Actinomycosis - Causes 

Causes of actinomycosis 

Actinomycosis is caused by a strain of bacteria called actinomycetales. Actinomycetales are found in many body cavities, such as inside the mouth and, less commonly, the bowel.

In women, they can also be found in the womb and fallopian tubes (through which eggs are released into the womb). 

How actinomycosis spreads

Actinomycetales are anaerobic bacteria, which means they cannot survive in oxygen-rich environments. Therefore, they do not cause illness when they are in one of the body’s cavities, such as the mouth or intestinal tract.

However, if actinomycetales break through the protective lining (mucous membrane) surrounding the cavities, they can penetrate deep into body tissue. As the deep layers of human tissue are low in oxygen, the bacteria are able to reproduce quickly and infect healthy tissue.


In an attempt to combat the infection, your immune system (the body’s natural defence against infection and illness) will send infection-fighting cells to the source of the infection. However, these cells do not have the ability to kill the bacteria and will quickly die.

As the infection-fighting cells die, they accumulate into a yellowish-coloured liquid called pus. Having failed to kill the infection, your immune system will attempt to limit its spread by using healthy tissue to form a protective barrier around the pus. This is how a pus-filled swelling, known as an abscess, is formed.

Unfortunately, the actinomycetales strain of bacteria has the ability to penetrate the protective barrier of an abscess and move into more healthy tissue. Your immune system will attempt to counter the infection by producing more abscesses.

Sinus tracts

Your body will eventually need to get rid of the accumulation of pus. To do this, small channels called sinus tracts will develop that lead from the abscesses to the surface of your skin.

The sinus tracts will leak pus, as well as lumps of bacteria. This takes the form of a yellow powdery substance sometimes referred to as ‘sulphur granules’.

Opportunistic infection

Actinomycosis is an opportunistic infection that does not cause symptoms unless an opportunity arises for it to penetrate body tissue.

Oral cervicofacial actinomycosis

Opportunities for oral cervicofacial actinomycosis include:

Thoracic actinomycosis

Most cases of thoracic actinomycosis are thought to be caused by small particles of food or other ingested material that get mixed up with the actinomycosis bacteria. Rather than passing harmlessly down into the stomach, the particles are mistakenly passed down into the windpipe and the airways of the lungs.

People with long-term drug or alcohol problems are particularly at risk of developing thoracic actinomycosis for two reasons:

  • being drunk or intoxicated increases your risk of accidentally ingesting material into your lungs
  • long-term drug and alcohol misuse weakens the immune system, which makes a person more vulnerable to developing an infection

Read more about drug misuse and alcohol misuse.

Abdominal actinomycosis

Abdominal actinomycosis occurs when something tears the wall of the intestine (bowel), allowing the bacteria to penetrate into deep tissue.

The intestine can tear as a result of an infection, such as a burst appendix that damages the wall of the intestine. Or it can be damaged through injury, for example, when someone mistakenly swallows a fish bone.

There have also been some reported cases of abdominal actinomycosis occurring as a complication of bowel or abdominal surgery.

Pelvic actinomycosis

Most cases of pelvic actinomycosis have been recorded in women who were using the intrauterine device (IUD) form of contraception. The IUD is a small, T-shaped contraceptive device made from plastic and copper that fits inside the womb. The women affected tend to be long-term users of the IUD (eight years or more).

One explanation for cases of pelvic actinomycosis in women who are using the IUD is that, over time, the IUD may damage the womb lining, allowing bacteria to penetrate deep tissue. However, no research has yet been done to find out whether or not this is the case.

It should be stressed that developing pelvic actinomycosis as a result of using an IUD is rare. In England, millions of women use the IUD device and there have only been a handful of reported cases of pelvic actinomycosis.

Page last reviewed: 14/08/2012

Next review due: 14/08/2014


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