Polymerase chain reaction amplification of wildebeest-associated and cervine-derived malignant catarrhal fever virus DNA

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.

Herpesvirus surveillance and discovery in zoo-housed ruminants

Gammaherpesvirus infections are ubiquitous in captive and free-ranging ruminants and are associated with a variety of clinical diseases ranging from subclinical or mild inflammatory syndromes to fatal diseases such as malignant catarrhal fever. Gammaherpesvirus infections have been fully characterized in only a few ruminant species, and the overall diversity, host range, and biologic effects of most are not known. This study investigated the presence and host distribution of gammaherpesviruses in ruminant species at two facilities, the San Diego Zoo and San Diego Zoo Safari Park. We tested antemortem (blood, nasal or oropharyngeal swabs) or postmortem (internal organs) samples from 715 healthy or diseased ruminants representing 96 species and subspecies, using a consensus-based herpesvirus PCR for a segment of the DNA polymerase (DPOL) gene. Among the 715 animals tested, 161 (22.5%) were PCR and sequencing positive for herpesvirus, while only 11 (6.83%) of the PCR positive animals showed clinical signs of malignant catarrhal fever. Forty-four DPOL genotypes were identified of which only 10 have been reported in GenBank. The data describe viral diversity within species and individuals, identify host ranges of potential new viruses, and address the proclivity and consequences of interspecies transmission during management practices in zoological parks. The discovery of new viruses with wide host ranges and presence of co-infection within individual animals also suggest that the evolutionary processes influencing Gammaherpesvirus diversity are more complex than previously recognized.

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.

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.

Detection of bovine gammaherpesviruses by a nested duplex PCR

The two bovine gammaherpesviruses (Alcelaphine herpesvirus 1, AlHV-1; Bovine herpesvirus 4, BoHV-4) are distributed worldwide in cattle populations. Since the animals are frequently infected latently with no or low seropositivity, a DNA based diagnostic method would be useful for surveys and detection of these viruses. In the present study a nested duplex PCR was established for the sensitive and specific simultaneous detection of both viruses. The primers were designed for the gene of the major capsid protein (ORF25). The assay did not amplify the capsid gene sequence of 10 related bovine herpesviruses and other gammaherpesviruses. The test was able to detect 1pfu (plaque forming unit) of AlHV-1 and BoHV-4. Among 146 clinical samples (lymph nodes and peripheral blood leukocytes, PBLs) 65 (44.52%) were found to be positives for AlHV-1 and 84 (57.53%) for BoHV-4. This nested duplex PCR assay could serve as a useful diagnostic method for rapid, sensitive, specific simultaneous detection of the two bovine gammaherpesviruses.

Polymerase chain reaction amplification and gene sequence analysis of a calicivirus from a feral rabbit

A reverse transcription-polymerase chain reaction (RT-PCR) amplification assay was used to detect calicivirus gene sequences in a liver tissue derived from a feral rabbit which died of a recent outbreak of rabbit haemorrhagic disease (RHD) in New Zealand. Five pairs of primers were designed to amplify five complementary DNA genomic sequence stretching from nucleotide positions 1594 to 7071, yielding amplified fragments of 361, 340, 805,670 and 386 bp for the primer pairs RC-1/RC-2, RC-3/RC-4, RC-5/RC-6, RC-7/RC-8 and RC-9/RC-10 respectively. The identity of the amplified fragments was confirmed by chemiluminescence Southern blot hybridization and direct cycle sequencing. The nucleotide sequences of the five amplified fragments were determined and comparisons of the nucleotide and deduced amino acid sequences revealed a close genetic relationship of the New Zealand isolate 97-10372 with overseas strains of RHD virus.

Molecular and clinicopathological diagnosis of malignant catarrhal fever in cattle, deer and buffalo in New Zealand

Fresh and formalin-fixed tissues and blood samples in ethylenediaminetetraacetate were collected from cattle, deer and buffalo with clinical signs suggestive of malignant catarrhal fever (MCF). In addition, formalin-fixed, paraffin-embedded tissue blocks collected from these animals and retrospectively from field cases of MCF were examined. DNA samples extracted from these samples were analysed by polymerase chain reaction (PCR) assay using primers specific for the sheep-associated (SA)- and wildebeest-associated (WA)-MCF viruses. Both the SA-MCF virus and WA-MCF virus PCR yielded positive results which were in nearly complete agreement with the histopathological diagnoses of MCF in fresh and formalin-fixed, paraffin-embedded tissue from 29 cattle, 24 deer and three buffaloes. Some blood samples tested by the two assays indicated that some of the infected cattle were possible carriers.

