Sexual activity is the primary method of transmission for several important
parasitic diseases and has resulted in a significant prevalence of enteric
parasitic infection among male homosexuals. The majority of parasitic
sexually transmitted diseases involve protozoan pathogens; however, nematode and arthropod illnesses are also included in this group.
Trichomoniasis, caused by Trichomonas vaginalis, is the most common parasitic STD.
Infection with this organism typically results in the signs and symptoms of
vaginitis.
Trichomoniasis can be diagnosed in the office setting by performing a microscopic evaluation of infected vaginal secretions and can be successfully treated with
metronidazole. Both
pediculosis pubis, caused by the crab louse Pthirus pubis, and
scabies, caused by the itch mite Sarcoptes scabiei, present with severe
pruritus. A papular or vesicular
rash and linear burrows seen in the finger webs and genital area are characteristic of
scabies.
Pediculosis pubis is diagnosed by observing adult lice or their nits in areas that bear coarse hair. The diagnosis of
scabies is confirmed by scraping suspicious burrows and viewing the mite or its byproducts under the microscope.
Lindane, 1% used in treating
scabies, is also very effective for treating
pediculosis pubis. Synthetic
pyrethrins, also applied as a cream or lotion, are less toxic alternatives for the treatment of either condition. Oral-anal and oral-genital sexual practices predispose male homosexuals to
infection with many enteric pathogens, including parasitic protozoans and helminths. The most common of these
parasitic infections are
amebiasis, caused by Entamoeba histolytica, and
giardiasis caused by Giardia lamblia. Both entities may cause acute or chronic
diarrhea, as well as other abdominal symptoms. Most gay men with
amebiasis are asymptomatic, and invasive disease in this group is extremely rare. Both
amebiasis and
giardiasis can be diagnosed on the basis of microscopic examination of stool specimens, although duodenal aspiration is occasionally necessary to confirm a diagnosis of
giardiasis. Multiple treatment regimens exist for
amebiasis.
Iodoquinol is a good choice for asymptomatic
cyst carriers, whereas the combination of
metronidazole plus
iodoquinol is used for symptomatic patients.
Quinacrine and
metronidazole are both efficacious in the treatment of
giardiasis.