Helminth-related Eosinophilia in African Immigrants, Gran Canaria

Of 788 recent African adult immigrants to Las Palmas de Gran Canaria, 213 (27.0%) had eosinophilia. The most frequent causes were filariasis (29.4%), schistosomiasis (17.2%), and hookworm infection (16.8%). Stool microscopy and filarial and schistosomal serologic tests gave the highest diagnostic yield. Country of origin and eosinophil count were associated with specific diagnoses.

µL antigens per well in carbonate buffer (pH 9.6). Serum diluted 1:100 was added and incubated for 1 h at 37°C. Horseradish peroxidase goat anti-human immunoglobulin G (Sigma, Saint Louis, MO, USA) was added at different dilutions. Washes were performed 3 times with 200 µL phosphate-buffered saline-Tween 20 per well. After incubation for 1 h at 37°C, the substrate solution (orthophenylenediamine-H 2 O 2 ) was added, and the reaction was stopped with 3N H 2 SO 4 .
Assay sensitivities were evaluated by using serum specimens from patients with a definite diagnosis of isolated helminthic disease (Table 1). In all patients, adequate parasitologic tests showed no other helminthic infection. To evaluate specificities, we used serum samples from Spanish blood donors; samples from healthy controls from sub-Saharan Africa; and samples from patients with isolated helminthic, protozoal, bacterial, or viral infections (Table 1). Healthy controls from sub-Saharan Africa were clinically evaluated; they did not have eosinophilia, and results of a systematic investigation for helminthic infections (using stool samples, urine samples, and Knotts test) were negative.
Moreover, an ELISA was used to test for strongyloidiasis with somatic larvae antigens from Strongyloides venezuelensis. Although the ELISA is 100% sensitive, its low specificity precluded its use as a diagnostic tool.
The SPSS 11.5 statistical package (available from http://www.spss.com) was used for analyses. The level of significance accepted was <0.05, and results were expressed as means plus standard deviation (SD). The receiver-operating-characteristic curve was used to establish ELISA cut-offs. The χ 2 and the Fisher exact tests were used to evaluate the association between demographic variables and final diagnoses, and the Student t test was used to compare the degree of eosinophilia among patients with single and multiple infections. Analysis of variance and post-hoc tests were used to compare the mean eosinophil counts in each final diagnosis.
One hundred fifty-four study participants (72.3%) were asymptomatic. In symptomatic patients (28.0%), the most frequent clinical features were lymphadenopathy (6.1%), pruritus (5.6%), and skin lesions (3.3%).  Table 2). The country of origin was statistically associated (p<0.05) with the final diagnosis: 77% of the patients with eosinophilia from Cameroon had filariasis, 63% of the patients from Mali had schistosomiasis, and 30.8% of the patients from Nigeria had hookworm infection.
The mean eosinophil count was significantly higher in patients with a final diagnosis than in those whose conditions were not diagnosed (871 ± 431 vs. 643 ± 179) (p<0.05), and the mean count was higher also in patients with 2 or more parasites than in patients with 1 (1,045 ± 641 vs. 827 ± 389) (p<0.05). Among patients with 1 helminthic disease, those with filariasis had higher eosinophil counts than those with schistosomiasis or geohelminthic infection (p<0.05) (Figure 2).
Eosinophilia is frequent in travelers and expatriates from tropical areas (6-12). However, its prevalence is vari-able (3.1%-50%), depending on the population studied (more frequent in immigrants than in travelers), the areas where infection occurs (mainly sub-Saharan Africa or Southeast Asia), and the design of the study (prospective or retrospective). In this prospective work, we studied a homogeneous population of immigrants who had recently arrived from Africa, and we detected eosinophilia in 27%.
Studies of persons with imported eosinophilia have made a diagnosis that identified the etiologic agent in 15% to 64% of cases (depending on the population, the selected eosinophil count, and the methods) (6-13). Using direct and serologic methods (10,13), we detected helminthic infections in 75% of the patients. In all series, the main diagnoses are filarial, schistosomal, and geohelminthic infections. Only 27.7% of our patients had related signs or symptoms, which indicates that a proper investigation can detect many asymptomatic infections.
The sensitivities of our serologic tests were >90%, with specificities of 85%-97%. Using D. immitis antigens for the immunodiagnosis of tropical filariasis (14), we obtained a sensitivity of 90% for microfilaremia, with 97% specificity. The utility of adult worm antigens of S. bovis for serodiagnosis of schistosomiasis has been recently demonstrated (3).
Our high diagnostic yield with filarial (30%) and schistosomal (28%) serologic testing is similar to that obtained by Whetham et al. in travelers returning from West Africa (10). Among the direct methods, stool microscopy was the most sensitive (35%). However, serologic testing detected another parasitic infection (mainly filarial or schistosomal) when direct tests showed only a geohelminthic infection (13.2%), which suggests that direct and indirect tests are complementary in this population. The proportion of Strongyloides spp. infection diagnosed was lower than in almost all other similar studies (6-12) because we could not ascertain it by stool positivity only, because of the low specificity of Strongyloides serologic testing available to us. Patients from Mali with eosinophilia had schistosomiasis more frequently, as reported in some European studies (15). However, we found a significant correlation between filarial or hookworm infection and immigration from Cameroon and Nigeria, respectively, an association not described previously. Finally, filariasis induces higher eosinophil counts than other parasitic infections, likely because the parasite inhabits blood and tissue and is not limited to the gut lumen. Our results show that 1) eosinophilia is frequent in recently arrived African immigrants, 2) helminthic infections can be diagnosed by using both parasitologic and serologic tests, 3) an immigrant's country of origin may suggest specific parasitic diseases, and 4) higher eosinophil counts usually indicate filariasis.