Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

I assume that people wouldn't voluntarily and regularly walk around barefoot on dog feces (or feces of any type), yet it's perplexing that some people regularly clean out horse stalls in bare feet (I've seen it done!). While horse manure may not be as inherently gross as dog poop, it's still feces, and like all feces contains a huge population of various bacteria, some of which can be harmful. The risks of barefoot mucking may also extend to bare feet inside boots, although I don't think sock-averse people need to panic.

An article in the International Journal of Infectious Diseases (Friederichs et al) describes infectious arthritis of the shoulder of a horse owner that was caused by Streptococcus zooepidemicus, a bacterium commonly found in horses but rarely associated with disease in people. The person didn't have a wound in the shoulder area or any other obvious route for the bacterium to get to the shoulder joint. They searched for a source of the infection and all they found was a chronic lesion on the person's foot. This, combined with the patient's history of taking care of his horses in "bare feet in boots", led them to implicate the foot as the source of infection.

The idea, I guess, is that socks would be a barrier to help prevent contamination of the foot wound. That makes sense to a degree - the person could contaminate his foot with S. zooepidemicus from his hands (probably acquired from touching the horse's nose) while removing the boots, or manure could work its way into boots and directly contaminate the wound. Both are possible, but we have to be a little cautious in interpreting these conclusions. However, this is a bacterium that is associated with horses and the foot lesion is certainly a possible route of entry.

Overall, this should be considered an interesting report of a very rare problem, not something that indicates a major concern. However, there are a few good points to take away from this story:

• If you have a wound or chronic lesion of any sort, make sure you take measures to reduce the risk of bacterial contamination when working around horses. This might be as simple as making sure it's covered by clothing, or something more involved like using an impermeable bandage.
• Hands are probably the major source of infection transmission, and good hand hygiene is important after horse or stall contact, particularly if you have an underlying disease.

This equIDblog entry was originally posted on our sister site, Worms & Germs Blog, on 20-Jan-10.

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I received the following question the other day: "I have a friend who had chemo embolization on tumor on liver in late June. She is in hospital now, and an abscess was discovered on liver.  Pathology results said "equine strep".  Her brother visited immediately after procedure, and he works with horse full time."

Streptococcus is a group of bacteria that includes many different species. There are two main species in horses Streptococcus equi subsp. equi (aka S. equi, the cause of strangles) and Streptococcus equi subsp. zooepidemicus (aka S. zooepidemicus, a cause of various types of infections). As you can guess by the 'equi' name, their natural host is the horse. Strep infections are very common in people, but rarely involve these two species. Nonetheless, infections with either Streptococcus equi or S. zooepidemicus can be found in people, but S. zooepidemicus is most common. Usually, these infections develop in people who are already sick for another reason, have compromised immune systems, or in young children. Interestingly, not everyone that is infected reports direct or even indirect contact with horses.

Back to the question: it's hard to say what's going on here based on the the general term "equine strep", but presumably the person has an infection with S. equi or S. zooepidemicus. Whether horses are actually involved will be tough (or impossible) to determine. It's a tempting hypothesis that the patient's brother carried the bacterium from the farm to the hospital, but I'd be wary about making a definitive statement about the bacterium's origin solely based on that. There are ways to investigate this further, such as trying to isolate Streptococcus species from horses on the farm, typing them and comparing them to the strain that caused disease in the person, but this type of testing is very costly and almost never performed, as human infection with these species is so uncommon.

This should be a good reminder that people who are sick and in hospital are at higher risk for developing infections, and they can get infections from bacteria that rarely cause disease in healthy individuals. While there is no proof of a link to horses (at least in this case), good infection control practices should be used whenever anyone visits someone in the hospital. That would include not wearing barn clothes to the hospital and paying close attention to handwashing.

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Mastitis (inflammation of the udder) is a relatively uncommon problem in mares. Some of the likely reasons that mares develop mastitis much less commonly than other animals (such as cows) is that they have comparatively small teats, and the udder, even when engorged, remains well tucked up between the hind legs. This decreases the risk that the teats will be traumatized or soiled compared to the large, low-hanging teats of a cow. Also, frequent nursing by foals (normally several times an hour) keeps the udder relatively empty and helps prevent build up of bacteria in and around the teat. The fact that people don’t frequently touch a mare’s teats and udder also helps prevent contamination with bacteria from our hands or from other sources that may be transmitted indirectly on dirty hands.

When a mare does develop mastitis, it can cause quite a significant problem, for both the mare and her foal. For one thing, mastitis is usually very painful! Even the most well behaved, tolerant mare will usually object to foal trying to nurse. Usually the mare will simply move away from the foal, but very persistent foals may also get kicked. Beyond this, problems for the foal are two-fold:

• The foal will not receive adequate nutrition and will quickly run down its body’s own meagre reserves, thus making it more prone to infections and other complications.
• If the foal is able to nurse at all from the inflamed part of the udder, it is drinking milk that is often heavily laden with the bacteria causing the infection, which represents an additional challenge to its body’s defenses and immature intestinal flora.

