The pathomorphology of malignant catarrhal fever. II. Multisystemic epithelial lesions

Sheep-Associated Malignant Catarrhal Fever: Role of Latent Virus and Macrophages in Vasculitis

Malignant catarrhal fever (MCF) is a sporadic, generally fatal disease caused by gammaherpesviruses in susceptible dead-end hosts. A key pathological process is systemic vasculitis in which productively infected cytotoxic T cells play a major role. Nonetheless, the pathogenesis of MCF vasculitis is not yet clear. We hypothesized that it develops due to an interaction between virus-infected cells and immune cells, and we undertook a retrospective in situ study on the rete mirabile arteries of confirmed ovine gammaherpesvirus-2 (OvHV-2)-associated MCF cases in cattle, buffalo, and bison. Our results suggest that the arteritis develops from an adventitial infiltration of inflammatory cells from the vasa vasorum, and recruitment of leukocytes from the arterial lumen that leads to a superimposed infiltration of the intima and media that can result in chronic changes including neointimal proliferation. We found macrophages and T cells to be the dominant infiltrating cells, and both could proliferate locally. Using RNA in situ hybridization and immunohistology, we showed that the process is accompanied by widespread viral infection, not only in infiltrating leukocytes but also in vascular endothelial cells, medial smooth muscle cells, and adventitial fibroblasts. Our results suggest that OvHV-2-infected T cells, monocytes, and locally proliferating macrophages contribute to the vasculitis in MCF. The initial trigger or insult that leads to leukocyte recruitment and activation is not yet known, but there is evidence that latently infected, activated endothelial cells play a role in this. Activated macrophages might then release the necessary pro-inflammatory mediators and, eventually, induce the characteristic vascular changes.

A review of the epidemiological, clinical, and pathological aspects of malignant catarrhal fever in Brazil

Sheep-associated malignant catarrhal fever (SA-MCF), the form of MCF that occurs in Brazil, is a severe, frequently fatal, infectious disease caused by ovine gammaherpesvirus-2 (OvHV-2), in which sheep are the asymptomatic hosts and cattle and other cloven-hoofed animals are the accidental hosts. This review provides a critical analysis of the historical, epidemiological aspects and the estimated economic impacts associated with SA-MCF in Brazil. Moreover, the clinical manifestations and pathological lesions associated with SA-MCF in cattle are reviewed and discussed and the phylogenetic distribution of OvHV-2 in Brazil is presented. OvHV-2 is the only MCF virus identified in animals from Brazil. It is recommended that a histopathologic diagnosis of SA-MCF be based on all aspects of vascular disease in the affected animal and not only lymphocytic/necrotizing vasculitis and/or fibrinoid change. Conformation of the intralesional participation of OvHV-2 in these alterations can be achieved by immunohistochemistry and/or in situ hybridization assays. Additionally, it is proposed that OvHV-2 should be considered as a possible infectious disease agent associated with the development of bovine respiratory disease in cattle. Furthermore, the possible role of the small intestine in the dissemination of OvHV-2 is discussed.

The effect of the TLR9 ligand CpG-oligodeoxynucleotide on the protective immune response to alcelaphine herpesvirus-1-mediated malignant catarrhal fever in cattle

We wished to determine the effect of of CpG ODN adjuvant on the magnitude and duration of protective immunity against alcelaphine herpesvirus-1 (AlHV-1) malignant catarrhal fever (MCF), a fatal lymphoproliferative disease of cattle. Immunity was associated with a mucosal barrier of virus-neutralising antibody. The results showed that CpG ODN included either with emulsigen adjuvant and attenuated AlHV-1 (atAlHV-1) or alone with atAlHV-1 did not affect the overall protection from clinical disease or duration of immunity achieved using emulsigen and atAlHV-1. This is in contrast to other similar studies in cattle with BoHV-1 or cattle and pigs with various other immunogens. In addition to this, several other novel observations were made, not reported previously. Firstly, we were able to statistically verify that vaccine protection against MCF was associated with virus-neutralising antibodies (nAbs) in nasal secretions but was not associated with antibodies in blood plasma, nor with total virus-specific antibody (tAb) titres in either nasal secretions or blood plasma. Furthermore, CpG ODN alone as adjuvant did not support the generation of virus-neutralising antibodies. Secondly, there was a significant boost in tAb in animals with MCF comparing titres before and after challenge. This was not seen with protected animals. Finally, there was a strong IFN-γ response in animals with emulsigen and atAlHV-1 immunisation, as measured by IFN-γ secreting PBMC in culture (and a lack of IL-4) that was not affected by the inclusion of CpG ODN. This suggests that nAbs at the oro-nasal-pharyngeal region are important in protection against AlHV-1 MCF.

