Typical actinomycosis in humans is a chronic disease caused by Actinomyces israelii, A gerencseriae and
Propionibacterium propionicus (previously Arachnia propionica). The infection is characterized by persisting
swelling, suppuration, and formation of abscesses with draining sinuses. Major types are cervicofacial, thoracic, and
abdominal. In addition to the pathogens in actinomycosis some Actinomyces species have also been isolated from
other mixed anaerobic infections, eye infections, blood and the urinary tract.
Period of communicability—How and when Actinomyces and Arachnia species become part of normal oral flora is
unknown; except for rare instances of human bite, infection is unrelated to specific exposure to an infected person.