Characterization of ovine gammaherpesvirus 2 in a goat by nanoplate digital PCR and other diagnostic methods

The Macavirus, ovine gammaherpesvirus 2 (OvGHV2), is the cause of sheep-associated malignant catarrhal fever (SA-MCF). Although SA-MCF occurs in a wide range of mammalian hosts, there are few descriptions of this disease and/or infection in goats. This report describes the findings observed in a goat that was infected by OvGHV2 and adds to the rare description of this infection in this animal species. A 6.5-year-old, female, Anglo Nubian goat, with a neurological syndrome, that was euthanized after severe esophageal obstruction was investigated to determine the cause of the brain disease. Histopathology revealed cerebral cortical edema, hemorrhagic rhombencephalitis, severe hepatic necrosis, and atrophic enteritis. An immunohistochemical (IHC) assay identified intracytoplasmic antigens of a malignant catarrhal fever virus (MCFV) within epithelial cells of the intestine, liver, lungs, and kidneys. A semi-nested PCR assay amplified the partial fragment of the OvGHV2 tegument protein gene from the intestine, confirming that the MCFV identified by IHC was OvGHV2. A qPCR assay that targeted the OvGHV2 polymerase gene revealed an elevated quantification cycle (Cq), while nanoplate-based digital PCR (dPCR) detected low viral copy load within the OvGHV2 DNA. Furthermore, the nucleic acids of several disease pathogens associated with diseases in ruminants were not amplified. However, the exact cause of the neurological syndrome remained obscure since nucleic acids of neurological disease pathogens such as bovine viral diarrhea virus, bovine alphaherpesvirus 1 and 5, Histophilus somni, and OvGHV2 were not detected from the brain. Collectively, the results of the Cq and dPCR confirmed that this goat was infected with a low viral load of OvGHV2, which probably was insufficient to induce the typical histopathological alterations and subsequent clinical manifestations associated with SA-MCF and/or infections by OvGHV2. Therefore, elevated viral loads of OvGHV2 would have been required for the development of histological lesions and/or clinical manifestations of SA-MCF in this goat. Furthermore, the dPCR methodology can be used for the efficient detection and quantification of OvGHV2 DNA in animals with or without clinical and/or histopathological evidence of SA-MCF. Additionally, since previous cases of OvGHV2 infections in goats did not have the typical clinical manifestations of SA-MCF, one wonders if this Macavirus can induce SA-MCF in goats.

Identification and characterisation of Gamma-herpesviruses in zoo artiodactyla

BACKGROUND

Viruses within the γ-herpesviruses subfamily include the causative agents of Malignant Catarrhal Fever (MCF) in several species of the order Artiodactyla. MCF is a usually fatal lymphoproliferative disease affecting non-adapted host species. In adapted host species these viruses become latent and recrudesce and transmit during times of stress or immunosuppression. The undetected presence of MCF-causing viruses (MCFVs) is a risk to non-adapted hosts, especially within non-sympatric zoological collections. This study investigated the presence of MCFVs in six different zoological collections in the UK, to evaluate the presence of subclinical/latent MCFVs in carrier animals.

METHODS

One-hundred and thirty eight samples belonging to 54 different species of Artiodactyla were tested by Consensus Pan-herpes PCR. The positive samples were sequenced and subjected to phylogenetic analyses to understand their own evolutionary relationships and those with their hosts.

RESULTS

Twenty-five samples from 18 different species tested positive. All viruses but one clustered in the γ-herpesvirus family and within the Macavirus as well as the non-Macavirus groups (caprinae and alcelaphinae/hippotraginae clusters, respectively). A strong association between virus and host species was evident in the Macavirus group and clustering within the caprinae group indicated potential pathogenicity.

CONCLUSION

This study shows the presence of pathogenic and non-pathogenic MCFVs, as well as other γ-herpesviruses, in Artiodactyla species of conservation importance and allowed the identification of new herpesviruses in some non-adapted species.

Ivermectin inhibits replication of the malignant catarrhal fever virus alcelaphine herpesvirus 1

Malignant catarrhal fever is a lymphoproliferative disease of cattle and other ungulates that is caused by genetically and antigenically related gamma herpesviruses of the genus Macavirus. Infection of the natural host species is efficient and asymptomatic but spread to susceptible hosts is often fatal with clinical signs including fever, depression, nasal and ocular discharge. There is no recognised treatment for MCF but a vaccine for one MCF virus, alcelaphine herpesvirus 1 (AlHV-1), has been described. In this paper we describe the inhibition of AlHV-1 replication and propagation by the anthelminthic drug ivermectin. Concentrations of 10 μM or greater led to significant reductions in both copy number and viable titre of virus tested in culture medium, with little replication detected at over 20 μM ivermectin. In the absence of alternative treatments, further testing of ivermectin as a candidate antiviral treatment for MCF may therefore be justified.

Cross-Reactivity of Neutralizing Antibodies among Malignant Catarrhal Fever Viruses

Some members of the gamma herpesvirus genus Macavirus are maintained in nature as subclinical infections in well-adapted ungulate hosts. Transmission of these viruses to poorly adapted hosts, such as American bison and cattle, can result in the frequently fatal disease malignant catarrhal fever (MCF). Based on phylogenetic analysis, the MCF viruses (MCFV) cluster into two subgroups corresponding to the reservoir hosts' subfamilies: Alcelaphinae/Hippotraginae and Caprinae. Antibody cross-reactivity among MCFVs has been demonstrated using techniques such as enzyme linked immunosorbent and immunofluorescence assays. However, minimal information is available as to whether virus neutralizing antibodies generated against one MCFV cross react with other members of the genus. This study tested the neutralizing activity of serum and plasma from select MCFV-infected reservoir hosts against alcelaphine herpesvirus 1 (AlHV-1) and ovine herpesvirus 2 (OvHV-2). Neutralizing antibody activity against AlHV-1 was detected in samples from infected hosts in the Alcelaphinae and Hippotraginae subfamilies, but not from hosts in the Caprinae subfamily. OvHV-2 neutralizing activity was demonstrated in samples from goats (Caprinae) but not from wildebeest (Alcelaphinae). These results show that neutralizing antibody cross reactivity is present to MCFVs within a virus subgroup but not between subgroups. This information is important for diagnosing infection with MCFVs and in the development of vaccines against MCF.

