A case of M urray V alley encephalitis in a 2‐year‐old A ustralian S tock H orse in south‐east Q ueensland

Case report This report summarises the findings from a case of naturally‐occurring M urray V alley encephalitis in a 2‐year‐old filly presenting with acute onset of depression and weakness. Serum samples tested at the onset of clinical signs were negative for H endra and K unjin virus antibodies, but positive for M urray V alley encephalitis virus ( MVEV ) using IgM ‐capture ELISA (1 : 300 dilution). A virus neutralisation assay performed 4 weeks later confirmed a titre of 1 : 160. Sera collected in the weeks preceding neurological signs returned a negative titre for MVEV 2 weeks prior followed by a titre of 1:80 in the week prior to illness. Serological surveillance conducted on 67 co‐located horses returned a positive titre of 1 : 20 in one in‐contact horse. There was no history of clinical disease in that horse. At 3 months after the onset of clinical signs in the index case, the filly continued to show mild facial paresis and hypermetria; the owners elected euthanasia and gave permission for necropsy. Histopathological analysis of the brain showed a mild meningoencephalitis. Conclusion The progression of a naturally‐occurring MVEV infection in a horse has been documented in this case.