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Equine rhinitis B virus (ERBV), genus Erbovirus, family Picornaviridae occurs as two serotypes, ERBV1 and ERBV2. An ERBV-specific nested reverse transcriptase-polymerase chain reaction (RT-PCR) that amplified a product within the 3D(pol) and 3' non-translated region of the viral genome was developed. The RT-PCR detected all 24 available ERBV1 isolates and one available ERBV2 isolate. The limit of detection for the prototype strain ERBV1.1436/71 was 0.1 50% tissue culture infectious doses. The RT-PCR was used to detect viral RNA in six of 17 nasopharyngeal swab samples from horses that had clinical signs of acute febrile respiratory disease but from which ERBV was not initially isolated in cell culture. The sequences of these six ERBV RT-PCR positive samples had 93-96% nucleotide identity with six other partially sequenced ERBV1 isolates and one ERBV2. ERBV was isolated from one of the six samples at fourth cell culture passage when it was shown that the addition of 20 mg/mL MgCl(2) to the cell culture medium enhanced the growth of the virus. This isolated virus was antigenically similar to ERBV2.313/75. Determination of the nucleotide sequence of the P1 region of the genome also indicated that the isolate was ERBV2, and it was therefore designated ERBV2.1576/99. This is the first reported isolation of ERBV in Australia. The study highlights the utility of PCR for the identification of viruses in clinical samples that may initially be considered negative by conventional cell culture isolation.

The restriction endonuclease DNA fingerprints of 57 isolates of equine herpesvirus 1 (EHV1; equine abortion virus) from abortion, perinatal foal mortalities and encephalitis from 15 epidemics that occurred in Australasia between 1975 and 1989 were examined using the enzymes Bam HI, EcoRI and Bgl II. There was a remarkable degree of uniformity in the restriction patterns; mobility differences were observed in only 14 of 52 (27%) of the fragments. Twelve of these 14 fragments were located within the repeat structures that bracket the unique short region of the genome or were located at the left terminus of the 150 kilobase pair genome. Based on the Bam HI fingerprints the commonest virus identified in our study was EHV1.IP (P is for prototype strain). There was a single notable exception in that the Bam HI fingerprints of all 8 isolates from one of 3 Victorian farms that experienced abortion in 1989 resembled a variant EHV1.IB that was identified as a cause of abortion in Central Kentucky in 1970 to 1974. We present evidence that EHV1.IB caused abortion in California in 1964 and has remained unaltered in its Bam HI restriction pattern. No antigenic differences were found among 4 distantly related EHV1 isolates, including the variant IB, using a panel of 5 monoclonal antibodies to glycoprotein C (gC), a glycoprotein recognised to be highly variable. The uniformity of these unrelated EHV1 isolates is further evidence for a recent origin for EHV1 and may help to explain the natural history of this virus in the horse in which it seems to be a cause of serious epidemics of abortion and perinatal mortality, and less commonly of encephalitis.

Representative strains of EHV isolated from an aborted foetus and from a horse with rhinopneumonitis in New Zealand had restriction endonuclease DNA fingerprints typical of those usually associated with these syndromes elsewhere and now designated EHV1 and 4 respectively. EHV1 was isolated from the brain and spinal cord of a 4-year-old gelding that died of myeloencephalitis. A mare on the same farm, at about the same time as the gelding developed myeloencephalitis, aborted and EHV1 was isolated from the tissues of the aborted foetus. Restriction endonuclease DNA fingerprints of the viruses isolated from myeloencephalitis and abortion were indistinguishable by Bam HI but were distinguishable using Bgl I, Pvu II, Xho I and Hind III. The restriction endonuclease DNA fingerprints of 3 EHV1 strains known to cause myeloencephalitis were compared with each other and with EHV1 strains not known to be associated with myeloencephalitis. The Bgl I Pvu II and Hind III DNA fingerprints of the 3 myeloencephalogenic strains appear distinguishable from non-myeloencephalogenic strains. Abortion was induced in a mare by intrauterine inoculation of EHV4. The Bam HI, Bgl I, Pvu II, Xho I and Hind III restriction endonuclease DNA fingerprints of the inoculum virus were indistinguishable from virus recovered from the foetus. It was concluded that passage of the virus through the foetus did not detectably alter the restriction endonuclease DNA fingerprint.

Lesions, grossly and histologically typical of pox infection, occurred in a white-backed magpie from Melbourne, Australia. Electron microscopic examination revealed typical poxvirus particles in lesion material. The disease was experimentally transmitted to other magpies, but chickens, turkeys, pigeons, and canaries were refractory to experimental infection with magpie poxvirus. The epidemiology of magpie pox and the probable occurrence of pox-like disease in other native Australian birds are discussed.