First report of malignant catarrhal fever in a captive pudu (Pudu puda)

A male, six-year-old pudu (Pudu puda) from an Italian zoo was submitted for postmortem examination after sudden death. Necroscopy revealed non-suppurative bronchopneumonia and degeneration of the liver and haemorrhagic lesions of the thymus, pericardium and spleen. Microscopically, multifocal perivascular mononuclear cell infiltrates were observed in the kidneys, lungs, spleen, and the portal triads of the liver. Histological examination of the brain showed meningitis, vasculitis and perivascular cuffs of mononuclear inflammatory cells. A region of the DNA polymerase gene of malignant catarrhal fever viruses was amplified by real-time PCR and nested PCR. PCR products from the tissue samples were sequenced and analysed. The sequences showed 99% similarity with a portion of the caprine herpesvirus 2 DNA polymerase gene. This is the first report of malignant catarrhal fever in a captive pudu.

Malignant catarrhal fever in a Red Angus cow

A 3-year-old cow was presented with bilateral corneal edema, increased respiratory effort, nasal discharge, and pyrexia. Ovine herpesvirus-2 was detected, confirming malignant catarrhal fever (MCF). The findings from this case suggest that MCF should be included in the differential diagnosis of mature cattle with ocular and nasal lesions, especially when sheep are present on the farm.

Virus im Schafspelz

In a double sense, the ovine gamma herpesvirus type 2 (OvHV-2) is a virus in sheep's skin. Not only is it present world wide in all sheep breeds but also it causes malignant catarrhal fever (MCF) in cattle pigs, elk, and bison. OvHV-2 cannot be propagated in cell culture. Therefore, new results from OvHV-2 research are based on molecular techniques and may be summarized as follows. OvHV-2 is transmitted by respiratory routes as well as by sexual intercourse. Lambs are infected within the first few months of life. Leucocytes, primarily latently infected lymphocytes, are responsible for disseminating the virus over the entire organism. On rare occasions, virus particles could be visualized by electron microscopy in explanted lymphocyte cultures. Structural antigens were detected by immunohistology in M-cells of diseased rabbits. Immunologically and cell biologically active genes have been detected on the viral genome.The products arising from those are thought to fine balance, the number of latently infected cells in sheep and to keep them alive without causing harm. Thus, it seems that this balance has been found through co-evolution, favoring both virus and natural host. In contrast, other host species that were exclude from the process of co-evolution, are bound to fall from MCF.

Host gene expression changes in cattle infected with Alcelaphine herpesvirus 1

Malignant catarrhal fever is a lymphoproliferative disease of cattle and other ungulates caused by infection with gamma-herpesviruses of the genus Macavirus. These viruses do not establish a productive infection but instead replicate in a cell-associated fashion in T lymphocytes, leading to systemic immune dysregulation and a generally fatal outcome. Despite significant progress in understanding the pathology of this disease, its pathogenesis remains unclear. To identify genes and pathways affected in clinical MCF, sixteen bovine GeneCHIP microarrays were used to assay RNA from kidney and lymph node of four MCF-affected and four control Bos taurus steers. This is the first expression study of AlHV-1-MCF in the bovine host. Over 250 genes showed significant changes in gene expression in either lymph node or kidney, while expression of 35 genes was altered in both tissues. Pathway and annotation analysis of the microarray data showed that immune response and inflammatory genes were up-regulated in the kidney while proliferation-associated transcripts were additionally increased in the lymph node. The genes that showed the largest expression rises in both diseased tissues included cytotoxic enzymes and pro-inflammatory chemokines. These data are consistent with disease-induced stimulation of inflammatory responses involving interferon-γ, including cytotoxic T cell recruitment and activation in peripheral tissues containing virus-infected cells. However it remains unclear whether the tissue damage in MCF lesions is due entirely to the activity of infected cells or whether uninfected T cells, recruited and activated at lesion sites through the action of infected cells, contribute to the pathogenesis of MCF.

[Clinical and pathological findings in an alpaca suffering from malignant catarrhal fever]

Malignant catarrhal fever (MCF) is a worldwide occurring sporadic disease of cloven-hoofed animals. For the first time, this case report describes clinical and pathological as well as histopathological findings in an alpaca suffering from MCF caused by ovine herpesvirus 2. Clinical symptoms comprised apathy, dehydration, anorexia, and emaciation. These symptoms were unspecific and did not correspond to any known course of MCF in cattle. However, the findings of the pathological and histopathological examination showed broad analogies to the main findings in other ruminants infected with MCF. In this alpaca, infection with ovine herpesvirus 2 was confirmed by postmortal PCR of tissue samples of lung, trachea, oesophagus, larynx and tonsils as well as conjunctival swabs.

Malignant catarrhal fever: understanding molecular diagnostics in context of epidemiology

Malignant catarrhal fever (MCF) is a frequently fatal disease, primarily of ruminants, caused by a group of gammaherpesviruses. Due to complexities of pathogenesis and epidemiology in various species, which are either clinically-susceptible or reservoir hosts, veterinary clinicians face significant challenges in laboratory diagnostics. The recent development of specific assays for viral DNA and antibodies has expanded and improved the inventory of laboratory tests and opened new opportunities for use of MCF diagnostics. Issues related to understanding and implementing appropriate assays for specific diagnostic needs must be addressed in order to take advantage of molecular diagnostics in the laboratory.

