Schistosomiasis is a chronic parasitic infection of the human vascular system. It is transmitted by contact with contaminated fresh water, where cercariae penetrate the skin. High prevalence areas include Africa and Southeast Asia. Acute infection can result in Katayama fever—a febrile illness with prominent eosinophilia that occurs 4 to 7 weeks after exposure.4 Diagnosis is primarily clinical with appropriate epidemiology, as serology may be negative early in infection. Praziquantel is the treatment of choice, though dosing varies by species, so expert consultation should be considered.
Soil-transmitted helminths, such as Ascaris (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworm (Ancyclostoma duodenale and Necator americanus), can also cause eosinophilia during larval tissue migration. Following infection by ingestion or skin penetration, an acute respiratory illness, termed Löffler’s syndrome, can develop with associated eosinophilia.1 Once the helminths reach the adult stage, eosinophilia subsides. Patients are most commonly treated with albendazole 400 mg orally for 3 days.4
Fascioliasis is common in sheep-rearing areas. Humans are infected through ingestion of aquatic plants (eg, watercress). Parasitic migration through the duodenal wall and liver parenchyma can lead to fever, right upper quadrant pain, and eosinophilia. The incubation period is 6 to 12 weeks. Diagnosis during acute infection is by serology.4
Filarial infections, eg lymphatic filariasis, loiasis, and onchocerciasis, can also cause eosinophilia. The rise in eosinophils can be triggered by either the adult worms or circulating microfilariae.4 Treatment of fascioliasis and filarial infections varies and expert consultation is recommended.
Eosinophilia associated with primary hematologic malignancy
Eosinophilia is a rare presentation of hematologic malignancy. Acute myeloid leukemia, acute lymphoblastic leukemia (ALL), chronic myeloid leukemia, and myeloproliferative disorders have all been associated with eosinophilia. Hepatosplenomegaly, generalized lymphadenopathy, and cytopenias in other cell lines are often noted. Also, the degree of eosinophilia is often more pronounced (>5 x 109/L). Patients with suspected hematologic malignancy should be urgently referred for expert consultation.5