Factsheets

EEHV Status in Thailand: The challenge of addressing the fatal disease in elephant conservation.

Information concerning EEHV

The historical background of EEHV

In 1988, a documented report recorded the demise of a juvenile Asian elephant in Switzerland as a result of Acute Hemorrhagic Disease. Following this, approximately 20 cases exhibiting similar symptoms were identified in other juvenile elephants across Europe and North America during the 1990s. Subsequently, in 1999, the first identification of the etiology was made in the United States of America, revealing a virus known as Elephant Endotheliotropic Herpesvirus (EEHV) as the causative agent.

In Thailand, the initial documentation of a juvenile Asian elephant’s demise due to symptoms associated with EEHV occurred in 2005. Five years thereafter, EEHV1A was discerned from cardiac tissue preserved through freezing. Subsequently, EEHV4 was detected in a three-year-old Asian elephant, marking the first such case reported in Asia and the second globally.

Know the causative agent 

Elephant Endotheliotropic Herpesvirus or EEHV, categorized within the Herpesviridae family, Betaherpesvirinae subfamily, Proboscivirus genus, and Elephantid betaherpesvirus species, is a double-stranded DNA virus responsible for acute, fatal hemorrhagic disease observed in both wild and captive juvenile (1 – 9 years old) Asian elephants (Elephas maximus) and African elephants (Loxodonta africana). This virus comprises eight genotypes, denoted as 1, 1A, 1B, 2, 3, 4, 5, and 6. Among these, EEHV 1, 1A, 1B, 3, 4, and 5 are identified in Asian species.

  • EEHV Strains affected African and Asian elephant

Transmission of EEHV 

EEHV primarily spreads through direct contact with the body fluids of infected elephants, including mucosal secretions such as saliva, breast milk, nasal secretions, vaginal secretions, shedding from skin lesions, and trunk-to-trunk contacts. There have been no reports of virus transmission via semen. The potential for indirect transmission through fomites remains uncertain. Importantly, EEHV is not transmissible to humans or other animals.

Clinical signs, symptoms, and post-mortem lesions

EEHV affects the circulatory system in elephants by damaging endothelial tissue. EEHV hemorrhagic disease (EEHV-HD) manifests as an acute, fatal disease occurring within 2 to 4 days, with mortality rates reaching up to 85% in elephants. Clinical indicators are primarily nonspecific, encompassing lethargy, selective appetite or complete anorexia, pyrexia, reduced trunk movement, lameness or stiffness of legs, abnormal sleeping pattern, and tachycardia. Commonly observed symptoms include edema of the head, neck, trunk, and thoracic limbs. Cyanosis of the tongue tip progressing caudally, tongue hemorrhage, and oral ulcers are frequently noted. Additionally, acute skin nodules may appear throughout the trunk. Mild gastrointestinal signs may be present, such as abdominal distension, colic pain, and mild diarrhea or constipation. Furthermore, neurological symptoms such as staggering gait, drowsiness, unresponsiveness to commands, and ataxia due to intracranial bleeding or cerebral hypoxia may ensue, potentially leading to death within 24 – 48 hours. EEHV4 primarily affects the gastrointestinal system, leading to diarrhea or bloody diarrhea. Co-infection of EEHV1A and EEHV4 has been reported. Post-mortem examination revealed extensive petechial and ecchymotic hemorrhages present in nearly all internal organs and tissues. Ulcerations are observed in the oral cavity, larynx, and large intestine, along with the presence of subacute myocarditis. Furthermore, histopathological analysis may reveal intranuclear inclusion bodies within the endothelial cell lining of visceral organs, particularly in the liver sinusoids and spleen.