The A2 gene of alcelaphine herpesvirus-1 is a transcriptional regulator affecting cytotoxicity in virus-infected T cells but is not required for malignant catarrhal fever induction in rabbits

Alcelaphine herpesvirus-1 (AlHV-1) causes malignant catarrhal fever (MCF). The A2 gene of AlHV-1 is a member of the bZIP transcription factor family. We wished to determine whether A2 is a virulence gene or not and whether it is involved in pathogenesis by interference with host transcription pathways. An A2 gene knockout (A2ΔAlHV-1) virus, revertant (A2revAlHV-1) virus, and wild-type virus (wtAlHV-1) were used to infect three groups of rabbits. A2ΔAlHV-1-infected rabbits succumbed to MCF, albeit with a delayed onset compared to the control groups, so A2 is not a critical virulence factor. Differential gene transcription analysis by RNAseq and qRT-PCR validation of a selection of these was performed in infected large granular lymphocyte (LGL) T cells obtained in culture from the MCF-affected animals. A2 was involved in the transcriptional regulation of immunological, cell cycle and apoptosis pathways. In particular, there was a bias towards γδ T cell receptor (TCR) expression and downregulation of αβ TCR. TCR signalling, apoptosis, cell cycle, IFN-γ and NFAT pathways were affected. Of particular interest was partial inhibition of the cytotoxicity-associated pathways involving perforin and the granzymes A and B in the A2ΔAlHV-1-infected LGLs compared to controls. In functional assays, A2ΔAlHV-1-infected LGLs were significantly less cytotoxic than wtAlHV-1- and A2revAlHV-1-infected LGLs using rabbit corneal epithelial cells (SIRC) as targets. This implies that A2 is involved in a pathway enhancing the expression of LGL cytotoxicity. This is important as virus-infected T cell cytotoxicity in vivo has been suggested as a potential mechanism of disease induction in MCF.

The pathology of malignant catarrhal fever, with an emphasis on ovine herpesvirus 2

The enigmatic pathogenesis of malignant catarrhal fever (MCF) involves dysregulated immune responses in susceptible ruminant species. Economically important outbreaks of MCF are due to 2 of the 10 viruses currently comprising the malignant catarrhal fever virus group: ovine herpesvirus 2 (OvHV-2) and alcelaphine herpesvirus 1 (AlHV-1). Attempts to develop effective vaccines for this group of viruses in the 1970s were sufficiently discouraging that they were temporarily abandoned. This review focuses on recent efforts to understand the pathogenesis of MCF, particularly the sheep-associated form of the disease, with the goal of developing rational control methods, including vaccination. The past 2 decades have seen several advances, including recognition of new members of the MCF virus group, better diagnostic assays, induction of disease by a natural route (aerosol), and clearer understanding of OvHV-2's shedding patterns by domestic sheep. A consistent theme in experimental studies of OvHV-2 in susceptible species is that there are 2 peaks of OvHV-2 gene expression: a preclinical peak involving the respiratory tract and a second in multiple organ systems leading to clinical disease. Latent and lytic gene expression may coexist in tissues during clinical stages in symptomatic animals.

Sheep-associated malignant catarrhal fever virus: prospects for vaccine development

Sheep-associated malignant catarrhal fever is emerging as a significant problem for several ruminant species worldwide. The inability to propagate the causative agent, ovine herpesvirus 2, in vitro has seriously hindered research efforts in the development of effective programs for control of the disease in clinically susceptible hosts. Recent molecular technologic advances have provided powerful tools for investigating this difficult-to-study virus. Identification of the infectious virus source, establishment of experimental animal models and completion of sequencing the genome for ovine herpesvirus 2 have put us in a position to pursue the development of vaccines for control of the disease. In this review, the authors briefly describe the current understanding of ovine herpesvirus 2 and prospectively discuss vaccine development against the virus.

