Bordetella infection from cat to child
Case reports of infections acquired from pets are sporadically found in the human medical literature. A common problem with these reports is the failure to look for true evidence of zoonotic transmission. The typical thought process is "We found this bug in a person, it's most often found in animals, so this person must have gotten it from their pet." Often, this likely is actually the case (although some evidence would be nice). In other instances, like the Pasteurella bone infection described in the Orthopedics paper I wrote about recently, this assumption is probably completely off-base.
Something that is usually missing from these reports is any investigation of the suspected pet. Finding the bacterium in question in/on the pet, and showing that it's the same strain as was found in the person goes a long way to supporting the conclusion that the pet was the source. It's not a 100% guarantee, since you can't say whether it went from pet-to-person or person-to-pet, but with a typically pet-associated bacterium its much more likely to have come from the pet, so finding the same strain in both pet and person is pretty solid evidence. Most case reports don't bother even trying to get this much information (but they still get published...).
A case report in an upcoming edition of Zoonoses and Public Health (Register et al 2012) is another example of a study that provides some information about a potential pet-associated infection, but stops short of the type of proof that is needed. To their credit, the pet wasn't available for testing and they are clear that it's a "possible" case of zoonotic transmission, which puts them a step up on other studies, but it's still too bad the additional information couldn't be reported.
The case report describes an 11-year-old girl with cystic fibrosis (CF). People with CF are at greatly increased risk of respiratory infections, including infections caused by microorganisms that typically don't cause disease in other people. This child had a sputum sample collected during a routine doctor's visit, when she didn't have any signs of respiratory infection. Bordetella bronchiseptica, a bacterium most often found in dogs and cats (and one of the causes of kennel cough (aka canine infectious respiratory disease syndrome) in dogs), was isolated from the sample. When this was explored further, it was revealed that child's family had obtained a new kitten three weeks earlier, and the kitten had signs of respiratory disease.
Unfortunately, the kitten had been removed from the household by the time B. bronchiseptica was diagnosed in the girl, so it couldn't be tested. (They don't say why the family got rid of the cat.) However, the authors at least took it a step further and did some detailed molecular characterization of the bacterial strain they recovered from the sputum sample. Different genetic traits suggested that the strain was feline in origin, and, combined with the fact that the child had contact with the kitten, this provided a little more support to the hypothesis that the cat was the source. It's not proof, but still interesting. They also determined that the B. bronchiseptica strain was missing a gene that's associated with helping cause disease, suggesting it's not as able to make people sick. That might explain why the child was carrying the strain in the absence of disease, although people can carry lots of different bacteria that can potentially cause disease without being clinically ill.
In the end, it was an interesting little report and the authors conclude with a couple of good statements:
"Acquisition of detailed clinical and epidemiological data paired with discriminatory genetic comparison of case isolates and contact isolates is needed to more firmly establish transmission patterns and identify likely contact risks." (A fancier way to say what I said above.)
"...it seems advisable to counsel CF patients regarding adherence to practices that minimize opportunities for zoonotic transmission of B. bronchiseptica from family pets or other potentially infected animals."
Bordetella bronchiseptica infection in a cancer patient...kitten suspected as source
A paper in the Journal of Neurooncology (Redelman-Sidi et al, 2011) describes "kitten-transmitted Bordetella bronchiseptica infection" in a cancer patient. The patient in question had a brain tumour that was surgically removed. The 56-year-old man was then started on chemotherapy, which in addition to killing cancer cells can also cause significant impairment of the immune system, which puts chemotherapy patients at high risk for infections of many kinds. This particular patient developed a persistent cough during treatment and was eventually diagnosed with B. bronchiseptica infection. This bacterium is one of the causes of kennel cough in dogs, and can cause respiratory infections in other species, including cats.
The man had acquired a kitten three weeks before he developed the cough. The kitten had (at some undefined time) conjuncitivitis and signs of respiratory disease. Unfortunately, as is too often the case in reports of supposed pet-associated disease in the medical literature, the kitten was not actually tested. Bordetella bronchiseptica is classically an animal-associated organism, the kitten was newly acquired and it had respiratory disease. These factors strongly suggests the kitten was the source. However, without testing of the kitten and investigation of other potential sources of infection, it's hard to be as definitive as the title suggests. The suspicion of the kitten being the origin is reasonable nonetheless.
Some statements from this report are contrary to my typical recommendations for pets and immunocompromised individuals.
Getting a young animal
- Kittens and puppies are entertaining, but they are also higher-risk animals compared to adult dogs and cats. They are more likely to harbour a variety of infectious agents. They are also more likely to bite or scratch through playful or rambunctious behaviour, and it's harder to properly assess their temperament. If an immunocompromised person wants to get a new pet, getting an mature animal is ideal.
Source of the kitten
- The paper unfortunately doesn't mention from where the kitten was obtained and whether there was a respiratory disease problem in other animals at the source. Animals in shelters, humane societies and pet stores are more likely to carry various infectious diseases because they are densely populated facilities, often have infection control challenges, house many high-risk animals and are stressful environments. Getting new animals from these places is not ideal for a high-risk person.
Veterinary care
- The kitten had signs of respiratory disease and was seen be a veterinarian. It doesn't appear that any testing was done and the kitten was just treated with antibiotics. That's pretty common, but in a situation where there is a high-risk person in the house, it's wise to be more aggressive with diagnostic testing to determine whether there may be any concerns for the person.
