滴虫病

Trichomonas vaginalis, a single-celled anaerobic protozoan, causes trichomoniasis. Unlike most parasites, it lacks mitochondria but contains hydrogenosomes that generate energy under anaerobic conditions. The parasite exists solely as a trophozoite, replicating through binary fission without forming cysts, allowing it to persist in the urogenital tract.

T. vaginalis uses surface adhesins and lectin-like proteins to adhere to vaginal epithelium. Once attached, it secretes cytotoxic proteins, including pore-forming proteins and cysteine proteases, that degrade cellular junctions. This triggers epithelial cell apoptosis and sloughing, causing mucosal inflammation and tissue damage that increases susceptibility to other infections.

T. vaginalis possesses four anterior flagella and a recurrent flagellum associated with an undulating membrane, producing characteristic jerky motility observable under wet mount microscopy. These structures, combined with its size comparable to a white blood cell, facilitate movement through the urogenital tract. Transmission occurs through direct sexual contact, as the organism survives only briefly outside the host.

T. vaginalis disrupts the normal vaginal microbiota and damages the epithelial barrier by secreting cytotoxic proteins. This destruction elevates vaginal pH above 4.5 and compromises epithelial integrity, facilitating bacterial overgrowth and increased susceptibility to other sexually transmitted infections, including HIV and conditions like american trypanosomiasis.

In women, T. vaginalis infection causes frothy, malodorous vaginal discharge, erythema, and sometimes a characteristic strawberry cervix appearance due to epithelial damage and inflammation. In men, the infection is often asymptomatic but may occasionally cause urethritis, prostatitis, or epididymitis. The difference reflects the parasite's primary colonization site in each sex.

T. vaginalis exists exclusively as a trophozoite, replicating asexually through binary fission without forming cysts. This adaptation limits environmental survival but ensures effective transmission through direct sexual contact. The absence of a cyst stage means the parasite cannot survive prolonged exposure to moist environments outside the host.

Hydrogenosomes are specialized organelles that replace mitochondria in T. vaginalis, generating energy through anaerobic metabolism within the host. This adaptation allows the parasite to thrive in the anaerobic environment of the urogenital tract. The presence of hydrogenosomes instead of mitochondria is a key distinguishing feature of this protozoan parasite.