ACTINOMYCES INFECTIONS

STEPHANIE SPECK

Bundeswehr Institute of Microbiology, Department of Virol­ogy and Rickettsiology, Munich, Germany

The actinomycetes comprise a heterologous group sharing the ability to form Gram-positive, branching filaments of less than 1 μm in diameter.

Actinomycosis, or ‘lumpy jaw’, is caused by infection with A. bovis, which results in a destructive osteomyelitis and soft-tissue reaction of the mandible. Actinomycosis is a non-contagious, endogenous, chronic disease of world­wide occurrence.

Actinomyces species are normal residents of the skin, oral mucosa and nasopharynx of their host animal. Infections tend to be endogenous and are favoured by cuts, abrasions of the skin or trauma to the oral mucosa, for example by rough feed. The lower and upper jaws are the most likely sites of infection. Actinomycosis associated with A. bovis infection has been described in a herd of captive llama (Lama glama) in Switzerland)⁶³). Chronic granulomatous inflammation in retropharyngeal lymph nodes and osteo­myelitis has been described in various deer species (Odo- coileus spp., Cervus elaphus), moose (Alces alces), pronghorn (Antilocapra americana), caribou (Rangifer tarandus) and mountain sheep ( Ovis spp.), but in many of these descrip­tions the presence of Actinomyces sp. was not confirmed¹-⁶⁴). Disease caused by the organism occurring in wild Euro­pean ruminants would not be unexpected, and ‘lumpy jaw’ lesions should be investigated for the presence of A. bovis. Actinomyces marimammalium has been isolated from mul­tiple organs of a dead male hooded seal ( Cystophara cristata) that had suffered from pneumonia, from the small intes­tine of a shot grey seal (Halichoerus grypus), and from the lung of a dead harbour porpoise (Phocoenaphocoena).

Actinomyces bovis often gains access through the dental alveoli or lesions in the oral mucosa. It causes chronic rarefying ostemomyelitis of the mandible and suppurative necrosis with progressive destruction of trabeculae and proliferation of periosteal new bone. The reaction may result in loss of teeth and large mandibular deformities. The lesions and tracts filled with pus may contain miliary pale granules (sulphur granules), which are grossly visibly colonies (of up to 3 mm in diameter) of A. bovis. These typical ‘club colonies’ are formed by filamentous and branching bacteria with mineralization of calcium phos­phate. Histologically, a pyogranulomatous response devel­ops with surrounding granulation tissue, mononuclear infiltration and fibrosis. The inflammation is usually local­ized and may be restricted to soft tissues of the oral cavity, but in rare cases other tissues are involved.

Infection with A. bovis in ungulates results in noticeable swelling of the jaw, resulting in difficulty with mastication. Severe mandibular swelling and purulent exudate secreted from fistulae was described in affected captive llama⁽⁶³⁾. Treatment of actinomycosis in captive individuals includes systemic antibiotic and local disinfectant treatment, and surgical intervention as well as supplementation of vita­mins and minerals.

Actinomycosis should be suspected when typical swell­ings and granulomatous lesions involving the mandibles of ungulates are seen. Specimens for laboratory diagnosis of Actinomyces spp. include pus, exudate, aspirates, tissue and scrapings from walls of abscesses. Thin sections of granulomas are useful for histopathology. Direct micros­copy can be performed on unstained sulphur granules placed on a microscope slide in a drop of 10% KOH and gently crushed by applying pressure on the cover slip. Gram-stained smears made from granules will show Gram­positive, branching filaments.

Actinomyces bovis infection in free-ranging ungulates occurs only sporadically therefore control is not necessary.