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

Indirect ELISA for analysis of malignant catarrhal fever virus-specific antibodies in a range of species

The culture-attenuated alcelaphine herpesvirus 1 (AlHV-1) C500 strain can be grown to high titre and has been used successfully as a candidate vaccine for wildebeest-associated malignant catarrhal fever (MCF). This vaccine virus was also used to develop an indirect ELISA to allow monitoring of virus-specific antibodies in vaccinated cattle. However the extraction method was expensive and time-consuming, and the resulting test was not suitable for use in sheep. Here we describe an improved antigen extraction method that also broadens the application of the assay, allowing its application to sheep samples. The updated assay was tested using control samples from cattle and sheep, and showed a high level of accuracy in both species. This novel assay should prove to be a useful tool in MCF diagnosis and in evaluation of MCF vaccine responses.

Field vaccination of locally-owned cattle against malignant catarrhal fever under environmentally challenging conditions in Tanzania

Malignant catarrhal fever (MCF), caused by alcelaphine herpesvirus-1 (AIHV-1) transmitted from wildebeest, is a lethal cattle disease with significant impacts on East African pastoralists. Development of a live attenuated MCF vaccine has prompted research into its use in communities at risk. This study reports results from the first utilisation of the MCF vaccine in locally-owned cattle under field conditions. The study involved a primary two-dose course vaccination of 1634 cattle, followed a year later, by boost vaccination of 385 of these cattle. It aimed to: (a) evaluate the antibody response to a two-dose AlHV-1 primary vaccination course, including initial response, antibody levels after one year, and clinical events post-vaccination; (b) assess how factors like age, reproductive status, body condition, and breed influence the initial response; and (c) compare antibody responses to single- and two-dose booster protocols one year after primary vaccination. Analyses were carried out using linear mixed-effects models and paired t-tests. Clinical incidents were reported in 11/1634 cattle vaccinated during the primary course and in 0/385 cattle during the boost regimens. The primary vaccination resulted in a 9-fold increase in comparison to pre-vaccination antibody levels and the response was consistent across animals of different ages, reproductive statuses and body conditions. While antibody levels declined 11 months after primary vaccination, they remained high, and a single-dose booster vaccination was sufficient to elicit a strong immune response, with only marginal increases after a second booster. The study provides evidence of high immunogenicity and low incidences of clinical events of the vaccine in cattle across individual host factors and immunologically vulnerable groups, under prevailing environmental conditions. It also indicates the utility of a single-dose booster regimen. These findings will support progress towards commercial production and larger-scale adoption which could generate important benefits for the livelihoods, and sustainability of pastoral livestock systems.

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.

Effect of Cattle-Specific Diseases on Carcass Inspection and Meat Quality

There are severe cattle-specific viral (foot and mouth, vesicular stomatitis, rinderpest, rift valley fever, malignant catarrhal fever, lumpy skin, rabies, bovine leukosis, bovine viral diarrhea, and bovine spongiform encephalopathy), bacterial (tuberculosis, black quarter, botulism, malignant oedema, leptospirosis, brucellosis, anthrax, hemogenic septicemia, actinomycosis, actinobacillosis, mastitis, and metritis), parasitic (lungworm, fasciolosis, cysticercosis, hydatid disease, and onchocercosis), and protozoal (trypanosomiasis, theileriosis, anaplasmosis, babesiosis, and sarcosporidiosis) diseases that affect the carcass judgment and meat quality. These diseases adversely affect cattle health, welfare, and red meat production. This chapter aims to describe the etiology, mode of transmission, ante-mortem and post-mortem findings, carcass and meat quality judgment, and differential diagnosis of these diseases.

Wildebeest-Derived Malignant Catarrhal Fever: A Bovine Peripheral T Cell Lymphoma Caused by Cross-Species Transmission of Alcelaphine Gammaherpesvirus 1

Gammaherpesviruses (γHVs) include viruses that can induce lymphoproliferative diseases and tumors. These viruses can persist in the long term in the absence of any pathological manifestation in their natural host. Alcelaphine gammaherpesvirus 1 (AlHV-1) belongs to the genus Macavirus and asymptomatically infects its natural host, the wildebeest (Connochaetes spp.). However, when transmitted to several susceptible species belonging to the order Artiodactyla, AlHV-1 is responsible for the induction of a lethal lymphoproliferative disease, named wildebeest-derived malignant catarrhal fever (WD-MCF). Understanding the pathogenic mechanisms responsible for the induction of WD-MCF is important to better control the risks of transmission and disease development in susceptible species. The aim of this review is to synthesize the current knowledge on WD-MCF with a particular focus on the mechanisms by which AlHV-1 induces the disease. We discuss the potential mechanisms of pathogenesis from viral entry into the host to the maintenance of viral genomes in infected CD8⁺ T lymphocytes, and we present current hypotheses to explain how AlHV-1 infection induces a peripheral T cell lymphoma-like disease.

