What is the recommended diagnostic work‑up and first‑line treatment for a patient presenting with gastrointestinal symptoms, eosinophilia, anemia, weight loss, and a history of travel to or residence in endemic rural areas with poor sanitation and occupational exposure to soil or animals?

Diagnostic Work-Up and First-Line Treatment for Suspected Helminth Infection

For a patient with gastrointestinal symptoms, eosinophilia, anemia, weight loss, and endemic exposure history, immediately initiate diagnostic testing with three separate concentrated stool specimens for ova and parasites, Strongyloides serology, and schistosomiasis serology (if freshwater exposure), while simultaneously starting empirical treatment with albendazole 400 mg plus ivermectin 200 μg/kg as single doses—but ONLY after excluding Loa loa infection in patients with West/Central African exposure. 1, 2

Critical Pre-Treatment Safety Assessment

Before administering any treatment, you must exclude Loa loa infection in patients with travel to West or Central Africa by checking for microfilariae on blood film, as ivermectin can cause fatal encephalopathy if Loa loa microfilariae are present. 1, 3, 4

Diagnostic Work-Up Algorithm

First-Line Investigations (Order Immediately)

• Three separate concentrated stool specimens for ova and parasites (not just one sample, as sensitivity improves with multiple specimens) 1, 4
• Strongyloides serology and culture (serology has higher sensitivity than stool microscopy for Strongyloides, which is critical because this parasite can cause fatal hyperinfection syndrome in immunocompromised patients) 1, 2, 5
• Schistosomiasis serology if any history of freshwater exposure in endemic areas (Africa, Southeast Asia, South America) 1, 2
• Complete blood count to quantify eosinophilia and assess anemia severity 1
• HIV testing per BHIVA guidelines, as HIV is associated with eosinophilia and affects treatment decisions 1

Essential Historical Details to Elicit

• Exact timing of freshwater swimming in lakes or rivers (schistosomiasis incubation is 2-8 weeks for acute Katayama syndrome) 1
• Barefoot walking on soil (hookworm, Strongyloides penetrate through skin) 1, 2
• Consumption of raw or undercooked meat (Taenia, Trichinella) or raw fish (Anisakis, Clonorchis) 1
• Occupational soil exposure with animals (Toxocara, hookworm) 1
• Geographic specificity beyond "rural endemic area"—need exact countries/regions to guide testing 1, 2

First-Line Empirical Treatment

Standard Regimen for Patients >24 Months

Administer albendazole 400 mg as a single dose PLUS ivermectin 200 μg/kg as a single dose to cover the most common geohelminths (Ascaris, hookworm, Strongyloides) that cause eosinophilia with negative initial stool microscopy during the prepatent period. 1, 2, 4

Mandatory Repeat Treatment

Repeat the same regimen at 8 weeks because eggs and immature schistosomulae are relatively resistant to initial treatment, and this second dose treats residual worms that have matured into adults. 1, 4

Special Populations

• Children 12-24 months: Discuss with tropical medicine expert before treating 1
• Children <12 months: Seek specialist advice; standard dosing not established 1

Syndrome-Specific Considerations

If Acute Katayama Syndrome Suspected

The combination of fever, urticarial rash, cough, and marked eosinophilia (often >5 × 10⁹/L) occurring 2-8 weeks after freshwater swimming in Africa makes acute schistosomiasis highly likely and justifies empirical treatment even with negative initial serology and stool microscopy. 1, 2

• Add corticosteroids (specific dosing requires expert consultation) to the praziquantel regimen 1, 2
• Serology and microscopy may be negative during this acute phase 1

If Strongyloidiasis Suspected

Strongyloides requires particular vigilance because it can persist lifelong through autoinfection and cause fatal hyperinfection syndrome (>70% mortality) in immunocompromised patients, including those receiving corticosteroids. 2, 5, 6

• Concentrated stool microscopy has lower sensitivity for Strongyloides compared to other soil-transmitted helminths 1
• Serology is essential and should not be omitted 1, 2
• High prevalence found in asymptomatic migrant populations 1

If Hookworm Suspected

Hookworm causes anemia (particularly in children), "ground itch" at skin penetration sites, and Loeffler's syndrome (wheeze, dry cough) during lung migration phase. 1, 2

• Eosinophilia is more pronounced during tissue migration phase 1
• Anemia may be severe and require iron supplementation 1, 7

Common Pitfalls to Avoid

Timing-Related Errors

Do not assume negative stool microscopy excludes helminth infection during the prepatent period (when larvae are migrating through tissues but not yet producing eggs). Eosinophilia may be transient and resolve when organisms reach the gut lumen, at which point stool microscopy becomes positive. 1

Serology Interpretation Errors

Cross-reactivity is common in helminth serology—for example, filarial serology may be positive in strongyloidiasis cases. Request specific serology only when epidemiology supports the diagnosis, as false positives occur when testing for parasites not endemic to the patient's exposure area. 1

Screening Limitations

Many helminth-infected patients do not have eosinophilia, so normal eosinophil counts do not exclude parasitic infection. Only tissue-invasive helminths cause eosinophilia; luminal parasites (like Giardia) do not. 3, 8

Eosinophilia alone has poor predictive value for specific parasitic infections (sensitivities 51-73%, specificities 48-65%) and should not be used as the sole screening tool. 8

Treatment Sequencing Errors

Never administer ivermectin or diethylcarbamazine (DEC) to patients with potential Loa loa infection without first checking for microfilariae on blood film, as these drugs can cause fatal encephalopathy if Loa loa microfilariae are present. If Loa loa is confirmed, use corticosteroids with albendazole first to reduce microfilarial load to <1000/mL before definitive treatment. 3, 4

When to Escalate Care

Urgent Evaluation Required

Any patient with eosinophilia plus evidence of end-organ damage (cardiac symptoms, respiratory distress, altered mental status, focal neurological deficits) requires urgent medical assessment and consideration of emergency treatment. 1, 3

Specialist Referral Indications

• Eosinophilia ≥1.5 × 10⁹/L persisting >3 months after infectious causes excluded or treated (refer to hematology) 1, 3
• Eosinophilia >5.0 × 10⁹/L at any time carries significant risk of end-organ damage 3
• Children 12-24 months requiring empirical treatment 1
• Immunocompromised patients with potential Strongyloides exposure (high mortality risk from hyperinfection) 2, 3, 5

Geographic-Specific Testing Priorities

All Endemic Tropical/Subtropical Regions

• Stool microscopy (×3), Strongyloides serology are universal first-line tests 1, 4

Africa (Especially Sub-Saharan)

• Schistosomiasis serology mandatory if any freshwater exposure 1, 2
• Check for Loa loa before ivermectin if West/Central Africa exposure 1, 3, 4

Southeast Asia

• Strongyloides and hookworm co-infection common 6
• Consider Opisthorchis, Clonorchis if raw fish consumption 1

South America

• Strongyloides highly endemic in rural areas 5
• Consider Toxocara if animal exposure 1