Infection with Borrelia species bacteria is associated with anorexia nervosa. In rare cases, anorexia nervosa may arise after infection with Streptococcus species bacteria. Anorexia (which is distinct from anorexia nervosa) is associated with the protozoan parasite Dientamoeba fragilis.
Parkinson's disease is associated with influenza A virus, as well as the protozoan parasite Toxoplasma gondii.