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.

Malignant catarrhal fever induced by alcelaphine herpesvirus 1 is associated with proliferation of CD8+ T cells supporting a latent infection

Alcelaphine herpesvirus 1 (AlHV-1), carried by wildebeest asymptomatically, causes malignant catarrhal fever (WD-MCF) when cross-species transmitted to a variety of susceptible species of the Artiodactyla order. Experimentally, WD-MCF can be induced in rabbits. The lesions observed are very similar to those described in natural host species. Here, we used the rabbit model and in vivo 5-Bromo-2'-Deoxyuridine (BrdU) incorporation to study WD-MCF pathogenesis. The results obtained can be summarized as follows. (i) AlHV-1 infection induces CD8(+) T cell proliferation detectable as early as 15 days post-inoculation. (ii) While the viral load in peripheral blood mononuclear cells remains below the detection level during most of the incubation period, it increases drastically few days before death. At that time, at least 10% of CD8(+ )cells carry the viral genome; while CD11b(+), IgM(+) and CD4(+) cells do not. (iii) RT-PCR analyses of mononuclear cells isolated from the spleen and the popliteal lymph node of infected rabbits revealed no expression of ORF25 and ORF9, low or no expression of ORF50, and high or no expression of ORF73. Based on these data, we propose a new model for the pathogenesis of WD-MCF. This model relies on proliferation of infected CD8(+) cells supporting a predominantly latent infection.

Production and utilization of interleukin-15 in malignant catarrhal fever

Malignant catarrhal fever (MCF) is an often fatal lymphoproliferative disease of ungulates caused by either alcelaphine herpesvirus-1 (AlHV-1) or ovine herpesvirus-2 (OvHV-2). The pathogenesis of MCF is poorly understood, but appears to involve an auto-destructive pathology whereby cytotoxic lymphocytes destroy areas of a variety of tissues. The cytokine interleukin-15 (IL-15) is involved in the development and maintenance of cytotoxic lymphocytes and may therefore have a role in the pathogenesis of MCF. Virus-infected large granular lymphocytes (LGLs) were obtained from the tissues of rabbits infected with AlHV-1 or OvHV-2. These cells exhibited a similar proliferative response to IL-15 and to IL-2 in culture, but their content of the activated cytotoxic enzyme (BLT-esterase) was maintained at higher levels in the presence of IL-15 compared with IL-2. The LGLs did not express IL-15 mRNA or produce IL-15 protein. By contrast, there was abundant expression of IL-15 mRNA and protein in affected tissues. IL-15 production was associated with necrotic lesions of the mesenteric lymph node and appendix of OvHV-2-infected rabbits, but was not found in the same tissues of rabbits infected with AlHV-1 in which there were no necrotic lesions. The cellular source of the IL-15 was predominantly lymphoid cells that did not express B cell or monocyte-macrophage markers. Only a few IL-15+ cells (<10%) co-localized with pan-T cells or CD8+ T cells. The abundance of IL-15 in tissue with lesions of MCF suggests that this cytokine may have a role in the pathogenesis of MCF.

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.

Malignant catarrhal fever associated with ovine herpesvirus-2 in free-ranging mule deer in Colorado

Malignant catarrhal fever (MCF) was diagnosed in four free-ranging mule deer (Odocoileus hemionus) in January and February of 2003. Diagnosis was based on typical histologic lesions of lymphocytic vasculitis and PCR identification of ovine herpesvirus-2 (OHV-2) viral genetic sequences in formalin-fixed tissues. The animals were from the Uncompahgre Plateau of southwestern Colorado. Deer from these herds occasionally resided in close proximity to domestic sheep (Ovis aries), the reservoir host of OHV-2, in agricultural valleys adjacent to their winter range. These cases indicate that fatal OHV-2 associated MCF can occur in free-ranging mule deer exposed to domestic sheep that overlap their range.

Malignant catarrhal fever-like lesions associated with ovine herpesvirus-2 infection in three goats

This is the first description of malignant catarrhal fever-like lesions associated with ovine herpesvirus-2 (OvHV-2) infection in goats with central nervous symptoms. The diagnosis was based on typical histological lesions characterized by systemic lymphohistiocytic and fibrinoid vasculitis and confirmed by polymerase chain reaction and subsequent phylogenetic analysis of the detected OvHV-2 sequences.

Malignant catarrhal fever in free-ranging cervids associated with OvHV-2 and CpHV-2 DNA

Pathologic lesions were summarized in 18 free-ranging cervids (15 moose [Alces alces], two roe deer [Capreolus capreolus], and one red deer [Cervus elaphus]) diagnosed with malignant catarrhal fever (MCF) after examination at the National Veterinary Institute, Oslo 1982-2005. Eye lesions (conjunctivitis, corneal opacity, fibrin clots in the anterior eye chamber) were the most frequent gross finding. Erosive-ulcerative mucosal lesions in the nose and mouth were also commonly found. Histopathology revealed a nonpurulent vasculitis and perivasculitis in the central nervous system (CNS) typical of MCF in 16 of the cases. The diagnosis in the remaining two animals was based upon histologic eye lesions consistent with MCF (CNS not available for examination). Polymerase chain reaction was run on samples from 15 individuals for evidence of MCF-virus DNA, and ovine herpesvirus-2 (OvHV-2) DNA was detected in five moose, one roe deer, and one red deer, and caprine herpesvirus-2 (CpHV-2) DNA was detected in two moose and one roe deer. Sera from 1,000 free-ranging cervids were tested for specific antibodies to MCF-associated viruses (MCFV) by competitive inhibition enzyme-linked immunosorbent assay. The seroprevalences were: red deer 5%, reindeer (Rangifer tarandus) 4%, roe deer 2%, and moose 0.4% (n = 250 for all four species). The results indicate that sheep and goat MCFV may cause serious disease in wild moose, roe deer, and red deer. The seropositive cervids most likely represent individuals infected with either OvHV-2 or CpHV-2, but may also reflect infections with other related MCFV.