Lesions from EEHV-infected elephant
Photo credit: Benjatham Thaitham

Diagnostic tools 

The initial diagnosis of EEHV relies on clinical signs and hematological parameters, particularly thrombocytopenia, which serves as a predictive marker for acute fatal EEHV-HD. Laboratory confirmation can be conducted through Polymerase Chain Reaction (PCR) detection. This method utilizes samples such as whole blood, feces, nasal/saliva/oral swabs, and frozen tissues from the heart, lung, spleen, liver, kidney, tongue, and intestine. Furthermore, serological analysis techniques such as Enzyme-Linked Immunosorbent Assay (ELISA) can be employed to identify elephants that have been exposed to the virus.

Prevention and control 

EEHV lacks a vaccination, and its treatment is contingent upon symptomatology. Elephants identified as carriers of EEHV typically do not require isolation from other elephants, as most elephants carry the virus without displaying symptoms. Furthermore, the majority of cases of EEHV-HD have been sporadic. To mitigate predisposing factors, it is advisable to avoid all forms of physical, emotional, and other stresses on the elephants. Strict healthcare and management protocols should be followed, including training younger calves to accept handling by the veterinary team for blood sample collection and drug administration. Additionally, close monitoring of behavioral changes should be implemented, coupled with periodic blood monitoring at intervals of 1 to 2 weeks. This protocol is necessitated by the ability of the virus to be detected in the bloodstream via PCR methodology, notably up to 10 – 14 days preceding the manifestation of outward symptoms indicative of EEHV-HD. Additionally, consistent oral administration of Vitamin C supplementation can be utilized to augment immune system functionality.

EEHV in Thailand

In Thailand, a number of cases of EEHV exhibiting symptoms have been documented by the ‘EEHV Task Force Thailand’, totaling 128 cases spanning from 2006 to 2023. These cases involved 85 fatalities and 43 instances of recovery, resulting in a mortality rate of 66.4%. The predominant genotype identified among these cases is EEHV1A. (updated 13th March, 2024)

Prompiram et al. (2021) conducted a study to investigate the occurrence of EEHV in both captive and wild Asian elephants in Thailand. Data collected and analyzed between 2000 and 2020 revealed an overall incidence of EEHV of 40.1% (n=65/162). Among deceased elephants, approximately 46.2% (n=12/26) tested positive for EEHV by PCR, while 85.7% (n=6/7) of sick elephants were similarly identified. Furthermore, 48.4% (n=44/91) of apparently healthy elephants demonstrated EEHV seropositivity (ELISA-positive), indicating prior infections. Notably, 30% (n=3/10) of deceased wild elephants were found to have been infected with EEHV. Statistical analysis showed no significant differences in EEHV detection rates across various age groups or sexes.

Conclusion

EEHV infection poses a significant threat to juvenile elephants and presents a formidable challenge to global elephant conservation efforts. Despite considerable research, several gaps in EEHV knowledge persist, including understanding its pathogenesis, identifying risk factors, elucidating transmission dynamics, refining diagnostic methods, advancing vaccine development, and exploring long-term immunity. To address these gaps effectively, collaborative research efforts involving virologists, immunologists, veterinarians, and elephant conservationists are essential. By collectively tackling these uncertainties, researchers can enhance EEHV prevention, diagnosis, and treatment strategies, ultimately improving the health and welfare of the endangered elephants both in captivity and in the wild.

The specific laboratory facilities in Thailand that specialize in EEHV (Elephant Endotheliotropic Herpesvirus) diagnosis

Central Region

  • The Monitoring and Surveillance Center for Zoonotic Diseases in Wildlife and Exotic Animals (MoZWE), Faculty of Veterinary Science, Mahidol University (PCR and ELISA for research project) 
  • Kamphaeng Saen Veterinary Diagnostic Center, Faculty of Veterinary Medicine, Kasetsart University 

Northern Region

Eastern Region 

Northeastern Region

Western Region 

Southern Region

References

Choenkwan Pabutta

The Monitoring and Surveillance Center
for Zoonotic Diseases in Wildlife and Exotic Animals (MoZWE)
Faculty of Veterinary Science, Mahidol University