i think it's a little parasitic bacteria

A kind of bacteria called MYCOPLASMA GENITALIUM, it's diametre is only 250 nanometres.

Mycoplasma species have been isolated from women with bacterial vaginosis. M. genitalium infection is associated with increased risk of cervicitis, pelvic inflammatory disease, preterm birth and spontaneous abortion, and infertility. Mycoplasmas are associated with fetal respiratory distress syndrome, bronchopulmonary dysplasia, intraventricular hemorrhage in preterm infants, and most commonly what is termed as -walking-pneumonia.

Mycoplasma is an eukartotes that usually has no nucleus.