The pathology of human West Nile Virus infection.

West Nile Virus (WNV) was identified by immunohistochemistry (IHC) and polymerase chain reaction (PCR) as the etiologic agent in 4 encephalitis fatalities in New York City in the late summer of 1999. The fatalities occurred in persons with a mean age of 81.5 years, each of whom had underlying medical problems. Cardinal clinical manifestations included fever and profound muscle weakness. Autopsy disclosed encephalitis in 2 instances and meningoencephalitis in the remaining 2. The inflammation was mostly mononuclear and formed microglial nodules and perivascular clusters in the white and gray matter. The brainstem, particularly the medulla, was involved most extensively. In 2 brains, cranial nerve roots had endoneural mononuclear inflammation. In addition, 1 person had acute pancreatitis. Based on our experience, we offer recommendations for the autopsy evaluation of suspected WNV fatalities.