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"Donaldson", a male Asian elephant calf at Whipsnade Zoo, died of EEHV in May 2009.[1]

Elephant endotheliotropic herpesvirus (EEHV) is a type of herpesvirus, native to African elephants, which can cause a highly fatal disease when transmitted in captivity to Asian elephants. In African elephants, the virus, which has been identified in wild populations, is generally benign, occasionally surfacing to cause small growths or lesions. When transmitted to Asian elephants, however, these strains can cause , which kills up to 90% of the affected individuals. The disease can be treated with the rapid application of antiviral drugs, but this is only effective in around a third of cases.

The first case of a fatal form of the disease was documented in 1995, though tissue samples from as early as the 1980s have since tested positive for the virus, and benign strains in wild African elephants were recorded in the 1970s. Since 1995, there have been fifty cases in North America and Europe, of which only six have been successfully cured. Those affected are mostly young animals born in captivity, though a small number of wild-born adults held in zoos have died, and a number of cases have recently been identified in Asia which may indicate a link with the wild population.

Contents

Virus and transmission

EEHV is a type of proboscivirus, a family of betaherpesviruses.[2] There are currently two known variants of the virus, EEHV1 and EEHV2 ; EEHV1 has two subtypes, a and b.[3]

EEHV1a (originally just known as EEHV1) was the first variant identified, which caused rapid death in Asian elephants.[4] It is believed to occur naturally in African elephants, and be transmitted to Asian elephants in captivity.[5] A subtype, EEHV1b, was identified in 2001.[6] EEHV1a is found in African elephants as well as Asian ones, whilst EEHV1b has not been identified outside of Asian elephants.[7]

EEHV2 is native to African elephants,[8] where it is found in the pulmonary system of wild animals.[9]

There are a further four varieties of elephantid herpesvirus - EIHV3, EIHV4, EIHV5 and EIHV6 - which are gamma herpesviruses, and not directly related to EEHV.[10]

The transmission method is unclear, though long-term contact between Asian and African elephants is now discouraged,[11] along with avoiding long-term contact between young captive-born Asian elephants and wild-born Asian elephants, as the latter may be carriers of the disease.[12] An analysis of a number of North American cases, which ruled out the direct transmission of the virus between any of the affected animals studied, strongly supported the idea of a significant Asian carrier population.[13] This is supported by the fact that some of the deceased calves had no possible contact with any African elephants.[14] Artificial insemination is not believed to be a transmission factor,[15] though some stillborn calves have tested positive for the virus, indicating it must be transmissible directly from the mother to the child in utero.[16] A program of enzyme-linked immunosorbent assay testing began in 2005, aiming to test blood samples from around a thousand elephants for antibodies to the virus in order to help identify carriers and possible transmission patterns.[17]

Effects and treatment

"Mac", seen here suckling from his mother when a month old, died in November 2008 of EEHV at the Houston Zoo.[18]

In a benign infection, such as that found in some African elephants, the virus can affect either the skin or the pulmonary system.[19] In the former case, it produces small pinkish nodules in the head and trunk, or small lymphoid patches around the genitals, which appear for a few weeks and then regress, suggesting an intermittently active infection which mostly remains dormant.[20] In the second case, it is found in pulmonary nodules.[21]

In a fatal attack, however, it manifests very quickly. In a number of cases, death has occurred within 24 hours of the onset of the infection,[22] while other cases do not last longer than around five days.[23] The virus attacks endothelial cells, rupturing capillaries and causing blood loss and haemorrhaging; once this reaches the heart, the haemorrhage kills quickly through shock. Symptoms include lethargy and an unwillingness to eat, a rapid heartbeat, and decreased blood-cell count, as well as cyanosis of the tongue, mouth ulcers, and oedema of the head and trunk.[24]

Rapid treatment with famciclovir, sustained for around a month, has cured six calves infected with EEHV1; however, this treatment is very expensive, only partially effective, and relies on early identification of the infection.[25]

A polymerase chain reaction test on a blood sample from affected animals will confirm a suspected case by identifying the viral DNA, though it is now common to start famciclovir treatment at the earliest possible moment rather than waiting for confirmation of the case.[26] Prior to the development of the test, or in circumstances where it is not available, the disease may be diagnosed as any of a number of other conditions which have a quick onset leading to rapid death, including encephalomyocarditis and salmonellosis.[27]

History

The virus has been identified in the pulmonary nodules of African elephants as far back as the 1970s.[28] The first recognised fatal case of EEHV in an Asian elephant was identified at the National Zoo, Washington D.C., in 1995; testing on stored tissue samples was able to identify a number of earlier deaths as being due to the same virus.[29] These cases have so far been identified as early as 1983.[30] Since this date, there have been a total of fifty cases in North America and Europe, six of which were successfully treated.[31] This gives a fatality rate of roughly 90% among known infections. In cases where antiviral medication was applied, treatment was effective in about one in three cases.[32] As a fraction of the overall population, it has been calculated that of the 78 Asian elephants born in captivity in North America between 1978 and 2007, 19 are known to have died of EEHV, and five more were successfully treated with antiviral medication.[33]

