Identifying and Managing Cases of EEHV Recrudescence, Updated July 2025

All elephants are considered latent carriers of elephant endotheliotropic herpesvirus (EEHV). Calves are born with maternal EEHV antibodies at levels that are equal to or exceed those found in the dam (Fuery et al. 2020, Nofs et al. 2013). Maternal antibodies start to wane around 18 months of age and may reach undetectable levels around 36 months of age. Absence of maternal antibodies at the time of primary infection is correlated with development of elephant endotheliotropic herpesvirus hemorrhagic disease (EEHV HD) (Fuery et al. 2020). Calves that have had a primary EEHV infection before maternal antibodies wane have shown immune response to the virus without treatment or development of clinical disease (D’Agostino, personal communication).

After a primary infection with an EEHV species, the virus remains latent in the body with periodic recrudescence as evidenced by intermittent low-level viremia and viral shedding in trunk wash secretions (Stanton et al., 2010). Animals that are exhibiting a recrudescent viremia and viral shedding may be a source of exposure to at-risk individuals but generally do not experience clinical disease. Blood viral levels reaching up to 25,000 vge/ml have been detected in calves experiencing recrudescent episodes without clinical disease (D’Agostino, personal communication; Molter, personal communication) or up to 80,000 vge/ml with mild clinical disease (Latimer, personal communication). Changes in CBC may be seen with a recrudescence indicative of positive immune response (leukocytosis, thrombocytosis).

Identification of a Recrudescent Case

• Review prior serology results to determine individual antibody status.
• Review prior surveillance results (whole blood PCR, trunk wash PCR) to determine infection/exposure status.
• If an individual has shown prior viremia or trunk wash shedding to the specific species of EEHV, the incident is likely a recrudescence and not a primary infection.

Guidelines for management of a recrudescent viremia

• Verify prior exposure and immunity status.
• Increase whole blood PCR and CBC monitoring (eg. every 2-3 days) along with examination for clinical signs of illness.
• If viral levels rise exponentially or there are CBC changes consistent with disease (e.g. monocytopenia, thrombocytopenia), consider initiating treatment.
• If viral levels stabilize, and if CBC changes remain normal or indicative of positive immune response, continue to monitor and return to routine surveillance.
• Viral levels may remain present in the blood for weeks to months.

References:
Bauer, Kendra L., Erin Latimer, and Mitch Finnegan. “Long-term, intermittent, low-level elephant endotheliotropic herpesvirus 1A viremia in a captive Asian elephant calf.” Journal of Veterinary Diagnostic Investigation 30.6 (2018): 917-919.

Fuery, Angela, et al. “Lethal hemorrhagic disease and clinical illness associated with elephant endotheliotropic herpesvirus 1 are caused by primary infection: Implications for the detection of diagnostic proteins.” Journal of virology 94.3 (2020): 10-1128.

Nofs, Sally A., et al. “Prenatal passive transfer of maternal immunity in Asian elephants (Elephas maximus).” Veterinary immunology and immunopathology 153.3-4 (2013): 308-311.

Stanton, Jeffrey J., et al. “Detection of pathogenic elephant endotheliotropic herpesvirus in routine trunk washes from healthy adult Asian elephants (Elephas maximus) by use of a realtime quantitative polymerase chain reaction assay.” American journal of veterinary research 71.8 (2010): 925-933.