<unk>  are bacteria in the genus<unk> , a group of obligate intracellular parasites of eukaryotic cells.<unk> l cells cannot carry out energy metabolism and they lack biosynthetic pathways.<unk>  strains are generally divided into three biovars based on the type of disease they cause. These are further subdivided into several serovars based on the surface antigens recognized by the immune system. Serovars A through C cause trachoma, which is the world's leading cause of preventable infectious blindness. Serovars D through K infect the genital tract, causing pelvic inflammatory disease, ectopic pregnancies, and infertility. Serovars L1 through L3 cause an invasive infection of the lymph nodes near the genitals, called lymphogranuloma venereum.<unk>  is thought to have diverged from other<unk>  species around 6 million years ago. This genus contains a total of nine species:<unk> , C. muridarum, C. pneumoniae, C. pecorum, C. suis, C. abortus, C. felis, C. caviae, and C. psittaci. The closest relative to<unk>  is C. muridarum, which infects mice.<unk>  along with C. pneumoniae have been found to infect humans to a greater extent.<unk>  exclusively infects humans. C. pneumoniae is found to also infect horses, marsupials, and frogs. Some of the other species can have a considerable impact on human health due to their known zoonotic transmission.
Chlamydia trachomatis
Neisseria gonorrhoeae
Trichomonas vaginalis
Mycoplasma genitalium
Haemophilus ducreyi
Treponema pallidum
Neisseria mucosa
Helicobacter suis