Comparative pathology of neurovirulent lineage 1 (NY99/385) and lineage 2 (SPU93/01) West Nile virus infections in BALBc mice

Vet Pathol. 2015 Jan;52(1):140-51. doi: 10.1177/0300985813520246. Epub 2014 Feb 10.


The pathology in mice infected with neurovirulent South African lineage 2 West Nile virus (WNV) strains has not previously been described. Three- to 4-month-old male BALBc mice were infected with South African neurovirulent lineage 2 (SPU93/01) or lineage 1 (NY385/99) WNV strains and the gross and microscopic central nervous system (CNS) and extra-CNS pathology of both investigated and compared. Mice infected with both lineages showed similar illness, paralysis, and death from days 7 to 11 postinfection (PI). Two survivors of each lineage were euthanized on day 21 PI. WNV infection was confirmed by nested real-time reverse transcription polymerase chain reaction of tissues, mostly brain, in the majority of mice euthanized sick or that died and in 1 healthy lineage 2 survivor. Gross lesions caused by both lineages were identical and included marked gastric and proximal small intestinal fluid distension as described in a previous mouse study, but intestinal microscopic lesions differed. CNS lesions were subtle. Immunohistochemical (IHC)-positive labeling for WNV E protein was found in neurons multifocally in the brain of 3 lineage 1-infected and 3 lineage 2-infected mice from days 9 to 11 PI, 4 of these including brainstem neurons, and of cecal myenteric ganglion neurons in 1 lineage 2-infected day 8 PI mouse. Findings supported hypotheses in hamsters that gastrointestinal lesions are likely of brainstem origin. Ultrastructurally, virus-associated cytoplasmic vesicular or crystalline structures, or amorphous structures, were found to label IHC positive in control-positive avian cardiomyocytes and mouse thalamic neurons, respectively, and WNV-like 50-nm particles, which were scarce, did not label.

Keywords: BALBc mice; West Nile virus lineages 1 and 2; histopathology; immunohistochemistry; neurovirulent; pathology; ultrastructure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Birds
  • Brain / pathology
  • Cricetinae
  • Female
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Myocytes, Cardiac / virology
  • Neurons / virology
  • Specific Pathogen-Free Organisms
  • West Nile Fever / pathology*
  • West Nile Fever / veterinary*
  • West Nile virus / physiology*
  • West Nile virus / ultrastructure