Actinomycosis is caused by a group of bacteria called actinomycetaceae.
Actinomycetaceae 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 (the tubes eggs are released through into the womb).
How actinomycosis spreads
Actinomycetaceae are anaerobic bacteria, which means they can't survive in oxygen-rich environments. They therefore don't cause illness when they're in the mouth or intestinal tract.
However, if the bacteria 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. But these cells are unable to kill the bacteria and will quickly die.
As the infection-fighting cells die, they accumulate into a yellowish-coloured liquid (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 an abscess (pus-filled swelling) develops.
Actinomycetaceae are able 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.
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".
Actinomycosis is an opportunistic infection that doesn't cause symptoms unless the chance arises for it to penetrate body tissue.
Oral cervicofacial actinomycosis
Opportunities for oral cervicofacial actinomycosis include:
Most cases of thoracic actinomycosis are thought to be caused by small food particles or other ingested material that gets 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.
This is because being drunk or intoxicated increases the risk of material being accidentally ingested into your lungs. Long-term alcohol misuse and drug misuse also weakens your immune system, making you more vulnerable to developing an infection.
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 the result of an infection, such as a burst appendix that damages the intestine wall. It can also be damaged through injury – for example, if you were to mistakenly swallow a fish bone.
There have also been some reported cases of abdominal actinomycosis occurring as a complication of bowel or abdominal surgery.
Most cases of pelvic actinomycosis have been recorded in women who were using an intrauterine device (IUD) form of contraception.
An IUD is a small, T-shaped contraceptive device made from plastic and copper that fits inside the womb. The women affected by the condition tend to be long-term users of an IUD (eight years or more).
One explanation for cases of pelvic actinomycosis in women who are using an IUD is that, over time, it may damage the womb lining, allowing bacteria to penetrate deep tissue. However, no research has been carried out to find out whether or not this is the case.
It's important to note that it's very rare to develop pelvic actinomycosis as a result of using an IUD. For example, in England, millions of women use the device and there have only been a handful of reported cases of pelvic actinomycosis. It only tends to occur if an IUD is left in place longer than the manufacturer recommends.