Demonstration of sheep-associated malignant catarrhal fever virions in sheep nasal secretions

Transmission patterns of malignant catarrhal fever in sheep and cattle in Karnataka, India

Malignant catarrhal fever (MCF) presents a sporadic yet significant threat to livestock and wildlife. A comprehensive investigation in Karnataka, India into the prevalence and transmission patterns of sheep-associated MCF (SA-MCF) was conducted. A total of 507 sheep peripheral blood leukocyte samples from 13 districts along with 27 cows and 10 buffalo samples from various regions in Karnataka were tested for SA-MCF infection i.e. Ovine gammaherpesvirus 2 (OvHV-2) using heminested PCR. Furthermore, serum samples collected from 73 cows and 15 buffalo suspected of MCF were tested using a commercially available ELISA kit. Additionally, histopathological examinations of affected tissues and phylogenetic analysis of viral tegument protein sequences were conducted. Our findings indicated a 20.11%, 33.33% and 20% positivity for OvHV-2 in sheep, cows and buffalo respectively by PCR. Statistical analysis revealed a significant association between the age of sheep and the detection of OvHV-2. Seven cows and one buffalo serum samples tested positive for ELISA. Clinical findings in bovids were consistent with typical MCF signs, and histopathological results revealed multi-organ involvement characterised by necrotising vasculitis and lymphoid hyperplasia. The nucleotide pairwise identity matrix revealed 99.5% identity between the sequences obtained in the study with sequences from other states. The phylogenetic analysis of partial tegument protein sequences from bovid and sheep samples suggested a close genetic relationship between the local OvHV-2 strains and those from various global regions. Crucially, this study underscores the widespread presence of SA-MCF in Karnataka, with significant implications for both livestock management and wildlife conservation.

Malignant catarrhal fever: An emerging yet neglected disease in captive sika deer (Cervus nippon) herds in China

Malignant catarrhal fever (MCF) is a fatal lymphoproliferative disease that represents a serious problem in the deer-rearing industry. To better understand an MCF-like disease that has emerged in northern China since 2015, we investigated ten cases by documenting clinical and epidemiological data and analysing causative agents and histopathological changes. In addition, a retrospective screen for Macavirus DNA and a questionnaire-based survey were conducted. Epizootic MCF in Chinese sika deer herds has emerged with a low morbidity of 3.8% (95% CI: 2.5%-5.1%) and a high mortality of 93.2% (95% CI: 86.6%-99.9%). The disease course varied from 3 to 12 days. Aetiologically, OvHV-2 was predominant in the MCFV, accounting for most MCF cases (21/23). In contrast, only two CpHV-2 isolates were phylogenetically closely related to CpHV-2. Diarrhoea and nasal discharges were the most frequent manifestations, although clinical signs varied in some cases. Pathologically typical lesions of haemorrhage, necrosis and lymphoid cell infiltration were readily observed in a variety of organs. Vasculitis caused by vascular and perivascular lymphoid cell infiltration was common. The retrospective survey suggested a low positive rate (3/275) of MCFV DNA in peripheral blood lymphocytes (PBL). The questionnaire-based survey suggested the disease was neglected by local veterinarians, who did not acknowledge the risk of co-rearing deer with reservoir species. Collectively, the emerging epizootic MCF in Chinese sika deer herds remains neglected, emphasizing the urgency of initiating full-field diagnoses and control strategies.

Caprine herpesvirus 2-associated malignant catarrhal fever of captive sika deer (Cervus nippon) in an intensive management system

Background

Caprine herpesvirus 2 (CpHV-2) infection usually induces chronic malignant catarrhal fever (MCF) in sika deer (Cervus nippon), with the primary signs of weight loss, dermatitis and alopecia.

Case presentation

Here, we report a case of CpHV-2-associated acute MCF in a sika deer herd raised in an intensive management system distant to the reservoir goats. Affected deer developed clinical signs of high fever (41 °C) followed by nasal discharge and lameness. Severe lesions of hemorrhage, necrosis and infiltration of lymphoid cells could readily be observed in the lung, kidney, heart valves and subcutaneous tissue surrounding a tendon. Etiologically, identical CpHV-2 specific DNA sequences were detected in peripheral blood lymphocyte (PBL) from the affected deer and reservoir goats.

