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Jean-François Magnaval, Antoine Berry, Tropical Pulmonary Eosinophilia, Clinical Infectious Diseases, Volume 40, Issue 4, 15 February 2005, Pages 635–636, https://doi.org/10.1086/427755
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SIR—In a recent article, Boggild et al. [1] tackled the problem of imported cases of tropical pulmonary eosinophilia (TPE). However, the diagnostic procedure that was used raised some concerns about the accuracy of the filarial etiology of the reported syndrome. TPE, as underlined by Boggild et al. [1], is characterized by pulmonary infiltrates and blood eosinophilia. This clinical picture can have various noninfectious or infectious etiologies; among the helminthiases, these include ancylostomiasis, strongyloidiasis, and visceral larva migrans (a major form of toxocariasis), which have been recognized as parasitic etiologies of pulmonary eosinophilia [2, 3]. Toxocariasis, a helminthozoonosis found worldwide, appears to be an especially common cause of pneumonitis with eosinophil infiltrates; 9 of 57 Argentine pediatric patients displayed this symptom [4].
How helminthiases other than bancroftian filariasis were ruled out was not reported by Boggild et al. [1]. Moreover, the diagnosis of filarial TPE was dependent on the results of an ELISA, the exact procedure of which was not described. ELISA that uses extracts of heterologous filaria worms is known to cross-react with serum samples from other roundworm diseases [5], but the use of recombinant antigens could resolve this problem [6]. Given these facts, we were surprised that Boggild et al. [1] did not test for circulating filarial antigens to ascertain the bancroftian origin of their TPE cases. Since its first use in the field by the middle of the 1990s [7], detection of the so-called Og4C3 antigen, by either immunochromatography (“card test”) or ELISA, has proven to be a specific and sensitive method for the immunodiagnosis of Wuchereria bancrofti infections [8]. It is currently considered a major tool for the control of lymphatic filariasis [9]. We recognize that this test is unable to detect Brugia malayi infections, but none of the patients included in the study by Boggild et al. [1] was from an area where Brugia lymphatic filariasis is endemic. Since the end of 2001, we have routinely used the commercial ELISA version of the Og4C3 assay (Tropbio). Of the patients attending the consultation unit of our hospital who were immigrants from or residents of a tropical area, 165 were tested by ELISA (Bordier Affinity Products) for the presence of filarial antibodies and Og4C3, on the basis of the presence of clinical signs consistent with a filarial infection (bancroftiasis, loiasis, or onchocerciasis), and/or blood eosinophilia. Of 17 patients who had significant filarial ELISA results (optical density of ⩾.900), 1 patient was found to be infected with hookworm, 5 had strongyloidiasis, and 2 probably had toxocariasis. None of the cross-reacting serum samples from these patients had detectable Og4C3 antigen.