A Vaccine Targeting Ovine Herpesvirus 2 Glycoprotein B Protects against Sheep-Associated Malignant Catarrhal Fever

Malignant catarrhal fever (MCF) is a complex and often fatal disease of ungulates. Effective vaccines are needed to avoid MCF outbreaks and mitigate losses. This study aimed to evaluate a sheep-associated MCF (SA-MCF) vaccine candidate targeting ovine herpesvirus 2 (OvHV-2) glycoprotein B (gB). Rabbits were used as a laboratory animal model to test the safety, immunogenicity, and protective efficacy of a chimeric virus consisting of a recombinant, non-pathogenic strain of alcelaphine herpesvirus-1 encoding OvHV-2 ORF8 to express gB (AlHV-1^∆ORF73/OvHV-2-ORF8). Viral-vectored immunizations were performed by using the AlHV-1^∆ORF73/OvHV-2-ORF8 chimera alone or as a DNA prime (OvHV-2-ORF8)-virus boost regimen. The viral vector was inoculated by intravenous or intramuscular routes and the DNA was delivered by intradermal shots using a gene gun. The vaccine candidates were deemed safe as no clinical signs were observed following any of the immunizations. Anti-OvHV-2 gB antibodies with neutralizing activity were induced by all immunogens. At three weeks post-final immunization, all animals were challenged intranasally with a lethal dose of OvHV-2. MCF protection rates ranging from 66.7% to 71.4% were observed in vaccinated rabbits, while all mock-vaccinated animals developed the disease. The significant protective efficacy obtained with the vaccine platforms tested in this study encourages further trials in relevant livestock species, such as cattle and bison.

Development of a recombinant ELISA for ovine herpesvirus 2, suitable for use in sheep

The minor capsid protein of ovine herpesvirus 2, identified as a potential antigen for serological testing, was over-expressed and purified to allow its assessment in ELISA. The corresponding gene sequence (OvHV-2 orf65, Ov65) was modified to incorporate epitope tags and internal restriction enzyme sites in an E. coli codon-optimised version of the gene. This codon-optimised gene was then subject to internal deletions to identify regions of the protein that could be removed while maintaining protein solubility and antigenicity. It was found that a derivative with deletion of the conserved 5'-end of the gene (Ov65delB) expressed a polypeptide that was soluble when over-expressed in bacteria and was detected by OvHV-2 specific sera. Proteomic analysis of the affinity purified Ov65delB showed that it contained multiple predicted Ov65 tryptic peptides but also showed contamination by co-purifying E. coli proteins. An indirect ELISA, based on this affinity-purified OV65delB, was optimised for use with sheep and cattle samples and cut-off values were established based on known negative serum samples. Analysis of groups of samples that were either presumed infected (UK sheep) or tested OvHV-2 positive or negative by PCR (cattle MCF diagnostic samples) showed that the assay had 95 % sensitivity and 96 % specificity for sheep serum; and 80 % sensitivity and 95 % specificity for cattle serum. The lower sensitivity with cattle samples appeared to be due to a lack of serological response in some MCF-affected cattle. This recombinant antigen therefore shows promise as the basis of an inexpensive, simple and reliable test that can be used to detect OvHV-2-specific antibody responses in both MCF-affected animals and in OvHV-2 reservoir hosts.

Analysis of immune responses to attenuated alcelaphine herpesvirus 1 formulated with and without adjuvant

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MCF vaccine was tested with and without adjuvant and containing inactivated virus.

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Adjuvant was required for optimal virus neutralising antibody responses.

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Storage of AlHV-1 with Emulsigen adjuvant significantly reduced virus viability.

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Vaccination with adjuvant-inactivated AlHV-1 did not reduce antibody responses.

The experimental vaccine for bovine malignant catarrhal fever consists of viable attenuated alcelaphine herpesvirus 1 (AlHV-1) derived by extensive culture passage, combined with an oil-in-water adjuvant, delivered intramuscularly. This immunisation strategy was over 80% effective in previous experimental and field trials and protection appeared to be associated with induction of virus-neutralising antibodies. Whether the vaccine virus is required to be viable at the point of immunisation and whether adjuvant is required to induce the appropriate immune responses remains unclear. To address these issues two studies were performed, firstly to analyse immune responses in the presence and absence of adjuvant and secondly, to investigate immune responses to vaccines containing adjuvant plus viable or inactivated AlHV-1.

The first study showed that viable attenuated AlHV-1 in the absence of adjuvant induced virus-specific antibodies but the titres of virus-neutralising antibodies were significantly lower than those induced by vaccine containing viable virus and adjuvant, suggesting adjuvant was required for optimal responses. In contrast, the second study found that the vaccine containing inactivated (>99.9%) AlHV-1 induced similar levels of virus-neutralising antibody to the equivalent formulation containing viable AlHV-1.

Together these studies suggest that the MCF vaccine acts as an antigen depot for induction of immune responses, requiring adjuvant and a suitable antigen source, which need not be viable virus. These observations may help in directing the development of alternative MCF vaccine formulations for distribution in the absence of an extensive cold chain.

