A rare parasitic disease, which normally only is transmitted by contaminated water, has been shown to be transmitted by gay sex between hiv-positive men. In the industrial world the disease is virtually absent, but that could change.

For this observation, Taiwanese researcher Chieng-Ching Hung received a doctorate from the University of Antwerp and the Institute of Tropical Medicine Antwerp.

Amebiasis, an infection with the single-celled amoeba Entamoebia histolytica, normally is very rare. You only catch it in a few developing countries where the amoeba is endemic, and where hygiene is somewhat substandard, leading to contact with contaminated water. It only becomes dangerous when the amoeba invades your intestinal lining and causes a bloody diarrhoea, or when it enters the bloodstream, where it, among other things, causes liver abscesses. All in all amebiasis takes some 70 000 lives a year, worldwide.

For some time now, physicians suspected the disease to be a bit overrepresented among HIV-positive male homosexuals. But it was difficult to come to conclusions from small numbers, and in addition the classical diagnostic test (putting the stool under the microscope) was not really dependable. Hung used modern molecular techniques, pinpointing the amoeba more precisely and, what's more, showing which amoebas were closely related. In other words: who had got the infection from whom.

In Taiwan, seropositive (hiv-infected) gay men were shown to be infected much more often with the amoeba than the healthy population, and also than seropositive heterosexuals. Also, Hung found men from different regions nevertheless to be infected by closely related amoebas. The most reasonable explanation is that the infection happened through homosexual (oral-anal) contact.

In today's mobile world this means that those people in turn can transmit the infection to regions where it normally is absent.

Not only amebiasis marches in the wake of hiv; Hung also confirmed in his Taiwanese cohort what is seen elsewhere: tuberculosis and hepatitis B and C are more virulent in combination with hiv, and more often present.