Tropical Eosinophilia
Definition And Classification
Disease Overview
- Hyper-responsive pulmonary syndrome secondary trapped microfilariae within lung tissue.
- Clinical manifestation lymphatic filariasis.
- Classified extrinsic pulmonary eosinophilic syndrome.
Etiology And Vectors
Causative Organisms
- Nematodes: Wuchereria bancrofti, Brugia malayi, Brugia timori.
- Unusual filariasis form occasionally involving Dirofilaria imitis.
Vectors
- Transmitted mosquito bites serving vectors.
- W. bancrofti vectors: Culex, Anopheles, Aedes mosquitoes.
- Predominantly filarial endemic regions (Indian subcontinent, South East Asia, South America, Africa).
- Higher incidence nonimmune individuals travelling endemic regions compared permanent residents possessing developed immunity.
Pathophysiology
Immune Response Cascade
- Type 1 hypersensitivity reaction microfilariae trapped pulmonary microcirculation, lymphatic system, bloodstream.
- Microfilariae released periodic lymphatic system.
- Trapped microcirculation triggers immune response releasing eosinophils.
- Eosinophils central pathogenesis.
- Eosinophil degranulation releases Eosinophilic Cationic Protein (ECP), Eosinophil-Derived Neurotoxin (EDN), Major Basic Proteins (MBP), Eosinophil Peroxidase (EPO).
- Clearance microfilariae simultaneous lung damage.
- Complement activation, opsonization antifilarial antibodies facilitate microfilariae clearance.
Airway Hyperactivity
- MBP-2 associated airway hyperactivity.
- Interleukin-4 (IL-4) induces airway hyperactivity.
- Interferon-gamma (IFN-gamma) suppresses airway hyperactivity.
- Generates overactive systemic, pulmonary Th2 response.
- Massive pulmonary eosinophilia, increased IL-4, IL-5, filarial-specific Immunoglobulin G (IgG), IgM, IgE antibodies.
Histopathology
Temporal Disease Progression
| Disease Stage | Microscopic Findings |
|---|---|
| Early | Histiocyte infiltration lung parenchyma causing initial symptoms. |
| Sub-Acute | Eosinophilic interstitial infiltration. Progression eosinophilic abscesses, eosinophilic granulomas, eosinophilic bronchopneumonia. |
| 6 Months To 2 Years | Mixed cell reaction including histiocytes, eosinophils, epithelioid cells, lymphocytes. |
| Untreated | Pulmonary fibrosis. |
Clinical Features
Systemic And Pulmonary Manifestations
- Slow onset.
- Dry cough, paroxysmal, nocturnal,.
- Dyspnea, wheezing,.
- Systemic symptoms: Fever, malaise, anorexia, weight loss.
- Chest auscultation reveals wheezing, crepitations.
Extrapulmonary Manifestations
- Lymphadenopathy,.
- Hepatosplenomegaly.
- Organomegaly abdominal palpation.
Evaluation And Diagnosis
Investigations
| Investigation | Characteristic Findings |
|---|---|
| Complete Blood Count | Leukocytosis, peripheral blood eosinophilia >3,000/mm3,. |
| Serum Immunoglobulin | Elevated quantitative IgE level,. |
| Indirect ELISA | Elevated filarial antibody titers,. |
| Stool Examination | Rule out alternate parasites causing pulmonary eosinophilia. |
| Chest X-Ray | Reticulonodular opacities, miliary mottling middle/lower zones. Snowflake-like appearance. Normal 20-30% cases. |
| Chest CT Scan | Bronchiectasis, lymphadenopathy, pleural effusion (utilized unestablished diagnosis). |
| Pulmonary Function Test | Mixed pattern, predominant restrictive, mild-to-moderate obstructive. |
Management
Pharmacotherapy
- Diethylcarbamazine (DEC) 6 mg/kg 21 days.
- Alternative DEC dosing: 10 mg/kg three divided doses 3 weeks (requires 2-3 spaced courses occasionally).
- Corticosteroids concomitant therapy reduces airway inflammation chronic setting.
- Ivermectin targets microfilariae.
- Albendazole targets adult worms.
Complications And Differential Diagnosis
Complications Untreated Disease
- Pulmonary fibrosis.
- Chronic bronchitis, chronic respiratory failure.
- Pulmonary hypertension, cor pulmonale secondary destructed microfilariae embolization lung capillaries.
Differential Diagnosis
- Infectious Eosinophilia: Strongyloides, Toxocara, Ascariasis.
- Respiratory: Bronchial asthma, Allergic Bronchopulmonary Aspergillosis (ABPA), Allergic rhinitis,.
- Eosinophilic Syndromes: Acute/chronic eosinophilic pneumonia, Churg–Strauss syndrome, DRESS syndrome.
- Infections: Miliary tuberculosis, Fungal pneumonia.