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 confirmation of ovine herpesvirus 2-induced malignant catarrhal fever lesions in cattle from Rio Grande do Norte, Brazil

Molecular findings that confirmed the participation of ovine herpesvirus 2 (OVH-2) in the lesions that were consistent with those observed in malignant catarrhal fever of cattle are described. Three mixed-breed cattle from Rio Grande do Norte state demonstrated clinical manifestations that included mucopurulent nasal discharge, corneal opacity and motor incoordination. Routine necropsy examination demonstrated ulcerations and hemorrhage of the oral cavity, corneal opacity, and lymph node enlargement. Significant histopathological findings included widespread necrotizing vasculitis, non-suppurative meningoencephalitis, lymphocytic interstitial nephritis and hepatitis, and thrombosis. PCR assay performed on DNA extracted from kidney and mesenteric lymph node of one animal amplified a product of 423 base pairs corresponding to a target sequence within the ovine herpesvirus 2 (OVH-2) tegument protein gene. Direct sequencing of the PCR products, from extracted DNA of the kidney and mesenteric lymph node of one cow, amplified the partial nucleotide sequences (423 base pairs) of OVH-2 tegument protein gene. Blast analysis confirmed that these sequences have 98-100% identity with similar OVH-2 sequences deposited in GenBank. Phylogenetic analyses, based on the deduced amino acid sequences, demonstrated that the strain of OVH-2 circulating in ruminants from the Brazilian states of Rio Grande do Norte and Minas Gerais are similar to that identified in other geographical locations. These findings confirmed the active participation of OVH-2 in the classical manifestations of sheep associated malignant catarrhal fever.

Duration of protective immunity and antibody responses in cattle immunised against alcelaphine herpesvirus-1-induced malignant catarrhal fever

Protection of cattle from alcelaphine herpesvirus-1 (AlHV-1)-induced malignant catarrhal fever (MCF) has been described previously, using an attenuated virus vaccine in an unlicensed adjuvant. The vaccine was hypothesised to induce a protective barrier of virus-neutralising antibody in the oro-nasal region, supported by the observation of high titre neutralising antibodies in nasal secretions of protected animals. Here we describe further analysis of this vaccine strategy, studying the effectiveness of the vaccine formulated with a licensed adjuvant; the duration of immunity induced; and the virus-specific antibody responses in plasma and nasal secretions. The results presented here show that the attenuated AlHV-1 vaccine in a licensed adjuvant protected cattle from fatal intranasal challenge with pathogenic AlHV-1 at three or six months. In addition, animals protected from MCF had significantly higher initial anti-viral antibody titres than animals that succumbed to disease; and these antibody titres remained relatively stable after challenge, while titres in vaccinated animals with MCF increased significantly prior to the onset of clinical disease. These data support the view that a mucosal barrier of neutralising antibody blocks infection of vaccinated animals and suggests that the magnitude of the initial response may correlate with long-term protection. Interestingly, the high titre virus-neutralising antibody responses seen in animals that succumbed to MCF after vaccination were not protective.

Malignant catarrhal fever of deer

Malignant catarrhal fever (MCF) is reviewed and recent findings described. It is defined as a fatal disease which affects many species of Bovidae and Cervidae, characterized by widespread necrosis and lymphoid cell proliferation and can be caused by at least two infectious agents. In Africa, a herpesvirus which infects its natural host, the wildebeest, without obvious symptoms causes substantial losses in cattle due to MCF. Elsewhere, the cause of MCF is unknown but circumstantial evidence implicates sheep as the source of infection. While cattle are infected only sporadically with this “sheep-associated” form ol disease, infection of farmed deer is common, representing the most serious disease threat to the industry.

It is considered that infection of sheep and wildebeest with their respective agents operates to their advantage, causing no disease in their natural host, while transmission to other ungulates has fatal consequences, eliminating these potentially competitive species.

Recent studies of the disease in deer and the transmission of MCF from deer to rabbits are described. The evidence suggests that the disease process involves a novel dysfunction of the immune system which results in a massive lymphoid proliferation and an atopic allergic response. It is considered that similar processes may also be involved as a component of other diseases of man and animals.