OvHV-2 Glycoprotein B Delivered by a Recombinant BoHV-4 Is Immunogenic and Induces Partial Protection against Sheep-Associated Malignant Catarrhal Fever in a Rabbit Model

An efficacious vaccine for sheep-associated malignant catarrhal fever (SA-MCF) is important for the livestock industry. Research towards SA-MCF vaccine development is hindered by the absence of culture systems to propagate the causative agent, ovine herpesvirus-2 (OvHV-2), which means its genome cannot be experimentally modified to generate an attenuated vaccine strain. Alternative approaches for vaccine development are needed to deliver OvHV-2 antigens. Bovine herpesvirus 4 (BoHV-4) has been evaluated as a vaccine vector for several viral antigens with promising results. In this study, we genetically engineered BoHV-4 to express OvHV-2 glycoprotein B (gB) and evaluated its efficacy as an SA-MCF vaccine using a rabbit model. The construction of a viable recombinant virus (BoHV-4-AΔTK-OvHV-2-gB) and confirmation of OvHV-2 gB expression were performed in vitro. The immunization of rabbits with BoHV-4-AΔTK-OvHV-2-gB elicited strong humoral responses to OvHV-2 gB, including neutralizing antibodies. Following intra-nasal challenge with a lethal dose of OvHV-2, 42.9% of the OvHV-2 gB vaccinated rabbits were protected against SA-MCF, while all rabbits in the mock-vaccinated group succumbed to SA-MCF. Overall, OvHV-2 gB delivered by the recombinant BoHV-4 was immunogenic and partly protective against SA-MCF in rabbits. These are promising results towards an SA-MCF vaccine; however, improvements are needed to increase protection rates.

Detection and characterisation of sheep-associated malignant catarrhal fever infection from ruminants by using tegument and gB gene sequences of OvHV-2

In this study, positive blood and organ samples were obtained from different mixed herds of sheep and cattle against ovine herpesvirus 2 (OvHV-2) infection. Target-positive DNA was sequenced and compared with worldwide distributed OvHV-2 sequences. Tegument gene (422 base pairs) and glycoprotein B (gB) gene (2800 base pairs) amplicons of OvHV-2 genome were used for understanding of epidemiology of malignant catarrhal fever (MCF) infection in Turkey. The results of nucleotide sequencing of polymerase chain reaction (PCR) products indicated presence of sheep-associated form for MCF infection in Turkey. Although the obtained sequences were genetically different from each other, it was found that genetic variations were limited.

A randomised vaccine field trial in Kenya demonstrates protection against wildebeest-associated malignant catarrhal fever in cattle

Wildebeest-associated malignant catarrhal fever (WA-MCF), a fatal disease of cattle caused by alcelaphine herpesvirus 1 (AlHV-1), is one of the most important seasonal diseases of cattle in wildebeest endemic areas, with annual incidence reaching 10%. Here we report efficacy of over 80% for a vaccine based on the attenuated AlHV-1 C500 strain, in preventing fatal WA-MCF in cattle exposed to natural wildebeest challenge. The study was conducted at Kapiti Plains Ranch Ltd, south-east of Nairobi, Kenya. In 2016, 146 cattle were selected for a randomised placebo-controlled trial. Cattle were stratified according to breed and age and randomly assigned to groups given vaccine or culture medium mixed with Emulsigen®. Cattle received prime and boost inoculations one month apart and few adverse reactions (n = 4) were observed. Indirect ELISA demonstrated that all cattle in the vaccine group developed a serological response to AlHV-1. The study herd was grazed with wildebeest from one month after booster vaccination. Three cattle, two that received vaccine and one control, succumbed to conditions unrelated to WA-MCF before the study ended. Twenty-five cattle succumbed to WA-MCF; four of the remaining 71 cattle in the vaccine group (5.6%) and 21 of the remaining 72 control cattle (29.2%; χ² = 13.6, df = 1, p < 0.001). All of the WA-MCF affected cattle were confirmed by PCR to be infected with AlHV-1 and in 23 cases exhibited histopathology typical of WA-MCF. Vaccine efficacy was determined to be 80.6% (95% CI 46.5-93.0%). Hence, the AlHV-1 C500 vaccine is a safe and potentially effective novel method for controlling WA-MCF in cattle. The implementation of this vaccine may have significant impacts on marginalised cattle keeping communities.

Field validation of clinical and laboratory diagnosis of wildebeest associated malignant catarrhal fever in cattle

Background

Wildebeest associated malignant catarrhal fever (WA-MCF) is a fatal disease of cattle. Outbreaks are seasonal and associated with close interaction between cattle and calving wildebeest. In Kenya, WA-MCF has a dramatic effect on cattle-keepers who lose up to 10% of their cattle herds per year. The objective of this study was to report the impact of WA-MCF on a commercial ranch and assess the performance of clinical diagnosis compared to laboratory diagnosis as a disease management tool.

A retrospective study of WA-MCF in cattle was conducted from 2014 to 2016 at Kapiti Plains Ranch Ltd., Kenya. During this period, 325 animals showed clinical signs of WA-MCF and of these, 123 were opportunistically sampled. In addition, 51 clinically healthy animals were sampled. Nested polymerase chain reaction (PCR) and indirect enzyme linked immunosorbent assay (ELISA) were used to confirm clinically diagnosed cases of WA-MCF. A latent class model (LCM) was used to evaluate the diagnostic parameters of clinical diagnosis and the tests in the absence of a gold standard.

Results

By PCR, 94% (95% C.I. 89–97%) of clinically affected animals were positive to WA-MCF while 63% (95% C.I. 54–71%) were positive by indirect ELISA. The LCM demonstrated the indirect ELISA had poor sensitivity 63.3% (95% PCI 54.4–71.7%) and specificity 62.6% (95% PCI 39.2–84.9%) while the nested PCR performed better with sensitivity 96.1% (95% PCI 90.7–99.7%) and specificity 92.9% (95% PCI 76.1–99.8%). The sensitivity and specificity of clinical diagnosis were 99.1% (95% PCI 96.8–100.0%) and 71.5% (95% PCI 48.0–97.2%) respectively.

