M. J. Studdert

The order Herpesvirales

The taxonomy of herpesviruses has been updated by the International Committee on Taxonomy of Viruses (ICTV). The former family Herpesviridae has been split into three families, which have been incorporated into the new order Herpesvirales. The revised family Herpesviridae retains the mammal, bird and reptile viruses, the new family Alloherpesviridae incorporates the fish and frog viruses, and the new family Malacoherpesviridae contains a bivalve virus. Three new genera have been created in the family Herpesviridae, namely Proboscivirus in the subfamily Betaherpesvirinae and Macavirus and Percavirus in the subfamily Gammaherpesvirinae. These genera have been formed by the transfer of species from established genera and the erection of new species, and other new species have been added to some of the established genera. In addition, the names of some nonhuman primate virus species have been changed. The family Alloherpesviridae has been populated by transfer of the genus Ictalurivirus and addition of the new species Cyprinid herpesvirus 3. The family Malacoherpesviridae incorporates the new genus Ostreavirus containing the new species Ostreid herpesvirus 1.

Equine Herpesviruses 4 (Equine Rhinopneumonitis Virus) and 1 (Equine Abortion Virus)

Publisher Summary The horse (Equus caballus) is unusual, in that it is host to three distinct alphaherpes viruses, designated as equine herpesvirus 1 (EHV1; equine abortion virus), EHV4 (equine rhinopneumonitis virus), and EHV3 (equine coital exanthema virus). EHV4 and EHVl are closely related viruses that, prior to 1981, were considered a single virus type or subtypes of a single virus. There was an assumption that this single virus, “EHV1,” caused an acute respiratory tract disease called “rhinopneumonitis,”which established a latent infection and then, as an unpredictable sequel in the case of a pregnant mare, underwent reactivation followed by viremic spread to the fetus, causing abortion. This chapter is concerned primarily with EHV4 and EHV1, with brief consideration of AHV3, highlighting its relationship to EHV1. Earlier, the reviews of “EHV1” may be consulted for a historic perspective and earlier references. However, each of these reviews carries ambiguities related to a belief that only a single virus type “EHV1,” rather than two distinct viruses, was involved. This chapter mainly focuses on the advances in our understanding of the molecular biology, including genetic and antigenic characteristics, of EHV4 and EHVl since 1981. A brief overview of the clinical syndromes and pathogenesis, epidemiology, laboratory diagnosis, vaccines, and immunity of EHV4 and EHVl is also given in this chapter.

A type-specific serological test to distinguish antibodies to equine herpesviruses 4 and 1.

SummaryWe describe a type-specific ELISA, which distinguishes antibody to equine herpesvirus 4 (EHV4; equine rhinopneumonitis) and EHV1 (equine abortion virus) thereby identifying horses that have been infected with either or both of these antigenically related viruses. The antigens used are parts of the EHV4 and EHV1 glycoprotein G (gG) homologues expressed inE. coli as fusion proteins [Crabb and Studdert, 1993: J Virol 67: 6332–6338). The expressed proteins comprise corresponding regions of the gG molecules that are highly divergent and encompass strong, typespecific epitopes. Plasma samples from 97 Thoroughbred and 174 Standardbred horses were tested, all of which were unvaccinated. All horses were strongly EHV4 ELISA positive while 30% were EHV1 ELISA positive. The type-specificity of the EHV1 gG antigen was tested in cross-absorption experiments and it was found that 96% (66 of 69) of EHV1 ELISA positive horses were true EHV1 antibody positives. It was also shown that 100% (26 of 26) horses known to have been exposed to EHV1, either by infection or immunisation with EHV1, had significant levels of antibody against the EHV1 gG antigen (i.e., all horses recognised the EHV1 epitope(s) contained within this molecule). Maintenance of EHV1 gG antibody was examined by testing sera obtained from mares four years after confirmed EHV1 abortion. Seven out of 10 of these mares remained EHV1 ELISA positive. In summary, the ELISA is highly specific and is sufficiently sensitive to detect all horses previously infected with EHV4 and most previously infected with EHV1.