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 of cattle is associated with low abundance of IL-2 transcript and a predominantly latent profile of ovine herpesvirus 2 gene expression

Background

Malignant catarrhal fever (MCF) is a lethal disease of cattle, characterized by vasculitis, necrosis, and accumulation of activated, dysregulated cytotoxic lymphocytes in various tissues. Ovine gamma herpesvirus 2 (OvHV-2) is a causative agent of MCF, which may trigger the disease through immunopathogenic pathways. Lymphocytes are the main target of the virus. However, the pathogenic basis of the disease is still mysterious.

Methods/Findings

We hypothesized that the gene expression patterns of OvHV-2 and the relative abundances of host cell transcripts in lymphnodes may be used to identify pathways that help to explain the pathogenesis of MCF. Therefore, viral and host cell gene expression patterns in lymph nodes of animals with MCF and healthy controls were analyzed by microarray. Two regions on the viral genome were transcriptionally active, one encoding an orthologue to the latency-associated nuclear antigen (ORF73) of other gamma herpesviruses, the other with no predicted open reading frame. A vast number of transcripts related to inflammatory processes, lymphocyte activation, cell proliferation and apoptosis were detected at different abundances. However, the IL-2 transcript was eminent among the transcripts, which were, compared to healthy controls, less abundant in animals with MCF. The ratio between CD4- and CD8-positive T-lymphocytes was decreased in the lymphnodes of animals with MCF compared to healthy controls. In contrast, the same ratio was stable, when peripheral blood lymphocytes were analyzed.

Conclusions/Significance

The phenotype of mice with a deficient IL-2-system almost perfectly matches the clinical signs observed in cattle with MCF, which feature a significantly decreased IL-2 transcript abundance, compared to healthy cattle. This supports the hypothesis that immunopathogenic events are linked to the pathogenesis of MCF. IL-2-deficiency may play an important role in the process. Therefore, this work opens new avenues for research on MCF.

An immunisation strategy for the protection of cattle against alcelaphine herpesvirus-1-induced malignant catarrhal fever

The aim of this study was to stimulate immunity in the oro-nasal-pharyngeal region of cattle to protect them from alcelaphine herpesvirus-1 (AlHV-1)-induced malignant catarrhal fever. Attenuated C500 strain AlHV-1 was used along with Freund's adjuvant intramuscularly (IM) in the upper neck region to immunise cattle. Virulent C500 strain AlHV-1 was used for intranasal challenge. Nine of ten cattle were protected. Protection was associated with high levels of neutralising antibody in nasal secretions. Some protected animals showed transient low levels of viral DNA in blood samples and in one lymph node sample after challenge whereas viral DNA was detected in the blood and in lymph node samples of all animals with MCF. This is the most promising immunisation strategy to date for the control of malignant catarrhal fever.

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.

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.

Febre catarral maligna em bovinos na Paraíba

É relatada a ocorrência de febre catarral maligna (FCM) em bovinos no estado da Paraíba. Descrevem-se seis casos esporádicos da doença, diagnosticados no período de 2000 a 2005, e um surto ocorrido em 1986-1987 no município de Taperoá. Em um caso foi feito o diagnóstico clínico e nos demais casos o diagnóstico foi realizado pela presença de vasculite difusa com degeneração fibrinóide e infiltrado mononuclear perivascular em diversos órgãos. Em 5 casos adoeceu apenas um bovino por rebanho, e em outro adoeceram 2 animais de um rebanho de 6 bovinos. Em 5 dos 6 casos a doença ocorreu no período de maio-agosto coincidindo com o fim da estação chuvosa e época de parição das ovelhas. Os sinais clínicos e achados de necropsia foram característicos da doença. Quatro dos seis animais morreram após um curso clínico de 5-8 dias e um foi eutanasiado após um curso de 40 dias. O surto descrito no município de Taperoá ocorreu de agosto de 1986 a dezembro de 1987, com morbidade de 8,22% e letalidade de 100%. A doença ocorreu após a introdução de um carneiro no rebanho ovino que convivia com os bovinos. O surto foi controlado somente após a eliminação de todos os ovinos da propriedade. Esses resultados demonstram que a febre catarral maligna é endêmica em bovinos na Paraíba, podendo também ocorrer surtos com alta morbidade e letalidade. Além disso, sugerem que, como descrito no Rio Grande do Sul e em outros países, alguns animais podem se recuperar. Os diagnósticos de FCM corresponderam a 3,1% dos 190 casos diagnosticados no Hospital Veterinário no período de 2000-2005, estimando-se que a doença afeta, anualmente, 0,125% dos bovinos no Estado.