Conclusion

In summary, domestic goats were the reservoir of the CpHV-2, which is the causative agent of the outbreak of MCF in the three hinds. The disease was probably transmitted via aerosol infection. In addition, necrosis and inflammation in subcutaneous tissue surrounding a tendon was the reason for lameness. Therefore, MCF should be put into a differential diagnostic list when similar disease occurs in sika deer herds.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1365-8) contains supplementary material, which is available to authorized users.

Alcelaphine gammaherpesvirus 1-induced malignant catarrhal fever in a Watusi ( Bos taurus africanus) steer in a North American game park

A 10-y-old Watusi ( Bos taurus africanus) steer housed at a drive-through game park in Winston, Oregon developed severe clinical illness including fever, marked nasal discharge, injected scleral and conjunctival membranes, plus oral hemorrhages and erosions. The animal responded poorly to supportive treatment and was euthanized. Additional gross findings at postmortem examination included papules and erosive lesions on the tongue, hemorrhagic large intestine, and multifocal cardiac hemorrhages. Histopathologic findings included multifocal lymphoplasmacytic vasculitis plus fibrin exudation in heart and tongue. Total DNA obtained from the splenic samples was positive for alcelaphine gammaherpesvirus 1 (AlHV-1) as tested by a multiplex PCR for malignant catarrhal fever (MCF) viruses. The AlHV-1 detection was further confirmed by amplification and sequencing of a viral DNA polymerase gene fragment, which was identical to AlHV-1 sequences in GenBank. This was the first diagnosis of clinical wildebeest-associated MCF on these premises, although wildebeest have been held at the park for over 25 y. This disease is sporadic in North America and should be considered as a differential diagnosis for febrile illness with ulcerative oral lesions in ruminants.

T-CELL LYMPHOCYTIC LEUKEMIA IN A FALLOW DEER (DAMA DAMA)

A 17-yr-old female fallow deer presented with ataxia, inappetence, decreased fecal output, and decreased mentation. A complete blood count demonstrated leukocytosis (24.1×10(3)/μl, n=1.16-7.38×10(3)/μl), characterized by lymphocytosis (22.89×10(3)/μl, n=0.18-3.65×10(3)/μl), anemia (packed cell volume 20%, n=29.0-55.8%), decreased red blood cell count (4.1×10(3)/μl, n=6.86-14.72×10(3)/μl), and decreased hemoglobin (7.5 g/dl, n=9.4-19.2 g/dl). Numerous mature, well-differentiated lymphocytes were noted on the blood film. Despite treatment and clinical improvement, the decision was made to euthanize the deer. Histopathology identified a monomorphic population of CD3 positive, CD79a negative small lymphocytes replacing most of the hematopoietic tissue in the bone marrow without evidence of tissue invasion. Results of viral screening were negative.

Alcelaphine Herpesvirus-1 (Malignant Catarrhal Fever Virus) in Wildebeest Placenta: Genetic Variation of ORF50 and A9.5 Alleles

Alcelaphine herpesvirus–1 (AlHV-1), a causative agent of malignant catarrhal fever in cattle, was detected in wildebeest (Connochaetes taurinus) placenta tissue for the first time. Although viral load was low, the finding of viral DNA in over 50% of 94 samples tested lends support to the possibility that placental tissue could play a role in disease transmission and that wildebeest calves are infected in utero. Two viral loci were sequenced to examine variation among virus samples obtained from wildebeest and cattle: the ORF50 gene, encoding the lytic cycle transactivator protein, and the A9.5 gene, encoding a novel polymorphic viral glycoprotein. ORF50 was well conserved with six newly discovered alleles differing at only one or two base positions. In contrast, while only three new A9.5 alleles were discovered, these differed by up to 13% at the nucleotide level and up to 20% at the amino acid level. Structural homology searching performed with the additional A9.5 sequences determined in this study adds power to recent analysis identifying the four-helix bundle cytokine interleukin-4 (IL4) as the major homologue. The majority of MCF virus samples obtained from Tanzanian cattle and wildebeest encoded A9.5 polypeptides identical to the previously characterized A9.5 allele present in the laboratory maintained AlHV-1 C500 strain. This supports the view that AlHV-1 C500 is suitable for the development of a vaccine for wildebeest-associated MCF.

