Confirmed case of encephalitis caused by Murray Valley encephalitis virus infection in a horse

A 5-year-old Australian stock horse in Monto, Queensland, Australia, developed neurological signs and was euthanized after a 6-day course of illness. Histological examination of the brain and spinal cord revealed moderate to severe subacute, nonsuppurative encephalomyelitis. Sections of spinal cord stained positively in immunohistochemistry with a flavivirus-specific monoclonal antibody. Reverse transcription polymerase chain reaction assay targeting the envelope gene of flavivirus yielded positive results from brain, spinal cord, cerebrospinal fluid, and facial nerve. A flavivirus was isolated from the cerebrum and spinal cord. Nucleotide sequences obtained from amplicons from both tissues and virus isolated in cell culture were compared with those in GenBank and had 96-98% identity with Murray Valley encephalitis virus. The partial envelope gene sequence of the viral isolate clustered into genotype 1 and was most closely related to a previous Queensland isolate.

Controlled exposure as a management tool for Glasser's disease.

In this study, nasal swabs taken from multiparous sows at weaning time or from sick pigs displaying symptoms of Glasser's disease from farms in Australia [date not given] were cultured and analysed by polymerase chain reaction (PCR). Within each genotype detected on a farm, representative isolates were serotyped by gel diffusion (GD) testing or indirect haemagglutination (IHA) test. Isolates which did not react in any of the tests were regarded as non-typable and were termed serovar NT. Serovars 1, 5, 12, 13 and 14 were classified as highly pathogenic; serovars 2, 4 and 15 being moderately pathogenic; serovar 8 being slightly pathogenic and serovars 3, 6, 7, 9 and 11 being non-pathogenic. Sows were inoculated with the strain of Haemophilus parasuis (serovars 4, 6 and 9 from Farms 1, 2 and 4, respectively) used for controlled challenge 3 and 5 weeks before farrowing. Before farrowing the sows were divided into control and treatment groups. Five to seven days after birth, the piglets of the treatment group were challenged with a strain from the farm which had were used to vaccinate the sows. The effectiveness of the controlled exposure was evaluated by number of piglets displaying clinical signs possibly related to infection, number of antibiotic treatments and pig mortality. Nasal swabs of sick pigs were taken twice a week to find a correlation to infection. A subsample of pigs was weighed after leaving the weaning sheds. The specificity of a realtime PCR amplifying the infB gene was evaluated with 68 H. parasuis isolates and 36 strains of closely related species. 239 samples of DNA from tissues and fluids of 16 experimentally challenged animals were also tested with the realtime PCR, and the results compared with culture and a conventional PCR. The farm experiments showed that none of the controlled challenge pigs showed any signs of illness due to Glasser's disease, although the treatment groups required more antibiotics than the controls. A total of 556 H. parasuis isolates were genotyped, while 150 isolates were serotyped. H. parasuis was detected on 19 of 20 farms, including 2 farms with an extensive history of freedom from Glasser's disease. Isolates belonging to serovars regarded as potentially pathogenic were obtained from healthy pigs at weaning on 8 of the 10 farms with a history of Glasser's disease outbreaks. Sampling 213 sick pigs yielded 115 isolates, 99 of which belonged to serovars that were either potentially pathogenic or of unknown pathogenicity. Only 16 isolates from these sick pigs were of a serovar known to be non-pathogenic. Healthy pigs also had H. parasuis, even on farms free of Glasser's disease. The realtime PCR gave positive results for all 68 H. parasuis isolates and negative results for all 36 non-target bacteria. When used on the clinical material from experimental infections, the realtime PCR produced significantly more positive results than the conventional PCR (165 compared to 86).