Horse whiskers-1A paper in the journal BMC Research Notes describes a case of meningitis in a 73-year-old man that was attributed to contact with a horse (Madzar et al 2015). The man was admitted to hospital with fever, headache, neck stiffness, malaise and drowsiness. He was ultimately diagnosed with meningitis caused by Streptococcus zooepidemicus (technically, Streptococcus equi subsp zooepidemicus). He recovered, but ended up with significant loss of vision in one eye.

As is frustratingly common, there was no apparent investigation of the source of infection. It’s good that physicians asked about animal contact, but it would be nice to see some more effort to confirm the source (e.g. try to isolate the same bug from the horse and show it was the same strain). The report says the man was working with a horse with strangles, which is a little strange since that disease is caused by S. equi subsp equi, not S. zooepidemicus. Some potential explanations include:

  • The hospital lab misidentified S. equi as S. zooepidemicus.
  • The horse had a S. zooepidemicus that looked like strangles and the diagnosis wasn’t confirmed.
  • The two infections were unrelated.

Strep zoo infections are rare in people, despite the bacterium being very common in horses, and also found occasionally in some other species like dogs. The rarity of the problem is highlighted by the fact that a single case report made it into the literature. If it wasn’t an oddball case, it wouldn’t have been written up.

I often hesitate to write about rare things like this. It can cause an overreaction if people don’t put it into context. This is one of many bacteria that can cause infection given the right circumstances, but  those “right circumstances” are rare. Every animal and person is carrying many microbes that could cause disease in another person or animal, but it usually doesn’t happen. For me, cases like this highlight the importance of good routine infection control and hygiene practices, as well as the need for physicians to collect animal contact information from patients.