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Volume 32, Number 12—December 2026
Letter
New World Ocular Dirofilariasis Caused by Dirofilaria repens Infection, United States
Suggested citation for this article
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.
and Domenico Otranto
References
- Glasgow BJ, Collins M, Helminiak L, Lieberman JA, Mathison BA, Yang S. New World ocular dirofilariasis caused by Dirofilaria repens infection, United States. Emerg Infect Dis. 2026;32:1193–5. DOIPubMedGoogle Scholar
- Glasgow BJ, Collins M, Helminiak L, Lieberman JA, Mathison BA, Yang S. New World ocular dirofilariasis caused by Dirofilaria repens infection, United States. Emerg Infect Dis. 2026;32:1193–5. DOIPubMedGoogle Scholar
- Zanfagnini LG, Chocobar MLE, Schmidt EMS, Weir W, Panarese R, Souza SF, et al. Unveiling filariid infections in dogs living in the Western Amazon, Brazil. Comp Immunol Microbiol Infect Dis. 2026;127:
102463 . DOIPubMedGoogle Scholar - López J, Valiente-Echeverría F, Carrasco M, Mercado R, Abarca K. Morphological and molecular identification of canine filariae in a semi-rural district of the Metropolitan Region in Chile [in Spanish]. Rev Chilena Infectol. 2012;29:248–89. DOIPubMedGoogle Scholar
- Ballesteros N, Castañeda S, Muñoz M, Flórez A, Pinilla JC, Ramírez JD. The first report of Dirofilaria repens infection in dogs from Colombia. Parasitol Res. 2023;122:2445–50. DOIPubMedGoogle Scholar
- Esteban-Mendoza MV, Arcila-Quiceno VH, Ríos Chacón C, Jaimes Dueñez JE, Tique Oviedo M, Díaz Bustos A, et al. Microfilaremic infection in canine filariosis in Colombia: a challenge in morphological and molecular diagnostics. Front Vet Sci. 2024;11:
1368307 . DOIPubMedGoogle Scholar
Suggested citation for this article: Dantas-Torres F, Otranto D. New world ocular dirofilariasis caused by Dirofilaria repens infection, United States. Emerg Infect Dis. 2026 Dec [date cited]. https://doi.org/10.3201/eid3212.261388
Original Publication Date: November 10, 2026
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Table of Contents – Volume 32, Number 12—December 2026
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Please use the form below to submit correspondence to the authors or contact them at the following address:
Filipe Dantas-Torres, Instituto Aggeu Magalhães, Fundação Oswaldo Cruz, Avenida Professor Moraes Rego s/n, Cidade Universitária, 50740-465 Recife, Pernambuco, Brazil
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