Importance of Serology in EEHV Surveillance and Case Management, Updated July 2025

Calves are born with maternal EEHV antibodies at levels that are equal to those found in the dam (Fuery et. al 2020, Nofs et al. 2013). In general, 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 in the presence of maternal antibodies have shown immune response to the virus without treatment or development of clinical disease (D’Agostino, personal communication). Seronegative calves that have survived EEHV HD have shown seroconversion after recovery. There are no reported cases of an elephant that survived EEHV HD getting sick again from the same EEHV type. There have been reported cases of elephants surviving EEHV HD from one EEHV type and later developing EEHV HD from a different EEHV type (EEHV Advisory Group, personal communication). This suggests that elephants likely develop lifelong immunity if primary infection results in appropriate immune response and seroconversion. However, immunity may not be cross protective between the various EEHV species and types.

Antibody testing is an important component of routine EEHV surveillance for at risk elephants. It is recommended that all elephants have a baseline serologic profile. At risk calves should have more frequent serology performed starting at birth and continuing every 6 months. The decision to discontinue regular serologic testing for an individual is at the discretion of the attending veterinarian and may be considered if an individual has successfully mounted an immune response to the EEHV species of concern through primary infection.

Serum testing for antibody status is performed through the EEHV Serology Testing Service at Baylor College of Medicine (Baylor College of Medicine EEHV Serology Testing Service). Specific test available include:

Using serology results in an EEHV response plan

Serostatus of an at-risk calf should be a factor in the institutional EEHV response plan. Serostatus, in conjunction with real time data on shedding activity in the herd can be incredibly beneficial in directing appropriate adjustments to at-risk calf monitoring, ensuring early identification of viremia, and treatment initiation decisions. Each institution should develop a plan for EEHV response based on routine surveillance results (see Routine Monitoring). The following are guidelines for the use of serology data in making EEHV surveillance and treatment related decisions.

Individual seronegative to one or more types of EEHV

• Routine weekly or twice weekly blood qPCR testing.
• If active EEHV shedding is noted in the herd through trunk wash qPCR for an EEHV species or type of concern, consider increasing blood qPCR surveillance for at-risk individuals.
• If viremia is detected in an at-risk individual, increase blood qPCR monitoring to daily or every other day.
• Initiate therapy if viremia level exhibits a rapid and/or logarithmic increase.

Individual seropositive to one or more types of EEHV

• Routine weekly or twice weekly blood qPCR testing if indicated by institutional protocol for the individual.
• If active EEHV shedding is noted in the herd through trunk wash qPCR, determine if increased blood qPCR surveillance is necessary for at-risk individuals based on the species or type of EEHV being shed and the individual’s serologic status.
• If the individual is seropositive for that EEHV species/type, continue with routine surveillance.
• If the individual develops viremia, verify the EEHV species and/or type. If the individual is seropositive for that species/type consider increasing blood qPCR for a short period of time to ensure there is no rapid and/or logarithmic increase.
• If viremia levels remain stable without rapid increase, it is likely a recrudescence (see Managing Recrudescence). Consider return to routine surveillance protocol.
• If viremia shows a rapid or logarithmic increase, consider initiating therapy.

References
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.