Abstract:
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.