Malignant catarrhal fever: inching toward understanding

Malignant catarrhal fever (MCF) is an often lethal infection of many species in the order Artiodactyla. It is caused by members of the MCF virus group within Gammaherpesvirinae. MCF is a worldwide problem and has a significant economic impact on highly disease-susceptible hosts, such as cattle, bison, and deer. Several epidemiologic forms of MCF, defined by the reservoir ruminant species from which the causative virus arises, are recognized. Wildebeest-associated MCF (WA-MCF) and sheep-associated MCF (SA-MCF) are the most prevalent and well-studied forms of the disease. Historical understanding of MCF is largely based on WA-MCF, in which the causative virus can be propagated in vitro. Characterization of SA-MCF has been constrained because the causative agent has never been successfully propagated in vitro. Development of molecular tools has enabled more definitive studies on SA-MCF. The current understanding of MCF, including its etiological agents, epidemiology, pathogenesis, and prevention, is the subject of the present review.

Molecular characterisation of ovine herpesvirus type 2 (OvHV-2) in Turkey

In this study, the physical examination of 22 cattle revealed clinical signs of malignant catarrhal fever (MCF). Peripheral blood leukocyte (PBL) samples of the 22 cattle, and nasal (n = 7) and conjunctival (n = 9) swab samples from 16 sheep from two different farms, were taken for laboratory examination. The clinical diagnosis of MCF in cows was confirmed by the detection of ovine herpesvirus type 2 (OvHV-2) DNA by polymerase chain reaction (PCR). OvHV-2 DNA was detected by nested-PCR in PBL of one cow with clinical signs and nasal (1/7)-conjunctival(1/9) swab samples of two sheep housed in the same barn. According to the sequence analysis, three slightly divergent viruses were detected. The results indicate the need for additional research in different regions of Turkey to gain a better understanding of the incidence of MCF and its implications for the livestock industry.

Sheep (Ovis aries) airway epithelial cells support ovine herpesvirus 2 lytic replication in vivo

Ovine herpesvirus 2 (OvHV-2) is the causative agent of sheep-associated malignant catarrhal fever (SA-MCF), a frequently fatal disease of some members of the order Artiodactyla. OvHV-2 is carried as a lifelong subclinical infection in sheep (Ovis aries). To date OvHV-2 has not been propagated in vitro and this has hampered studies of viral pathogenesis and efforts to develop a vaccine to protect animals from SA-MCF. Lytic OvHV-2 replication occurs in the lungs of experimentally infected sheep at early times post-inoculation (PI) and in the nasal cavities of naturally infected sheep during virus shedding episodes. Identification of specific cell types supporting lytic virus replication in vivo provides information that can be used in the development of an in vitro propagation system for the virus. Using fluorescence immunohistochemical techniques, we identified lytically infected alveolar epithelial cells in the lungs of sheep early during infection. Lytically infected epithelial cells were also detected in samples of nasal secretions collected from naturally infected sheep during episodes of virus shedding. This is the first reported identification in the natural reservoir species of specific cell types that support OvHV-2 lytic replication in vivo.

Malignant catarrhal fever: a review

Malignant catarrhal fever (MCF) is a fatal lymphoproliferative disease of cattle and other ungulates caused by the ruminant gamma-herpesviruses alcelaphine herpesvirus 1 (AlHV-1) and ovine herpesvirus 2 (OvHV-2). These viruses cause inapparent infection in their reservoir hosts (wildebeest for AlHV-1 and sheep for OvHV-2), but fatal lymphoproliferative disease when they infect MCF-susceptible hosts, including cattle, deer, bison, water buffalo and pigs. MCF is an important disease wherever reservoir and MCF-susceptible species mix and currently is a particular problem in Bali cattle in Indonesia, bison in the USA and in pastoralist cattle herds in Eastern and Southern Africa. MCF is characterised by the accumulation of lymphocytes (predominantly CD8(+) T lymphocytes) in a variety of organs, often associated with tissue necrosis. Only a small proportion of these lymphocytes appear to contain virus, although recent results with virus gene-specific probes indicate that more infected cells may be present than previously thought. The tissue damage in MCF is hypothesised to be caused by the indiscriminate activity of MHC-unrestricted cytotoxic T/natural killer cells. The pathogenesis of MCF and the virus life cycle are poorly understood and, currently, there is no effective disease control. Recent sequencing of the OvHV-2 genome and construction of an AlHV-1 bacterial artificial chromosome (BAC) are facilitating studies to understand the pathogenesis of this extraordinary disease. Furthermore, new and improved methods of disease diagnosis have been developed and promising vaccine strategies are being tested. The next few years are likely to be exciting and productive for MCF research.

