Myelitis is acute, but the retroviruses (such as HIV and HTLV) can cause chronic myelitis. Poliomyelitis, or gray matter myelitis, is usually caused by infection of anterior horn of the spinal cord by the enteroviruses (polioviruses, enteroviruses (EV) 70 and 71, echoviruses, coxsackieviruses A and B) and the flaviviruses (West Nile, Japanese encephalitis, tick-borne encephalitis). On the other hand, transverse myelitis or leukomyelitis, or white matter myelitis, are often caused by the herpesviruses and influenza virus. It can be due to direct viral invasion or via immune mediated mechanisms. Bacterial myelitis includes "Mycoplasma Pneumoniae", which is a common agent for respiratory
Supernumerary body part considered to have lost much or all of their original function through evolution. These body parts can be classed as additional to the required functioning of the body. In human anatomy the vermiform appendix is sometimes classed as a vestigial remnant. Prosthesis is an artificial extension that replaces a body part, and cybernetics is the study of computer technology in relation to organisms which can include replacement or additional body parts. Body integrity identity disorder (BIID) is a psychiatric disorder in which a person thinks that they have one or more additional limbs than they should, despite having two arms