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Volume 19, Number 11—November 2013

Subcutaneous Infection with Dirofilaria spp. Nematode in Human, France

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To the Editor: The article by Foissac et al. titled Subcutaneous infection with Dirofilaria immitis nematode in human, France (1) presents an interesting and challenging diagnostic dilemma. The paper described, but did not illustrate, the worm as having a strongly ridged external surface of the cuticle—a feature known not to exist on Dirofilaria immitis, the dog heartworm. However, molecular sequencing of the specimen demonstrated much closer similarity to D. immitis than to D. repens, the most common cause of zoonotic subcutaneous dirofilariasis infection in Europe.

Well-described morphologic features of parasites, including in tissue sections, have long been the standard for diagnosis. More recently, molecular diagnostics have helped in many of these difficult cases. However, in some cases, the morphology and molecular diagnosis are discordant. On the basis of the data in the article, the worm does not seem to represent D. repens. A more likely possibility is some other species for which no sequences are yet available for comparison. In such a worm, the regions sequenced must be similar to D. immitis, and distinct from D. repens, to achieve the observed results.


When one encounters a case such as this, where well-validated morphologic features (Figure) are contradictory to the molecular analysis, one must exercise caution in arriving at a final diagnosis. One disadvantage of morphologic and molecular diagnostics is an absence of information on poorly described and characterized pathogens or new pathogens that have yet to be identified. No good algorithm exists to resolve these conflicts other than to explore all possibilities. The diagnosis in the described case is probably best left as a Dirofilaria species of the Dirofilaria (Nochtiella) type, members of which exhibit marked cuticular ridging, and not D. (Dirofilaria) immitis type, members of which have as a feature an absence of cuticular ridging.


Mark L. Eberhard

Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA



  1. 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;19:1712 . DOIPubMed




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DOI: 10.3201/eid1911.130606

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Table of Contents – Volume 19, Number 11—November 2013


Please use the form below to submit correspondence to the authors or contact them at the following address:

Mark L. Eberhard, Centers for Disease Control and Prevention, 1600 Clifton Rd NE, Mailstop D65, Atlanta, GA 30333, USA

Charles Mary, Laboratoire de Parasitologie, Hôpital de la Timone, 264 Rue Saint Pierre, 13385 Marseille, France

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Page created: October 31, 2013
Page updated: October 31, 2013
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