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.

A real-time PCR assay for measuring alcelaphine herpesvirus-1 DNA

Alcelaphine herpesvirus-1 (AlHV-1) is a rhadinovirus that causes malignant catarrhal fever in certain ruminant species and is an important pathogen in Africa and other areas where carrier species and clinically susceptible ruminants intermingle. In this study, a real-time PCR for AlHV-1 DNA was developed and compared to an established nested PCR. The nested PCR amplifies a region of the AlHV-1 gene coding for a transactivator protein (ORF 50), while the real-time PCR assay targets the AlHV-1 gene coding for a tegument protein (ORF 3). The real-time PCR assay reproducibly detected 10 copies of target DNA. In a dilution series of the target DNA there was linearity of the assay across 8 orders of magnitude (10(1)-10(9) copies). The nested PCR was more sensitive (approximately with 1 log) than the real-time PCR. The assay specifically amplified samples containing only AlHV-1, but not other common herpesviruses of cattle. In conclusion, we have developed a rapid, relatively sensitive, and reliable real-time PCR assay specific for AlHV-1. Similar to the real-time PCR for Ovine herpesvirus-2, this assay should prove useful for differential diagnostics of clinical MCF and for research to better define the epidemiology of AlHV-1 in wildebeest as well as in animals with wildebeest-associated MCF.

Viral diseases of the ruminant nervous system

This article presents the etiology, epidemiology, clinical features,and diagnosis of the primary viral neurologic diseases observed in ruminants. In general, these viral neurologic diseases are uncommon but often fatal. Rabies virus is perhaps the most important cause of encephalitis in cattle because of the public health implications. Other viral encephalitis diseases in ruminants include bovine herpesvirus encephalomyelitis, pseudorabies, malignant catarrhal fever, ovine and caprine lentiviral encephalitis, West Nile virus encephalitis, Borna disease, paramyxoviral sporadic bovine encephalomyelitis,and ovine encephalomyelitis (louping-ill).

Malignant catarrhal fever-like disease in Barbary red deer (Cervus elaphus barbarus) naturally infected with a virus resembling alcelaphine herpesvirus 2

Eight Barbary red deer (Cervus elaphus barbarus) developed clinical signs suggestive of malignant catarrhal fever (MCF) over a 28-day period. These animals were housed outdoors with four other species of ruminants. Affected red deer had lethargy, ocular signs, and nasal discharge and were euthanatized within 48 h. Lesions included ulcers of the muzzle, lips, and oral cavity associated with infiltrates of neutrophils and lymphocytes. Serologically, six of seven red deer tested during the outbreak were positive by competitive enzyme-linked immunosorbent assay for antibodies to a shared MCF virus antigen. PCR using oligonucleotide primers designed for a conserved protein of alcelaphine herpesviruses 1 (AlHV-1) and 2 (AlHV-2) and for conserved regions of a herpesvirus DNA polymerase gene was positive for tissues from all eight clinically affected animals and negative for eight out of eight red deer without clinical signs of MCF. DNA sequencing of PCR amplicons from the diseased red deer indicated that they were infected with a novel herpesvirus closely related to AlHV-2; immunohistochemistry using polyclonal anti-AlHV-2 serum and in situ hybridization demonstrated the presence of virus within salivary glands adjacent to oral lesions of affected animals. A survey of other ruminants near the outbreak subsequently showed that normal Jackson's hartebeest (Alcelaphus buselaphus jacksoni) that were cohoused with the diseased red deer were infected with the same virus and were shedding the virus in nasal excretions. These findings suggest that a herpesvirus closely related to AlHV-2 caused the MCF-like disease epizootic in Barbary red deer and that the virus may have originated from Jackson's hartebeest.

