Emerg Infect Dis. 2008 October; 14(10): 1616?1619.
doi: 10.3201/eid1410.080703.
PMCID: PMC2609862
New Hosts for Equine Herpesvirus 9
Mark D. Schrenzel,corresponding author Tammy A. Tucker, Taryn A. Donovan, Martin D.M. Busch, Annabel G. Wise, Roger K. Maes, and Matti Kiupel
Zoological Society of San Diego, Escondido, California, USA (M.D. Schrenzel, T.A. Tucker)
Animal Medical Center, New York, New York, USA (T.A. Donovan)
IDEXX Laboratories, Ludwigsburg, Germany (M.D.M. Busch)
Michigan State University, Lansing, Michigan, USA (A.G. Wise, R.K. Maes, M. Kiupel)
Abstract
Equine herpesvirus 9 was detected in a polar bear with progressive encephalitis; the source was traced to 2 members of a potential equid reservoir species, Grevy?s zebras. The virus was also found in an aborted Persian onager. Thus, the natural host range is extended to 6 species in 3 mammalian orders.
Keywords: equine herpesvirus-9, polar bear, Grevy?s zebra, Persian onager, inter-species, transmission, dispatch
Equine herpesvirus (EHV) 9, a varicellovirus in the subfamily Alphaherpesvirinae, is the newest member of the equine herpesviruses. EHV-9 is most closely related to the recently emergent neurotropic pathogen, EHV-1, but was first described in an outbreak of disease in Thomson?s gazelles (Gazella thomsoni) and subsequently in a giraffe (Giraffa camelopardalis reticulata) with encephalitis (1?3; M. Kiupel, pers. comm.). Initial findings of the virus? virulence and potential for transmission between equids and artiodactyls were alarming and provided the impetus for experimental studies, which showed that disease could be induced in members of an additional 8 mammalian taxa: dogs, cats, horses, mice, hamsters, pigs, goats, and marmosets (4?6).
Preliminary data suggest that equids are natural hosts of EHV-9 and experience little or no illness when infected. Seroconversion was detected in 60% of wild Burchell?s zebras (Equus burchelli) in Tanzania without any associated illness (3). When domestic horses (E. caballus) were infected by intranasal inoculation with 107 PFU of EHV-9, only mild disease developed and clinical signs were limited to transient fever (6). Natural coadaptation of EHV-9 and equids was corroborated by the severity of disease seen in nonequids: fulminant encephalitis with extensive neuronal necrosis in both spontaneous cases and experimental models (2?6). Antigenic and genetic similarities of EHV-9 with other equine herpesviruses are, likewise, consistent with the theory that equids are primary hosts. However, active infection has never been conclusively documented in any member of the Equidae (2?6).
The potential vulnerability of diverse species to EHV-9 has raised concern about the virus as an anthropozoonotic pathogen (2?6). Of additional note is the lack of known reservoir species and infectivity in nonlaboratory environments. We report natural EHV-9 infection and resultant disease in an ursid and 2 equid species, confirming the virus? promiscuity and pathogenicity and supporting its natural residence in wild equids.....