The affected animals are mostly young Asian elephants aged under 18 who had been born in captivity, though some cases have affected newborns or adult elephants born in the wild, and three recorded cases have affected African elephants.[34] In recent years, a number of cases have been attributed to EEHV1 among wild Asian elephants.[35]

The first suspected case in Asia was in 2005, though it was not until the fifth suspected case that the presence of the virus could be confirmed. This case was reported in 2006, with the death of a young wild-born female calf at an elephant sanctuary in Cambodia. The virus was identified as part of the EEHV1 group, the same as previously identified in the North American and European captive populations, but there was no plausible transmission path for the virus from those cases to Asia.[36] It is unclear if this infection reflects an endemic infection in the wild population, or if the other captive elephants in the sanctuary were carriers, and further research has been noted as "urgently required" to study the situation in regions with wild Asian elephant populations.[37]

Notes

  1. ^ Database entry at elephant.se
  2. ^ Koehl, 2009
  3. ^ Koehl, 2009, quotes "five or six" variants with 1 having two subtypes. Mikota, 2007, quotes three variants only, listing 1 and 3 as both having two subtypes. Cracknell, 2008, gives 1, 1b, 2, 3a, 3b and 4; note that EEHV1 is sometimes used as synonymous with EEHV1a. However, all but EEHV1 and EEHV2 are gammaherpesviruses, not betaherpesviruses, and so are not forms of EEHV.
  4. ^ Fickel et al, 2001
  5. ^ Ehlers et. al., 2006
  6. ^ Fickel et al, 2001.
  7. ^ Cracknell, 2008
  8. ^ Fickel et al, 2001, as reported by Cracknell, 2008
  9. ^ Koehl, 2009
  10. ^ Wellehan et. al., 2008; note that many of these are often given as being strains of EEHV.
  11. ^ Mikota, 2007.
  12. ^ Koehl, 2009
  13. ^ Koehl, 2009.
  14. ^ Mikota, 2007.
  15. ^ Koehl, 2009, notes that the three calves of a single elephant all died from distinct strains of the disease.
  16. ^ "Tracking an Elephant Killer", 2005
  17. ^ "Tracking an Elephant Killer", 2005.
  18. ^ Database entry at elephant.se
  19. ^ Mikota, 2007.
  20. ^ This is apparently an EEHV1a infection. Koehl, 2009
  21. ^ This is characteristic of EEHV2. Koehl, 2009
  22. ^ Koehl, 2009
  23. ^ Mikota, 2007.
  24. ^ Mikota, 2007.
  25. ^ Koehl, 2009
  26. ^ Koehl, 2009; "Tracking an Elephant Killer", 2005
  27. ^ Mikota, 2007.
  28. ^ Mikota, 2007.
  29. ^ "Tracking an Elephant Killer", 2005.
  30. ^ Koehl, 2009. Six fatal cases of the disease are identified from 1983 to 1994.
  31. ^ Koehl, 2009, quotes 49 cases, but does not include the May 2009 death of a calf at Whipsnade Zoo in this calculation.
  32. ^ "Tracking an Elephant Killer", 2005. As of 2005, there were twelve cases where famciclovir had been used, eight of which were fatal.
  33. ^ Koehl, 2009
  34. ^ Koehl, 2009. The two fatal cases Koehl lists for African elephants were Kijana, an eleven-month old male in 1996, and Gypsie, a twelve-year-old female in 1984.
  35. ^ Koehl, 2009
  36. ^ Reid et al, 2006
  37. ^ Koehl, 2009

References

  • Ehlers B., Dural G., Marschall M. (2006). "Endotheliotropic elephant herpesvirus, the first betaherpesvirus with a thymidine kinase gene". Journal of General Virology 87: 2781–2789.  doi:10.1099/vir.0.81977-0 PubMed:16963736
  • M. M. Garner, et al (2009). "Clinico-pathologic Features of Fatal Disease Attributed to New Variants of Endotheliotropic Herpesviruses in Two Asian Elephants (Elephas maximus)". Veterinary Pathology 46: 97–104.  PubMed:19112123
  • Fickel J, Richman LK, Montali R, Schaftenaar W, Göritz F, Hildebrandt TB, Pitra C (2001). "A variant of the endotheliotropic herpesvirus in Asian elephants (Elephas maximus) in European zoos.". Veterinary Microbiology 82 (2): 103–109.  PubMed:11423201 doi:doi:10.1016/S0378-1135(01)00363-7
  • Reid CE, Hildebrandt TB, Marx N, Hunt M, Thy N, Reynes JM, Schaftenaar W, Fickel J (2006). "Endotheliotropic elephant herpes virus (EEHV) infection. The first PCR-confirmed fatal case in Asia.". Veterinary Quarterly 28 (2): 61–64.  PubMed:16841568
  • James F.X. Wellehan; April J. Johnson; April L. Childressa; Kendal E. Harr; Ramiro Isaza (2008). "Six novel gammaherpesviruses of Afrotheria provide insight into the early divergence of the Gammaherpesvirinae". Veterinary Microbiology 127 (3-4): 249–257.  doi:10.1016/j.vetmic.2007.08.024 PubMed:17884307
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