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: polymerase chain reaction survey for ovine herpesvirus 2 and other persistent herpesvirus and retrovirus infections of dairy cattle and bison

Using a polymerase chain reaction (PCR) test for sequences of ovine herpesvirus 2 (OHV2), this virus was shown to be significantly associated with sheep-associated malignant catarrhal fever (SA-MCF) in terminal cases of disease in 34 cattle and 53 bison. Ovine herpesvirus 2 was not detected in cattle (38) and bison (10) that succumbed to other diseases. Other persistent herpesviruses, retroviruses, and pestivirus, some of which have been previously isolated from cases of SA-MCF, were not associated with the disease. These included bovine herpesvirus 4 (BHV4), bovine lymphotrophic herpesvirus (BLHV), bovine syncytial virus (BSV, also known as bovine spumavirus), bovine immunodeficiency virus (BIV), and bovine viral diarrhea virus (BVDV). A PCR survey for OHV2 in DNA from individual cow's peripheral blood lymphocytes in 4 dairies showed that the 1 dairy that was in close contact to sheep had a prevalence of OHV2 of 21.3%, whereas the 3 other dairies had no OHV2. Prevalence of the other herpesviruses and retroviruses in the dairy cows was variable, ranging from 2% to 51% for BHV4, 52% to 78.7% for BLHV, and 10% to 34% for BSV. Bovine lymphotrophic herpesvirus and BSV were also found in a few (1-4 of 21 tested) cases of terminal SA-MCF, but BIV and BVDV were not found in either the dairy cows sampled, or in the cases of SA-MCE No significant correlation was found between the presence of any 2 viruses (OHV2, BHV4, BLHV, BSV) in the dairy cows or terminal cases of SA-MCE

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.

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 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.

Phenotyping of lymphocyte subsets in the vascular and epithelial lesions of a cow with malignant catarrhal fever

Surface marker analysis of lymphoid cells infiltrating the vascular and epithelial lesions of a cow with malignant catarrhal fever (MCF) was conducted by immunohistochemistry using ten monoclonal antibodies. The majority of lymphoid cells in these lesions had BoCD8, BoCD6 or BoCD2, but they rarely possessed N-cell (BoCD5+/BoCD4-/BoCD8-, non-T non-B) markers. Similar reactivity was seen in lymphoid cells of perivascular infiltrates in the liver, heart and brain, and in T-dependent areas of lymph nodes. These results suggest involvement of cytotoxic T-lymphocytes in the pathogenesis of MCF.

The detection of Alcelaphine herpesvirus-1 DNA by in situ hybridization of tissues from rabbits affected with malignant catarrhal fever

Tissue sections and cultured lymphocytes from rabbits clinically affected following experimental infection with Alcelaphine herpesvirus-1 (AHV-1) were assessed for the presence of viral DNA by in situ hybridization with the cloned major HindII repeat sequence of this virus. Small numbers of virus-infected cells were consistently detected only in submandibular lymph nodes, while other tissues showed no evidence of viral DNA. Virus titration in culture suggested that there were higher titres of virus in the lymph nodes, spleen and lung of infected animals than in the kidney or peripheral blood lymphocytes and confirmed the low level of virus in these animals. Substantially more viral DNA was detected by in situ hybridization in lymphocytes following at least 24 h of culture, suggesting that viral replication is normally repressed by the host.

A diagnostic method to detect alcelaphine herpesvirus-1 of malignant catarrhal fever using the polymerase chain reaction

A sensitive diagnostic method specific for alcelaphine herpesvirus-1, causative agent of malignant catarrhal fever, has been developed. Based on the nucleotide sequence of the alcelaphine herpesvirus-1 genomic DNA, a pair of 30 nucleotide primers was selected and synthesized for detecting the virus genome using the polymerase chain reaction (PCR). The virus genome was detected in crude cell lysate using the amplification reaction.

