Mycoplasmas: Brain invaders?

Mycoplasmas of humans and animals are usually associated with respiratory, autoimmune, genital and joint diseases. Human mycoplasmas have also been known to affect the brain. Severe central nervous system (CNS) diseases, such as encephalitis, have been linked to Mycoplasma pneumoniae and ureaplasma infections. Less well known is the sheep and goat pathogen, Mycoplasma agalactiae, which has been found in large quantities in the brain where it may be responsible for non-purulent encephalitis as well as ataxia in young animals. Experimental intra-mammary infections of sheep with this mycoplasma have resulted in histopathological changes in the CNS. The cattle pathogen, M. bovis, has been reported occasionally in the brains of calves and adult cattle showing a range of histopathological lesions including abscesses and fibrinous meningitis. Two avian pathogens, M. gallisepticum and M. synoviae have been isolated from the brains of poultry showing meningeal vasculitis and encephalitis. There have been no reported detections of two other avian pathogens, M. meleagridis or M. iowae in the CNS. Over the last few decades, mycoplasmas have been isolated from the brains of sea mammals dying in large numbers in the North Sea although it was concluded that their role may be secondary to underlying viral disease. Finally, evidence has been advanced that certain Spiroplasma species may have a role in the development of the transmissible spongiform encephalopathies (TSE). Invasion of the brain by mycoplasmas may be as a result of direct entry following damage to the inner ear as seen with M. bovis or across the blood brain barrier by mechanisms as yet uncertain.