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THE purpose of this letter is to draw urgent attention to a case of fatal haemorrhagic disease attributable to elephant endotheliotropic herpesvirus type 5 (EEHV-5) infection in a captive Asian elephant (Elephas maximus), as a prelude to more detailed reports of the clinical and pathological findings (in preparation).
The affected animal was a 20-month-old captive-bred Asian elephant born and living at a collection in the UK within a herd of four adult female Asian elephants. It developed a rapidly progressive disease characterised by severe oedema, haemorrhage of mucosal membranes and cyanosis. Treatment followed protocols for extensive antiviral and supportive therapy and included drainage of the pericardial effusion under ultrasonographic guidance. Despite all efforts, the health of the animal deteriorated necessitating euthanasia. Postmortem findings were consistent with previously reported fatal cases of EEHV, revealing marked oedema and multiorgan haemorrhages (Fig 1). Histologically, typical intraendothelial herpesviral inclusion bodies were present in the heart, liver, adrenal glands and lung, consistent with a diagnosis of acute EEHV infection.
The presence of the EEHV-5 nucleic acid was initially detected at the AHVLA – Weybridge, using both published and unpublished PCR methods, and results were additionally confirmed by the National Elephant Herpesvirus Laboratory (Latimer and others 2011). Both laboratories sequenced several gene fragments that were consistent with those of EEHV-5 (Latimer and others 2011). All samples tested negative for EEHV-1 using a realtime TaqMan PCR, a realtime PCR using Sybr Green and a conventional nested EEHV-1 PCR (Stanton and others 2010, Latimer and others 2011, Hardman and others 2012).
Herpesviruses in elephants were first described in 1971 in pulmonary nodules of African elephants (Loxodonta africana) (McCully and others 1971). In 1995, further molecular work placed these viruses in the Betaherpesvirinae subfamily (Richman and others 1999). To date, seven distinct elephant endotheliotropic betaherpesviruses (EEHVs) and six further elephant gammaherpesviruses (EGHVs) have been detected and characterised (Wellehan and others 2008, Latimer and others 2011). Acute disease attributable to EEHV has become a serious threat to the sustainability of captive and wild elephant populations worldwide and retrospective studies suggest that, so far, more than 80 confirmed cases of EEHV fatalities have occurred worldwide (Reid and others 2006, Latimer and others 2011). EEHV-1 is the most commonly detected subtype in Asian elephants with mortality of 85 per cent, but studies to date have revealed that EEHV-2, -3 and -4 may also result in fatal haemorrhagic disease in African (EEHV-2) (Richman and others 1999) and Asian elephants (EEHV-3 and -4) (Garner and others 2009, Latimer and others 2011). Until now, all cases confirmed within UK collections were attributable to EEHV-1 strains. To the authors' knowledge, there has previously been no evidence of EEHV-5 having been associated with fatality in either elephant species worldwide.⇓
EEHV-5 was first detected in a 59-year-old wild-born female Asian elephant in 2007 during routine examination of whole blood and a recent case report describes sequential EEHV-5 infections of Asian elephants within a zoo herd in the USA. None of the affected animals presented with serious disease (Latimer and others 2011, Atkins and others 2012). To date, EEHV-5 has not been detected in any of the other elephants housed with the group of the current case.
In the absence of effective treatment or vaccination, further EEHV fatalities in elephants will occur both in captivity and in the wild. Coordinated efforts between zoo stakeholders, government bodies and charitable funding bodies will be required to fund research in order to establish effective control measures and to develop a vaccine. EEHV-5 must be added to the list of known EEHV subtypes capable of causing fatal disease, and thus be included in diagnostic testing of individual fatalities, routine screening and epidemiological studies of captive elephant populations as a whole.
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