The streptococci are a large family of gram (+) bacteria. The streptococci are classified by the degree of hemolysis they cause on blood agar and by the so-called "Lancefield" classification scheme that is based on antigenic differences in their cell wall carbohydrates.

• The Lancefield groups most commonly causing disease in humans are Groups A, B and C (less commonly D, G, L and M).

Group A streptococcal disease in humans:

Group A S. pyogenes is associated with a variety of diseases in humans:

• pharyngitis ("strept" throat")
• rheumatic fever
• necrotizing fasciitis
• streptococcal toxic shock syndrome

Of particular interest is the common problem of recurrent Group A strept throat and otitis media within families/households, particularly those with young children.

THE QUESTION OFTEN ARISES AS TO WHETHER DOGS IN A HOUSEHOLD CAN SERVE AS SOURCES OF INFECTION FOR HUMANS WITH GROUP A STREPTOCOCCUS (GAS)?:

This point is still debated in the literature. Clearly, human beings are the primary reservoir for GAS, not dogs, so when animals in a household are infected, this is probably an example of a reverse zoonosis (animals are colonized subsequent to spread from a human being). Some studies (Crowder et al., 1978; Wilson et al., 1995) have found no correlation between the presence of dogs in a household and human GAS infections, while others (Mayer and VanOre, 1983; Copperman, 1982) have documented resolution of chronic GAS in households after isolation of the organism from, and treatment of, dogs.

• This tutorial's author has personally been involved in two clinical situations in which a GAS was cultured from both the household dog and from children suffering from recurrent pharyngitis. In both of these cases, all of the people in the house had been treated simultaneously with antibiotics without clearing up the problem, but when all the people in the household and the dog were simultaneously put on antibiotics, the problem resolved.

How about cats?:

To this author's knowledge, there is only one case report of zoonotic GAS involving cats. (Roos et al., 1988)

Diagnosis of GAS infection in dogs:

It is important to realize that dogs are asymptomatic for GAS colonization. Therefore, judgment as to whether an animal may be a carrier must be based upon careful culturing and laboratory identification of an organism.

• Historically, cultures for GAS in dogs have been taken from the caudal wall of the pharynx or, ideally, the tonsils.
  • This generally requires sedation so as to avoid contamination of the swab with extraneous oral surface commensal bacteria that will outgrow and mask GAS.
• More recently, it has been suggested that the optimum site to culture for detection of GAS in dogs is the conjunctival sac.
  • In either case, it is critically important to have any organisms typed to be sure that both the human and animal isolates are identical, above and beyond simply both being hemolytic Streptococcus.
    • To accomplish this, it is important that veterinarians and physicians communicate and work closely together.

Treatment:

The antibiotic of choice for S. pyogenes is penicillin.

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