The pathology of "sheep-associated" malignant catarrhal fever in the hamster

Lesions induced in hamsters by inoculation with the "sheep-associated" agents of malignant catarrhal fever (SA-MCF) isolated from a red deer (Cervus elaphus), designated D/1 and of bovine origin (C/2), are described. Clinical signs in hamsters inoculated with the D/1 isolate occurred as early as 13 days after infection although the mean incubation period in animals that developed signs was 27 days. Increased numbers of polymorphonuclear leucocytes were present in the blood of clinically affected hamsters. Gross lesions included erosions of epithelium in the buccal cavity, haemorrhage of the forestomach, dilated fluid-filled intestines and enlargement of the mesenteric lymph node. Microscopic lesions were widespread throughout the body but had a predilection for epithelial surfaces. They consisted of hyperplasia of certain lymph nodes, vasculitis and interstitial accumulations of mononuclear cells of lymphoid appearance in non-lymphoid tissues. Cytolysis was also seen. Lesions produced by the C/2 isolate were similar and both isolates produced disease comparable with that seen in naturally occurring cases in cattle and deer. It is suggested that disease might arise through a dysfunction of the immune system following infection of host large granular lymphocytes by the SA-MCF agent, in a way similar to that suggested for the rabbit.

The pathology of wildebeest-associated malignant catarrhal fever in hamsters, rats and guinea-pigs

Lesions typical of malignant catarrhal fever were found in hamsters, rats and guinea-pigs inoculated with a rabbit-passaged strain (C-500) of alcelaphine herpesvirus-1. Lesions found during primary passage included proliferation of lymphoid tissues, multisystemic mononuclear cell infiltrates, vasculitis and necrosis, especially in the alimentary tract. The character, severity and distribution of lesions remained stable in affected hamsters during serial passage of disease, whereas lympho-proliferation became dominant in rats. The lesions in rats typically affected lymph nodes, heart and kidney and appear similar to those caused by oncogenic herpesviruses. Because rodents are susceptible to malignant catarrhal fever, the prospect is advanced that they can be used to elucidate the pathogenesis of both lymphoproliferative and cytolytic aspects of the disease.

Changes in blood coagulation parameters of red deer (Cervus elaphus) experimentally infected with malignant catarrhal fever

Changes in blood coagulation parameters were followed in four red deer (Cervus elaphus) experimentally infected with malignant catarrhal fever (MCF) of deer. Blood platelet counts, activated partial thromboplastin time (APTT), one-stage prothrombin time (OSPT), activated clotting time (ACT), plasma anti-thrombin III (ATIII) activity, fibrinogen degradation production (FDP) and fibrinogen levels were measured. Inoculated deer became pyrexic after 17 or 19 days. Thereafter they developed watery diarrhoea which rapidly became haemorrhagic. The course of the clinical disease ranged from four to six days before the animals were killed or died. All inoculated deer developed abnormalities in laboratory parameters of blood coagulation. These varied within and between animals, but the coagulation profiles of all four animals remained abnormal until death. Post-mortem findings included extensive systemic petechiation, severe haemorrhage in the alimentary canal and vasculitis with disseminated thrombosis. Abnormal coagulation parameters included extension of APTT and OSPT, increased FDP, decreased ATIII and platelet counts and increased fibrinogen levels. The increases in fibrinogen were compatible with the acute phase response. The other coagulation abnormalities and haemorrhage and thrombosis were indicative of disseminated intravascular coagulation (DIC) with consumption coagulopathy, ACT remained normal in all deer although final clot quality was considered poor.

Chronic eosinophilic dermatitis: a manifestation of a multisystemic, eosinophilic, epitheliotropic disease in five horses

A generalized, chronic, progressive, exfoliative dermatitis in five horses is described. Histologically, the lesion is characterized by a superficial and deep perivascular dermatitis which is eosinophil-rich with a marked lymphocytic and plasmacytic component, accompanied by marked acanthosis and hyperkeratosis. More severe cases progress to a lichenoid pattern with the same cellular composition with focal eosinophilic spongiosis and eosinophilic subcorneal pustules. Clinically, the disease is associated with chronic, severe weight loss and is fulminating. The skin lesions are accompanied by lymphoplasmacytic and eosinophilic infiltrates and formation of eosinophilic granulomas in other epithelial organs, most noticeably the pancreas, in which a chronic, fibrosing pancreatitis develops. Other epithelial organs involved to various degrees are salivary glands, the gastrointestinal system, including the oral cavity and esophagus, biliary epithelium and bronchial epithelium. The etiology of this disease is unknown.

