By Dr Sumit Mehra, Respiratory and Sleep Physician, Dr Alice Culliford, Respiratory Registrar and Dr Mabel Gaastra Medical Registrar, Joondalup
There is a wide differential for acute eosinophilia in association with respiratory symptoms, most commonly asthma, vasculitis and eosinophilic pneumonias.
However unusual infectious causes, particularly parasites, should be considered, especially where a relevant history of travel is present.
Interestingly, Type 2 inflammation, involving eosinophils and driving conditions such as asthma, eczema, chronic rhinosinusitis, eosinophilic esophagitis and food allergies, originally evolved to combat parasitic worms.
Loeffler’s syndrome
This is a transient respiratory illness characterised by lung inflammation and pulmonary and peripheral eosinophilia.
It results from larval migration through the lungs, where parasite invasion into the alveolar space triggers an eosinophilic response. Ascaris lumbricoides (Ascariasis) and Strongyloides stercoralis (Strongyloidiasis) are common causes.
Ascariasis is more prevalent in areas with poor sanitation and is acquired through ingestion of contaminated food or water. Respiratory symptoms such as cough and wheeze precede gastrointestinal symptoms as the parasites migrate to the gut.
Migratory infiltrates on chest X-ray, marked peripheral eosinophilia, clinical presentation, and exposure history support diagnosis. Larvae may appear in sputum, but eggs are more often detected in stool. Treatment includes albendazole or mebendazole.
Strongyloidiasis is endemic in tropical and subtropical regions, including Australia’s Northern Territory. It typically follows skin contact with contaminated soil, especially in those walking barefoot.
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Immunocompromised patients, particularly those on steroids, are at risk of life-threatening hyperinfection.
Clinical signs include GI symptoms, urticarial rash, and respiratory symptoms during larval lung migration. Imaging shows patchy, migratory infiltrates, and eosinophilia is common.
Unlike other helminths, S.stercoralis can complete its life cycle within humans, leading to false-negative stool tests. Ivermectin is the first-line treatment.
Visceral larva migrans
Pulmonary visceral larva migrans is a parasitic condition caused by migrating Toxocara canis or Toxocara cati larvae, typically acquired through ingestion of eggs from soil contaminated with dog or cat faeces.
It primarily affects children and immunocompromised individuals in areas with poor sanitation and pet exposure. After ingestion, larvae penetrate the intestinal wall and migrate via the bloodstream to visceral organs such as the lungs, liver, and eyes.
As Toxocara invades these organs, it triggers intense eosinophilia and leucocytosis, resulting in a granulomatous response. Patients may develop fever and respiratory symptoms like dry cough, wheeze, and dyspnoea.
In children, hepatomegaly and fatigue are common. Marked eosinophilia and elevated IgE result from a T-cell response to a parasitic protein.
Diagnosis is supported by clinical features, positive Toxocara IgG serology, and chest X-ray findings such as ground-glass opacities and patchy infiltrates.
As with Loeffler’s syndrome, treatment targets the parasitic infection, with supportive care as needed for vulnerable groups. Prognosis is excellent with treatment, though chronic infection and inflammation may cause pulmonary fibrosis.
Schistosomiasis
Caused by the trematode Schistosoma, it is endemic to tropical regions such as Japan, the Philippines, China, Indonesia, Africa, and Latin America. The lungs can be affected in both acute and chronic stages.
In acute schistosomiasis (AS), respiratory symptoms like dyspnoea and cough result from immunoallergic reactions to parasite eggs in the lungs, often appearing on CT as nodular lesions.
Eosinophilia occurs in 75% of AS cases within weeks, reflecting the acute immune response.
In chronic schistosomiasis (CS), eggs in the pulmonary vasculature trigger granulomatous inflammation that may progress to fibrosis. While serum eosinophilia is less common in CS, granulomas show high eosinophil concentrations.
Diagnosis is confirmed by microscopic detection of eggs in stool or respiratory samples. If eggs are absent, AS can be diagnosed clinically based on symptoms, eosinophilia, and relevant travel history.
Treatment is a single dose of praziquantel, which usually offers a complete cure.
Allergic Bronchopulmonary Aspergillosis
Aspergillus fumigatus is the primary non-parasitic cause of infectious eosinophilia in the lung.
Allergic Bronchopulmonary Aspergillosis (ABPA) is a hypersensitivity reaction to airway colonisation by Aspergillus fungus and is nearly exclusively seen in patients with asthma or cystic fibrosis.
Presentation is with recurrent asthma exacerbations, often with mucus expectoration. Blood eosinophilia (>500 cells/uL) is characteristic, in addition to raised total serum IgE level.
Specific IgE and IgG to Aspergillus confirms the diagnosis, and sputum often cultures Aspergillus fungus.
HRCT is the gold standard imaging choice, showing fleeting opacities bronchiectasis (which is usually central and involving upper and middle lobes) plus findings related to mucus impaction and bronchiolar obstruction.
Other manifestations include centrilobular nodules, ground glass changes, peripheral consolidation and gas trapping.
Acute ABPA is traditionally managed with a tapering course of oral steroids. Azole antifungals may be used as steroid-sparing agents, though relapse after cessation is common.
Emerging smaller studies suggest a possible role for asthma biologics in patients with recurrent ABPA exacerbations or inability to taper off oral glucocorticoids, though long-term studies on efficacy and safety are pending.
Author competing interests – nil
Key messages
- Parasitic infections are important causes of eosinophilic lung disease, particularly in those with relevant travel or exposure history
- Symptoms can be non-specific and require prompt targeted treatment to avoid chronic disease, so consideration of specific investigations is worthwhile
- ABPA is an important non-parasitic cause seen in asthma.
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