Persistence of Wolbachia DNA in Dirofilaria immitis-infected canines after doxycycline-only treatment in Rio de Janeiro State, Brazil
8 affiliations
- 1Boehringer Ingelheim, Duluth, GA USA
- 2Programa de Pós-Graduação em Ciências Veterinárias, Universidade Federal Rural do Rio de Janeiro, Seropédica, RJ Brazil
- 3Laboratório de Quimioterapia Experimental em Parasitologia Veterinária, Universidade Federal Rural do Rio de Janeiro, Seropédica, RJ Brazil
- 4Departamento de Patologia e Clínica Veterinária, Universidade Federal Fluminense, Niterói, RJ Brazil
- 5Laboratório de Parasitologia Clínica Veterinária, Universidade Federal do Paraná, Curitiba, PR Brazil
- 6Departamento de Patologia Básica, Universidade Federal do Paraná, Curitiba, PR Brazil
- 7Boehringer Ingelheim, Athens, GA USA
- 8TRS Labs Inc.,, Athens, GA USA
Abstract
Background: Wolbachia are obligatory bacterial endosymbionts of Dirofilaria immitis heartworms, necessary for worm development, reproductive capability, and viability. We quantitatively examined microfilariae and Wolbachia in doxycycline-treated, heartworm-positive dogs.
Methods: Microfilaremic heartworm-positive dogs were identified in municipalities within the target areas of Rio de Janeiro and enrolled in this study. Dog owners agreed to allow blood draws from their dogs on day 0 and days 60 and 90 (± 5 days), and to administer doxycycline 10 mg/kg BID for 28 days, with weekly phone follow-up to help ensure compliance. Modified Knott’s tests were performed on each experimental day; a portion of each sample was retained and frozen at − 20 °C, and the remaining quantities were submitted for digital PCR (dPCR) of microfilarial and Wolbachia burdens. None of the dogs enrolled in the study received any macrocyclic lactone during the study.
Results: Thirty-one microfilaremic dogs completed the study, with 27 remaining microfilaremic throughout. Wolbachia were cleared from 25 of the dogs by day 90, demonstrating that the doxycycline dose was fully effective in those cases. Interestingly, 6 dogs remained dPCR positive on the quantitative assessment, and the proportions of Wolbachia/D. immitis on days 60 and 90 were significantly (p < .0001) lower than on day 0. Results of the comparisons of proportions for day 60 vs. day 90 were not statistically significant (p = 0.3127).
Conclusions: This study demonstrates that Wolbachia DNA may persist in some dogs for 90 days after doxycycline-only therapy. These data may reflect the lack of macrocyclic lactone use or higher adult burdens in some dogs; however, it is not possible to confidently conclude these factors entirely underpin our observations. We suggest that further studies should investigate whether this is related to lack of efficacy of doxycycline in certain Wolbachia subpopulations or to other factors.
Graphical Abstract:
Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1186/s13071-026-07621-9.
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BibTeX
@article{carithers2026persistence,
title = {{Persistence of Wolbachia DNA in Dirofilaria immitis-infected canines after doxycycline-only treatment in Rio de Janeiro State, Brazil}},
author = {Doug Carithers and Bruno Alberigi and Fabio Scott and Flavya Mendes-de-Almeida and Debora Borges and Norma Labarthe and Yara Brandão and Regiane S. Cunha and Edneia A. de Souza Ramos and Marcelo Molento and Stephen Yoon and John McCall and John Harrington},
journal = {Parasites \& Vectors},
year = {2026},
month = sep,
doi = {10.1186/s13071-026-07621-9},
url = {https://doi.org/10.1186/s13071-026-07621-9},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Persistence of Wolbachia DNA in Dirofilaria immitis-infected canines after doxycycline-only treatment in Rio de Janeiro State, Brazil
AU - Doug Carithers
AU - Bruno Alberigi
AU - Fabio Scott
AU - Flavya Mendes-de-Almeida
AU - Debora Borges
AU - Norma Labarthe
AU - Yara Brandão
AU - Regiane S. Cunha
AU - Edneia A. de Souza Ramos
AU - Marcelo Molento
AU - Stephen Yoon
AU - John McCall
AU - John Harrington
PY - 2026
DA - 2026/09/01
JO - Parasites & Vectors
DO - 10.1186/s13071-026-07621-9
UR - https://doi.org/10.1186/s13071-026-07621-9
AB - Background: Wolbachia are obligatory bacterial endosymbionts of Dirofilaria immitis heartworms, necessary for worm development, reproductive capability, and viability. We quantitatively examined microfilariae and Wolbachia in doxycycline-treated, heartworm-positive dogs. Methods: Microfilaremic heartworm-positive dogs were identified in municipalities within the target areas of Rio de Janeiro and enrolled in this study. Dog owners agreed to allow blood draws from their dogs on day 0 and days 60 and 90 (± 5 days), and to administer doxycycline 10 mg/kg BID for 28 days, with weekly phone follow-up to help ensure compliance. Modified Knott’s tests were performed on each experimental day; a portion of each sample was retained and frozen at − 20 °C, and the remaining quantities were submitted for digital PCR (dPCR) of microfilarial and Wolbachia burdens. None of the dogs enrolled in the study received any macrocyclic lactone during the study. Results: Thirty-one microfilaremic dogs completed the study, with 27 remaining microfilaremic throughout. Wolbachia were cleared from 25 of the dogs by day 90, demonstrating that the doxycycline dose was fully effective in those cases. Interestingly, 6 dogs remained dPCR positive on the quantitative assessment, and the proportions of Wolbachia/D. immitis on days 60 and 90 were significantly (p < .0001) lower than on day 0. Results of the comparisons of proportions for day 60 vs. day 90 were not statistically significant (p = 0.3127). Conclusions: This study demonstrates that Wolbachia DNA may persist in some dogs for 90 days after doxycycline-only therapy. These data may reflect the lack of macrocyclic lactone use or higher adult burdens in some dogs; however, it is not possible to confidently conclude these factors entirely underpin our observations. We suggest that further studies should investigate whether this is related to lack of efficacy of doxycycline in certain Wolbachia subpopulations or to other factors. Graphical Abstract: Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1186/s13071-026-07621-9.
SN - 1756-3305
ER -