Subcutaneous Infection with Dirofilaria spp. Nematode in Human, France

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In Response: We agree with Eberhard (1) that it is difficult to make a species identification when data derived from morphologic examinations do not correlate with those of molecular diagnostics. Errors may be the result of poor indexing of sequences deposited in sequence databases or inaccurate estimation of the degree of genomic polymorphisms within a species and between closely related species. On the other hand, a morphologic difference between 2 organisms, if it is associated with only 1 characteristic, should not be considered sufficient to classify them as 2 distinct species. Such a phenotypic variation may be the result of a single mutation or deletion. Consequently, the absence of a certain character does not exclude the categorization of an organism as a given species.
Molecular identification of the Dirofilaria spp. worm in our clinical case was made on the basis of 2 distinct sequences, each of which exhibited marked differences between D. immitis and D. repens (2). The first sequence targeted internal transcribed spacer regions of ribosomal genes and revealed up to 100% homology with D. immitis sequences from GenBank, whereas a maximum homology of 80% was observed with D. repens sequences from GenBank. The second sequence targeted the cytochrome oxidase 1 gene and showed 100% homology with D. immitis, whereas < 90% homology was observed for D. repens. For both analyzed targets, GenBank contained several sequences for D. immitis and D. repens that were deposited by various investigators, and all sequences yielded consistent results. Therefore, there is no basis to suggest that the sequences deposited in GenBank were incorrect.
Nevertheless, we agree that an alternate hypothesis is possible. The worm reported in our article could conceivably belong to a species that differs slightly from both D. immitis and D. repens, displaying morphologic similarities with D. repens but being more closely associated with D. immitis at the genomic level.

Charles Mary

, Maud Foissac, Matthieu Million, Philippe Parola, and Renaud Piarroux

Author affiliations: Assistance Publique–Hôpitaux de Marseille, Marseille, France (C. Mary, M. Foissac, M. Million, P. Parola, R. Piarroux); Aix-Marseille Université, Marseille (C. Mary, M. Foissac, M. Million, P. Parola)

References

Eberhard ML. Subcutaneous infection with Dirofilaria spp. nematode in human, France [letter]. Emerg Infect Dis. 2013;19:zzz–zzz. DOI
Foissac M, Million M, Mary C, Dales JP, Souraud JB, Piarroux R, Subcutaneous infection with Dirofilaria immitis nematode in human, France. Emerg Infect Dis. 2013;19:171–2 . DOI PubMed

Suggested citation for this article: Foissac M, Million M, Mary C, Dales J-P, Souraud J-B, Piarroux R, et al. Subcutaneous infection with Dirofilaria spp. nematode in human, France [letter]. Emerg Infect Dis [Internet]. 2013 Nov [date cited]. http://dx.doi.org/10.3201/eid1911.131176