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Author: Marie Hartley, Staff Writer, 2010. Reviewed and updated by Dr Amanda Oakley Dermatologist, Hamilton, New Zealand; and Vanessa Ngan, Staff Writer; June 2014.

Table of contents

What is actinomycosis?

Actinomycosis is a chronic or slowly progressive infection caused by various bacterial species of the Actinomyces genus, most commonly Actinomyces israelii. Actinomyces are normal inhabitants of the mouth, gastrointestinal tract, and female genital tract, and do not cause an infection unless there is a break in the skin or mucosa. Actinomyces also appear to require the presence of other accompanying bacteria in order to cause disease.

The disease is characterised by the formation of an abscess and draining sinus tracts (small tunnels which open onto the surface of the skin or mucous membranes and drain pus). The draining pus contains yellow granules called sulphur granules. These are named from the colour of the granules, not their content.

Actinomycosis is to be differentiated from actinomycetoma, which is a chronic infection of the skin and subcutaneous tissue, usually involving the foot (see mycetoma). Actinomycetoma is caused by different species of Actinomyces that are found in soil and plant material in tropical regions.

Who is at risk of actinomycosis?

Actinomycosis is relatively rare, but the following factors increase the risk of infection:

  • Poor oral hygiene followed by dental surgery or trauma
  • Impaired immunity eg immunosuppressive medications or chronic conditions such as diabetes mellitus
  • Malnutrition
  • Residence in tropical countries

What are the clinical features of actinomycosis?

Cervicofacial actinomycosis

Cervicofacial (neck and head) actinomycosis is the most common form of infection, accounting for 50–70% of cases. Dental surgery, oral or facial trauma, or local tissue damage caused by cancer or radiation therapy commonly precede infection. The infection usually begins with a slowly progressive, non-painful, hard lump in the cheek or around the jaw. This evolves into abscesses and draining sinus tracts. Surrounding tissues become swollen. Fever and other symptoms of systemic infection are sometimes present. Actinomycosis around the jaw can cause trismus (prolonged spasm of the jaw muscles).

Lymph nodes are not usually enlarged and there is generally little pain, unless adjacent structures are compressed. The infection slowly spreads to surrounding tissues and organs such as the scalp, eyes, ears, tongue, larynx, and trachea. Invasion of adjacent bone occasionally occurs. Infection may spread to the meninges (the membranes surrounding the brain and spinal cord) causing meningitis.

Abdominal actinomycosis

Abdominal disease (10–20% of cases) usually follows a break in the gastrointestinal mucosa, eg following surgery, appendicitis, diverticulitis, or ingestion of foreign bodies such as chicken or fish bones. This disease is difficult to diagnose as patients often have non-specific slowly progressive symptoms such as fever, weight loss, diarrhoea or constipation, and abdominal pain. Any abdominal organ can become involved by direct spread of the disease. Sinus tracts are occasionally found extending to the skin of the abdominal wall or to the mucosal tissue of the rectum or anus.

Pulmonary actinomycosis

Pulmonary disease (15–20% of cases) is usually caused by aspiration (inhalation) of oral or gastrointestinal secretions. The infection presents with slowly progressive non-specific symptoms such as cough, sputum production, breathing difficulties, and chest pain. The infection can slowly spread to involve local structures such as the heart and the chest wall, with sinus tracts occasionally extending to the skin of the chest.

Pelvic actinomycosis

Pelvic actinomycosis is rare and is associated with the use of intrauterine contraceptive devices. Common symptoms of this infection include lower abdominal discomfort, abnormal vaginal bleeding, and vaginal discharge.

Primary cutaneous actinomycosis

Primary cutaneous actinomycosis is very uncommon and affects exposed skin after direct implantation of the organism during an injury.

How is actinomycosis diagnosed?

  • Material obtained from aspirating an abscess or sinus tract, or from a biopsy specimen can be cultured in the laboratory; strict growth conditions are required to grow Actinomyces. Often a variety of accompanying bacteria will be present.
  • Sulphur granules may be examined under a microscope for features characteristic of Actinomyces; however this is not a conclusive test, as another bacterium called Nocardia has a similar appearance.

What is the treatment for actinomycosis?

The goal of actinomycosis treatment is to treat the infection with large doses of antibiotics and surgery to create unfavourable aerobic conditions for the growth of Actinomyces species.

  • Actinomycosis is treated with antibiotics, such as penicillin. High doses of intravenous penicillin followed by oral penicillin is usually needed to penetrate areas of fibrosis and suppuration. Prolonged treatment is often required to prevent relapse.
  • Alternative antibiotics include tetracyclines, erythromycin, and clindamycin.
  • Surgical management includes drainage of deep abscesses, excision of sinus tracts and removal of bulky infected masses.
  • Combination treatment of penicillin and surgery nearly always produces a cure



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