Various pathogens—bacterial (shigellosis, Campylobacter infection, or Salmonella infection), viral (hepatitis A, B, and C viruses), and parasitic (giardiasis or amebiasis)—are transmitted via sexual practices, especially those that can involve fecal-oral contamination. In order of decreasing risk, these practices are
Although some of the above bacterial and parasitic pathogens may cause proctitis, they usually cause infection higher in the intestinal tract; symptoms include diarrhea, fever, bloating, nausea, and abdominal pain. Multiple infections are frequent, especially in people who have many sex partners and who engage in sexual practices that lead to direct or indirect oral-rectal contact.
Most of these pathogens can cause infections without symptoms; asymptomatic infection is the rule with Entamoeba dispar (formerly, nonpathogenic Entamoeba histolytica), which commonly occurs in homosexual men.
(See also Overview of Sexually Transmitted Diseases.)