Low gH/gL (Sub)Species-Specific Antibody Levels Indicate Elephants at Risk of Fatal Elephant Endotheliotropic Herpesvirus Hemorrhagic Disease

Elephant endotheliotropic herpesviruses (EEHVs), of which eleven (sub)species are currently distinguished, infect either Asian (Elephas maximus) or African elephants (Loxodonta species). While all adult elephants are latently infected with at least one EEHV (sub)species, young elephants, specifically those with low to non-detectable EEHV-specific antibody levels, may develop fatal hemorrhagic disease (EEHV-HD) upon infection. However, animals with high antibody levels against EEHV(1A) gB, an immunodominant antigen recognized by antibodies elicited against multiple (sub)species, may also occasionally succumb to EEHV-HD. To better define which animals are at risk of EEHV-HD, gB and gH/gL ELISAs were developed for each of the Asian elephant EEHV subspecies and assessed using 396 sera from 164 Asian elephants from European zoos. Antibody levels measured against gB of different (sub)species correlated strongly with one another, suggesting high cross-reactivity. Antibody levels against gH/gL of different subspecies were far less correlated and allowed differentiation between these (sub)species. Importantly, while high gB-specific antibody levels were detected in the sera of several EEHV-HD fatalities, all fatalities (n = 23) had low antibody levels against gH/gL of the subspecies causing disease. Overall, our data indicate that (sub)species-specific gH/gL ELISAs can be used to identify animals at risk of EEHV-HD when infected with a particular EEHV (sub)species.

Young elephants in a large herd maintain high levels of elephant endotheliotropic herpesvirus-specific antibodies and do not succumb to fatal haemorrhagic disease

Elephant endotheliotropic herpesviruses (EEHVs) have co-existed with elephants for millions of years, yet may cause fatal haemorrhagic disease (EEHV-HD), typically in elephants between 1 and 10 years of age. EEHV is omnipresent in (sub)adult elephants, and young elephants with low EEHV-specific antibody levels are at risk for EEHV-HD, suggesting that fatal disease may occur due to an insufficiently controlled primary infection. To further address this hypothesis, sera of three large elephant cohorts were subjected to a multiple EEHV species ELISA: (I) 96 Asian elephants between 0 and 57 years, including 13 EEHV-HD fatalities, from European zoo herds typically sized five to six elephants, (II) a herd of 64 orphaned elephants aged 0-15 years at the Elephant Transit Home in Sri Lanka and (III) 31 elephants aged 8-63 years, part of a large herd of 93 elephants at Pinnawala Elephant Orphanage, Sri Lanka. All Sri Lankan elephants showed high EEHV-specific antibody levels regardless of their age. While antibody levels of most European zoo elephants were comparable to those of Sri Lankan elephants, the average antibody level of the European juveniles (1-5 years of age) was significantly lower than those of age-matched Sri Lankan individuals. Moreover, the European juveniles showed a gradual decrease between 1 and 4 years of age, to be attributed to waning maternal antibodies. Maintenance of high levels of antibodies in spite of waning maternal antibodies in young Sri Lankan elephants is likely due to the larger herd size that increases the likelihood of contact with EEHV-shedding elephants. Together with the observation that low levels of EEHV-specific antibodies correlate with increased numbers of EEHV-HD fatalities, these results suggest that infection in presence of high maternal antibody levels may protect calves from developing EEHV-HD, while at the same time activating an immune response protective in future encounters with this virus.

EEHV1A glycoprotein B subunit vaccine elicits humoral and cell-mediated immune responses in mice

Asian elephants are an endangered species facing many threats, including severe hemorrhagic disease (HD) caused by the elephant endotheliotropic herpesvirus (EEHV). EEHV-HD is the leading cause of death in captive juvenile Asian elephants in North America and Europe, and also affects elephants in their natural range countries. Significant challenges exist for successful treatment of EEHV-HD, which include timely recognition of disease onset and limited availability of highly effective treatment options. To address this problem, our goal is to prevent lethal disease in young elephants by developing a vaccine that elicits robust and durable humoral and cell-mediated immunity against EEHV. EEHV glycoprotein B (gB) is a major target for cellular and humoral immunity in elephants previously exposed to EEHV. Therefore, we generated a vaccine containing recombinant EEHV1A gB together with a liposome formulated TLR-4 and saponin combination adjuvant (SLA-LSQ). CD-1 mice that received one or two vaccinations with the vaccine elicited significant anti-gB antibody and polyfunctional CD4⁺ and CD8⁺ T cell responses, while no adverse effects of vaccination were observed. Overall, our findings demonstrate that an adjuvanted gB protein subunit vaccine stimulates robust humoral and cell-mediated immune responses and supports its potential use in elephants.

