Subclinical infection of captive Asian elephants (Elephas maximus) in Thailand with elephant endotheliotropic herpesvirus

Sripiboon, Supaphen; Ditcham, William; Vaughan-Higgins, Rebecca; Jackson, Bethany; Robertson, Ian D.; Thitaram, Chatchote; Angkawanish, Taweepoke; Phatthanakunanan, Sakuna; Lertwatcharasarakul, Preeda; Warren, K.

doi:10.1007/s00705-019-04469-6

Cited by 9 publications

(12 citation statements)

References 20 publications

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“…This is consistent with a previous study in Thailand, which used different antigens to survey the EEHV antibody and found an incidence of about 42% [13]. For PCR detection, the present study found infection in 1.2% of blood samples and 5.3% of trunk swabs, which were slightly higher rates than in a previous study that found 0.5% EEHV infection in blood samples [7]. Sample collection in the form of trunk swabs appeared to be more sensitive than that of blood, which is similar to findings in the previous studies that collected samples from trunk wash [8,10,11].…”

Section: Discussionsupporting

confidence: 92%

“…Positive samples were serum from elephants with a history of EEHV infection (PCR positive); they recently tested positive by ELISA in a previous study [13]. Negative samples were collected from elephants with no history of EEHV infection, which tested negative by both PCR and ELISA [6,7,13].…”

Section: Elisamentioning

confidence: 99%

“…The conventional method of diagnosing EEHV is by polymerase chain reaction (PCR) to detect viral DNA. Whole blood is commonly used to identify EEHV by PCR in living animals, while EEHV in dead animals is detected within visceral organs [6][7][8][9]. Routine monitoring of EEHV in elephant herds is important to detect preclinical viremia for early medical intervention and to identify carriers to prevent disease transmission.…”

Section: Introductionmentioning

confidence: 99%

“…Routine monitoring of EEHV in elephant herds is important to detect preclinical viremia for early medical intervention and to identify carriers to prevent disease transmission. From routine monitoring, the occurrence of EEHV in healthy elephants (carriers) was found to be between 1.78% and 5.5%, as detected by PCR using whole blood samples [6,7]. This suggests that PCR detection alone might not be sufficiently sensitive to detect EEHV infection due to its reliance on the viremia period to allow viruses to move out from host cells, and also require frequent monitoring.…”

Section: Introductionmentioning

confidence: 99%

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The occurrence of elephant endotheliotropic herpesvirus infection in wild and captive Asian elephants in Thailand: Investigation based on viral DNA and host antibody

et al. 2021

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Background and Aim: Elephant endotheliotropic herpesvirus (EEHV) is a serious disease, threatening the life of young elephants. Many elephants have been infected with no clinical signs and may serve as carriers spreading this disease. It is important to monitor the disease through clinical signs and molecular diagnosis. In this study we investigated the occurrence of EEHV and the efficiency of different techniques used to monitor EEHV infection in various samples and populations of Asian elephants. Materials and Methods: Blood and trunk swabs were collected from live elephants, while visceral organs (lung, digestive tract, spleen, lymph nodes, and kidney) were collected from dead elephants. EEHV was detected by polymerase chain reaction (PCR) in whole blood, trunk swabs, and visceral organs as samples, while elephant anti-EEHV immunoglobulin G (IgG) in serum was detected by enzyme-linked immunosorbent assay (ELISA). A total of 162 samples were analyzed in this study: 129 from healthy, 26 from dead, and 7 from sick elephants. Results: The present study showed that the overall incidence of EEHV was 40.1% (n=65/162). Approximately 46.2% (n=12/26) and 85.7% (n=6/7) of dead and sick elephants were positive for EEHV by PCR, respectively. All sick elephants that were young and affected by EEHV clinical disease tested negative for the IgG antibody ELISA, suggesting primary EEHV infection in this group. In addition, 2.3% (n=3/129) of subclinical infections were detected using PCR, and trunk swab samples showed slightly higher sensitivity (5.3%, n=2/38) to detect EEHV than whole blood (1.2%, n=1/84). As many as, 48.4% (n=44/91) of healthy elephants were EEHV seropositive (ELISA-positive), suggesting that many elephants in Thailand had previously been infected. Overall, 30% of dead wild elephants had been infected with EEHV (n=3/10). Moreover, statistical analysis revealed no significant differences in the EEHV detection rate between different age groups or sexes (p>0.05). Conclusion: PCR is better than ELISA to detect EEHV active infection in dead/sick elephants and to monitor EEHV in young elephants. ELISA is suitable for detecting previous EEHV infection and carriers, particularly adults. Theoretically, we could use both PCR and ELISA to increase the sensitivity of testing, along with observing abnormal behavior to efficiently monitor this disease. Identification of EEHV carriers within elephant populations is important to prevent transmission to healthy individuals, especially young elephants with high mortality from EEHV. This is the first report from Thailand regarding EEHV infection in wild elephants, showing the importance of preventing disease transmission between captive and wild elephants.

