Pathogenesis of tropical pulmonary eosinophilia: parasitic alveolitis and parallels with asthma

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Tropical pulmonary eosinophilia (TPE), a disease originally described in India in 1940 (l), is one of the many PIE (pulmonary infiltrates with peripheral blood eosinophilia) syndromes. TPE is an interstitial lung disease thought to result from immunological hyper-responsiveness to the human lymphatic-dwelling filarial parasites Wuchereria bancrofti and Bvugia malayi, although other non-filarial helminth-induced PIE syndromes resembling TPE have been described recently (2). TPE is characterized by paroxysmal bouts of cough and wheezing, pulmonary infiltrates; with laboratory studies demonstrating extreme peripheral eosinophilia (>2500 cells per ~1) and high serum levels of total, as well as filaria-specific, IgE and IgG antibodies (3). TPE is especially prominent in India and South-east Asia, although isolated cases have been reported from endemic areas elsewhere. The prevalence of TPE in the U.K. is unclear. Case reports in the literature are sporadic and probably underplay its true incidence, especially as this disease may go unrecognized or be misdiagnosed (4). With a doubling in the number of travellers returning from all endemic areas in the past 5 years (5) and a lo-fold increase in immigration rates since 1987 (6), it is inevitable that the disease burden will rise. Of the approximately 90 million people infected worldwide with these parasitic filarial nematodes, less than 1% manifest with symptoms of TPE (7). However, it is not clear what determines that unusual response to filarial infection. TPE can readily be distinguished from other PIE syndromes by the patient’s history of residence in the tropics, by the presence of extraordinarily high levels of both serum IgE and antifilarial antibodies, and by the dramatic therapeutic response to the filaricide diethylcarbamazine (DEC). Patients’ symptoms may masquerade as asthma for many years; it is essential, therefore, to take a detailed travel history from patients with suspected disease so that correct treatment may be offered early.