A pet can be a wonderful thing for a person living cancer, by providing social and emotional support, along with other benefits. Pet ownership always carries some risk of zoonotic infections, and the risk is higher in people with compromised immune systems. Rarely, if ever, is pet ownership inappropriate for a cancer patient, although certain pets and certain situations might be, and high-risk individuals need to think about possible risks and measures to reduce those risks.
People with cancer or other problems affecting their immune system should ensure that their physician knows that they own pets. Veterinarians need to play a role as a member of the overall healthcare team too. Optimizing pet health can help reduce the risk of human infection. Prompt and proper diagnostic testing can identify potential issues. Proper counseling can reduce risky situations from inappropriate pets, inappropriate contacts and other factors that might make exposure to a nasty infection from a pet more likely.
Bordetella pneumonia in a person from dog vaccine
An article in an upcoming edition of Transplant Infectious Disease (Gisel et al) describes a case of Bordetella bronchiseptica pneumonia in a person who had received a kidney and pancreas transplant. This person had to board her dogs at a veterinary clinic while she was hospitalized for a bowel obstruction that occurred after surgery. The clinic required her dogs to be vaccinated against Bordetella bronchiseptica, a cause of canine "kennel cough." They were vaccinated intranasally (i.e. up the nose) with a modified live vaccine comprised of live B. bronchiseptica that is modified so it is unlikely to cause disease but can still induce a good immune response. The owner developed pneumonia after returning home and B. bronchiseptica was isolated. Specific testing was not performed to confirm that the vaccine strain caused disease, so it's possible that she was infected by the normal (i.e. "wild type") B. bronchiseptica (which still would have presumably come from the dogs).
Immunosuppressed individuals are at high risk for infection by microorganisms that usually don't cause disease in otherwise healthy people. Bordetella bronchiseptica is a good example of this. Care should be taken around pets by anyone whose immune system is compromised. Here are some recommendations pertaining to kennel cough vaccination:
- Immunosuppressed individuals should not receive modified live vaccines themselves, and it is probably prudent to extend this recommendation to avoid modified live vaccination of their pets with vaccines like the Bordetella (kennel cough) vaccine.
- If vaccination for kennel cough is required for entering a kennel or vet clinic, an exemption should be sought because of the potential risk to the immunocompromised person.
- If vaccination must be performed, injectable vaccination is preferred. It doesn't produce as good immunity in the dog compared with intranasal vaccination but the risks to the immunocompromised owner would be much less.
- If intranasal vaccination with modified live kennel cough vaccine is used, immunocompromised owners should not be in the same room during vaccination. They should avoid contact with the dog's mouth, nose and face for at least a few days after vaccination and should wash their hands (or use a hand sanitizer) regularly after contact with the dog.
- If respiratory disease develops in someone exposed to a dog recently vaccinated against kennel cough, the potential for vaccine-associated disease should be mentioned to the physician.
Can I get kennel cough from my dog?
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Kennel cough is a highly infectious respiratory disease in dogs. The disease got its name because infection and outbreaks often occur in kennels, where many dogs from various backgrounds are mixed together. Some of the dogs in kennels may be carrying infectious diseases, and other dogs may be very susceptible these diseases - putting them all together in what can be a stressful environment for any dog creates a recipe for infection.
Kennel cough itself is more of a syndrome than a specific disease. It can be caused by a few different bacteria and viruses (and combinations thereof) that produce the same type of clinical signs. These pathogens include Bordetella bronchiseptica, Mycoplasma, canine parainfluenza virus, canine adenovirus-2, canine distemper virus and canine herpesvirus. Of these, only Bordetella bronchiseptica is a potential concern in terms of transmission to humans. Bordetella bronchiseptica can cause respiratory infections in people, but this is probalby quite rare and largely confined to high-risk individuals, like those with a weakened immune system, who have had their spleen removed, who already have underlying respiratory disease of another kind, and pregnant women. The evidence of transmission of B. bronchiseptica from pets to people is relatively weak and circumstantial - it is not clear whether the human Bordetella infections in these cases were truly due to contact with a pet.
In households with individuals with a weakened immune system (e.g. HIV/AIDS, transplant or cancer patients), some measures that can be taken to help reduce the risk of transmission of Bordetella from pets include:
- Avoid boarding dogs at kennels or veterinary clinics. If boarding cannot be avoided, ensure that dogs have been properly vaccinated against Bordetella bronchiseptica, and that the kennel or clinic requires all other dogs boarding there to be vaccinated as well.
- Avoid obtaining a dog directly from from an animal shelter.
- Wash your hands regularly after handling any dog, particularly if you've touched the dog's nose or mouth.
- Don't allow dogs to lick your face or hands.
The Bordetella vaccine for dogs is a modified live vaccine, meaning that a live but less virulent (pathogenic) form of the bacterium is administered to "prime" the immune system against regular Bordetella. Concern has been raised by some people that exposure to the vaccine strain could actually cause disease in high-risk individuals, whose immune systems might be unable to fight off even this "weaker" version of the bacteria. It is unclear whether exposure to the vaccine strain actually poses any risk. Nonetheless, it is reasonable to pay extra attention to avoiding contact with the dog's face for a day or two after vaccination. Also, it is probably wise for immunocompromised owners to not hold the dog when it is being vaccinated, in order to reduce the risk of exposure to the vaccine.
