Coming home from an exotic vacation with a belly full of amoeba can be unpleasant - but this poor patient didn't even get to go on a holiday.

A recent medical case study describes the diagnosis of a 67-year-old male with an infection of Entamoeba histolytica, apparently transmitted while having sex with his jet-setting partner.

The infection itself isn't rare. Some 50 million people worldwide are infected with this potentially deadly form of amoeba, usually as a result of ingesting contaminated food or water in a region where the parasite is endemic.

The protozoan's cysts can also camp out in soil or under dirty fingernails, finding their way inside the gut when an unsuspecting soul pops their hands in their mouth.

However it happens to get inside the body, E. histolytica can easily replicate in the intestines before heading back out into the environment nestled in the host's faeces.

Some stubborn amoeba choose to stay around a while and see the sights, invading the intestinal lining to take a ride in your bloodstream to visit other organs, including the lungs, brain, and liver.

Fortunately, public sanitation makes the pathogen all but impossible to pick up from local food and water supplies in developed countries.

When French doctors came across a patient with bloody diarrhoea, low grade fever, and liver abscesses in July 2018, a pathology test confirmed the disease-causing amoeba was to blame.

Curiously, he presented a rare example of a patient with both intestinal and liver forms of the disease, something which isn't all that common in the medical literature.

Even stranger still was the question of transmission. The patient had never set foot outside of Europe.

But the doctors soon learned the man had a sexual partner who had recently been on a bit of a world tour, making her way through South America, India, Burma, Vietnam, and Laos.

More tellingly, she'd confessed to having an intimate relationship with another man diagnosed with intestinal amoebiasis (we're not sure how she knew, but that's what the case study reports).

It's not unknown for the amoeba to be passed between individuals engaging sexually with partners of the same sex.

A series of case studies published in 2012 describes the parasite presenting as penile ulcerations among men who engaged in anal intercourse, for example. Another study from 2009 investigated a possible infection within a mixed group of sexually involved individuals in Canada.

But cases picked up from a heterosexual partner are extremely rare. Still, even though the woman hadn't experienced symptoms herself, she was considered to be the most likely source of the infection.

Exactly how the amoeba made its way between the hosts in this event is left to our imaginations. The study refers only to 'heterosexual intercourse', so we're not sure if some creative foreplay was involved that allowed the parasite to move house.

The fact remains - E. histolytica should be considered a potential STI for anybody living in or visiting a country where such infections are rife.

"For individuals who have travelled to endemic areas, amoebiasis could be considered in addition to syphilis, HIV, hepatitis B and C when screening for sexually transmitted infections," the team of physicians advise in their case report.

The unidentified patient in this particular study made a full and rapid recovery after being treated with the drugs metronidazole and tiliquinol-tilbroquinol.

He was one of the lucky ones. Some 100,000 people around the world die of amoebiasis every year, mostly in developing nations with inadequate water treatment programs.

It's not clear how many cases might be sexually transmitted, or whether improved sexual health education might help reduce the rate of E. histolytica infection.

Given that STIs are on the rise in places such as the US, now is as good a time as any to remind people how important it is to play safe.

Amoebas really are the least of your concerns.

This research was published in BMJ Case Reports.