Conclusions

Clinical diagnosis was demonstrated to be an effective method to identify affected animals although animals may be incorrectly classified resulting in financial loss. The study revealed indirect ELISA as a poor test and nested PCR to be a more appropriate confirmatory test for diagnosing acute WA-MCF. However, the logistics of PCR make it unsuitable for field diagnosis of WA-MCF. The future of WA-MCF diagnosis should be aimed at development of penside techniques, which will allow for fast detection in the field.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1818-8) contains supplementary material, which is available to authorized users.

Seroprevalence of malignant catarrhal fever virus in captive wildebeest (Connochaetes sp.) in France

Alcelaphine herpesvirus 1 (AlHV-1) is a gammaherpesvirus carried asymptomatically by wildebeests (Connochaetes sp.) in sub-Saharan Africa. Although asymptomatic in wildebeest, AlHV-1 infection in a number of other ruminant species causes a severe and fatal lymphoproliferative disease named wildebeest-derived malignant catarrhal fever (WD-MCF). Several endangered species of captive ruminants are highly susceptible to developing WD-MCF if infected by AlHV-1, which is a critical concern in zoos, game reserves and wildlife parks where wildebeests are also kept in captivity. Here, we investigated the seroprevalence of AlHV-1 in 52 captive wildebeests randomly sampled from five different zoos in France. We found 46% (24/52) seropositive animals and detected AlHV-1 DNA in one of them, demonstrating that AlHV-1 infection is present in captive wildebeests in France. In an interesting manner, the repartition of seropositive wildebeests was not homogenous between zoos with 100% (20/20) of seronegative animals in three parks. These results further highlight the importance of considering WD-MCF as a threat for clinically susceptible species and encourage for testing AlHV-1 infection in captive wildebeests as a management control strategy.

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

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

Malignant catarrhal fever: recent update

Malignant catarrhal fever (MCF) is a serious, usually fatal disease affecting many species of ungulates of the subfamily Bovinae and family Cervidae including pigs and caused by a herpesvirus under the genus Macavirus in the subfamily Gammaherpesvirinae. Ten Macaviruses have been identified to date and 6 were found to be associated with clinical MCF. Alcelaphine herpesvirus 1 (AlHV-1), which causes inapparent infection in wildebeest and ovine herpesvirus 2 (OvHV-2), which is associated with subclinical infections in sheep are the two most important herpes viruses that cause clinical wildebeest associated MCF (WA-MCF) and sheep-associated MCF (SA-MCF), respectively. The disease is characterized by accumulation of lymphocytes (predominantly CD8+ T cells) in a variety of organs, often associated with tissue necrosis. AIHV-1 can be recovered from animals, while OvHV-2 has never been recovered from affected animals, only OvHV-2 specific DNA is detected in cultured lymphoblastoid cells from infected animals. Diagnosis is normally achieved by observing the clinical signs, characteristic histopathological changes, ELISA and detection of viral DNA in the infected animals. Detection of viral DNA by PCR is becoming the method of choice for diagnosing the SA-MCF. Currently, there is no effective disease control measure. Attenuated AlHV-1 virus vaccine has been developed with varying degree of success for control of WAMCF in Africa. Separation of reservoir host from susceptible host or raising of OvHV-2 free sheep is the only solution for control of SA-MCF. In India, our group first confirmed SA-MCF in Kashmir. The present article updates current epidemiology, diagnosis, prevention and control of MCF with special reference to India.

One Health Research in Northern Tanzania - Challenges and Progress

East Africa has one of the world's fastest growing human populations-many of whom are dependent on livestock-as well as some of the world's largest wildlife populations. Humans, livestock, and wildlife often interact closely, intimately linking human, animal, and environmental health. The concept of One Health captures this interconnectedness, including the social structures and beliefs driving interactions between species and their environments. East African policymakers and researchers are recognising and encouraging One Health research, with both groups increasingly playing a leading role in this subject area. One Health research requires interaction between scientists from different disciplines, such as the biological and social sciences and human and veterinary medicine. Different disciplines draw on norms, methodologies, and terminologies that have evolved within their respective institutions and that may be distinct from or in conflict with one another. These differences impact interdisciplinary research, both around theoretical and methodological approaches and during project operationalisation. We present experiential knowledge gained from numerous ongoing projects in northern Tanzania, including those dealing with bacterial zoonoses associated with febrile illness, foodborne disease, and anthrax. We use the examples to illustrate differences between and within social and biological sciences and between industrialised and traditional societies, for example, with regard to consenting procedures or the ethical treatment of animals. We describe challenges encountered in ethical approval processes, consenting procedures, and field and laboratory logistics and offer suggestions for improvement. While considerable investment of time in sensitisation, communication, and collaboration is needed to overcome interdisciplinary challenges inherent in One Health research, this can yield great rewards in paving the way for successful implementation of One Health projects. Furthermore, continued investment in African institutions and scientists will strengthen the role of East Africa as a world leader in One Health research.

The efficacy of alcelaphine herpesvirus-1 (AlHV-1) immunization with the adjuvants Emulsigen® and the monomeric TLR5 ligand FliC in zebu cattle against AlHV-1 malignant catarrhal fever induced by experimental virus challenge

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Vaccination induces a pharyngeal antibody response in shorthorn zebu cross (SZC).

