Streptococcus zooepidemicus is an important cause of infections in horses. This bacterium can also be found in healthy horses. When you consider the large number of horses that are infected and the larger number of healthy horses that are carriers, along with the close contact that people have with horses, it’s pretty obvious that people are regularly exposed to "Strep zoo". This bacterium is not well-adapted to survive in people and cause infections, so human infections are quite uncommon, but they can occur. There are periodic reports of S. zooepidemicus infections in people, with varying degrees of association with horse-contact.
An upcoming edition of journal Epidemiology and Infection contains a report of S. zooepidemicus meningitis in a 51-year-old woman (Minces et al, 2010). This person had a mild upper respiratory tract infection, then developed signs of meningitis (including fever, unresponsiveness, respiratory distress). A spinal tap was performed and S. zooepidemicus was isolated. The woman fortunately responded to treatment and recovered.
Upon initial questioning of the patient’s mother, no animal contact or ingestion of unpasteurized dairy products (another risk factor) was reported. However, it was later revealed that the woman’s daughter had started horseback riding at a friend’s farm approximately one month earlier. The type of contact that the woman had with horses (if any) at the farm was not reported, nor was there any investigation of S. zooepidemicus shedding by horses on the farm.
Based on the fact that this is typically an equine-associated bacterium and the history of contact (albeit potentially limited or indirect) with horses, horse contact was blamed for the infection. It’s a reasonable conclusion but it’s far from certain because of the nature of the contact, the lack of any proof of the same strain of S. zooepidemicus in horses on the farm, and previous reports of infections occurring in people with no contact with horses.
Exposure to S. zooepidemicus is an inherent risk of having contact with horses. It’s nothing to lose sleep over and is probably relatively low on the list of potential health problems associated with horse contact. The risk is probably greatest in people with compromised immune systems and other general risk factors for disease such as advancing age and pregnancy. Good general hygiene measures, avoiding contact with sick horses and close attention to hand hygiene probably minimize these already low risks.
This Worms & Germs blog entry was originally posted on equIDblog on 25-May-10.