A COMPARISON OF THE SPREAD OF MURRAY-VALLEY ENCEPHALITIS VIRUSES OF HIGH OR LOW NEUROINVASIVENESS IN THE TISSUES OF SWISS MICE AFTER PERIPHERAL INOCULATION

A Murray Valley encephalitis virus (MVE) field isolate of high neuroin vasiveness (BH3479) and a neutralization escape variant of low neuroin vasiveness (BHv1) selected from BH3479 (which differ by a single amino acid at residue 277 in the envelope glycoprotein) were examined for t heir distribution in the tissues of weanling Swiss mice at various tim es after footpad inoculation. BH3479 was first detected in lymph nodes draining the inoculated limb at 24 hr postinoculation (pi) and was fo und in serum between 36 and 72 hr pi. BH3479 was first detected in the central nervous system (CNS) at 4 days pi and reached maximum CNS tit ers (>10(9) PFU/g) between 6 and 9 days pi. All BH3479-infected mice d eveloped encephalitis and died before 10 days pi. In contrast, BHv1 wa s not detected in lymph nodes draining the footpad at any time after i noculation; BHv1 was first detected in the serum between 60 and 72 hr pi-24 hr later, and at a 20-fold lower titer than for BH3479. BHv1 was first detected in the CNS at 7 days pi 3 days later and at a 300-fold lower titer than for BH3479. After 10 days pi, BHv1 could not be isol ated from the CNS or from other host tissues. Most BHv1-infected mice experienced a subclinical infection; the mortality rate from BHv1 infe ction was less than 1%. Both viruses appeared to enter the CNS via the olfactory lobes. BH3479 spread throughout the CNS in a rostral to cau dal direction over 3-4 days. In contrast, BHv1 infection in the CNS wa s restricted to the olfactory lobes and adjacent structures of the for ebrain. (C) 1996 Academic Press, Inc.