Immunohistochemical study of experimental malignant catarrhal fever in rabbits

Malignant catarrhal fever (MCF) is an often-fatal lymphoproliferative disease of a variety of ungulates that occurs worldwide. It is caused by either of the highly related but distinct gammaherpesviruses alcelaphine herpesvirus-1 (AlHV-1, wildebeest reservoir) or ovine herpesvirus-2 (OvHV-2, sheep reservoir). MCF in rabbits is an excellent model as it closely resembles the disease in susceptible ungulates that include cattle, deer and bison. In this study, newly available and previously characterized monoclonal antibodies specific for rabbit leucocyte differentiation molecules were used to perform a detailed immunohistochemical examination of both AlHV-1 MCF and OvHV-2 MCF in rabbits. Differences in the MCF caused by the two viruses included: less tissue necrosis and more lymphoid cell accumulations in AlHV-1 MCF compared with OvHV-2 MCF, and in particular marked tissue necrosis in the mesenteric lymph node, appendix and liver of OvHV-2-infected animals when compared with either other tissues in OvHV-2 MCF or AlHV-1 MCF lesions in any tissue. In both AlHV-1 MCF and OvHV-2 MCF, lymphoid cell accumulations in lymphoid and non-lymphoid tissues consisted mainly of T-cells with a corresponding absence of B-cells. CD8(+) T-cells accounted for a proportion of these in the non-lymphoid tissues, but there was evidence for the accumulation of an unidentified T-cell subset/subsets as well. This study extends our understanding of the mechanisms of immuno-pathogenesis of MCF.

Malignant catarrhal fever in pigs and a genetic comparison of porcine and ruminant virus isolates in Finland

An outbreak of the sheep-associated form of malignant catarrhal fever (MCF) in a Finnish sow herd was diagnosed by histopathology and confirmed by PCR. Several gilts and sows were suffering from high fever and anorexia and had aborted, and six of them had died. Typical signs of lymphoproliferation and vasculitis were observed histologically in several tissues, including the uterus. Ovine herpesvirus-2 (OvHV-2) was detected by PCR in two sows. Sequences of the OvHV-2 tegument protein gene obtained from the sows and from three cases of sheep-associated mcf in Finnish cattle were compared and found to be identical. These are the first confirmed cases of mcf in pigs in Finland.

Experimental aerosol infection of cattle (Bos taurus) with ovine herpesvirus 2 using nasal secretions from infected sheep

Infection of clinically susceptible ruminants, including domesticated cattle and American bison, with ovine herpesvirus 2 (OvHV-2) can result in the fatal lymphoproliferative and vasculitis syndrome known as malignant catarrhal fever (MCF). A reliable experimental infection model is needed to study the pathogenesis of MCF and to develop effective vaccination strategies to control the disease. An experimental aerosol infection model using sheep, the natural carriers of OvHV-2, has been developed (Taus et al., 2005). Using the protocol and OvHV-2 inoculum established in the previous study, eight calves were nebulized with four different doses of OvHV-2 in nasal secretions from infected sheep. Two control calves were nebulized with nasal secretions from uninfected sheep. Infection status of all calves was monitored using competitive inhibition ELISA, PCR and clinical parameters. Six of eight nebulized calves became infected with OvHV-2. One calf receiving the highest dose of virus developed typical clinical, gross and histological changes of MCF. This study showed that nasal secretions collected from sheep experiencing OvHV-2 shedding episodes were infectious for cattle and capable of inducing MCF. The data also indicate that cattle are relatively resistant to disease following infection. The use of more susceptible species as experimental animal models, such as bison and selected cervid species should be examined.

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.

Sheep-associated malignant catarrhal fever involving 3-5-week-old calves in Saudi Arabia

Between late December 1999 and late April 2000, three locally bred Friesian calves (ageing 25, 28 and 35 days) in a dairy farm, at Al-Ahsa locality of the eastern region of Saudi Arabia showed dullness and inappetence. Their rectal temperatures ranged between 41 and 41.5 degrees C. One to 2 days later and onwards, the calves showed lacrimation, nasal discharge, salivation, oedema of the head, conjunctivitis, exo-ophthalmia and corneal opacity. One calf showed diarrhoea. The superficial lymph nodes were oedematous and swollen. The calves died after 7, 5 and 8 days, respectively, following the onset of the disease. Calves and rabbits were experimentally infected with materials from the naturally infected calves. The rabbits showed fever, mild conjunctivitis and one rabbit showed wet faeces. The experimentally inoculated calves showed rise in temperature and mild symptoms but none of them died. The virus from the naturally infected calves and from the experimentally infected rabbits was identified as malignant catarrhal fever (MCF) virus using both the complement fixation test and the fluorescent antibody test, employing a reference anti-serum against the WC 11 strain of MCF virus. Serological survey for MCF antibodies in cattle, sheep and goats from the affected farm revealed that 54% of the examined animals were positive. The situation of MCF in Saudi Arabia was discussed in relation to sheep and wild game. This paper constitutes the first report of MCF in Saudi Arabia and the Gulf region.