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

Elephant endotheliotropic herpesviruses (EEHVs) may cause acute, often lethal, hemorrhagic disease (EEHV-HD) in young elephants. Prevalence of EEHV in different elephant populations is still largely unknown. In order to improve diagnostic tools for the detection of EEHV infections and to obtain insight into its spread among elephants, we developed novel ELISAs based on EEHV1A gB and gH/gL. Performance of the ELISAs was assessed using sera 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, indicating that EEHV prevalence has been highly underestimated so far. 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. 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.

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

Background

Elephant 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.

Methods

A 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.

Results

Antibody 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%).

Conclusions

This 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 material

The online version of this article (10.1186/s12985-019-1142-8) contains supplementary material, which is available to authorized users.

A novel antigen capture ELISA for the specific detection of IgG antibodies to elephant endotheliotropic herpes virus

BACKGROUND

Elephants are classified as critically endangered animals by the International Union for Conservation of Species (IUCN). Elephant endotheliotropic herpesvirus (EEHV) poses a large threat to breeding programs of captive Asian elephants by causing fatal haemorrhagic disease. EEHV infection is detected by PCR in samples from both clinically ill and asymptomatic elephants with an active infection, whereas latent carriers can be distinguished exclusively via serological assays. To date, identification of latent carriers has been challenging, since there are no serological assays capable of detecting seropositive elephants.

RESULTS

Here we describe a novel ELISA that specifically detects EEHV antibodies circulating in Asian elephant plasma/serum. Approximately 80 % of PCR positive elephants display EEHV-specific antibodies. Monitoring three Asian elephant herds from European zoos revealed that the serostatus of elephants within a herd varied from non-detectable to high titers. The antibody titers showed typical herpes-like rise-and-fall patterns in time which occur in all seropositive animals in the herd more or less simultaneously.

CONCLUSIONS

This study shows that the developed ELISA is suitable to detect antibodies specific to EEHV. It allows study of EEHV seroprevalence in Asian elephants. Results confirm that EEHV prevalence among Asian elephants (whether captive-born or wild-caught) is high.

Preliminary validation of assays to measure parameters of calcium metabolism in captive Asian and African elephants in western Europe

Hypocalcemia is a well known cause of dystocia in animals, including elephants in captivity. In order to study calcium metabolism in elephants, it is of utmost importance to use properly validated assays, as these might be prone to specific matrix effects in elephant blood. The aim of the current study was to conduct preliminary work for validation of various parameters involved in calcium metabolism in both blood and urine of captive elephants. Basal values of these parameters were compared between Asian elephants (Elephas maximus) and African elephants (Loxodonta africana). Preliminary testing of total calcium, inorganic phosphorus, and creatinine appeared valid for use in plasma and creatinine in urine in both species. Furthermore, measurements of bone alkaline phosphatase and N-terminal telopeptide of type I collagen appeared valid for use in Asian elephants. Mean heparinized plasma ionized calcium concentration and pH were not significantly affected by 3 cycles of freezing and thawing. Storage at 4 °C, room temperature, and 37 °C for 6, 12, and 24 hr did not alter the heparinized plasma ionized calcium concentration in Asian elephants. The following linear regression equation using pH (range: 6.858-7.887) and ionized calcium concentration in heparinized plasma was utilized: iCa(7.4) (mmol/l) = -2.1075 + 0.3130·pH(actual) + 0.8296·iCa(actual) (mmol/l). Mean basal values for pH and plasma in Asian elephant whole blood were 7.40 ± 0.048 and 7.49 ± 0.077, respectively. The urinary specific gravity and creatinine concentrations in both Asian and African elephants were significantly correlated and both were significantly lower in Asian elephants.

Dystocia and fetotomy associated with cerebral aplasia in a greater one-horned rhinoceros (Rhinoceros unicornis)

The captive greater one-horned rhinoceros population consists of 176 animals. Since 1971, a total of 226 calves were born into this captive population. However, 24% of the offspring born were either stillborn or did not survive the first 3 months. The causes for this high rate of stillbirth and neonate mortality have not yet been documented. Here, we report on the veterinary management of a dystocia and foetotomy resulting from a malpositioned greater one-horned rhinoceros foetus. The dead foetus presented with a forelimb flexed at the shoulder joint, with all other joints extended. The foetus was dissected into five parts and extracted during two anaesthesias on two consecutive days. The dam recovered fully and came into oestrous 31 days after surgery. Post-mortem and CT examination of the malformed foetal head revealed cranioschisis with cerebral aplasia and cerebellar hypoplasia. The cerebral aplasia presented here and in other recent cases suggests that neural tube defects and cranial malformations may be associated with more captive rhinoceros stillbirths than previously considered. Epidemiologic studies of these phenomena and possible nutritional deficiencies or hereditary defects are warranted.