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Direct challenge with the AlHV-1 virus is effective at inducing MCF in SZC.

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Attenuated AlHV–1 + Emulsigen^® vaccine efficacy in SZC calculated to be 50%.

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Bacterial flagellin is not a good adjuvant as inclusion reduced antibody response.

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We provide evidence that non-fatal AlHV-1 infections occur in SZC.

Malignant catarrhal fever (MCF) is a fatal disease of cattle that, in East Africa, follows contact with wildebeest excreting alcelaphine herpesvirus 1 (AlHV-1). Recently an attenuated vaccine (atAlHV-1) was tested under experimental challenge on Friesian-Holstein (FH) cattle and gave a vaccine efficacy (VE) of approximately 90%. However testing under field conditions on an East African breed, the shorthorn zebu cross (SZC), gave a VE of 56% suggesting that FH and SZC cattle may respond differently to the vaccine. To investigate, a challenge trial was carried out using SZC. Additionally three adjuvant combinations were tested: (i) Emulsigen^®, (ii) bacterial flagellin (FliC) and (iii) Emulsigen^® + bacterial flagellin. We report 100% seroconversion in all immunized cattle. The group inoculated with atAlHV-1 + Emulsigen^® had significantly higher antibody titres than groups inoculated with FliC, the smallest number of animals that became infected and the fewest fatalities, suggesting this was the most effective combination. A larger study is required to more accurately determine the protective effect of this regime in SZC. There was an apparent inhibition of the antibody response in cattle inoculated with atAlHV-1 + FliC, suggesting FliC might induce an immune suppressive mechanism. The VE in SZC (50–60%) was less than that in FH (80–90%). We speculate that this might be due to increased risk of disease in vaccinated SZC (suggesting that the vaccine may be less effective at stimulating an appropriate immune response in this breed) and/or increased survival in unvaccinated SZC (suggesting that these cattle may have a degree of prior immunity against infection with AlHV-1).

Replacement of Glycoprotein B in Alcelaphine Herpesvirus 1 by Its Ovine Herpesvirus 2 Homolog : Implications in Vaccine Development for Sheep-Associated Malignant Catarrhal Fever

Vaccine development is a top priority in malignant catarrhal fever (MCF) research. In the case of sheep-associated MCF (SA-MCF) caused by ovine herpesvirus 2 (OvHV-2), progress toward this objective has been hindered by the absence of methods to attenuate or modify the virus, since it cannot be propagated in vitro. As an alternative for vaccine development, in this study, we tested the hypothesis that one of the SA-MCF vaccine candidate targets, OvHV-2 glycoprotein B (gB), could be expressed by a nonpathogenic alcelaphine herpesvirus 1 (AlHV-1) and then evaluated the potential of the AlHV-1/OvHV-2 chimera to be used as a vaccine and a diagnostic tool. The construction and characterization of an AlHV-1/OvHV-2 chimeric virus that is nonpathogenic and expresses an OvHV-2 vaccine target are significant steps toward the development of an SA-MCF vaccine and also provide a valuable means to study OvHV-2 biology.

A field vaccine trial in Tanzania demonstrates partial protection against malignant catarrhal fever in cattle

Malignant catarrhal fever (MCF) is a fatal lymphoproliferative disease of cattle that, in East Africa, results from transmission of the causative virus, alcelaphine herpesvirus 1 (AlHV-1), from wildebeest. A vaccine field trial involving an attenuated AlHV-1 virus vaccine was performed over two wildebeest calving seasons on the Simanjiro Plain of northern Tanzania. Each of the two phases of the field trial consisted of groups of 50 vaccinated and unvaccinated cattle, which were subsequently exposed to AlHV-1 challenge by herding toward wildebeest. Vaccination resulted in the induction of virus-specific and virus-neutralizing antibodies. Some cattle in the unvaccinated groups also developed virus-specific antibody responses but only after the start of the challenge phase of the trial. PCR of DNA from blood samples detected AlHV-1 infection in both groups of cattle but the frequency of infection was significantly lower in the vaccinated groups. Some infected animals showed clinical signs suggestive of MCF but few animals went on to develop fatal MCF, with similar numbers in vaccinated and unvaccinated groups. This study demonstrated a baseline level of MCF-seropositivity among cattle in northern Tanzania of 1% and showed that AlHV-1 virus-neutralizing antibodies could be induced in Tanzanian zebu shorthorn cross cattle by our attenuated vaccine, a correlate of protection in previous experimental trials. The vaccine reduced infection rates by 56% in cattle exposed to wildebeest but protection from fatal MCF could not be determined due to the low number of fatal cases.

Alcelaphine herpesvirus 1 glycoprotein B: recombinant expression and antibody recognition

The gammaherpesvirus alcelaphine herpesvirus 1 (AlHV-1) causes fatal malignant catarrhal fever (MCF) in susceptible species including cattle, but infects its reservoir host, wildebeest, without causing disease. Pathology in cattle may be influenced by virus-host cell interactions mediated by the virus glycoproteins. Cloning and expression of a haemagglutinin-tagged version of the AlHV-1 glycoprotein B (gB) was used to demonstrate that the AlHV-1-specific monoclonal antibody 12B5 recognised gB and that gB was the main component of the gp115 complex of AlHV-1, a glycoprotein complex of five components identified on the surface of AlHV-1 by immunoprecipitation and radiolabelling. Analysis of AlHV-1 virus particles showed that the native form of gB was detected by mAb 12B5 as a band of about 70 kDa, whilst recombinant gB expressed by transfected HEK293T cells appeared to be subject to additional cleavage and incomplete post-translational processing. Antibody 12B5 recognised an epitope on the N-terminal furin-cleaved fragment of gB on AlHV-1 virus particles. It could be used to detect recombinant and virus-expressed gB on western blots and on the surface of infected cells by flow cytometry, whilst recombinant gB was detected on the surface of transfected cells by immunofluorescence. Recombinant gB has potential as an antigen for ELISA detection of MCF virus infection and as a candidate vaccine antigen.