Caprine herpesvirus-2 in association with naturally occurring malignant catarrhal fever in captive sika deer (Cervus nippon)

Three female sika deer from a single captive herd were submitted for postmortem examination over a 139-day period. The first 2 deer submitted were reported to have lost body mass for 20 days to 1 month before euthanasia. One of these deer had diarrhea, the other had a crusting dermatitis on the nasal planum and inner aspects of both pinnae. The third hind did not have any signs of disease before it was found seizuring and was immediately euthanatized. Microscopically, all 3 animals had a lymphocytic vasculitis typical of malignant catarrhal fever (MCF), with the most severe lesions in the brain. All 3 deer were polymerase chain reaction (PCR) positive for caprine herpesvirus 2 (CpHV-2) and were negative for ovine herpesvirus 2 (OHV-2). Two healthy goats that were housed adjacent to the deer were also PCR positive for CpHV-2 and PCR negative for OHV-2. The CpHV-2, PCR amplicons from the hinds, and the 2 healthy goats had an identical single base polymorphism. A male sika deer that was housed with the hinds and a fawn from 1 of the hinds remained asymptomatic and were PCR negative for CpHV-2. This represents the first report of mortality with MCF-like lesions in association with CpHV-2.

Identification and quantification of ovine gammaherpesvirus 2 DNA in fresh and stored tissues of pigs with symptoms of porcine malignant catarrhal fever

Cases of porcine malignant catarrhal fever were analyzed by a combination of identification and quantitation of ovine gammaherpesvirus 2 DNA in a variety of paraffin-embedded tissues from diseased pigs, serology, and exclusion of primary porcine gammaherpesviruses. In spite of reduced signal due to fixation and paraffin embedding, ovine gammaherpesvirus 2 DNA in pig brains exceeded the amounts found in sheep brains by orders of magnitude.

[Porcine malignant catarrhal fever: diagnostic findings and first detection of the pathogenic agent in diseased swine in Switzerland]

For the first time Ovine Herpesvirus 2 (OvHV-2) was identified in Swiss pigs as the causative agent of Porcine Malignant Catarrhal Fever (MCF). Diseased animals from two farms were observed to show weakness, anorexia, fever up to 41 degrees C, and neurological symptoms, i.e. ataxia, convulsions and hyperesthesia, erosion on the snout and in the oral and nasal mucosa, as well as multiple skin lesions. Histopathological findings included severe non-purulent inflammation with mononuclear cell infiltration in several organs. Most dominant were meningo-encephalitis, disseminated nephritis as well as purulent catarrhalic bronchopneumonia. The findings were quite reminiscent of the lesions due to MCF in cattle and give therefore substantial proof to use Porcine Malignant Catarrhal Fever as the term for the disease. Identification of the causative agent was done with a quantitative PCR specific for OvHV-2. Different tissues from diseased animals were positive. Furthermore, one animal which had been ill for more than five days tested positive for antibodies against an epitope conserved among MCF viruses. Serum samples from diseased animals reacted negative towards Classical Swine Fever- and Pseudorabies virus antigen. A weakly positive reaction against porcine enterovirus type I argued against the involvement of enteroviruses in the observed disease. Moreover, by means of different conventional PCRs, we detected the newly discovered porcine lymphotropic herpesviruses for the first time in Switzerland and could at the same time exclude their involvement in Porcine Malignant Catarrhal Fever.

Caprine herpesvirus-2-associated malignant catarrhal fever in white-tailed deer (Odocoileus virginianus)

A subacute disease presenting primarily as alopecia and weight loss occurred in 2 white-tailed deer (Odocoileus virginianus) on farms in Minnesota and in Texas. A presumptive diagnosis of malignant catarrhal fever (MCF) was made on the basis of histological lesions. Antibody against an epitope conserved among the MCF group viruses was detected in the serum of both deer. DNA samples from the deer were subjected to a variety of PCR amplifications. Alignment of the amplified sequences from the diseased animals revealed that they were 100% identical to each other and to the same DNA fragment from the newly recognized member of the MCF virus group endemic in domestic goats (Capra hircus), provisionally named caprine herpesvirus 2 (CpHV-2). A seroprevalence survey from one of the deer farms showed a high rate of subclincal infection in the deer population. This study provides further confirmation that CpHV-2 is a pathogen, at least for deer, and emphasizes the risk of loss from MCF when mixing cervids with goats.

Mural folliculitis and alopecia caused by infection with goat-associated malignant catarrhal fever virus in two sika deer

Two sika deer from a zoo in Florida were examined because of chronic hair loss and skin lesions. No common causes of alopecia were identified in either deer. One deer was treated with prednisone, but the condition worsened when the dosage was decreased. Both deer were euthanatized after several months because of continued disease. The predominant histologic lesion in skin specimens was granulomatous mural folliculitis. Serologic testing and sequencing of fragments produced with a consensus polymerase chain reaction assay indicated that both deer were infected with caprine herpesvirus-2, a newly recognized member of the malignant catarrhal fever group of viruses. Disease in these deer was substantially different from that typically seen following infection with ovine herpesvirus-2, the sheep-associated malignant catarrhal fever virus. Findings in these deer establish the pathogenicity of caprine herpesvirus-2 in sika deer and illustrate the ability of this group of complex herpesviruses to cause a wide variety of clinical abnormalities in diverse species.

Malignant catarrhal fever in a bison (Bison bison) feedlot, 1993-2000

A fatal enteric syndrome was identified in American bison (Bison bison) at a large feedlot in the American Midwest in early 1998. An estimated 150 bison died of the syndrome between January 1998 and December 1999. The syndrome was identified as malignant catarrhal fever (MCF), primarily the alimentary form. Clinical onset was acute, and most affected bison died within 1-3 days; none recovered. Consistent lesions were hemorrhagic cystitis, ulcerative enterotyphlocolitis, and arteritis-phlebitis. Vasculitis was milder and more localized than that in cattle with MCF, and in contrast to the situation in cattle, lymphadenomegaly was minimal. Virtually all affected bison examined were positive for ovine herpesvirus 2 (OvHV-2) by polymerase chain reaction (PCR) assay. A retrospective study of archived tissues established that MCF occurred in the yard as early as 1993. A prospective study was undertaken to establish the importance of MCF relative to other fatal diseases at the feedlot. The fate of a group of 300 healthy male bison in a consignment of 1,101 animals was followed for up to 7 months to slaughter. At entry, 23% (71/300) of bison were seropositive for MCF viruses, and 11% (8/71) of these seropositive bison were PCR positive for OvHV-2. Forty seronegative bison were selected at random from the group, and all were PCR negative for OvHV-2. There was no change in seroprevalence in the group during the investigation. The minimum infection rate for MCF virus was 36.3% (93/256). Twenty-two (7.3%) of the 300 bison in the feedlot died. Of these, 15 had MCF, 4 had acute or chronic pneumonia, and 3 were unexamined. Losses in the entire consignment were higher (98/1,101; 8.8% death loss); 76% of deaths were attributable to MCF. The study failed to reveal a relationship between subclinical infection and development of clinical disease.

