<unk>  () is an obligate intracellular parasitic protozoan (specifically an apicomplexan) that causes<unk> oplasmosis. Found worldwide,<unk>  is capable of infecting virtually all warm-blooded animals, but felids, such as domestic cats, are the only known definitive hosts in which the parasite may undergo sexual reproduction.<unk>  has been shown to alter the behavior of infected rodents in ways that increase the rodents' chances of being preyed upon by felids. Support for this "manipulation hypothesis" stems from studies showing that<unk> -infected rats have a decreased aversion to cat urine. Because cats are the only hosts within which<unk>  can sexually reproduce to complete and begin its lifecycle, such behavioral manipulations are thought to be evolutionary adaptations that increase the parasite's reproductive success. Rats that do not avoid cats' habitations will more likely become cat prey.<unk>  infection in mice lowers general anxiety, increases explorative behaviors and surprisingly increases a general loss of aversion to predators without selectivity toward cats. There is a positive correlation between the severity of the behavioral alterations and the cyst load, which reflects indirectly the level of inflammation during brain colonization. These results point toward unspecific and immune related changes in the infected mice brains associated with altered behaviors. These results refute the thought of a selective loss of cat fear with possible reference to favoring non-sexual transmission between intermediate hosts. The primary mechanisms of<unk> –induced behavioral changes in rodents are now known to occur through epigenetic remodeling in neurons that govern the relevant behaviors; which, for example, modifies epigenetic methylation to cause hypomethylation of arginine vasopressin-related genes in the medial amygdala, such that predator aversion is greatly decreased. Widespread histone-lysine acetylation in cortical astrocytes appears to be another epigenetic mechanism employed by<unk> . Differences are also observed between infected and non-infected humans in their aversion to cat urine, but with divergent trajectories by gender. In humans, particularly infants and those with weakened immunity, such as HIV/AIDS patients;<unk>  infection may cause a serious – and occasionally fatal – illness:<unk> oplasmosis.<unk>  is one of the most common parasites in developed countries; serological studies estimate that 30–50% of the global population has been exposed to, and may be chronically infected with,<unk> ; although infection rates differ significantly from country to country. For example, estimates have shown the highest IgG seroprevalence to be in Ethiopia, at 64.2%, as of 2018. Mild, flu-like symptoms occasionally occur during the first few weeks following exposure; otherwise, symptoms are not readily observable in healthy human adults. This asymptomatic state of infection is referred to as a latent infection, and it has recently been associated with numerous subtle, yet adverse or pathological, behavioral alterations in humans, though some newer studies found this association to be weak and concluded:"On the whole, there was little evidence that<unk>  was related to increased risk of psychiatric disorder, poor impulse control, personality aberrations or neurocognitive impairment." A number of studies have suggested that subtle behavioral or personality changes may occur in infected humans, and infection with the parasite has recently been associated with a number of neurological disorders – particularly schizophrenia and bipolar disorder. A 2015 study also found cognitive deficits in adults to be associated with joint infection by both<unk>  and Helicobacter pylori in a regression model with controls for race-ethnicity and educational attainment. Although a causal relationship between latent<unk> oplasmosis with these neurological phenomena has not yet been established, preliminary evidence suggests that<unk>  infection may induce some of the same alterations in the human brain as those observed in mice. 180px
Toxoplasma gondii
Mycoplasma
Cryptosporidium
Leishmania
Cytomegalovirus
Coxa vara
Candidatus Phytoplasma fraxini
Treponema pallidum