Streptococcus equi subspecies zooepidemicus is a commensal organism of horses. It can be found on the skin, tonsils, and upper respiratory and urogenital tracts. It is an opportunistic pathogen and has been associated with respiratory infection and suppurative disease in many animals. Septicemia, wound infections, and acute fatal hemorrhagic streptococcal pneumonia have been associated with S zooepidemicus infection in dogs. While infections in people are rare, most cases have been associated with consumption of unpasteurized milk or direct contact with horses.

In this case report a 1-year-old male Jack Russell terrier presented with a 9-month history of lower respiratory tract problems, pyrexia, and bilateral mucopurulent nasal discharge. During placement of a nasal catheter for oxygen therapy, the dog sneezed, spreading mucous secretions into the handler’s eyes, nose, and facial area. The handler’s face and eyes were rinsed with saline. A pure growth of beta-hemolytic Streptococcus was grown from the dog’s nasal swabs and transtracheal lavage samples. He was treated with intravenous antibiotic treatment, fluid therapy, and coupage/nebulization for 5 days in the hospital; then treated with oral antibiotic therapy after discharge. The dog responded well and cultures were negative 6 weeks after presentation.

Two days after exposure, the handler began to feel unwell. A general practitioner recommended penicillin for 5 days, but the handler did not improve. S zooepidemicus was isolated from the patient’s throat and nose. Further diagnostics suggested that the patient’s symptoms (conjunctivitis, headache, and neck stiffness) were due to S zooepidemicus. The handler was treated with intravenous cefalexin for 5 days; then oral cefalexin for 7 more days. A prospective study at the farm was conducted several weeks later. All cultures from horses, owners, and environmental samples tested negative. Another dog tested positive for a different strain of S zooepidemicus, but had no evidence of clinical signs.

Commentary: The epidemiology of disease caused by S zooepidemicus in dogs is not well understood. It has been associated with respiratory conditions, such as canine infectious respiratory disease (CIRD) and hemorrhagic streptococcal pneumonia (most commonly in kennel-type situations). Multiple pathogens are involved in the CIRD complex (kennel cough), including viruses, bacteria and environmental factors. Although this case of apparent transmission from a dog to a human may be unusual, it is a good reminder to wear appropriate protective equipment when dealing with dogs with respiratory signs.

Zoonotic transmission of Streptococcus equi subsp zooepidemicus from a dog to a handler. Abbott Y, Acke E, Khan S, et al. J MED MICROBIOL 59:120-123, 2010.