The infection in the mare is usually bacterial in nature, and the culprits tend to be opportunistic bacteria that can be found around any horse, especially Streptococcus zooepidemicus, but also Staphylococcus, Actinobacillus, Pseudomonas, Klebsiella and Escherichia coli. In mild cases the infection will be limited to the udder. In severe cases, and especially with Gram-negative infections, mares can develop systemic illness due to endotoxemia or septicemia, which can lead to complications like colitis and laminitis (founder). Mastitis may occur in only one half (gland) of the udder, or in both parts of the udder at the same time.

Mastitis is diagnosed by culturing bacteria from the milk. It’s very important to take a culture sample before beginning treatment in case the bacteria involved aren’t sensitive to the initial antibiotic treatment. Mares are usually also treated with an anti-inflammatory to help keep them more comfortable. However, the most important component of therapy is stripping the udder (i.e. milking the mare out) as often as possible to remove the bacteria and all the inflammatory debris. Hot packing the udder helps to promote drainage, and hand walking helps decrease edema and swelling around the udder.

Most mares recover from mastitis in 5-7 days with proper treatment, but it’s important to initiate treatment as early as possible, before the infection becomes severe. Signs to look for that may indicate a lactating mare is developing mastitis include:

• The mare being persistently reluctant to allow the foal to nurse
• Abnormal swelling of the udder, particularly if it is hot and painful on palpation
• Abnormal-looking milk (often watery with white flecks/chunckies) from one or both teats
• Sudden development of ventral edema around the udder
• Reluctance to walk or abnormal gait in the hind limbs
• Non-specific signs like fever, lack of appetite, and depression

If you suspect your mare may be developing mastitis, she should be examined by a veterinarian as soon as possible. It is also very important to monitor the foal in these situations – if the foal is not able to get sufficient milk from the mare, it may need to be supplemented by bottle or bucket feeding until the mare recovers.

• Avoid touching the teats and udder of normal mares whenever possible in order to decrease the risk of contaminating the teats with bacteria from your hands.
• If you need to touch/check the udder, wash your hand thoroughly first with soap and water (preferably warm water - most mares appreciate that!).

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Streptococcus zooepidemicus (technically Streptococcus equi subspecies zooepidemicus), commonly called Strep zoo, is an important bacterium in equine medicine. It is one of the most common bacteria isolated from infections in horses. Like other streptococci, S. zooepidemicus is a Gram positive coccus, meaning that it stains purple with Gram stain and has a ball shape (coccus). Streptococci tend to stick together in chains (see picture right) which are often described as "string of pearls."

Streptococcus zooepidemicus can be found in the upper respiratory tract of healthy horses. In most instances, it lives there without causing any problems.  Strep zoo is considered an opportunistic pathogen - a bacterium that can live in harmony with its host, but can also cause disease in certain situations. Strep zoo  can cause a variety of infections, including most commonly pneumonia, lung abscesses and guttural pouch infections. More severe conditions, like bloodstream infections, joint infections and meningitis, can also occur, but are uncommon and most often affect neonatal foals.

Diagnosis of disease caused by S. zooepidemicus requires culture of appropriate samples collected from the horse. Care should be taken when interpreting cultures of samples collected from the nasal passages or upper respiratory tract, since S. zooepidemicus is often present there even in normal animals, so finding it does not necessarily mean it is causing disease.

Unlike some bacteria that cause infections in horses, S. zooepidemicus tends to be susceptible to numerous antibiotics, including penicillin and trimethoprim-sulfa. However, since some strains can be resistant to various drugs, culturing the bacterium and testing its susceptibility to antibiotics in the lab is still required to determine the optimum treatment, .

Strep zoo is of minimal risk to people. Human infections caused by this bacterium have been reported but they are considered very rare.

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Microbiologists like to confuse people. The names of different bacteria are often changed as new information is discovered and species are grouped, separated or completely reclassified.  One can imagine that this eventually makes for some confusing situations.

One example of this is Streptococcus equi (aka Strep equi), the cause of the highly infectious disease strangles, and its close relative Streptococcus zooepidemicus (aka Strep zoo). Streptococcus zooepidemicus is commonly found in the respiratory tracts of healthy horses and can cause secondary infections, but it is not highly transmissible like Strep equi.  Technically, however, both of these organisms are actually Streptococcus equi. The S. equi that causes strangles is Streptococcus equi subspecies equi, while the other one is Streptococcus equi subspecies zooepidemicus. Usually, people just refer to them as S. equi and S. zooepidemicus for simplicity's sake, and in most situations, that's enough for people to understand what they're dealing with. However, sometimes there can be confusion if a diagnostic laboratory reports the full name of the organism and someone doesn't notice the "zooepidemicus" at the end, and panic ensues about a non-existent strangles case/outbreak until someone reads the report properly.  The take-home message here is read all diagnostic test results carefully and if in doubt, call for clarification.

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