Evidence of high EEHV antibody seroprevalence and spatial variation among captive Asian elephants (Elephas maximus) in Thailand

Abstract

BackgroundElephant endotheliotropic herpesviruses (EEHV) can cause an acute highly fatal hemorrhagic disease in young Asian elephants (Elephas maximus), both ex situ and in situ. Amongst eight EEHV types described so far, type 1 (subtype 1A and 1B) is the predominant disease-associated type. Little is known about routes of infection and pathogenesis of EEHV, and knowledge of disease prevalence, especially in range countries, is limited.MethodsA large cross-sectional serological survey was conducted in captive elephants (n = 994) throughout Thailand using an EEHV-1A glycoprotein B protein antigen specific antibody ELISA.ResultsAntibody seroprevalence was 42.3%, with 420 of 994 elephants testing positive. Associations between seropositivity and potential risk factors for EEHV infection were assessed and included: elephant age, sex, camp cluster size, management type (extensive versus intensive), sampling period (wet vs. dry season) and location of camp (region). Univariable regression analysis identified management system and region as risk factors for the presence of EEHV antibodies in elephants, with region being significant in the final multivariable regression model. Prevalence was highest in the North region of the country (49.4%).ConclusionsThis study produced baseline serological data for captive elephants throughout Thailand, and showed a significant EEHV burden likely to be maintained in the captive population.Electronic supplementary materialThe online version of this article (10.1186/s12985-019-1142-8) contains supplementary material, which is available to authorized users.

Lethal Hemorrhagic Disease and Clinical Illness Associated with Elephant Endotheliotropic Herpesvirus 1 Are Caused by Primary Infection: Implications for the Detection of Diagnostic Proteins

“…Previous studies relied on an EEHV gB ELISA to show that 80% of elephants in North America and Europe and 42% within a large group of elephants tested in Thailand were seropositive for EEHV infection (8,9). In our study, in contrast, 100% of healthy adult elephants had evidence of prior EEHV infection.…”

“…The results showed that as many as 80% of elephants tested in North American and European zoos were EEHV seropositive. A follow-up study using the same assay determined a seroprevalence of 42.3% among captive Asian elephants in Thailand (9). Because gB is relatively well conserved, the possibility that serologic responses detected against the protein can distinguish among infections with the different EEHVs endemic within Asian elephant populations appears remote.…”

Elephant Endotheliotropic Herpesvirus Is Omnipresent in Elephants in European Zoos and an Asian Elephant Range Country

“…Van den Doel et al, (2015) designed an EEHV-specific ELISA with E. coli -expressed EEHV1A glycoprotein B (gB) as the antigen [ 12 ]. This assay has been used to test two large cohorts of elephant sera and showed that 37% of elephants from Western zoos [ 12 ] and 42% of captive elephants in Thailand [ 13 ] were seropositive for EEHV. Although it was shown that EEHV infections were relatively wide-spread, 24% of the elephants with PCR-confirmed EEHV infection were designated EEHV seronegative in this assay [ 12 ], indicating that this assay probably underestimates EEHV seropositivity.…”

Elephant endotheliotropic herpesvirus is omnipresent in elephants in European zoos and an Asian elephant range country

“…In 2015, Van den Doel and coworkers showed that 37% of the European zoo elephants tested (N=125) were seropositive to EEHV (12), while in 2019 Angkawanish and coworkers reported that 42% of 994 Thai elephants living under human care were EEHV seropositive (13). Both serosurveys used the 'bacterial' gB ELISA, of which this study showed that it underestimates EEHV seropositivity as compared to the novel ELISAs (Fig.…”