Wildebeest-associated malignant catarrhal fever: perspectives for integrated control of a lymphoproliferative disease of cattle in sub-Saharan Africa

Wildebeest-associated malignant catarrhal fever (WA-MCF), an acute lymphoproliferative disease of cattle caused by alcelaphine herpesvirus 1 (AlHV-1), remains a significant constraint to cattle production in nomadic pastoralist systems in eastern and southern Africa. The transmission of WA-MCF is dependent on the presence of the wildlife reservoir, i.e. wildebeest, belonging to the species Connochaetes taurinus and Connochaetes gnou; hence, the distribution of WA-MCF is largely restricted to Kenya, Tanzania and the Republic of South Africa, where wildebeest are present. WA-MCF is analogous to sheep-associated MCF (SA-MCF) in many aspects, with the latter having sheep as its reservoir host and a more global distribution, mainly in developed countries with intensive livestock production systems. However, unlike SA-MCF, the geographic seclusion of WA-MCF may have contributed to an apparent neglect in research efforts aimed at increased biological understanding and control of the disease. This review aims to highlight the importance of WA-MCF and the need for intensified research towards measures for its integrated control. We discuss current knowledge on transmission and geographical distribution in eastern and southern Africa and the burden of WA-MCF in affected vulnerable pastoral communities in Africa. Recent findings towards vaccine development and pertinent knowledge gaps for future research efforts on WA-MCF are also considered. Finally, integrated control of WA-MCF based on a logical three-pronged framework is proposed, contextualizing vaccine development, next-generation diagnostics, and diversity studies targeted to the viral pathogen and cattle hosts.

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

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

The economic impact of malignant catarrhal fever on pastoralist livelihoods

This study is the first to partially quantify the potential economic benefits that a vaccine, effective at protecting cattle against malignant catarrhal fever (MCF), could accrue to pastoralists living in East Africa. The benefits would result from the removal of household resource and management costs that are traditionally incurred avoiding the disease. MCF, a fatal disease of cattle caused by a virus transmitted from wildebeest calves, has plagued Maasai communities in East Africa for generations. The threat of the disease forces the Maasai to move cattle to less productive grazing areas to avoid wildebeest during calving season when forage quality is critical. To assess the management and resource costs associated with moving, we used household survey data. To estimate the costs associated with changes in livestock body condition that result from being herded away from wildebeest calving grounds, we exploited an ongoing MCF vaccine field trial and we used a hedonic price regression, a statistical model that allows estimation of the marginal contribution of a good's attributes to its market price. We found that 90 percent of households move, on average, 82 percent of all cattle away from home to avoid MCF. In doing so, a herd's productive contributions to the household was reduced, with 64 percent of milk being unavailable for sale or consumption by the family members remaining at the boma (the children, women, and the elderly). In contrast cattle that remained on the wildebeest calving grounds during the calving season (and survived MCF) remained fully productive to the family and gained body condition compared to cattle that moved away. This gain was, however, short-lived. We estimated the market value of these condition gains and losses using hedonic regression. The value of a vaccine for MCF is the removal of the costs incurred in avoiding the disease.

Antibodies to ovine herpesvirus 2 glycoproteins decrease virus infectivity and prevent malignant catarrhal fever in rabbits

Ovine herpesvirus-2 (OvHV-2) is the etiological agent of sheep-associated malignant catarrhal fever (SA-MCF), a fatal lymphoproliferative disease of many species in the order Artiodactyla. Development of a vaccine is critical to prevent mortality. Because OvHV-2 has not been cultured in vitro, SA-MCF research is hindered by the lack of in vitro tools to study viral constituents and specific host immune responses. As an alternative, in this study the neutralizing activity of antibodies against OvHV-2 glycoproteins gB and gH/gL was evaluated in vivo using rabbits. OvHV-2-specific antibodies were developed in rabbits by immunization using biolistic delivery of plasmids expressing the genes of interest. A lethal dose of OvHV-2 was incubated with the antisera and then nebulized into rabbits. Virus neutralization was assessed by measuring infection parameters associated with the virus infectious dose. Anti-gB or anti-gH/gL antibodies alone blocked infection in five out of six rabbits (83%), while a combination of anti-gB and anti-gH/gL antibodies protected all six rabbits (100%) from infection. These results indicate that antibodies to OvHV-2 gB and gH/gL are capable of neutralizing virions, and consequently, reduce virus infectivity and prevent SA-MCF in rabbits. Thus, OvHV-2 gB and gH/gL are suitable targets to be tested in a SA-MCF vaccine aimed at stimulating neutralizing antibody responses.