Ocular lesions of bovine malignant catarrhal fever

The ocular lesions of bovine malignant catarrhal fever were characterized in 15 naturally occurring and eight experimentally induced cases of the disease. Consistent findings included: lymphocytic vasculitis of retinal, scleral, posterior ciliary, and uveal vessels; uveitis, especially involving ciliary processes, ciliary body, and iris; and keratitis with corneal edema, neovascularization, and epithelial and endothelial degeneration. Lymphocytic ciliary neuritis and optic meningitis were found less frequently. Ultrastructural examination of the ciliary body and iris from one experimental calf confirmed that most infiltrating mononuclear cells were lymphocytes. The uveitis, vasculitis, and keratitis of malignant catarrhal fever were probably immune-mediated.

Malignant catarrhal fever in farmed Rusa deer (Cervus timorensis). 1. Clinico-pathological observations

A sporadic fatal disease is described in 7 Rusa deer (Cervus timorensis) from 5 deer farms in Victoria. Bilateral ophthalmia and wasting were the most significant signs in a clinical course varying from 4 to 34 days. Bilateral hypopyon, peripheral corneal opacities and interstitial mononuclear cell infiltration of the renal cortex with pronounced mural thickening and dilatation of vessels at the cortico-medullary junction were the only consistent lesions. Haemorrhagic ileitis, colitis and typhlitis were the major lesions in two deer that died 4 and 6 days after onset of clinical disease. Ecchymotic haemorrhages and sub-serosal haematomas on the intestines and mesentery were the main finding in cases with a longer clinical course. Other gross lesions varied between cases. The most significant histological lesion was fibrinoid necrotising vasculitis with adventitial lymphoid cell infiltration characteristic of bovine malignant catarrhal fever. Mucosal erosions seen in protracted cases of this disease were associated with lymphoid cell infiltration into foci of degenerating epithelial cells. In many lymph nodes there was severe follicular necroses. In chronic cases extensive proliferation of lymphoblastoid cells was seen in the parafollicular cortex and medullary sinuses of nodes which also showed discrete follicular necrosis.

Malignant catarrhal fever in farmed Rusa deer (Cervus timorensis). 2. Animal transmission and virological studies

A disease with clinical signs and histological lesions similar to malignant catarrhal fever in cattle was transmitted from Rusa deer (Cervus timorensis) to rabbits. This was accomplished on 3 separate occasions, and the disease was serially passaged in rabbits up to 11 times. The clinical signs in affected rabbits were pyrexia, depression, anorexia, mucopurulent conjunctivitis, nasal discharge and diarrhoea. These signs were seen in 27 of 38 inoculated rabbits with the mean incubation period being 12 days (range 8 to 20 days). Histologically, affected rabbits exhibited mononuclear perivascular cuffing and vasculitis in the brain, heart, liver and kidney. Lymph nodes and spleen showed destruction and loss of mature lymphocytes and lymphoid follicles and an increased number of large lymphoblastoid cells. These clinical signs and lesions were not detected in control rabbits. The disease was not transmitted to cattle, sheep, guinea pigs or mice, nor was an agent isolated in cattle, deer or rabbit tissue cultures, or in chicken embryos.

The pathomorphology of malignant catarrhal fever. I. Generalized lymphoid vasculitis

A histologic, ultrastructural and immunohistochemical study of the vasculitis in the rete mirabile of 18 calves with experimental and two calves with spontaneous malignant catarrhal fevel showed lesions similar to those reported in graft rejection and some other lymphocyte-associated vasculopathies. The calves were examined at early, mid and late stages of clinical disease. Vascular lesions in the carotid rete were representative of those in other tissues examined. The magnitude of the arterial wall mononuclear cell infiltrate and the degree of arterial wall necrosis and degeneration increased with progression of the clinical disease. The predominant site of mononuclear cell accumulation was the adventitia. There was less medial and intimal involvement. The mononuclear infiltrate was composed of lymphocytes and macrophages with neutrophils and plasma cells rarely present. Endothelial hyperplasia, fibrinoid change and thrombosis were uncommon. Many changes contrasted with those recognized in an active Arthus reaction where adventitial change was minimal and most inflammatory cells were neutrophils or plasma cells. IgG and C3 rarely were detected in vessel walls with fluorescent antibody techniques. Serum immunoglobulins as measured by radial immunodiffusion were not elevated. Viral structures were not seen in tissues examined ultrastructurally.