Experimental infection of rabbits with ovine herpesvirus 2 from sheep nasal secretions

Malignant catarrhal fever (MCF) is a generally fatal disease that primarily occurs in ruminants and is caused by a group of gammaherpesviruses. Outside of Africa MCF is mainly caused by ovine herpesvirus 2 (OvHV-2) which is carried subclinically by sheep. Cell-free virus is present in nasal secretions of shedding sheep and aerosol is the primary mode of transmission. Although OvHV-2 has never been propagated in vitro, experimental infection involving intranasal nebulization with nasal secretions from shedding sheep has been used to induce MCF in cattle and bison. This method of inoculation has never been tested in rabbits, which are the primary small animal model. The objectives of this study were to determine whether rabbits become infected with OvHV-2 after intranasal nebulization with cell-free virus from sheep nasal secretions and whether they develop MCF with consistent gross and histologic lesions. Five of eight rabbits became infected, showed clinical signs and developed histologic lesions typical of MCF including multisystemic vasculitis and perivascular lymphoid accumulation. These lesions are similar to those reported in rabbits infected by intravenous injection with tissues from clinically affected animals containing cell-associated virus. Viral DNA and mRNA transcripts of a structural viral protein were present in tissues from affected rabbits suggesting that viral replication occurred, although the significance in terms of pathogenesis is unknown. This work demonstrates that OvHV-2 infection of rabbits by intranasal nebulization is a potentially useful model that mimics the natural route of infection and may be used to study viral replication and pathogenesis.

Intra-nasal inoculation of American bison (Bison bison) with ovine herpesvirus-2 (OvHV-2) reliably reproduces malignant catarrhal fever

Sheep-associated malignant catarrhal fever (MCF) due to infection with ovine herpesvirus 2 (OvHV-2) is common in commercial herds of American bison ( Bison bison). Inability to propagate OvHV-2 in vitro has been a constraint on experimental studies of the disease. We sought to establish whether nasal secretions from sheep that shed OvHV-2 might induce the disease in bison and to define a minimum challenge dose. Fourteen bison were nebulized with sheep nasal sections containing 10(3)-10(7) OvHV-2 deoxyribonucleic acid (DNA) copies. Most challenged bison (11/14, 78.6%) developed clinical signs at 29-52 days postnebulization (DPN). The mean incubation time was 42.18 (+/-7.33 SD) DPN. Using real-time polymerase chain reaction, we detected OvHV-2 DNA in peripheral blood leukocytes at 21-31 DPN. All bison that developed MCF had antibodies against the MCF group viruses. Gross and histologic lesions were typical of the acute disease. There was no morphologic evidence of a dose-related difference in the severity or distribution of lesions. This is the first successful reproduction of MCF in bison using a nasal route of exposure. Experimentally challenged bison are more susceptible to MCF, compared with experimentally challenged domestic cattle in a previous experiment. Bison are a pertinent ruminant species in which the pathogenesis of the disease can be investigated.