Alkaline phosphatase in nasal secretion of cattle: biochemical and molecular characterisation

Background

Nasal secretion (NS) was investigated as a source of information regarding the mucosal and systemic immune status of cattle challenged by respiratory disease. A method for the collection of substantial volumes (~12 ml) of NS from cattle was developed to establish a reference range of analytes that are present in the NS of healthy cattle. Biochemical profiles of NS from a group of 38 healthy Holstein-Friesian cows revealed high alkaline phosphatase (AP) activity of up to 2392 IU/L. The character and source of the high activity of AP in bovine NS was investigated.

Results

Histochemical analysis confirmed the localization of the AP enzyme activity to epithelial cells and serous glands of the nasal respiratory mucosa. Analysis of mRNA levels from nasal mucosa by end point RT-PCR and PCR product sequencing confirmed that the AP was locally produced and is identical at the nucleotide level to the non-specific AP splice variant found in bovine liver, bone and kidney. Analysis by isoelectric focussing confirmed that AP was produced locally at a high level in nasal epithelium demonstrating that AP from nasal secretion and nasal mucosa had similar pI bands, though differing from those of the liver, kidney, bone and intestine, suggesting different post-translational modification (PTM) of AP in these tissues.

Conclusions

A nasal isozyme of AP has been identified that is present at a high activity in NS, resulting from local production and showing distinctive PTM and may be active in NS as an anti-endotoxin mediator.

Identification of immuno-reactive capsid proteins of malignant catarrhal fever viruses

Malignant catarrhal fever (MCF) is a fatal disease of cattle and other ungulates caused by certain gamma-herpesviruses including alcelaphine herpesvirus-1 (AlHV-1) and ovine herpesvirus-2 (OvHV-2). An attenuated virus vaccine based on AlHV-1 has been shown to induce virus-neutralising antibodies in plasma and nasal secretions of protected cattle but the targets of virus-specific antibodies are unknown. Proteomic analysis and western blotting of virus extracts allowed the identification of eight candidate AlHV-1 virion antigens. Recombinant expression of selected candidates and their OvHV-2 orthologues confirmed that two polypeptides, the products of the ORF17.5 and ORF65 genes, were antigens recognised by antibodies from natural MCF cases or from AlHV-1 vaccinated cattle. These proteins have potential as diagnostic and/or vaccine antigens.

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.

Malignant catarrhal fever in American bison (Bison bison) experimentally infected with alcelaphine herpesvirus 2

Malignant catarrhal fever (MCF), due to ovine herpesvirus 2 (OvHV-2), causes appreciable death loss in ranched bison (Bison bison) throughout North America. No vaccine exists to protect animals from disease. Since OvHV-2 has not been propagated in vitro, one strategy to develop a modified live vaccine is to use a closely related, non-pathogenic member of the malignant catarrhal fever virus family as a vector expressing potentially protective OvHV-2 epitopes. To date, no controlled experimental challenge studies with alcelaphine herpesvirus 2 (AlHV-2) derived from topi (Damaliscus lunatus jimela) have been reported The unique or light DNA segment of the AlHV-2 genome was sequenced and annotated and the virus was tested for its ability to infect and induce disease in American bison. Yearling bison were inoculated intranasally (n=4) or intramuscularly (n=3) with 2 × 10(-4.7) TCID50 of AlHV-2, and monitored for infection and the development of disease. Six inoculated bison became infected with AlHV-2. Two of the six animals developed clinical signs and had gross and histological lesions consistent with terminal MCF, which differed in distribution from those in bison with MCF due to OvHV-2. One other animal developed minor clinical signs and had gross and histological pulmonary lesions consistent with early (pre-clinical) stages of MCF. Unmodified low cell culture passage AlHV-2 derived from topi is an unsuitable vaccine vector for the prevention of MCF. However, the annotated genome might be useful in identifying genes which could be deleted to potentially attenuate the virus for bison.

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.

A novel spliced gene in alcelaphine herpesvirus 1 encodes a glycoprotein which is secreted in vitro

Herpesviruses often contain cryptic, spliced genes that are not obvious from the initial in silico annotation. Alcelaphine herpesvirus 1 (AlHV-1) contains 72 annotated ORFs but there are also a number of gaps between these that may have protein-coding potential. Comparative analysis of coding potential between AlHV-1 and the related ovine herpesvirus 2 (OvHV-2) revealed a putative novel spliced gene that we have termed A9.5. Analysis of cDNA clones from AlHV-1-infected cells revealed three overlapping clones corresponding to A9.5 and the coding sequence was confirmed by reverse transcription PCR of RNA from AlHV-1-infected cattle tissues. The A9.5 gene was predicted to encode a secreted glycoprotein with molecular mass 19 kDa. Empirical analysis showed that a recombinant haemagglutinin-tagged A9.5 fusion protein was secreted from transfected cells and had a molecular mass of 45 kDa, which was reduced to 20 kDa by endoglycosidase F treatment, confirming that A9.5 was a secreted glycoprotein. In situ RNA hybridization showed that A9.5 was expressed in cells associated with malignant catarrhal fever (MCF) lesions in infected cattle. Detailed analysis of the available OvHV-2 sequences revealed an homologous gene (Ov9.5) with conserved splicing signals and predicted amino acid sequence features in both sequenced isolates of this related virus. We have therefore identified a novel spliced gene in two related macaviruses that is expressed in MCF lesions. Future work will determine its importance for the pathogenesis of disease.

