A series of strange but rare infections or the sign of a new problem? That’s always the question we have to think about when there’s a report of a new disease. Determining that can be a challenge, and often “time will tell” is the true answer.

A paper in the most recent edition of the New England Journal of Medicine (Ramakers et al. 2017) gives us one more for the list, and involves a species we don’t talk about much in terms of zoonotic diseases: guinea pigs.

The report describes 3 people with Chlamydia caviae infection, a bacterium associated with guinea pigs that has been considered pretty harmless to people. However, the case series details 3 cases of infection in otherwise healthy adults in their 30s, a group that’s not high-risk for infections from low-risk bacteria such as C. caviae. All 3 developed severe pneumonia, and two of them ended up in ICU on ventilators. This compounds the surprise and concern, because infections by bacteria that rarely cause disease in people usually manifest as mild disease. That was the situation with the only previous report of C. caviae infection in a person, where mild conjunctivitis was the only clinical problem.

Fortunately, all three patients ultimately recovered.

There was no link between the individuals themselves, and the cases occurred over a three year period. A guinea pig link is assumed because of the association of this bacterium with guinea pigs. One patient’s guinea pig had signs of respiratory tract disease before the person got sick, and (unlike most reports), there was an investigation of the animal. C. caviae was isolated from the guinea pig, and it was identical to the strain found in the person. That’s pretty convincing evidence.

A few questions remain:

  • Were there more people affected? Most people with respiratory tract disease don’t get tested for the presence of bacteria like this. That’s especially true with milder disease. So, are these cases a unique series, or do they represent a small subset of the total number of infections that occurred?
  • Is this a new problem or was it simply found because of better current-day diagnostic testing? Surveillance bias (i.e. the apparent increase in a disease because we are looking more or looking better) is a common issue.
  • What do we do now? Does this change how we approach guinea pigs?

The last question is an important one, and one that doesn’t come with good answers. For me, the take home messages would be:

  • Guinea pig contact poses some infectious disease risk, like contact with any animal.
  • Animals that are sick usually pose more risk.
  • A guinea pig with respiratory disease should be approached with an increased level of hygiene and infection control (e.g. no kissing, good hand washing) in case it’s C. caviae.
  • Veterinarians should be aware of the risk (albeit probably very low) so that they can counsel owners and take necessary precautions themselves when handling guinea pigs.
  • Physicians need to query pet ownership/contact and recent events of pet illness when presented with a sick patient.
  • Contact with a guinea pig with respiratory disease should be reported to the physician if a person develops signs of respiratory disease, and C. caviae infection should be considered.