Detection and multigenic characterization of a herpesvirus associated with malignant catarrhal fever in white-tailed deer (Odocoileus virginianus) from Missouri

Between 1998 and 2001, tissues from four captive white-tailed deer were observed to have histologic lesions of systemic lymphocytic vasculitis. These lesions suggested malignant catarrhal fever, although epizootic hemorrhagic disease and bluetongue were included in the differential diagnosis. Initial diagnostic efforts, including virus isolation and reverse transcription-PCR for epizootic hemorrhagic disease virus and bluetongue virus, failed to identify an etiologic agent. However, consensus primer PCR targeted to the herpesvirus DNA polymerase gene detected viral genomic DNA in each of these four cases. Nucleotide sequence analysis of the amplified product demonstrated that the detected virus was identical over the compared region to the recently described malignant catarrhal fever virus of white-tailed deer (H. Li, N. Dyer, J. Keller, and T. B. Crawford, J. Clin. Microbiol. 38:1313-1318, 2000). Additional nucleotide sequencing of both the DNA polymerase gene and DNA packaging gene followed by phylogenetic analysis solidified this newly recognized herpesvirus as a member of the Gammaherpesvirinae and suggests that this virus, along with ovine herpesvirus 2, alcelaphine herpesvirus 1, alcelaphine herpesvirus 2 and caprine herpesvirus 2, may be part of a separate clade within this subfamily.

[Malignant catarrhal fever in Switzerland: 2. Evaluation of the diagnosis]

Malignant catarrhal fever (MCF) is a mostly fatal lymphoproliferative disease of cattle. In 1995 a PCR based method was introduced for the detection of the ovine herpesvirus 2 (OvHV-2), which is regarded as the causative agent of the sheep-associated form of the disease. This PCR can be regarded as a gold standard for the in vivo diagnosis of sheep-associated MCF in cattle (Müller-Doblies et al., 1998). This semi-nested PCR was now used as a reference test for the reassessment of diagnostic criteria in the clinical and post mortem diagnosis that could previously not be quantitated. Based on 83 suspected cases with a complete clinical record the clinical signs were weighted and grouped according to their sensitivity and specificity into lead signs indicative of MCF and frequently accompanying signs supportive for the diagnosis of MCF and general clinical signs that were less reliable for the diagnosis. Differential diagnoses are discussed, which are of particular significance due to their status as OIE list A diseases e.g. foot-and-mouth disease or rinderpest. 38 PCR confirmed cattle with MCF served for the quantitative analysis of organ lesions. For the post mortem diagnosis an essential set of organ samples is defined to permit a reliable histological diagnosis, as the gross pathology often did not give any indication for the diagnosis. These criteria should help to improve the diagnostic efficiency and to select the appropriate laboratory diagnostic procedures for MCF-suspected cattle.

Epizootic malignant catarrhal fever in three bison herds: differences from cattle and association with ovine herpesvirus-2

Three bison herds in Colorado experienced high mortality from malignant catarrhal fever (MCF). In comparison with cattle, the bison had a more rapidly progressive disease, fewer clinical signs, and milder inflammatory histologic lesions. There was consistent association with ovine herpesvirus-2 (OHV-2). Contact with sheep was not consistent. Of 17 animals in herd A, 15 died of acute MCF; 1 was slaughtered while healthy; and 1 developed clinical signs of MCF, was treated with corticosteroids and antibiotics, and died of fungal abomasitis and rhinitis after 5 months. In herds B and C, approximately 300 of 900 and 18 of 20 died of MCF following brief clinical disease. The nearest sheep were 1 mile away from herd A, but direct contact with sheep could be documented in herds B and C. Complete gross and histologic examinations were conducted on 34 animals, including all animals in herd A, and MCF was diagnosed in 31. In addition, field necropsies were performed on all dead animals in herd B and most in herd C and MCF was diagnosed on the basis of the gross lesions in most animals. Clinical signs of each animal in herd A were recorded. Illness was brief, usually 8-48 hours. Clinical signs were subtle; separation from the herd was often observed. In all 3 herds, hemorrhagic cystitis and multifocal ulceration of the alimentary tract were consistently found at necropsy. Mild lymphocytic vasculitis was present in multiple organs. Ovine herpesvirus-2 was found by polymerase chain reaction (PCR) in 71 of 105 formalin-fixed tissue specimens from 29 of 31 animals with MCF. In herd A, blood samples from 13 animals were collected at 5 time points and tested by PCR for the presence of OHV-2 viral sequences in peripheral blood leukocytes. Nine bison with a positive PCR test and 4 with negative results prior to clinical illness died of MCF.