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.

An essential role for γ-herpesvirus latency-associated nuclear antigen homolog in an acute lymphoproliferative disease of cattle

Wildebeests carry asymptomatically alcelaphine herpesvirus 1 (AlHV-1), a γ-herpesvirus inducing malignant catarrhal fever (MCF) to several ruminant species (including cattle). This acute and lethal lymphoproliferative disease occurs after a prolonged asymptomatic incubation period after transmission. Our recent findings with the rabbit model indicated that AlHV-1 infection is not productive during MCF. Here, we investigated whether latency establishment could explain this apparent absence of productive infection and sought to determine its role in MCF pathogenesis. First, whole-genome cellular and viral gene expression analyses were performed in lymph nodes of MCF-developing calves. Whereas a severe disruption in cellular genes was observed, only 10% of the entire AlHV-1 genome was expressed, contrasting with the 45% observed during productive infection in vitro. In vivo, the expressed viral genes included the latency-associated nuclear antigen homolog ORF73 but none of the regions known to be essential for productive infection. Next, genomic conformation analyses revealed that AlHV-1 was essentially episomal, further suggesting that MCF might be the consequence of a latent infection rather than abortive lytic infection. This hypothesis was further supported by the high frequencies of infected CD8(+) T cells during MCF using immunodetection of ORF73 protein and single-cell RT-PCR approaches. Finally, the role of latency-associated ORF73 was addressed. A lack of ORF73 did not impair initial virus replication in vivo, but it rendered AlHV-1 unable to induce MCF and persist in vivo and conferred protection against a lethal challenge with a WT virus. Together, these findings suggest that a latent infection is essential for MCF induction.

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.

Important mammalian veterinary viral immunodiseases and their control

This paper offers an overview of important veterinary viral diseases of mammals stemming from aberrant immune response. Diseases reviewed comprise those due to lentiviruses of equine infectious anaemia, visna/maedi and caprine arthritis encephalitis and feline immunodeficiency. Diseases caused by viruses of feline infectious peritonitis, feline leukaemia, canine distemper and aquatic counterparts, Aleutian disease and malignant catarrhal fever. We also consider prospects of immunoprophylaxis for the diseases and briefly other control measures. It should be realised that the outlook for effective vaccines for many of the diseases is remote. This paper describes the current status of vaccine research and the difficulties encountered during their development.

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 induced by Alcelaphine herpesvirus 1 is characterized by an expansion of activated CD3+CD8+CD4- T cells expressing a cytotoxic phenotype in both lymphoid and non-lymphoid tissues

Alcelaphine herpesvirus 1 (AlHV-1) is carried by wildebeest asymptomatically. It causes a fatal lymphoproliferative disease named wildebeest-derived malignant catarrhal fever (WD-MCF) when cross-species transmitted to a variety of susceptible species of the Artiodactyla order. WD-MCF can be reproduced experimentally in rabbits. In a previous report, we demonstrated that WD-MCF induced by AlHV-1 is associated with a severe proliferation of CD8(+) T cells in the lymphoid tissues. Here, we further studied the mononuclear leukocytic populations in both the lymphoid (throughout the infection and at time of euthanasia) and non-lymphoid (at time of euthanasia) organs during WD-MCF induced experimentally in rabbits. To reach that goal, we performed multi-colour flow cytometry stainings. The results obtained demonstrate that the development of WD-MCF correlates in peripheral blood with a severe increase of CD8(+) cell percentages; and that CD3(+)CD8(+)CD4(-) T cells were the predominant cell type in both lymphoid and non-lymphoid organs at time of euthanasia. Further characterization of the mononuclear leukocytes isolated from both lymphoid and non-lymphoid tissues revealed that the CD8(+) T cells express high levels of the activation markers CD25 and CD44, produce high amount of gamma-interferon (IFN-γ) and perforin, and showed a reduction of interleukin-2 (IL-2) gene expression. These data demonstrate that the development of WD-MCF is associated with the expansion and infiltration of activated and cytotoxic CD3(+)CD8(+)CD4(-) T cells secreting high amount of IFN-γ but low IL-2.

Experimental nebulization of American bison (Bison bison) with low doses of ovine herpesvirus 2 from sheep nasal secretions

Malignant catarrhal fever (MCF), caused by ovine herpesvirus 2 (OvHV-2), is an important cause of mortality in ranched American bison and domestic cattle in North America. Previous studies showed that bison can be infected by intranasal nebulization with sheep nasal secretions containing OvHV-2 and provided preliminary information on viral doses required for infection and disease progression. The goals of this study were to establish optimal minimal infectious and minimal lethal doses of OvHV-2 by the intranasal route in bison, evaluate the influence of dose on incubation period and other clinical parameters and determine if bison seropositive for antibody against MCF-group viruses are resistant to developing MCF after intranasal challenge. In this study, the minimal infectious dose and minimal lethal dose overlap, suggesting that experimental production of subclinically infected bison is impractical. Dose is inversely related to both incubation period and the period between nebulization and first detection of >1000 OvHV-2 DNA copies/500 ng total DNA in peripheral blood leukocytes. Interestingly, all of the bison seropositive for anti-MCF-group viral antibody prior to inoculation died of MCF after nebulization. We conclude that previous exposure to an MCF-group virus does not necessarily provide resistance to OvHV-2-induced MCF in bison.