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

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

Investigation of sheep-associated malignant catarrhal fever virus infection in ruminants by PCR and competitive inhibition enzyme-linked immunosorbent assay

Development of control measures for the gammaherpesviral disease of cattle known as sheep-associated malignant catarrhal fever (SA-MCF) has been hampered by a lack of accurate diagnostic tests either for the causative virus or for antibody against that virus. A recently developed competitive-inhibition enzyme-linked immunosorbent assay (CI-ELISA) for the detection of antibody to malignant catarrhal fever (MCF) virus (MCFV) in ruminants based on a monoclonal antibody to a widely conserved epitope of MCFV (H. Li, D. T. Shen, D. P. Knowles, J. R. Gorham, and T. B. Crawford, J. Clin. Microbiol. 32:1674-1679, 1994) and a PCR assay based on previously reported primers (S. I. F. Baxter, I. Pow, A. Bridgen, and H. W. Reid, Arch. Virol. 132:145-159, 1993) were used to detect anti-MCFV antibody and SA-MCFV DNA in sheep and other ruminants. The PCR amplified a specific 238-bp SA-MCFV genomic DNA fragment from peripheral blood lymphocytes of adult sheep and other ruminants with clinical MCF. Of 144 samples from randomly selected healthy adult sheep, 143 (99%) were positive by PCR and 136 (94%) were positive by CI-ELISA. The agreement between the two assays exceeded 95%. Of nine samples collected from cattle and deer with clinical MCF of apparent sheep origin, seven were CI-ELISA positive and all 9 were PCR positive. Among 59 serum samples from presuckling lambs, none contained antibody detectable by CI-ELISA. After suckling, maternal anti-MCFV antibody was detectable for about 10 +/- 3 weeks. Although all colostrum and milk samples from infected ewes were strongly PCR positive, the appearance of detectable SA-MCFV DNA in lambs was correlated generally with antibody patterns, which suggests that the natural infection event in sheep may not occur during the perinatal period but occurs sometime later in life.

Detection of infectious bursal disease virus by reverse transcription-polymerase chain reaction amplification of the virus segment A gene

A reverse transcription-polymerase chain reaction (RT-PCR) amplification assay was developed to detect infectious bursal disease virus (IBDV) gene sequences in clinical samples, infected cell cultures and chicken embryos. Two pairs of primers were designed to amplify the 5'- and 3'-termini of segment A genes that partially code for the IBDV proteins VP2 and VP3, respectively. One primer pair specifies a 309-bp fragment, the other a 520-bp fragment. Direct RT-PCR analysis of 5 bursal samples of chickens derived from a suspected first outbreak of infectious bursal disease in New Zealand yielded the 309-bp and 520-bp by fragments. The identity of both amplified fragments was confirmed by restriction endonuclease analysis, chemiluminescence Southern blot hybridization and direct cycle sequencing. RT-PCR amplification of RNAs extracted from 4 out of 5 IBDV isolates propagated in Vero cells, chicken embryo fibroblasts and specific pathogen-free chicken embryos yielded IBDV-specific fragments of unpredicted small sizes.

Identification and analysis of an alcelaphine herpesvirus 1 (AHV-1) cDNA clone expressing a fusion protein recognized by AHV-1-neutralizing antisera

Rabbit antiserum to psoralen-inactivated alcelaphine herpesvirus 1 (AHV-1) virions was shown to react specifically with AHV-1-infected cells by indirect immunofluorescence. Western blot analysis using this antiserum identified a 15-kD virion protein that was also detected in infected-cell proteins between 12 and 144 h p.i., and a 37-kD protein present in infected cells between 24 and 120 h p.i. A cDNA library was constructed using mRNA obtained from AHV-1-infected fetal mouflon sheep kidney (FMSK) cells at 48 h p.i., when infected-cell proteins detected by antiserum were in abundance. Screening of the library with the rabbit anti-AHV-1 serum identified several positive clones. Southern blot analysis showed that one clone, designated 8'a, hybridized to a 4.4 kb HindIII fragment of AHV-1 DNA. This AHV-1 cDNA clone expressed a fusion protein that was recognized by serum from a naturally and asymptomatically infected white-bearded wildebeest (Connochaetes taurinus albojubatus). The insert was sequenced and found to contain 833 bp. A search of the GenBank database for related sequences revealed greater than 40% homology to several other gammaherpesviruses: herpesvirus saimiri, cottontail herpesvirus, and Epstein-Barr virus.