Newly recognized herpesvirus causing malignant catarrhal fever in white-tailed deer (Odocoileus virginianus)

Malignant catarrhal fever (MCF) was diagnosed by clinical signs and lesions in five out of six white-tailed deer (Odocoileus virginianus) in a North American zoo. The clinical signs and histopathological lesions in these deer were typical of MCF. Antibody to an epitope conserved among the MCF viruses was detected in the sera collected from the deer. PCR failed to amplify viral sequences from DNA extracted from peripheral blood leukocytes (PBL) and/or spleens of the deer with primers specific for ovine herpesvirus 2 (OHV-2) or specific for alcelaphine herpesvirus 1 (AHV-1). By using degenerate primers targeting a conserved region of a herpesviral DNA polymerase gene, a DNA fragment was amplified from the PBL or spleens of all six deer and sequenced. Alignment of the sequences demonstrated that the virus in the deer belongs to the Gammaherpesvirinae subfamily, exhibiting 82% identity to OHV-2, 71% to AHV-1, and 60% to a newly identified bovine lymphotropic herpesvirus. This virus, which causes classical MCF in white-tailed deer, is a newly recognized agent belonging to the MCF group of gammaherpesviruses. It is the third reported pathogenic MCF virus, genetically distinct but closely related to OHV-2 and AHV-1. The reservoir for the virus has not been identified.

Suspected sheep-associated malignant catarrhal fever in a zero-grazed dairy herd in Kenya

An outbreak of a disease characterised by very high mortality occurred in a group of nine calves (1B4 months old) in a zero-grazing unit 2-3 weeks after an introduction of an apparently healthy alien sheep into the calf pen. Five of the six calves which contracted the disease died. The main clinical signs observed were marked depression, persistently high body temperature (40,5-41,5 degrees C), copious mucopurulent nasal and ocular discharges, dyspnoea, bilateral keratoconjunctivitis with corneal opacity, enlargement of the superficial lymph nodes and marked erythema and/or superficial erosions of the buccal mucosae. At necropsy there were lesions in the upper respiratory and digestive tracts, lymph nodes, brain, eyes, liver, kidneys and the urinary bladder. The lesions were histopathologically characterized by fibrinoid vasculitis which was accompanied by lymphocytic infiltration in the parenchyma of the affected tissues. Based on the evidence of contact between the calves and the recently introduced foreign sheep, the characteristic clinical signs and histopathological findings, a diagnosis of sheep-associated malignant catarrhal fever was made.

Field validation of laboratory tests for clinical diagnosis of sheep-associated malignant catarrhal fever

Until recently, sheep-associated malignant catarrhal fever (SA-MCF) was diagnosed mainly on the basis of clinical presentation and histopathological changes. Using clinically diagnosed field cases, we have evaluated a seminested PCR and a competitive inhibition enzyme-linked immunosorbent assay (CI-ELISA) and compared these assays in the diagnosis of SA-MCF in cattle with histopathology as a provisional "gold standard." Samples from 44 cattle with clinical signs suggestive of SA-MCF were examined by histopathology, PCR, and CI-ELISA. In addition, samples from healthy cattle were evaluated by PCR (n = 96) and CI-ELISA (n = 75). Based on histopathology, 38 of the 44 clinical cases were classified as SA-MCF positive, 3 were classified as inconclusive, and 3 were classified as SA-MCF negative. The sensitivity of PCR was 95 to 97%, whereas the specificity ranged between 94 and 100%. The CI-ELISA showed a sensitivity of 56 to 87% and a specificity between 91 and 100%. In the field, there is good correlation between the diagnoses of SA-MCF by histopathology, PCR, and CI-ELISA. These data also confirm the close association of ovine herpesvirus 2 with SA-MCF in Switzerland.

[Malignant catarrhal fever in zoo ruminants]

An outbreak of malignant catarrhal fever (MCF) in Indian gauer (Bos gaurus gaurus) and Javan banteng (Bos javanicus javanicus) occurred in the year 1964 and killed almost all animals of the groups of these species kept at the Munich zoo at that time. In the consecutive years at highly irregular intervals cases of the head-and-eye-form of MCF occurred sporadically at the zoo in European and American bison (Bison bonasus, B. bison' bison, B. bison athabascae), elk (Alces alces), red deer (Cervus elaphus), Père David's deer (Elaphurus davidianus) and again in gaur and banteng. The clinical and pathomorphological observations, including those of prophylactic and tentative treatment are reported. The subspecies of caprinae and alcelaphinae potentionally latently infected with viral agents of MCF kept at the zoo over the reported period are listed. Some details concerning housing, taking care of the animals etc. of the latently infected carriers of the family caprinae and the susceptible species of bovidae and cervidae are also given as far as they are of epidemiological interest. The results of the retrospective analysis and the results of testing paraffin-embedded tissue samples for the presence of ovine herpesvirus-2 (OHV-2)-specific DNA and alcelaphine herpesvirus-1 (AHV-1)-specific DNA from 1964 up to 1997 are discussed. The negative results for OHV-2-specific DNA suggest that MCF at Munich zoo until 1979 could have been "wildebeest-associated", also because until 1974 blue wildebeest (Connochaetes taurinus taurinus) and until 1983 white-tailed gnu (Connochaetes gnou) were kept. However, positive results for OHV-2-specific DNA in the tissues collected from 1985 onwards, strongly suggest the "sheep-associated" MCF.

