the world where these parasites are endemic and (i) they have compatible signs and/or symptoms of infection (independent of the time elapsed since their arrival into Canada) and/or (ii) they have evidence of peripheral blood eosinophilia. Clinicians should also be aware that persons infected with the retrovirus human T-lymphotropic virus 1 (HTLV-1) have a modified immune response that complicates the treatment of strongyloidiasis.³⁴⁶

Some areas of the world are endemic for both Strongyloides and HTLV-1, and clinicians should therefore consider screening for the retrovirus if a patient (i) tests positive for Strongyloides and originates from an area with high prevalence of HTLV-1 (i.e., South America, the Caribbean, Japan or Africa) and/or (ii) has persistent strongyloidiasis that responds poorly to antiparasitic treatment.

Serologic testing after treatment for schistosomiasis is not recommended, as the antibodies tend to persist over time. By comparison, several studies have reported declining strongyloides antibody titres 6 to 12 months after successful treatment,^48,340–343 and the use of serologic testing has been advocated as a marker for clearance of this parasite. Although there is a body of evidence demonstrating this post-treatment effect,^48,340–343 this finding has not been universally observed.³¹⁵

all treated individuals should be followed prospectively for clinical signs or symptoms of persistent infection and to ensure that eosinophil counts remain within or return to normal limits within six months of receiving effective treatment. Should patients have persistent symptoms and/or eosinophilia after six months, further investigations — including the option of repeat serologic testing for Strongyloides — should be pursued.