Camelidae and Cervidae West Nile Encephalomyelitis – NAVLE Study Guide

Overview and Clinical Importance

West Nile virus (WNV) is an arthropod-borne flavivirus that causes neurological disease in multiple mammalian species, including camelids (llamas, alpacas) and cervids (deer, elk, reindeer, moose). First isolated in Uganda in 1937, WNV was introduced to North America in 1999 and has since become endemic throughout the Americas. WNV infection in camelids and cervids represents an important differential diagnosis for veterinarians evaluating neurological disease during mosquito season.

Camelids and cervids are considered dead-end hosts, meaning they develop insufficient viremia to transmit the virus back to mosquito vectors. However, clinical disease can be severe, and mortality rates in neurologically affected animals range from 30-50%. Understanding the pathogenesis, clinical presentation, and management of WNV encephalomyelitis in these species is essential for NAVLE and BCSE examination success.

Etiology and Viral Characteristics

Viral Classification

West Nile virus belongs to the family Flaviviridae, genus Flavivirus. It is closely related to other encephalitic flaviviruses including Japanese encephalitis virus, St. Louis encephalitis virus, and Murray Valley encephalitis virus. The virus is a single-stranded, positive-sense RNA virus with an enveloped, icosahedral structure measuring approximately 45-50 nm in diameter.