streptococcal pharyngitis ("strep throat") **21.2

"strep throat"

-one of the most common reasons people in the seek medical care `concern: risk of pot-streptocococal sequelae

Causative Agent

-Streptococcus pyogenes `gram positive coccus that grows in chains ~differentiated by: colony morphology on blood agar ``S. pyogenes colonies are surrounded by a characteristic clear zone of beta-hemolysis A few other streptococci and some other bacteria are also beta-hemolytic requiring further tests to identify S pyogenes -referred to as the group A streptococcus (GAS) ((Lancefield)) `characterized by the "A" carbohydrate in its cell wall. **antibodies that bind to the A group are the basis of the rapid diagnostic tests done on the throat specimens in the physicians office `distinguished by variations of a surface antigen called M protein (important virulence factors) ~M proteins: strains with certain types cause strep throat, others with different are more likely to cause skin infections

Epidemiology

-effects only humans -spread: `shouting, coughing, and sneezing

Pathogenesis

-structural components of of the cell wall that allow the bacterium to avoid host defenses / destructive enzymes and toxins released by the bacterial cell that damage or kill host cells proteins in the cell wall allow bacteria to attach to to host cells `m protein is an important adhesion involved in attachment (antibodies that bind to prevent infection) -80 antigenic types of M protein among the many strains of s. pyogenes and antibodies to one type don't prevent infection by another strain that has a different kind -once it colonizes host tissues produces enzymes such as DNase, hyaluronidase, and proteases that break down intracellular connections and allow the organism to spread rapidly to other cells

signs + symptoms

Signs -sore throat , difficulty swallowing, and fever `incubation period: 3-5 days Symptoms -red with patches of pus and scattered tiny hemorrhages -lymph nodes: enlarged and tender -Abdominal pain may develop in young adults and older children -recovery time: about 1 week **mild symptoms or none at all