Detection of ovine herpesvirus 2 major capsid gene transcripts as an indicator of virus replication in shedding sheep and clinically affected animals

The aim of this study was to identify tissues where ovine herpesvirus 2 (OvHV-2) replication occurs in vivo. A reverse-transcriptase PCR targeting the OvHV-2 major capsid protein gene (ORF 25) was developed and the presence of transcripts used as an indicator of virus replication in naturally infected sheep, and cattle and bison with sheep-associated malignant catarrhal fever (SA-MCF). ORF 25 transcripts were detected in 18 of 60 (30%) turbinate, trachea, and lung samples from five sheep experiencing a shedding episode; 12 of the 18 positive samples were turbinates. ORF 25 transcripts were not detected in any other tissue from the shedding sheep (n=55). In contrast, 86 of 102 (84%) samples from clinically affected bovine and bison tissues, including brain, kidney, intestine, and bladder, had ORF 25 transcripts. The data strongly suggest that OvHV-2 replication is localized to the respiratory tract of shedding sheep, predominantly in the turbinate, while it occurs in virtually all tissues of cattle and bison with SA-MCF. These findings represent an important initial step in understanding viral pathogenesis, and in potentially establishing a system for OvHV-2 propagation in vitro.

A devastating outbreak of malignant catarrhal fever in a bison feedlot

In early 2003, an outbreak of malignant catarrhal fever (MCF) occurred in a bison feedlot in southern Idaho. The outbreak resulted in a 51.2% (n = 825) mortality rate among bison, which had been exposed to sheep for 19 days. Diagnosis was made by detection of ovine herpesvirus 2 (sheep-associated MCF virus) DNA in tissues or peripheral blood by polymerase chain reaction (PCR), and by histological examination of tissue lesions. Peak losses occurred between 41 and 55 days postmean exposure time (PME), and reached a maximum of 41 head per day. No known cases of MCF were observed among the 177 head of bison that arrived in the lot 3 1/2 weeks after the departure of the sheep. Of the several thousand head of beef cattle in the lot during the outbreak, only a single case of MCF was identified. This outbreak illustrates the devastating impact the MCF virus can have on bison under certain exposure conditions, the high threat posed by adolescent lambs to susceptible species, the significantly greater susceptibility of bison than beef cattle to MCF, and the lack of horizontal transmission from clinically affected bison to herdmates.

Comparison of ovine herpesvirus 2 genomes isolated from domestic sheep (Ovis aries) and a clinically affected cow (Bos bovis)

The rhadinovirus Ovine herpesvirus 2 (OvHV-2) is the causative agent of sheep-associated malignant catarrhal fever. OvHV-2 primarily affects ruminants and has a worldwide distribution. In this study, a composite sequence of OvHV-2 genomic DNA isolated from nasal secretions of sheep experiencing virus-shedding episodes was determined and compared with the sequence of OvHV-2 DNA isolated from a lymphoblastoid cell line derived from a clinically affected cow. The study confirmed the OvHV-2 sequence information determined for the cell line-isolated DNA and showed no apparently significant changes in the OvHV-2 genome during passage through a clinically susceptible species with subsequent maintenance in vitro. Amino acid identity between the predicted open reading frames (ORFs) of the two genomes was 94-100%, except for ORF73, which had an identity of 83%. Polymorphism in ORF73 was due primarily to variability in the G/E-rich repetitive central region of the ORF.

Pathogenesis of gammaherpesvirus infections

Gammaherpesviruses are members of an emerging subfamily among the Herpesviridae. Two genera are discriminated: (i) lymphocryptovirus, including its type species Epstein-Barr virus (EBV), and (ii) rhadinovirus, including viruses of interest for medicine, veterinary medicine, and biomedical research, i.e. alcelaphine herpesvirus 1, bovine herpesvirus 4, equine herpesvirus 2, human herpesvirus 8, mouse herpesvirus 68, and ovine herpesvirus 2 (OvHV-2). The perception that these viruses have a narrow host range is misleading, since they cover a surprisingly wide host range, both on the cellular and the organism's level. For example, the natural range of OvHV-2 infection extends over a common animal order. While the host range determinants of EBV are well known, the corresponding features of the rhadinoviruses need still to be defined. Similarly, the gene expression patterns of the veterinary rhadinoviruses during latency require further characterization. In vivo, the gammaherpesviruses have evolved to actively protect their latently infected cells from being destroyed by immune functions of their native host. In return, those reservoir hosts have evolved to being infected and transmit the virus without overt disease symptoms. However, a balanced immune response needs to be in control over the number of infected cells. Virus excretion is usually at low level and may occur either constantly or intermittently. Animal species that are targeted by the virus but did not participate in the process of co-evolution as well as hosts with immune deficiencies are known to loose control over the amount of latently infected cells, which results in the development of lethal diseases, such as malignant catarrhal fever or Kaposi's sarcoma.

