Thats because this type of infection (like shigellosis, amebiasis, and giardiasis) are very easily spread by a certain activity practiced by gay men. Its not exclusive to gays, heterosexuals can transmit it too if they indulge in the same activity. However, it is common in gay relationships. I will leave it to your imagination to discover the activity because i really dont want to post it here.

Respect

GIASI