Background
Actinomycosis is a chronic bacterial disease. Localized swelling with suppuration, abscess formation, tissue fibrosis, and draining sinuses characterize this disease. Gram-positive, pleomorphic non–spore-forming, non–acid-fast anaerobic or microaerophilic bacilli of the genus Actinomyces and the order Actinomycetales cause actinomycosis. Actinomyces are very closely related to Nocardia species; both were once considered to be fungal organisms.
Infections of the oral and cervicofacial regions are the most commonly recognized infections; however, the thoracic region, abdominopelvic region, and the CNS are also frequently involved. Actinomyces israelii, Actinomyces naeslundii, Actinomyces odontolyticus, Actinomyces viscosus, and Actinomyces meyeri most frequently cause human actinomycosis. Actinomyces gerencseriae may also cause disease in humans. Three former Centers for Disease Control and Prevention (CDC) coryneform bacteria now have been added to the Actinomyces group and are thought to be potential causes for disease; these include Actinomyces neuii,[1] Actinomyces radingae, and Actinomyces turicensis. Actinomyces radicidentis, a recently described species, has been isolated with polymerase chain reaction from patients with endodontic infections.[2]
Actinomyces species grow well in enriched media with brain-heart infusion and may be aided in growth by an atmosphere of 6-10% ambient carbon dioxide. They grow best at 37°C. Colonies can appear at 3-7 days, but, to ensure that no growth is missed, observe cultures for 21 days.
Propionibacterium propionicus and related species of bacteria can also cause actinomycosislike disease. Other bacteria that are frequently isolated from clinical specimens concomitantly with Actinomyces in human infection include Actinobacillus actinomycetemcomitans, Eikenella corrodens, and species of Fusobacterium, Bacteroides, Capnocytophaga, Staphylococcus, Streptococcus, and Enterococcus.
Pathophysiology
Actinomyces species that cause human disease are not found in nature but are normal flora of the oropharynx, GI tract, and female genital tract. This is not an exogenous infection; therefore, no person-to-person spread of the pathogen occurs.
In general, Actinomyces species, being members of the normal flora, are agents of low pathogenicity and require disruption of the mucosal barrier to cause disease. Oral and cervicofacial diseases are commonly associated with dental procedures, trauma, oral surgery, or dental sepsis. Pulmonary infections usually arise after aspiration of oropharyngeal or GI secretions. GI infection frequently follows loss of mucosal integrity, such as with surgery, appendicitis, diverticulitis, trauma, or foreign bodies. Numerous reports have linked the use of intrauterine contraceptive devices to the development of actinomycosis of the female genital tract.[3] The presence of a foreign body in this setting appears to trigger infection.
Other bacterial species that often are copathogens to Actinomyces species may aid spread of infection by inhibiting host defenses and reducing local oxygen tension. Once the organism is established locally, it spreads to surrounding tissues in a progressive manner, leading to a chronic, indurated, suppurative infection often with draining sinuses and fibrosis. In tissues, Actinomyces grow in microscopic or macroscopic clusters of tangled filaments surrounded by neutrophils. When visible, these clusters are pale yellow and exude through sinus tracts; they are called sulfur granules. This is not an exclusive finding of actinomycosis, and its absence does not rule out the diagnosis. Other conditions, such as eumycetoma and nocardiosis, have been linked to the production of sulfur granules.
Epidemiology
Frequency
United States
The disease is uncommon. Studies in the Cleveland area in the 1970s showed incidence to be about 1 per 300,000 persons.
International
Studies in Germany and the Netherlands in the 1960s showed incidence of 1 per 100,000 persons. No data are available on the incidence of disease in developing nations.
Sex
A male-to-female infection ratio of 3:1 is encountered in most series. Unconfirmed explanations for this comprise poorer oral hygiene and augmented oral trauma in males.
Age
Infection can develop in individuals of all ages; however, it is rare in the pediatric population and in patients older than 60 years. Most cases are encountered in individuals in the mid decades of life.
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