Malignant catarrhal fever-like disease in sheep after intranasal inoculation with ovine herpesvirus-2

A malignant catarrhal fever (MCF)-like disease was induced experimentally in 3 sheep after aerosol inoculation with ovine herpesvirus-2 (OvHV-2). Each of 3 OvHV-2-negative sheep was nebulized with 2 ml of nasal secretions containing approximately 3.07 X 10(9) OvHV-2 DNA copies from a sheep experiencing an intensive viral-shedding episode. Ovine herpesvirus-2 DNA became detectable by polymerase chain reaction in the peripheral blood leukocytes of all 3 sheep within 3 days, and all 3 seroconverted between 6 and 8 days postinfection (PI). The sheep developed clinical signs, with copious mucopurulent nasal discharge and fever around 14 days PI. One of the 3 clinically affected sheep was euthanized at 18 days PI. Major lesions at necropsy were multifocal linear erosions and ulcers in mucosa of the cheeks, tongue, pharynx, and proximal esophagus and mild disseminated pneumonia. Microscopically, there was extensive moderate superficial histiocytic-lymphocytic rhinitis with epithelial dissociation and degeneration. Moderate multifocal histiocytic bronchointerstitial pneumonia was associated with loss of terminal bronchiolar epithelium. Lymphocytic vasculitis was present only in the lung. The remaining 2 sheep recovered clinically, approximately 25 days PI. The study revealed that clinical signs and lesions resembling MCF can develop when uninfected sheep are exposed to a high dose of aerosolized OvHV-2.

Experimental infection of sheep with ovine herpesvirus 2 via aerosolization of nasal secretions

Ovine herpesvirus 2 (OvHV-2) is the causative agent of sheep-associated malignant catarrhal fever in clinically susceptible ruminants, including cattle, bison and deer. Studies of OvHV-2 have been hampered by the lack of an in vitro propagation system. Here, the use of nasal secretions collected from OvHV-2-infected sheep experiencing intense virus shedding episodes as a source of infectious virus for experimental animal infections was examined. OvHV-2 uninfected sheep were nebulized with nasal secretions containing approximately 10(8) to 10(1) copies of OvHV-2 DNA. The time to detectable viral DNA in peripheral blood leukocytes (7-12 days post-infection) and virus-specific antibody in plasma (9-32 days post-infection) varied with the dose of inocula administered. Here, the use of nasal secretions as a source of infectious OvHV-2 was defined and the minimum infectious dose of a pool of nasal secretions that can be used in further studies of viral pathogenesis and vaccine development was determined.

Shedding of ovine herpesvirus 2 in sheep nasal secretions: the predominant mode for transmission

Ovine herpesvirus 2 (OvHV-2), the major causative agent of malignant catarrhal fever in ruminant species worldwide, has never been propagated in vitro. Using real-time PCR, a striking, short-lived, peak of viral DNA, ranging from 10(5) to over 10(8) copies/2 microg of DNA, was detected in nasal secretions from over 60.7% of adolescent sheep (n = 56) at some point during the period from 6 to 9 months of age. In contrast, only about 18% of adult sheep (n = 33) experienced a shedding episode during the study period. The general pattern of the appearance of viral DNA in nasal secretions was a dramatic rise and subsequent fall within 24 to 36 h, implying a single cycle of viral replication. These episodes occurred sporadically and infrequently, but over the 3-month period most of the 56 lambs (33, or 60.7%) experienced at least one episode. No corresponding fluctuations in DNA levels were found in either peripheral blood leukocytes or plasma. In a DNase protection assay, complete, enveloped OvHV-2 virions were demonstrated in the nasal secretions of all sheep examined during the time when they were experiencing an intense shedding episode. OvHV-2 infectivity in nasal secretions was also demonstrated by aerosolization of the secretions into OvHV-2-negative sheep. The data herein show that nasal shedding is the major mode of OvHV-2 transmission among domestic sheep and that adolescents represent the highest risk group for transmission.