Epidemiological studies of equine herpesvirus 1 (EHV-1) in Thoroughbred foals: a review of studies conducted in the Hunter Valley of New South Wales between 1995 and 1997

Sero-epidemiological studies conducted between 1995 and 1997 on two large Thoroughbred stud farms in the Hunter Valley of NSW showed clear evidence of EHV-1 infection in foals as young as 30 days of age. Similarly, serological evidence suggested that these foals were infected with EHV-1 from their dams or from other lactating mares in the group, with subsequent foal to foal spread of infection prior to weaning. These studies also provided evidence of EHV-1 infection of foals at and subsequent to weaning, with foal to foal spread of EHV-1 amongst the weanlings. These data indicated that the mare and foal population was a reservoir of EHV-1, from which new cases of infection propagated through the foal population both before and after weaning. The results of these studies support the long standing management practices of separating pregnant mares from other groups of horses to reduce the incidence of EHV-1 abortion. Also, these results have important implications for currently recommended vaccination regimens, as the efficacy of vaccination in already latently infected horses is unknown.

Genomic Heterogeneity of Equine Betaherpesviruses

The genomes of 51 isolates of slowly cytopathic equine herpesviruses were examined by digestion with restriction endonucleases. Forty-seven of the isolates showed considerable fragment pattern heterogeneity although common fragments were evident, especially when any two isolates were compared or when they were digested with SalI. Fifteen of the 47 viruses, selected for their diverse fragment patterns, showed a high degree of homology in Southern blot hybridization. In contrast, four viruses, representing three epidemiologically distinct isolations, shared few, if any, comigrating fragments with the 47 equine herpesvirus 2 (EHV-2) isolates, although they shared comigrating fragments with each other. These four viruses showed reduced homology to a representative EHV-2 isolate by Southern blot hybridization under stringent conditions. Although not sharply delineated from EHV-2, these four viruses grew very slowly and had low yields in vitro, and preliminary data suggested they had a significantly smaller genome than EHV-2 (148 +/- 12 kb compared to 190 kb). These four viruses may be prototypic of a novel equine betaherpesvirus.

Epidemiology of EHV-1 and EHV-4 in the mare and foal populations on a Hunter Valley stud farm: are mares the source of EHV-1 for unweaned foals.

The prevalence of EHV-1 and EHV-4 antibody-positive horses was determined using a type specific ELISA on serum samples collected from 229 mares and their foals resident on a large Thoroughbred stud farm in the Hunter Valley of New South Wales in February 1995. More than 99% of all mares and foals tested were EHV-4 antibody positive, while the prevalence of EHV-1 antibody positive mares and foals were 26.2 and 11.4%, respectively. Examination of the ELISA absorbance data for the individual mares and foals suggested that the EHV-1 antibody positive foals had been infected recently with EHV-1 and that a sub-group of the mare population was the likely source of infectious virus for the unweaned foals.

Viruses and virus-like particles in the faeces of dogs with and without diarrhoea.

SUMMARY Negative staining electron microscopy was used to identify viruses in 157 normal and 29 diarrhoeal faecal samples collected from 156 dogs admitted to an animal shelter during an 8 month period (March to October) in 1982. Seven distinct viral types were detected: 21–26 nm parvovirus‐like particles, 28–31 nm astrovirus‐like particles, a previously undescribed 34–35 nm ‘round’ virus particle, coronavirus, coronavirus‐like particles (CVLP), rotavirus and papova‐like virus. Parvovirus‐like particles alone were detected in 14 diarrhoeal and 50 normal faeces, astrovirus‐like particles in 3 normal faeces, “round” viruses in 4 normal faeces, coronavirus in 2 diarhoeal and 5 normal faeces, CVLP in one diarrhoeal and one normal faeces, rotavirus in 2 normal faeces, papova‐like virus in one normal faeces, both parvovirus‐like particles and coronavirus in 2 diarrhoeal and 2 normal faeces, parvovirus‐like particles and rotavirus in one normal faeces and parvovirus‐like and papova‐like virus in one normal faeces. The significance of these findings in canine and human disease is discussed.