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Section: Discussionsupporting

confidence: 92%

Section: Elisamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The occurrence of elephant endotheliotropic herpesvirus infection in wild and captive Asian elephants in Thailand: Investigation based on viral DNA and host antibody

et al. 2021

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“…Currently, both the assessment of EEHV infections of individuals animals and the assessment of herd prevalence are largely performed using PCR on blood samples (5, 6, 9). Latent EEHV infections can only be detected upon reactivation, hence detection of EEHV prevalence by PCR requires longitudinal sampling over an extended period of time.…”

Section: Introductionmentioning

confidence: 99%

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

Hoornweg

Schaftenaar²,

Maurer

et al. 2020

Preprint

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Elephant endotheliotropic herpesviruses (EEHVs) are a group of evolutionary divergent herpesviruses that may cause acute, often lethal, hemorrhagic disease (EEHV-HD) in young elephants. Although EEHV was first discovered over 20 years ago, its prevalence in different elephant populations is still largely unknown, partially due to the lack of readily available, sensitive serological assays. In order to improve diagnostic tools for the detection of EEHV infections and to obtain insight in its spread among elephants, we developed novel ELISAs focusing on EEHV1A gB and gH/gL as antigens. Performance of the ELISAs was assessed using sera taken from 41 European zoo elephants and 69 semi-captive elephants from Laos, one of the Asian elephant range countries. Sera from all (sub)adult animals tested (≥5 years of age) showed high reactivity with both gB and gH/gL, whereas reactivity towards the antigens was generally lower for sera of juvenile animals (1 > 5 years). Only one (juvenile) animal, which was sampled directly after succumbing to EEHV-HD, was found to be seronegative for EEHV. The two other EEHV-HD cases tested showed low antibody levels, suggesting that all three cases died upon a primary EEHV infection. Direct comparison with another EEHV-specific ELISA previously used in two large serosurveys, showed that EEHV prevalence was underestimated before, likely due to aberrant folding of the antigen used. In conclusion, our study suggests that essentially all (semi-)captive (sub)adult elephants in European zoos and in Laos carry EEHV, and that young elephants with low antibody levels are at risk of dying from EEHV-HD.ImportanceOver the last 30 years, nearly 20% of all Asian elephants born in Western zoos succumbed to acute hemorrhagic disease caused by elephant endotheliotropic herpesvirus (EEHV-HD). Yet, the prevalence of EEHV in captive and wild elephant populations is still largely unknown, mainly due to the lack of readily available, sensitive serological assays. For this study two highly sensitive EEHV-specific ELISAs were developed. Using these assays, it was shown that nearly all elephants tested were seropositive for EEHV, with highest antibody levels detected in (sub)adult elephants. In contrast, antibody levels in EEHV-HD cases were very low or non-detectable. Lack of antibodies may thus be a risk factor for developing severe disease. As the novel ELISAs are low-tech in nature, these assays may easily be disseminated to local laboratories in zoos and elephant range countries in order to determine EEHV serostatus of individual animals or complete herds and (wild) populations.

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Clinical characteristics of elephant endotheliotropic herpesvirus (EEHV) cases in Asian elephants (Elephas maximus) in Thailand during 2006–2019

Yun

Sripiboon

Pringproa

et al. 2021

Veterinary Quarterly

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Background Elephant endotheliotropic herpesvirus causes a hemorrhagic disease (EEHV-HD) that is a major cause of death in juvenile Asian elephants with EEHV1 and EEHV4 being the most prevalent. Aim To perform a retrospective clinical data analysis. Methods Records of a total of 103 cases in Thailand confirmed by polymerase chain reaction (PCR) on blood and/or tissue samples. Results The severity of clinical signs varied among EEHV subtypes. EEHV1A was the most prevalent with 58%, followed by EEHV4 with 34%, EEHV1B with 5.8% and EEHV1&4 co-infection with 1.9%. Overall case fatality rate was 66%. When compared among subtypes, 100% case fatality rate was associated with EEHV1&4 co-infection, 83% with EEHV1B, 75% with EEHV1A, and the lowest at 40% for EEHV4. Calves 2- to 4-year old were in the highest age risk group and exhibited more severe clinical signs with the highest mortality. Majority of cases were found in weaned or trained claves and higher number of cases were observed in rainy season. A gender predilection could not be demonstrated. Severely affected elephants presented with thrombocytopenia, depletion of monocytes, lymphocytes and heterophils, a monocyte:heterophil (M:H) ratio lower than 2.37, hypoproteinemia (both albumin and globulin), severe grade of heterophil toxicity, and low red blood cell counts and pack cell volumes. Survival was not affected by antiviral drug treatment in the severely compromised animals. Conclusion Early detection by laboratory testing and aggressive application of therapies comprising of supportive and anti-viral treatment can improve survival outcomes of this disease.

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Subclinical infection of captive Asian elephants (Elephas maximus) in Thailand with elephant endotheliotropic herpesvirus

Cited by 9 publications

References 20 publications

The occurrence of elephant endotheliotropic herpesvirus infection in wild and captive Asian elephants in Thailand: Investigation based on viral DNA and host antibody

The occurrence of elephant endotheliotropic herpesvirus infection in wild and captive Asian elephants in Thailand: Investigation based on viral DNA and host antibody

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

Clinical characteristics of elephant endotheliotropic herpesvirus (EEHV) cases in Asian elephants (Elephas maximus) in Thailand during 2006–2019

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