All animals pose some risk of infection to people, to one degree or another, but the risk varies a lot between animal species. I guess I’ve always considered guinea pigs to be relatively benig, with a few zoonotic disease concerns but with bites probably being the biggest risk.

I still think that’s true, but a couple of recent studies show that there are a few other things to to keep in mind.

A paper coming out in January’s edition of Emerging Infectious Diseases (Gruszynski et al., Streptococcus equi subsp zooepidemicus infections associated with guinea pigs) describes infections caused by a bacterium, commonly known as Strep zoo, that is typically found in horses, and occasionally in other species like dogs.

The first case was an adult in Virginia who started off with flu-like disease and then deteriorated, developing a serious systemic infection, shock and necrotizing fasciitis (flesh eating disease). Strep zoo was isolated from the patient’s wounds. He spent several months in hospital and a rehabilitation centre, but survived.

The second patient was an elderly man, also from Virginia, who was related to the first patient. He went to the hospital with vague, predominantly flu-like signs, and developed pneumonia, septic shock and multi-organ failure. Strep zoo was isolated from his bloodstream. He was hospitalized for 18 days but survived.

Two infections by the same bug in people who have contact with each other certainly suggests there’s a common source or one infected the other.  But where do guinea pigs come into this story?

A relative of the first patient mentioned that he had recently purchased four guinea pigs, and that one had died shortly thereafter. The second patient had cleaned the guinea pig cage a couple of days before he became ill. So, it was logical to consider the guinea pigs as a possible source. Unfortunately the response was over-the-top. They euthanized all the guinea pigs and then tested them. Strep zoo was found in two of the guinea pigs, and the guinea pig and human isolates were indistinguishable. Presumably, the pigs were infected first and passed it to the two people through regular contact.

What does this mean, in the grand scheme of things?

  • Probably nothing major.
  • It’s a reminder that infections (including serious ones) can result from even normal contact with species we don’t often consider to be high risk.
  • It shows the importance of physicians querying pet contact.
  • It highlights the need for good basic infection control and hygiene practices around animals.

It also shows the common, but what I’d consider to be excessive, response that can occur when people finally do consider an animal source. It’s not clear whether the pigs were euthanized at the owner’s direction or whether public health pushed for it.

Euthanasia is the easy way out, since it removes any need to think about ongoing risk (euthanizing the animals before even testing them makes no sense at all to me). If the owner wasn’t going to take them back (or their interim caretaker wasn’t comfortable keeping them) and they were unwilling to re-home the pigs because of fear of infecting someone else, I can see how that decision would be made. It’s a stressful time when people are sick, and the fear of it happening again would be understandable.


  • This bacterium is a rare cause of disease, and some people (e.g. horse owners) are exposed to it quite regularly.
  • It might only be present in the guinea pigs for a short period of time. We don’t know if they can be long-term carriers, and it’s possible they would get rid of it after a short period of time in a household (versus a stressful breeding colony or pet store environment).
  • Strep zoo-free guinea pigs would still pose some risk.

There’s never a simple answer for situations like this, and the full story would be interesting to know.