Vaccination against highly pathogenic avian influenza H5N1 virus in zoos using an adjuvanted inactivated H5N2 vaccine

Highly pathogenic avian influenza (HPAI) H5N1 virus infections have recently caused unprecedented morbidity and mortality in a wide range of avian species. European Commission directive 2005/744/EC allowed vaccination in zoos under strict conditions, while reducing confinement measures. Vaccination with a commercial H5N2 vaccine with vaccine doses adapted to mean body weight per species was safe, and proved immunogenic throughout the range of species tested, with some variations between and within taxonomic orders. After booster vaccination the overall homologous geometric mean titre (GMT) to the vaccine strain, measured in 334 birds, was 190 (95% CI: 152-236), and 80.5% of vaccinated birds developed a titre of >or=40. Titres to the HPAI H5N1 virus followed a similar trend, but were lower (GMT: 61 (95% CI: 49-76); 61%>or=40). The breadth of the immune response was further demonstrated by measuring antibody titres against prototype strains of four antigenic clades of currently circulating H5N1 viruses. These data indicate that vaccination should be regarded as a beneficial component of the preventive measures (including increased bio-security and monitoring) that can be undertaken in zoos to prevent an outbreak of and decrease environmental contamination by HPAI H5N1 virus, while alleviating confinement measures.

Endotheliotropic elephant herpes virus (EEHV) infection. The first PCR-confirmed fatal case in Asia

Since 1995, 4 suspected cases of Endotheliotropic Elephant Herpes Virus (EEHV) infection, i.e. based on clinical presentation, have occurred in Asia without resulting in epidemic outbreaks as expected. In order to confirm the presence of EEHV on the continent of Asia, viral DNA particles from liver samples of a wild-caught 3-year-old elephant found dead at a Cambodian elephant sanctuary and clinically diagnosed with EEHV, were PCR processed using known EEHV strain primers. The presence of EEHV viral nucleic acids was confirmed and the nucleic acids had a 99% sequence similarity to the U.S.A strain (gene bank locus: AF117265) and 97% sequence similarity to the European strain (gene bank locus: AF354746) assigning this case to the EEHV-1 cluster. More than the confirmation of EEHV on the continent of Asia, is the phylogenic relationship to the USA and European strains with no corresponding contact or transport of USA or European elephants to Asia. Thus, this brings many of the traditional theories into question. Although almost forgotten, this disease is still ramped in captive elephant populations worldwide and continues to devastate particularly the neonatal and weaning-age population. Special attention and continued research are needed specifically in the area of basic virology and epidemiology.

Highly pathogenic avian influenza (H7N7): vaccination of zoo birds and transmission to non-poultry species

In 2003 an outbreak of highly pathogenic avian influenza virus (H7N7) struck poultry in The Netherlands. A European Commission directive made vaccination of valuable species in zoo collections possible under strict conditions. We determined pre- and post-vaccination antibody titres in 211 birds by haemagglutination inhibition test as a measure of vaccine efficacy. After booster vaccination, 81.5% of vaccinated birds developed a titre of > or =40, while overall geometric mean titre (GMT) was 190 (95% CI: 144-251). Birds of the orders Anseriformes, Galliformes and Phoenicopteriformes showed higher GMT, and larger percentages developed titres > or =40 than those of the other orders. Antibody response decreased with increasing mean body weight in birds > or =1.5 kg body weight. In the vicinity of the outbreak, H7N7 was detected by RT-PCR in wild species (mallards and mute swans) kept in captivity together with infected poultry, illustrating the potential threat of transmission from poultry into other avian species, and the importance of protecting valuable avian species by means of vaccination.