Equine respiratory viruses in foals in New Zealand

Abstract AIMS: To identify the respiratory viruses that are present among foals in New Zealand and to establish the age at which foals first become infected with these viruses. METHODS: Foals were recruited to the study in October/November 1995 at the age of 1 month (Group A) or in March/April 1996 at the age of 4–6 months (Groups B and C). Nasal swabs and blood samples were collected at monthly intervals. Nasal swabs and peripheral blood leucocytes (PBL) harvested from heparinised blood samples were used for virus isolation; serum harvested from whole-blood samples was used for serological testing for the presence of antibodies against equine herpesvirus (EHV)-1 or -4, equine rhinitis-A virus (ERAV), equine rhinitis-B virus (ERBV), equine adenovirus 1 (EAdV-1), equine arteritis virus (EAV), reovirus 3 and parainfluenza virus type 3 (PIV3). Twelve foals were sampled until December 1996; the remaining 19 foals were lost from the study at various times prior to this date. RESULTS: The only viruses isolated were EHV-2 and EHV-5. EHV-2 was isolated from 155/157 PBL samples collected during the period of study and from 40/172 nasal swabs collected from 18 foals. All isolations from nasal swabs, except one, were made over a period of 2–4 months from January to April (Group A), March to April (Group B) or May to July (Group C). EHV-5 was isolated from either PBL, nasal swabs, or both, from 15 foals on 32 occasions. All foals were positive for antibodies to EHV-1 or EHV-4, as tested by serum neutralisation (SN), on at least one sampling occasion and all but one were positive for EHV-1 antibodies measured by enzyme-linked immunosorbent assay (ELISA) on at least one sampling occasion. Recent EHV-1 infection was evident at least once during the period of study in 18/23 (78%) foals for which at least two samples were collected. SN antibodies to ERBV were evident in 19/23 (83%) foals on at least one sampling occasion and 15/23 foals showed evidence of seroconversion to ERBV. Antibodies to ERAV were only detected in serum samples collected from foals in Group A and probably represented maternally-derived antibodies. Haemagglutination inhibition (HI) antibody titres ≥1:10 to EAdV-1were evident in 21/23 (91%) foals on at least one sampling occasion and 16/23 foals showed serological evidence of recent EAdV-1 infection. None of the 67 serum samples tested were positive for antibodies to EAV, reovirus 3 or PIV3. There was no clear association between infection with any of the viruses isolated or tested for and the presence of overt clinical signs of respiratory disease. CONCLUSIONS: There was serological and/or virological evidence that EHV-1, EHV-2, EHV-5, EAdV-1 and ERBV infections were present among foals in New Zealand. EHV-2 infection was first detected in foals as young as 3 months of age. The isolation of EHV-2 from nasal swabs preceded serological evidence of infection with other respiratory viruses, suggesting that EHV-2 may predispose foals to other viral infections.

Outbreak of equine herpesvirus type 1 myeloencephalitis: new insights from virus identification by PCR and the application of an EHV-1-specific antibody detection ELISA.

Five of 10 pregnant, lactating mares, each with a foal at foot, developed neurological disease. Three of them became recumbent, developed complications and were euthanased; of the two that survived, one aborted an equine herpesvirus type 1 (EHV-1)-positive fetus 68 days after the first signs were observed in the index case and the other gave birth to a healthy foal on day 283 but remained ataxic and incontinent. The diagnosis of EHV-1 myeloencephalitis was supported by postmortem findings, PCR identification of the virus and by serological tests with an EHV-1 -specific ELISA. At the time of the index case, the 10 foals all had a heavy mucopurulent nasal discharge, and PCR and the ELISA were used to detect and monitor EHV-1 infection in them. The status of EHV-1 infection in the five in-contact mares was similarly monitored. Sera from three of the affected mares, taken seven days after the index case were negative or had borderline EHv-1 -specific antibody titres. In later serum samples there was an increase in the titres of EHv-1 -specific antibody in two of the affected mares. In contrast, sera from the five unaffected in-contact mares were all EHv-1 -antibody positive when they were first tested seven or 13 days after the index case.

Restriction endonuclease DNA fingerprinting of respiratory, foetal and perinatal foal isolates of equine herpesvirus type 1

SummaryDNA was prepared from 43 equine herpesvirus type 1 (EHV1) isolates, 11 of which were from horses with respiratory disease, 22 from aborted equine foetuses, and 10 from foals that died perinatally. The restriction endonuclease DNA fingerprints of 10 of the 11 respiratory isolates, known with certainty to have been recovered from horses with respiratory disease, were entirely different from all but 3 of the 32 foetal or perinatal foal isolates. The exceptional respiratory isolate, EHV1 Army 183, had a foetal (F) strain fingerprint but this virus cannot be said with certainty to have been isolated from the respiratory tract. The 3 exceptional foetal isolates, had respiratory (R) strain fingerprints, and were recovered from single sporadic abortions.There are no exceptions to the view that only R strains have been isolated from naturally occuring respiratory disease. Also it is clear that major epizootics of abortion (abortion storms) and of perinatal foal mortality are caused by F strains. The data together with an analysis of the epidemiological patterns, particularly in Australia, strongly support the view that F and R strains be regarded as separate species, EHV1 and 4 respectively.