Development of an enzyme-linked immunosorbent assay for the detection of antibodies against malignant catarrhal fever viruses in cattle serum

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.

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.

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

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

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.

Evaluation of glycoprotein Ov8 as a potential antigen for an OvHV-2-specific diagnostic assay

Gammaherpesviruses in the genus Macavirus establish clinically unapparent persistent infections in reservoir species. Transmission of some of these viruses, including alcelaphine herpesvirus 1 (AlHV-1) and ovine herpesvirus 2 (OvHV-2), to clinically susceptible species in the order Artiodactyla can result in malignant catarrhal fever (MCF), a usually fatal lymphoproliferative disease. Serology can be used to identify MCF virus (MCFV)-infected carrier animals. However, all current serological assays utilize AlHV-1 antigens, thus none is specific for OvHV-2. In situations where sheep and other MCFV carriers are present, such as in zoos and game farms, an OvHV-2-specific assay would determine if OvHV-2 is present in the population. In this study, a recombinant protein containing a truncated OvHV-2 Ov8 glycoprotein was expressed and evaluated as a suitable target antigen to specifically detect OvHV-2 infection using an enzyme linked immunosorbent assay (ELISA). A competitive inhibition (CI)-ELISA that detects an epitope conserved among all MCFVs was used to categorize, as positive or negative, sera from 205 domestic sheep. The Ov8 assay showed 100% diagnostic sensitivity, 98.97% diagnostic specificity, 99.07% positive predictive value, and 100% negative predictive value and very high agreement (kappa = 0.990 and 95% CI = 0.971–1.000) with the CI-ELISA. Sera from animals infected with MCFVs other than OvHV-2 did not cross-react with Ov8 (100% negative predictive value). These data support the use of the Ov8 ELISA as an OvHV-2-specific diagnostic assay.

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.

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).

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.

Cross-sectional study indicates nearly a quarter of sheep population in Karnataka state of India is infected with ovine herpesvirus 2

In a cross-sectional study, prevalence of ovine herpesvirus 2 (family: Herpesviridae, subfamily: Gammaherpesvirinae, genus Macavirus and species: Ovine herpesvirus 2) infection was estimated in sheep population of Karnataka state in India. Based on the three stage cluster sampling method, whole blood samples (356) of sheep were collected from 11 sheep-dense districts of the state. The samples were tested for presence of OvHV-2 genome by recommended hemi-nested polymerase chain reaction (PCR) test. The true prevalence of OvHV-2 infection in sheep population of Karnataka was 24.44 %. Of the 11 district surveyed, highest true prevalence of 42.42 % (CI 25.56-59.29) was found in Raichur followed by Tumkur (39.02 %, CI 24.09-53.96). Inverse distance weighted interpolation of prevalence indicated that OvHV-2 prevalence within a given district is not uniform and there are areas of varied prevalence. The nucleotide sequence of the 422 bp DNA fragment, amplified in PCR, matched 99 % with OvHV-2 reference sequence and other sequences reported from India. Grouping of OvHV-2 sequences obtained from Karnataka with those from Andhra Pradesh, Tamil Nadu and Jammu and Kashmir in the neighbour joining tree indicated a close relationship among the OvHV-2s circulating in India. This is the first study in the country where systematic screening of sheep population of a state for the presence of OvHV-2 infection has been carried out, which indicated a widespread prevalence calling for an urgent need for policy measures to prevent economic losses due to the disease in susceptible cattle and buffalo species.

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.

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.

Malignant catarrhal fever: understanding molecular diagnostics in context of epidemiology

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

Malignant catarrhal fever: a review

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