CATARACT SURGERY WITH FOLDABLE INTRAOCULAR LENS IMPLANTS IN CAPTIVE LOWLAND GORILLAS (GORILLA GORILLA GORILLA)

Two juvenile, male, captive-born lowland gorillas (Gorilla gorilla gorilla) with the same father but different mothers developed bilateral cataracts. The cataracts were surgically removed within 6 yr and 3 mo, respectively, of diagnosis, and foldable intraocular lenses were implanted. Although vision was not restored in one eye with a mature, 6-yr-old cataract in gorilla A, surgical intervention on the other eye was performed before a complete cataract developed, and vision was fully restored. Gorilla B was treated at the age of 17 mo, and normal visual development proceeded in both eyes. This animal developed bilateral after-cataract and therefore needed a second intervention in both eyes using Nd:YAG laser treatment. The genetic component of juvenile cataracts should be considered in breeding management programs.

Use of vaccination against foot and mouth disease in zoo animals, endangered species and exceptionally valuable animals

A historical review of foot and mouth disease (FMD) in non-domestic species is given and the use of FMD vaccines to protect those species is described. Several non-domestic species are susceptible to FMD. Legislation in many countries, based on the definition of FMD-free status as determined by the Office International des Epizooties (OIE: World organisation for animal health), forms an important barrier against the use of vaccines. National authorities may even feel obliged to slaughter animals of threatened species protected by international agreements during an outbreak of FMD to preserve their FMD-free status. The importance of international breeding programmes for endangered species is forcing the international community to reconsider the role that vaccination against FMD should play in animal health prevention programmes of captive populations. Much research is still required in regard to vaccine types and diagnostic procedures. Species-specific differences in susceptibility to FMD make this a challenging research topic for zoological institutions.

A variant of the endotheliotropic herpesvirus in Asian elephants (Elephas maximus) in European zoos

Newly discovered, lethal elephant endotheliotropic herpesviruses (EEHV) have been identified in both Asian (Elephas maximus) and African (Loxodonta africana) elephants. Carried by otherwise healthy African elephants they can be fatal mainly for young Asian elephants. Since zoos often harbour both elephant species, we conducted a survey on the presence of EEHV in Asian elephants from 12 European zoos, 3 circuses and 1 Israeli zoo. Here, we demonstrate that all EEHV that have affected Asian elephants so far belong to the EEHV1 group. We also describe the detection and the partial sequencing of an endotheliotropic herpesvirus variant (named EEHV1b) in Asian elephants, being either an EEHV endogenous to Asian elephants or indicating different sources (African elephants) of infection.

Characterisation of a recently isolated lyssavirus in frugivorous zoo bats

In July 1997 a lyssavirus was isolated in Denmark from a colony of Egyptian flying foxes (Rousettus aegyptiacus) originating from a Dutch zoo. Sequencing of a 400 nucleotides coding region of the nucleoprotein and of a major part of the G-protein ectodomain encoding region of the newly isolated virus, revealed a very high similarity with European Bat Lyssavirus subtype 1a (EBL-1a). For characterisation of the recently isolated lyssavirus in frugivorous zoo bats, 16 frugivorous bats (Rousettus aegyptiacus) of the same colony and 80 mice were experimentally infected with the Rousettus isolate or with a well defined EBL-1a strain isolated from a Dutch insectivorous bat (Eptesicus serotinus). Inoculation viruses were titrated in mice to determine LD50's of both isolates. Clinical signs of inoculated bats were recorded during 6 weeks. After showing neurological signs or at the end of the experimental infection all animals were euthanized. During the experimental infection sera and various tissues of inoculated bats were collected. Immunoassays, mouse inoculation tests (MIT) and polymerase chain reaction (PCR) were employed for detection of lyssavirus specific antibodies, antigen or RNA. Five bats inoculated with the Rousettus isolate and 2 bats inoculated with the Eptesicus isolate showed neurological signs. The remaining 9 bats survived and cleared the virus; at least under the detection limit of the used assays. Despite a much higher pathogenicity of the Rousettus isolate observed in mice, LD25's in bats were quite the same for the 2 isolates. The pathogenicity of both isolates suggested that like many other mammals, Rousettus aegyptiacus bats could be victims of lyssavirus infection besides reservoir hosts of infectious EBL1a. There was no significant difference in detecting the different lyssavirus isolates in Rousettus aegyptiacus bats. An employed immunoperoxidase staining (IP) method was very useful for sensitive detection and localization of lyssavirus antigen in histologic preparates.

