Equine herpeviruses in zoo-dwelling zebras reactivated by stress, study finds

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A Grevy's zebra in dense bush. Photo: Jesse Hull CC BY 2.0 via Wikimedia Commons
A Grevy’s zebra in dense bush. Photo: Jesse Hull CC BY 2.0 via Wikimedia Commons

Environmental stressors appear to trigger reactivation of equine herpesviruses in wild equids, the findings of research suggest.

The study focused on the relocation of an endangered Grevy’s zebra over a distance of about 850km by road from a zoo in France to in one in Berlin.

There, the mare named Ekwe joined a resident group of three mares, Franzi, Kianga and Zawadi.

For the first four days after arrival in Berlin, Ekwe was kept in an enclosure separated by a wire fence from the enclosure of the resident mares.

From day 5, they shared an enclosure for the first time, but were separated again from day 10 for more than a fortnight to allow for additional feeding of roughage to Ekwe.

Based on a previous study, the three resident mares in Berlin were known to be latently infected with at least two EHV strains, EHV-1, and Equus zebra-Herpesvirus.

The EHV infection status of the new mare before translocation was unknown.

Peter Seeber and his colleagues assessed the frequency of sporadic EHV shedding in the zebras in Berlin daily for 14 days following the arrival of Ekwe, as well as two control periods before (comprising 25 days) and after, comprising 10 sample days up to 49 days after Ekwe’s arrival.

They also measured fecal glucocorticoid metabolite (fGCM) concentrations daily in all individuals from 6 days before, to 14 days after Ekwe’s arrival, to assess whether the animals were under stress.

The study team found significantly higher EHV shedding frequencies during the 14 days after the arrival of the mare, compared to each of the two control periods.

All animals showed significantly elevated fGCM concentrations, compared to levels recorded before the arrival of Ekwe.

“An increase in fGCM concentration was significantly associated with an increased likelihood of EHV shedding,” they reported in the open-access journal PeerJ.

“Although the small number of animals in the study limits the conclusions that can be drawn from the study, taken together, our results support the hypothesis that environmental stressors induce viral reactivation in wild equids.

“Our results suggest that potentials stressors such as group restructuring and translocation should be considered in the management of zoological collections to reduce the risk of fatal EHV infections in novel hosts.

“Moreover, environmental stressors may play an important role in EHV reactivation and spread in wild equid populations,” they wrote.

Equine herpesviruses are common pathogens among equids and are responsible for considerable economic losses.

Acute EHV infection can cause fever, nasal discharge, inflammation of the upper respiratory tract, degenerative neurological disease, conjunctivitis, pneumonia, and abortion.

EHVs can infect a wide range of host species other than equids, with novel hosts including Thomson’s gazelle, giraffe, llamas, alpacas, polar bears, brown bears and guinea pigs.

In these novel hosts, EHV infections are typically more severe than in equids and often fatal. Transmission of EHV occurs only during phases of acute viral replication when the virus is actively shed into the environment by its host.

However, all herpesviruses share the ability to establish latent infections which can last for the lifetime of their hosts.

The full study team comprised Peter Seeber​, Benoît Quintard, Florian Sicks, Martin Dehnhard, Alex Greenwood and Mathias Franz.

Seeber PA, Quintard B, Sicks F, Dehnhard M, Greenwood AD, Franz M. (2018) Environmental stressors may cause equine herpesvirus reactivation in captive Grévy’s zebras (Equus grevyi) PeerJ 6:e5422 https://doi.org/10.7717/peerj.5422

The study, published under a Creative Commons License, can be read here

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