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Doctoral thesis, 2000

Differential diagnosis and aspects on epidemiology and pathogenesis of equine herpesviruses

Nordengrahn, Ann;

Abstract

Herpesviruses constitute a family of DNA viruses found in virtually all animal species. In horse five herpesviruses have been identified namely Equine herpesvirus (EHV) type 1, 3 and 4 belonging to the subfamily alphaherpesvirinae and Equine herpesvirus type 2 and 5 belonging to the gammaherpesvirinae. EHV-1 and 4 are the major causes of abortion and respiratory disease respectively and both cause large economical losses. EHV-2 has been associated with respiratory disease, immunosuppression and is a predisposing factor for more severe secondary infections. EHV-5 is a new virus first isolated in Australia from horses suffering from upper respiratory disease. This thesis is dealing with the diagnosis, epidemiology and pathogenesis ofEHV-1,2,4 and 5.

EHV-2 is a predisposing factor for bacterial infection particularly with Rhodococcus equi and this role was studied by vaccination of foals with an EHV-2 subunit (ISCOM) vaccine. Foals vaccinated twice developed neutralising antibodies and were protected against the pneumonia while the non-vaccinated control group developed respiratory disease including pneumonia with abscesses containing R.equi which in some cases was fatal. Natural infection induce neutralising EHV-2 antibody as detected by a blocking ELISA. This ELISA recorded a much higher number of seropositive horses in a stable with annual EHV-2/R.equi infections compared to a stable with no such problems. Thus, the blocking ELISA was found to be a reliable tool for detecting recent EHV-2 infections. Likewise antibodies induced by a newly acquired EHV-2 infection in foals were also detected by the blocking ELISA and all foals tested were found to have experienced an EHV-2 infection by the age of 4 to 6 months.

The prevalence of EHV-2 and EHV-5 were studied by type-specific Polymerase chain reaction (PCR). Up to 68% of tested horses in Sweden were EHV-2 positive, i.e. had virus DNA in peripheral blood leukocytes, while 100% ofthe tested foals in Sweden and Hungary were positive before 2 to 8 months of age. No EHV-5 positive horses were found in Sweden while 4 out of 27 tested foals in Hungary had EHV-5 specific DNA by the age of 13 to 23 weeks showing that EHV-5 cause infections later in life.

Convalescent sera from horses contain EHV-l/EHV-4 cross-reactive antibody which up to recently made differentiation virtually impossible. A new indirect ELISA that differentiate between the two virus types showed that the epidemiology between EHV-1 and EHV-4 differ considerably. While almost 100% of the horses were seropositive to EHV-4, the number of EHV-1 seropositive horses varied between 9 and 56 % in different stables. Most foals had maternally-derived antibodies to EHV-4 until 4 to 6 months of age, after which they all became infected with EHV-4 and seroconverted. Only 2 out of 48 foals had maternal antibodies to EHV-1 and very few became infected.

Keywords

EHV-1, -2, -4, -5; differential diagnosis; R. equi; ISCOM; ELISA; PCR

Published in

Acta Universitatis Agriculturae Sueciae. Veterinaria

2000, number: 72
ISBN: 91-576- 5914-1
Publisher: Swedish University of Agricultural Sciences

Authors' information

Nordengrahn, Ann
Swedish University of Agricultural Sciences, Department of Veterinary Microbiology
Nordengrahn, Ann
National Veterinary Institute (SVA)

UKÄ Subject classification

Clinical Science

URI (permanent link to this page)

https://res.slu.se/id/publ/117471