Fecal progesterone, estrogen, and androgen metabolites for noninvasive monitoring of reproductive function in the female Indian rhinoceros, Rhinoceros unicornis

This investigation aimed to establish noninvasive methods for endocrine monitoring of estrous cycles and pregnancy in the Indian rhinoceros. Fecal samples were collected 1-3 times per week from nonpregnant and pregnant captive females (n = 7). Enzyme immunoassays for fecal progesterone, androgen, and estrogen metabolites, respectively, were tested for their ability to determine follicular and luteal phases and to characterize endocrine profiles during pregnancy. Antibodies used were raised against pregnanediol (20 alpha-OH-pregnanes), 20-oxo-pregnanes, epiandrosterone (17-oxo-androstanes), and total estrogens. Androgens and estrogens were found to be reliable indicators of the follicular phase, whereas 20 alpha-OH- and 20-oxo-pregnanes were reliable indicators of luteal function. Progesterone metabolites were also reliable indicators of pregnancy, whereas 17-oxo-androstanes and estrogens were basal throughout gestation. Estrous cycles were regular throughout the year, with an average cycle length of 43.4 +/- 1.5 (n = 27) days; the length of the follicular phase, as indicated by elevated estrogen levels, was 15.9 +/- 1.0 days, whereas the luteal phase, as indicated by elevated 20-oxo-pregnane levels, was 19.1 +/- 0.4 days. Fecal pregnane values were already increasing while follicular estrogen values were still decreasing. The length of the diestrus, indicated by basal steroid levels between declining 20-oxo-pregnanes and subsequently increasing estrogens, was 11.4 +/- 1.2 days. Pregnane levels increased from the 3rd month of gestation onward and levels exceeded luteal phase concentrations approximately 10 times by the 7th month of gestation onward. HPLC separation of immunoreactive fecal metabolites indicated the presence of estrone, estradiol-17beta, and several 17-oxo-androstanes, 20 alpha-OH-pregnanes, and 20-oxo-pregnanes. Concentrations of a peak with an elution profile similar to that of pregnanediol increased as pregnancy progressed. Postpartum fecal estrogen and 17-oxo-androstane concentrations in one animal indicated follicular development comparable to the follicular phase of the estrous cycle, but this was not followed by a subsequent luteal phase. In conclusion, estrous cycle and pregnancy in Indian rhinoceroses can be monitored using fecal steroid analysis. Pregnane metabolites were reliable indicators of the corpus luteum and pregnancy, whereas fecal 17-oxo-androstanes and estrogens were indicators of the follicular phase.

Noninvasive reproductive monitoring in the okapi (Okapia johnstoni)

Fecal progestagen analysis in okapis (Okapia johnstoni) was used for diagnosis of pregnancy and reproductive disorders, including a comparison of urinary and fecal progestagen analysis and endocrine data on the postpartum period. Data were generated on reliability of fecal progestagen analysis in early pregnancy diagnosis, and case reports were compiled involving single animals with missing luteal activity, abortion after twin pregnancy, and abortions due to deficient placental progestagen production. There was approximately 100-200-fold higher progestagen concentration in feces than in urine, thus explaining the high reliability of fecal progestagen evaluations in diagnosing luteal function and pregnancy. The postpartum period was characterized by lactational anestrus of several months duration, and a postpartum estrous cycle about 2-3 wk after parturition was observed in two of eight animals. An animal with five abortions due to deficient placental progestagen production was treated with altrenogest in a subsequent pregnancy and carried the fetus to term.

[Oxytetracycline and oral herd treatment: a literature review]

Pharmacotherapeutic, pharmacodynamic and pharmacokinetic aspects of oral mass medication with oxytetracycline (OTC) in pigs, calves and poultry are discussed in this review. Clinical studies with successful therapeutic results are scarce in literature; however, OTC is still frequently used for mass medication. Some practical advice to improve the bioavailability of OTC is given. This mainly concerns the reduction of the interaction between calcium ions and OTC. OTC may be useful for oral mass medication when applied as a prophylactic drug. Pharmacological studies are required in order to provide more knowledge about the efficacy of OTC-mass medication. Additional information can be acquired from the field by improving and extending the reciprocal co-operation between field veterinarians and diagnostic laboratories. This may lead to a more justified choice from the various possibilities of antimicrobial use in livestock.

[Studies on intersucking in dairy cattle (author's transl)]

Intersucking occurred on nearly 50 per cent of the farms in the Province of Utrecht. The incidence was not affected by housing systems, the size of the herd and the surface area available to each cow in cubicle stalls. It is unlikely that the animals imitate intersucking by others. Intersucking often occurs prior to evening milking, the sucking animal usually forming a steady pair with the suckled cow. Of four A.I. bulls studied, one had a significantly higher proportion of intersucking heifers among his offspring than the others. Some other factors possibly affecting the incidence of intersucking, such as the rearing system, composition of the ration and the space allotted to each cow for feeding were not studied because of insufficient information or inadequate variation of the material.