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To the Editor: B.J. Glasgow et al. (1) provided evidence of Dirofilaria repens infection in the Americas with robust molecular data and phylogenetic analyses. They stated, “[t]he patient had no medical history or recent travel of note,” but the patient’s travel history over the preceding months would help assess whether the infection was autochthonous, because D. repens nematodes have a relatively long prepatent period (6–9 months in dogs), and human infections can remain unnoticed for prolonged periods. Nonetheless, the chronology described provides strong evidence of local acquisition in California, USA.
Previous reports of D. repens nematodes in the Americas are inconclusive (2–4). A study from Brazil identified microfilariae as D. repens on morphological and histochemical grounds but provided no genetic confirmation (2). A study from Chile found only 83.5% identity to D. repens in 10 of 12 internal transcribed spacer 2 sequences; the other 2 showed 99%–100% identity to the roundworm Acanthocheilonema reconditum.
A study reported the presence of D. repens nematodes in Colombia (4), but the short cox1 sequences (176–235 bp) provided (GenBank accession nos. OR029394–6) were 97.7%–98.7% identical to A. reconditum (accession nos. MW656249.1, MT230063.1). Another study in Colombia morphologically identified microfilariae from 57 dogs as A. reconditum, 15 as D. repens, and 3 as D. immitis (5). However, 12S ribosomal RNA sequencing identified D. repens–like microfilariae from 14 dogs as A. reconditum and 1 as D. immitis.
If autochthonous transmission of D. repens nematodes occurs in the Americas, the parasite might be circulating among dogs, the principal reservoir hosts, or wild canids (e.g., coyotes in California). Veterinary parasitologists should carefully examine filarioids in the subgenus Nochtiella in the United States, both morphologically and molecularly, because other zoonotic nematode species morphologically similar to D. repens (e.g., D. striata, D. tenuis, and D. ursi) occur in US wildlife.
Author affiliation: Aggeu Magalhães Institute, Oswaldo Cruz Foundation, Recife, Brazil (F. Dantas-Torres); University of Bari Aldo Moro, Bari, Italy (D. Otranto); City University of Hong Kong, Hong Kong (D. Otranto); Chulalongkorn University, Bangkok, Thailand (D. Otranto)