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Post-Recovery Bordetella Shedding in Dogs: For How Long and Do We Need to be Concerned?

Date:
Authors: Dr. Olivia Swailes
Document Type: FAQs
Topics: Infectious Disease
Species: Canine

A shelter staff member has concerns that a dog who recovered from “kennel cough” is potentially still shedding Bordetella. Factors that can influence bacterial shedding are discussed, as well as whether or not shelter staff should be concerned about post-recovery shedding of Bordetella in dogs.

Question:

If a shelter dog has a Bordetella infection and recovers without any treatment and then receives Doxycycline for 30 days as part of a heartworm protocol approximately one month later, could the dog still be shedding Bordetella for up to three months?  We would very much appreciate hearing from you soon. Thank you so much for your time.   

Answer:

I am afraid your question is difficult to answer with certainty, but I hope that this will be helpful to you.  As I am sure you are aware, a variety of other pathogens can be involved in the Canine Infectious Respiratory Disease Complex (CIRDC), including other bacteria as well as several viruses (for more information please see our CIRDC information sheet).  Therefore, this animal may not have had bordetellosis, but instead one or more of the other pathogens.  Most of these other CIRDC pathogens are shed by an infected animal for less than two weeks, though Bordetella bronchiseptica is an exception and may be shed for months (generally the maximum is considered to be 2-3 months, though there is likely individual variation). 

There are a number of factors in this particular dog’s case that may decrease the likelihood that he or she was shedding Bordetella for that amount of time.  If the dog in question were vaccinated with an intranasal Bordetella/canine parainfluenza vaccine during its stay in the shelter, for example, the additional immune response stimulated by vaccination would reduce the likelihood of long-term shedding.  An experimental study by Iemura et al. demonstrated that puppies vaccinated with an intranasal Bordetella/canine parainfluenza vaccine and then subsequently exposed to Bordetella had fewer clinical signs and shed the bacteria for less time than their non-vaccinated counterparts.  Unvaccinated puppies were still shedding the bacteria four weeks after exposure (unfortunately the study did not continue beyond the 4-week point).  It is important to note that these animals were in a highly controlled environment for the purposes of this study, and this may not accurately reflect the vaccine’s effect on bacterial shedding out in the “real” world.  No research could be found that performed a similar experiment within a shelter setting.

The fact that this dog was also treated with doxycycline as a part of its heartworm treatment protocol should, in theory, also reduce the likelihood of long-term bacterial shedding.  However, though doxycycline is a common antibiotic of choice for CIRDC, Bordetella can be resistant to doxycycline.  Because this dog recovered from its “kennel cough” without treatment, it is likely that the animal’s immune system cleared the vast majority of the pathogen(s) that were causing illness without any intervention.  If it was in fact Bordetella, and it was susceptible to doxycycline, the doxycycline treatment should theoretically have further reduced the likelihood of bacterial shedding.  

Individual variation between dogs dictates that clearance of any infection is highly dependent on that animal’s immune status, and therefore it is unfortunately not feasible to give a straightforward yes or no answer to this question.  While it is possible that this dog could have been shedding up to 3 months after its initial illness, it is considered unlikely based on the scenario you have described.  The doxycycline treatment should have increased clearance of any remaining bacteria (provided it was not a doxycycline-resistant Bordetella).  If he or she was vaccinated with an intranasal Bordetella/parainfluenza vaccine, the chances that this dog would still be shedding 3 months later are even smaller, provided the dog has a competent immune system. 

Perhaps the most important question is how concerning is it if a dog is shedding Bordetella after recovery from CIRDC. In a study by Lavan and Knesl, samples were taken from over five hundred clinically healthy dogs upon intake to various shelters across the United States (prior to vaccination).  These samples were PCR tested for CIRDC pathogens, including Bordetella bronchiseptica.  More than 47% of the dogs in this study were PCR positive for at least one of the pathogens being investigated, with 40.8% of the PCR positive dogs being positive for Bordetella (equivalent to 19.5% of all of the dogs tested).  In this study, Bordetella was the second most common CIRDC pathogen in terms of number of PCR positive dogs.  Therefore, many clinically healthy dogs in and out of shelters may be shedding Bordetella organisms at any given time, and potentially exposing other dogs.  The particular dog you are asking about likely poses no more risk at this point than any of these other dogs that are silently shedding Bordetella and interacting with other dogs in public spaces unrestricted because they are not clinically ill.

I hope you found this helpful, please let us know if you have any more questions.

Olivia Swailes, DVM
Maddie’s Shelter Medicine Intern
Shelter Medicine Program
University of Wisconsin –Madison
School of Veterinary Medicine