Search

Etiologic investigations of hypereosinophilia, often accompanied by IgE elevation, depends on the patient's geographic origin and travel history. In France, helminth diseases are the only parasitoses associated with hypereosinophilia. Some, such as oxyurosis in children, are frequent but generally mild. More severe but less frequent infections include distomatoses, trichinellosis, taeniasis, echinococcosis and visceral larva migrans. Among subjects originating from or having travelled to tropical areas with poor hygiene, eosinophilia may be due to early intense polyparasitism and has little etiologic value. In Gabon, a warm, humid country in equatorial Africa, schoolchildren harbor an average of three different parasites capable of inducing hypereosinophilia or serum IgE elevation. These children's eosinophil counts start to rise at very young age, after weaning and contact with soil, and continue to increase rapidly until adulthood. Average values across all age groups are 1580 eosinophils/mm3 and 3300 kU IgE/L. Direct diagnosis of chronic parasitic infections is often possible in this setting, and specific treatments can be prescribed. In contrast, hypereosinophilia has less etiologic significance in patients originating from or having travelled to the tropics and who present to European parasitology units. Direct examination is rarely positive, and the etiologic diagnosis will thus be guided by epidemiologic, clinical and serologic findings. These findings are sometimes sufficient to initiate probabilistic treatment with albendazole, ivermectin and praziquentel.

The attractiveness of tropical and subtropical travel destinations for European tourists as well as the continuous influx of immigrants originating from such areas force the general practitioner to consider the possibility of parasitic infections. Besides the classic microscopic examination for ova and parasites, a serological examination for antibodies has its value especially in the case of an infection with tissue parasites, for an early diagnosis during prepetancy or as a screening test in case of a blood eosinophilia after known exposure risk. The current report highlights possible diagnostic strategies, referring especially to the significance of a serological examination.

Recently, the term of clinical immunoparasitology has been coined to indicate the application of immunological methods to the laboratory diagnosis of parasitic infections. In particular, serological diagnosis (indirect diagnosis) is useful especially in the cases of toxocarosis, trichinellosis, echinococcosis, cysticercosis, toxoplasmosis, amoebic abscess, some filariasis, visceral leishmaniasis, schistosomiasis. When possible, for infections caused by protozoa or helminths, the "gold standard" is represented by direct diagnosis performed by microscopic and/or macroscopic observation of the parasite. In any case, immunological results must be interpreted in consideration of the clinical picture of the patient and confirmed possibly by finding the parasite or its genome, even using molecular methods. Furthermore, since the presence of specific antibodies can reveal an acquired infection, but not necessarily a disease, it is particularly helpful, in addition to a qualitative evaluation, a quantitative one, by determining the serum antibody titre. After recovery, the antibody levels decrease, however, they may persist for long periods, for this reason they do not help in evaluating the treatment outcome. Interpretation of serological results may be difficult when the patients originate from areas where the suspected infection is endemic, in that case, a serum positivity could reflect an old exposition to the parasite, therefore it is not related to the present clinical status. Furthermore, serology may frequently result falsely negative in not immunocompetent subjects (organ transplanted, HIV positive individuals, premature babies, diabetics). Clinicians can interpret correctly the serological results only if the Parasitology laboratory inform them about the significant diagnostic values, the sensitivity and the specificity of the test in use. At present time, many diagnostic kits for immunoparasitology are commercially available, and industries are developing newer and newer ones (which are not always validated). In relation to this aspect, it should be helpful, for each of parasitic infection, to establish reference centers, not only to control the quality of commercial kits, but also as a reference point to those laboratories which use "in house" kits. To this regard, the recent establishment of a European Centre for Control of Infectious Diseases will help. The antigen characteristics (crude, E/S, recombinant, synthetic) for assays searching for antibodies (IHA, IFA, EIA, WB) of different classes, the controls to choose for these assays, the specimen requirements will be discussed. The recent findings on the serological diagnosis of intestinal protozoa infections, malaria, leishmaniasis, echinococcosis, cysticercosis, trichinellosis, toxocariasis, schistosomiasis, strongyloidiasis will be presented.