Malignant catarrhal fever in bison, acute and chronic cases

Acute malignant catarrhal fever (MCF) was diagnosed in 10 bison from 6 herds and ranging from 1 to 6 years of age. The pattern of clinical signs and morphologic lesions differed among bison. Combinations of corneal opacity, lacrimation, nasal discharge, depression, excess salivation, anorexia, diarrhea, melena, and hematuria were observed. Vasculitis characterized by lymphoid infiltrates in the adventia with variable extension into media and intima was found in multiple tissues in each animal. Fibrinoid vascular necrosis was rare. Ulceration in the alimentary tract was found in 9/10 bison, and ulceration or hemorrhage in the urinary bladder was found in 8/10 bison. Lymphoid infiltrates were present in 7 of 9 livers and 9 of 9 kidneys examined histologically. Hyperplasia of lymph nodes was observed in 5 bison. Chronic MCF was diagnosed in 1 bison with an 80-day course of illness that began with lacrimation, corneal opacity, mucoid nasal discharge, depression, and anorexia. These signs ceased after 15 days but circling and blindness developed on day 76. Chronic vascular lesions characterized by endothelial cell hypertrophy, intimal thickening, fragmentation of the internal elastic membrane, smooth muscle hypertrophy, and adventitial infiltrates of lymphocytes and plasma cells were found in many organs. The retinal arteries had chronic inflammation and acute transmural fibrinoid necrosis. The retinas were infarcted. Polymerase chain reaction technique for amplification of ovine herpesvirus 2 sequences was performed on formalin-fixed tissues, and viral sequences were detected in 1-7 tissues from each animal. These viral sequences were not found in tissues of 4 bison not affected by MCF.

Chronic and recovered cases of sheep-associated malignant catarrhal fever in cattle

Malignant catarrhal fever (MCF) is traditionally regarded as a disease with a short clinical course, low morbidity and high case fatality rate. Owing to the limitations of the assays used for laboratory diagnosis. It was difficult in characterise the clinical spectrum of sheep-associated MCF, particularly when the cattle recovered from an MCF-like clinical syndrome. Over a period of three years, 11 cattle that survived MCF for up to two-and-a-half years were identified on four premises. A clinical diagnosis of MCF was confirmed by the detection of ovine herpesvirus-2 DNA in peripheral blood leucocytes using a polymerase chain reaction (PCR) assay that detects a specific 238 base-pair fragment of viral genomic DNA. Of the 11 cattle examined, six recovered clinically with the exception of bilateral corneal oedema with stromal keratitis (four animals) and unilateral perforating keratitis (one animal). The 10 animals available for postmortem examination had disseminated subacute to chronic arteriopathy. Recovery was associated with the resolution of the acute lymphoid panarteritis that characterises the acute phase of MCF, and with the development of generalised chronic obliterative arteriosclerosis. Bilateral leucomata were due in part to the focal destruction of corneal endothelium secondary to acute endothelialitis. Formalin-fixed tissues and/or unfixed lymphoid cells from all 11 cattle were positive for sheep-associated MCF by PCR. These observations indicate that recovery and chronic disease are a significant part of the clinical spectrum of MCF and that such cases occur with some frequency in the area studied. The affected cattle remain persistently infected by the putative sheep-associated MCF gammaherpesvirus.

Characterisation of the lymphoproliferation in rabbits experimentally affected with malignant catarrhal fever

Malignant catarrhal fever (MCF) in rabbits caused by the three Herpesviruses: alcelaphine herpesvirus-1 (AHV-1), ovine herpesvirus-2 (OHV-2) and hippotragine herpesvirus-1 (HipHV-1) induced hyperplasia of lymphoid tissues and accumulations of mononuclear lymphoid cells in non-lymphoid tissues. However, certain lymph nodes were affected preferentially. The lymphoid cells in non-lymphoid tissues were CD43+ T-cells which showed evidence of in situ multiplication. A more detailed phenotypic analysis of splenocytes and lymph node cells in AHV-1 infected rabbits suggested that the hyperplasia was probably due to the expansion of CD8+ T-cells. On the basis of these data and the observations of other authors, that no or very little viral expression can be detected in lesions of MCF affected animals, we propose that the pathogenesis of MCF results from a dysregulation of a secretory T-cell activator. The variable pathology induced by the three viruses may reflect a quantitative or qualitative differences in this proposed activator.

Surface marker analysis of the vascular and epithelia lesions in cattle with sheep-associated malignant catarrhal fever

Surface marker analysis of the vascular and epithelial lesions in cattle with sheep associated malignant catarrhal fever (MCF) were done by immunohistochemistry using 7 monoclonal antibodies. MHC class I and II antigens were expressed in the degenerated portion of the vascular walls in addition to infiltrated leukocytes. The major population of mononuclear cells in these lesions were phenotypically macrophages. The other cells had BoCD4 or BoCD8, but rarely gamma delta T cell markers. These results suggest involvement of MHC restriction and macrophages, in addition to autoaggressive cytotoxic T lymphocytes, in the development of MCF vascular lesion.

An epizootic of malignant catarrhal fever in a large captive herd of white-tailed deer (Odocoileus virginianus)

Over a 4-mo period 23 of 28 white-tailed deer kept at a small zoo in New Jersey (USA) died. Clinical signs prior to death were minimal and consisted of depression, central nervous system disorders, and watery diarrhea in a few animals only. Histopathology revealed widespread acute vascular lesions, ranging from modest accumulations of blast-like mononuclear cells and edema in the adventitia through to disruption of the tunica media and thrombosis. These vascular lesions were seen in a variety of organs but were most prominent in lung, heart, liver and intestine. Severe vascular changes were associated with necrosis. Lymphoreticular hyperplasia was evident in the lymphoid tissue of all animals.

Epidemiologic and pathologic aspects of an epizootic of malignant catarrhal fever in exotic hoofstock

An epizootic of malignant catarrhal fever (MCF) occurred at the Los Angeles Zoological Park which resulted in the deaths of four exotic ungulates. The source of infection was considered to be a newly purchased wildebeest bull (Connochaetes taurinus taurinus) that had been negative for antibody to MCF virus by an indirect immunofluorescent test. The need to re-evaluate regulations for the transportation and housing of young wildebeest is emphasized by this MCF outbreak. The diagnostic technology now available for identifying asymptomatic carriers of MCF virus and the present understanding of the behavior and pathogenesis of this highly cell-associated herpesvirus in exotic ruminants should provide a basis for the prevention and control of MCF in zoological parks.