Chronic Eosinophilia Causes and Clinical Significance

Infectious Causes

Helminths are the most common identifiable cause of eosinophilia in returning travelers and migrants, with diagnosis rates varying from 19%-80% 1, 2
The American College of Tropical Medicine and Hygiene notes that common helminth infections causing eosinophilia include Strongyloides stercoralis, which can persist lifelong and cause hyperinfection syndrome in immunocompromised patients 1
Schistosomiasis is a significant cause of eosinophilia, particularly in those with a history of freshwater exposure in Africa 3
Filariasis is another cause of eosinophilia, especially in those with travel history to West Africa 3
Hookworm (Ancylostoma duodenale, Necator americanus) and Ascaris lumbricoides are also associated with eosinophilia 3
Onchocerciasis (Onchocerca volvulus) is associated with river exposure in Africa, parts of Central/South America, and the Arabian peninsula, and can cause eosinophilia 4
Toxocariasis (T. canis, T. catis) can cause visceral larva migrans and eosinophilia 4
Coccidioidomycosis and paracoccidioidomycosis can cause eosinophilia, especially in immunocompromised patients 5, 4

Allergic/atopic disorders constitute approximately 80% of cases of secondary reactive eosinophilia, according to the American Academy of Allergy, Asthma, and Immunology 3
The American College of Rheumatology notes that common allergic/atopic disorders causing eosinophilia include asthma, food allergies, and atopic dermatitis 3
Non-steroidal anti-inflammatory drugs, beta-lactam antibiotics, and nitrofurantoin are common medications that can cause eosinophilia, as reported by the American College of Clinical Pharmacy 3

Persistent eosinophilia, especially at high levels (>1.5 × 10⁹/L), can cause significant end-organ damage, including myocarditis, endomyocardial fibrosis, pulmonary infiltrates, meningitis, encephalitis, and skin rashes, according to the American Heart Association 1, 3
The American Lung Association notes that target organs commonly affected by eosinophilia include the heart, lungs, central nervous system, and skin 3
Schistosomiasis can lead to bladder carcinoma (S. haematobium) and portal hypertension, while strongyloidiasis can cause hyperinfection syndrome with high mortality in immunocompromised patients, as reported by the Centers for Disease Control and Prevention 1
Onchocerciasis can cause dermatitis, keratitis, anterior uveitis, and choroidoretinitis, according to the World Health Organization 4

A detailed travel history is essential for diagnosing helminth infections, as geographic area visited helps narrow down potential causes, according to the American Society of Tropical Medicine and Hygiene 6
The American College of Physicians recommends considering the timing of exposure, as eosinophilia may be transient during the tissue migration phase of infection 6
Serological tests for helminths may not become positive until 4-12 weeks after infection, and for persistent eosinophilia ≥1.5 × 10⁹/L for more than 3 months with no identified cause, referral to hematology is recommended, as noted by the American Society of Hematology 6, 1

Many people with helminth infection do not have eosinophilia, so testing for eosinophilia alone is not an adequate screening strategy, according to the American College of Tropical Medicine and Hygiene 1
Serological tests may exhibit cross-reactivity between different helminth species, as reported by the Centers for Disease Control and Prevention 3
Stool microscopy may be negative during the tissue migration phase of infection when eosinophilia is present, and patients with eosinophilia and evidence of end-organ damage need urgent medical assessment, according to the American College of Emergency Physicians 6, 1

Hookworm infection typically causes significant eosinophilia with counts often exceeding 3,000 eosinophils/mm³ of blood, which requires prompt treatment with albendazole 400 mg as a single dose to prevent potential complications 7, 8
Hookworm (Ancylostoma duodenale and Necator americanus) is one of the most common helminth infections causing eosinophilia in returning travelers and migrants, with diagnosis rates varying from 19%-80% 7
Eosinophilia occurs as part of the immune response to larval migration through the lungs (Loeffler's syndrome) and intestinal phases of infection 9, 10

Initial skin penetration may cause a transient itchy rash called "ground itch" 8
During larval migration through the lungs, patients may develop fever, urticaria, wheeze, dry cough, and rarely hemoptysis (Loeffler's syndrome) 10
Migratory pulmonary infiltrates visible on chest radiograph 10
Intestinal phase symptoms include nausea, vomiting, diarrhea, and abdominal pain 8
Heavy infections may result in iron-deficiency anemia, particularly in young children 8

Peripheral blood eosinophilia (>0.5 × 10⁹/L) is a key finding 7
Concentrated stool microscopy is the primary diagnostic test for detecting hookworm eggs 8
Many people with helminth infection do not have eosinophilia, so testing for eosinophilia alone is not an adequate screening strategy 7

Albendazole 400 mg as a single dose is the recommended treatment for hookworm infection 8
For patients with asymptomatic eosinophilia aged >24 months with suspected helminth infection, empirical treatment with albendazole 400 mg plus ivermectin 200 μg/kg as single doses is recommended 7, 11

For patients with significant respiratory symptoms due to larval migration, consider empirical treatment with single-dose ivermectin 200 μg/kg and albendazole 400 mg 10
Consider retreatment one month after resolution of pulmonary symptoms to ensure adult worms are treated 10

Monitor eosinophil counts after treatment to confirm resolution 7
If eosinophilia persists ≥1.5 × 10⁹/L for more than 3 months with no identified cause after treatment, referral to a hematologist is recommended 7

Heavy hookworm infections can lead to iron deficiency anemia due to intestinal blood loss 8
Persistent untreated eosinophilia may lead to end-organ damage affecting the heart, lungs, and central nervous system 7

Concentrated stool microscopy or alternative tests should be performed for all patients, as recommended by the Journal of Infection guidelines 12
Strongyloides serology is recommended due to its high diagnostic yield across all regions, according to the Journal of Infection guidelines 12, 13
Schistosomiasis serology is indicated if there is freshwater exposure in endemic areas, as suggested by the Journal of Infection guidelines 13
HIV testing is recommended per guidelines, as HIV is associated with eosinophilia, though helminth co-infection is more likely, according to the Journal of Infection guidelines 12, 13