Implications of emerging streptococcal diseases

Q. Please update me on streptococcal diseases in dogs and cats.

A. Drs. Kate Hurley and Patricia Pesavento gave an excellent lecture on emerging streptococcal diseases at the 2009 American College of Veterinary Internal Medicine Forum in Montreal, Canada. Some relevant points in this lecture are provided.

Streptococci species are being recognized now as potential veterinary pathogens. The higher rate of isolation of streptococci species in recent reports may be due to improved detection methods, an increase in virulence or an expanding population of compromised hosts.

Streptococcus canis

Several outbreaks of necrotizing Streptococcus canis infections have occurred in shelter cats. In confirmed outbreaks, S. canis infection followed or accompanied upper respiratory infection, manifesting clinically as severe sinusitis and/or abscesses. It affected between one-third and two-thirds of cats in these shelters. These outbreaks resolved after treating all affected and exposed cats with antibiotics susceptible to S. canis.

A recent outbreak among feral cats occurred at a shelter in Southern California in which 37 feral cats were confined in a single room. Clinical signs included ulceration and oozing of one or more feet; death occurred in some cases within four to six days of exposure. Thereafter, about 45 of 325 cats were found dead in cages over the course of about two years. About 25 of these cats died within four to seven days of admission, so the deaths were thought to be related to streptococcal infection. Four cases were confirmed with histopathology showing necrotizing inflammation involving the feet. All affected cats were euthanized.

Initial control measures in this shelter included thoroughly cleaning and spraying cages with bleach and moving all newly admitted feral cats to an isolation room. However, the outbreak persisted in spite of these measures. Eventually, it was noted that a rabies pole, heavily contaminated with hair, saliva and blood, was being used to handle the feral cats. The rabies pole was removed, and the cages were again carefully disinfected as exposed cats were euthanized. The outbreak resolved with this action.

Streptococcus canis, though typically considered a commensal and extracellular pathogen in cats, is capable of causing severe life-threatening invasive infections, such as necrotizing fasciitis, sinusitis, bacteremia and toxic-shock-like syndrome. Streptococcus canis is present in up to 10 percent of cultures from the nasal cavity of cats with chronic upper respiratory infections. Streptococcus canis infection in cats has been associated with epidemics of arthritis, cervical lymphadenitis, urogenital infections, upper respiratory infections and neonatal septicemia. Most of these reported cases reflect time-limited outbreaks of disease in young, intensively housed, closed-colony animals.

Streptococcus zooepidemicus

Outbreaks of Streptococcus zooepidemicus causing hemorrhagic pneumonia have been reported at shelters in Nevada, Florida, Wisconsin and New York and at a boarding kennel in Colorado. The first outbreaks occurred at very large municipal shelters in which dogs were not vaccinated on intake and other canine respiratory viral and bacterial agents were frequently isolated. However, subsequent outbreaks have been documented at facilities lacking these obvious risk factors. In the outbreak at the Colorado boarding kennel, at least three otherwise healthy, fully vaccinated adult dogs died of hemorrhagic pneumonia.

One outbreak occurred over a period of a little more than a year at an open-intake animal shelter admitting more than 50,000 animals annually. Shelter staff estimated there had been more than 1,000 cases. Most cases were in adult dogs and occurred within seven to 14 days of intake, but some of the dogs had been in the shelter for six weeks or more. The dogs died within hours of developing clinical signs. Streptococcus zooepidemicus was isolated from the lungs of affected dogs, from oropharyngeal swabs of neighboring dogs and from the environment. Other respiratory pathogens were also isolated frequently but inconsistently.

All dogs with clinical signs of respiratory disease were euthanized. Healthy dogs were grouped in specific wards and treated with a two-week course of cephalexin. Wards were emptied and thoroughly cleaned, disinfected with quaternary ammonium followed by bleach and dried. Newly admitted dogs were kept in separate wards from exposed dogs. No further cases were detected after this strategy was implemented.

Basics of outbreak control

Streptococcal outbreaks have been successfully managed with these steps:

> Isolate and treat clinically affected and exposed animals with a two-week course of an antibiotic effective against this gram-positive bacteria. Euthanasia should be considered if humane care and safe housing cannot be provided throughout treatment.

> Start treatment early. Antibiotics are often not beneficial by the time overt clinical signs are detected.

> House clinically affected animals separately from exposed (but apparently healthy) animals.

> Treat newly admitted animals, particularly if complete decontamination of premises or isolation of exposed animals is not possible.

> Inform individuals of the possible risks to other pets if animals are sent offsite to private homes (e.g., rescue or foster groups) for treatment.

> Quarantine affected animals until two weeks after complete resolution of clinical signs.

> Completely clean, disinfect and dry all locations where affected animals were housed.