Malignant catarrhal fever-like disease in sheep after intranasal inoculation with ovine herpesvirus-2.

A malignant catarrhal fever (MCF)-like disease was induced experimentally in 3 sheep after aerosol inoculation with ovine herpesvirus-2 (OvHV-2). Each of 3 OvHV-2-negative sheep was nebulized with 2 ml of nasal secretions containing approximately 3.07 X 10(9) OvHV-2 DNA copies from a sheep experiencing an intensive viral-shedding episode. Ovine herpesvirus-2 DNA became detectable by polymerase chain reaction in the peripheral blood leukocytes of all 3 sheep within 3 days, and all 3 seroconverted between 6 and 8 days postinfection (PI). The sheep developed clinical signs, with copious mucopurulent nasal discharge and fever around 14 days PI. One of the 3 clinically affected sheep was euthanized at 18 days PI. Major lesions at necropsy were multifocal linear erosions and ulcers in mucosa of the cheeks, tongue, pharynx, and proximal esophagus and mild disseminated pneumonia. Microscopically, there was extensive moderate superficial histiocytic-lymphocytic rhinitis with epithelial dissociation and degeneration. Moderate multifocal histiocytic bronchointerstitial pneumonia was associated with loss of terminal bronchiolar epithelium. Lymphocytic vasculitis was present only in the lung. The remaining 2 sheep recovered clinically, approximately 25 days PI. The study revealed that clinical signs and lesions resembling MCF can develop when uninfected sheep are exposed to a high dose of aerosolized OvHV-2.     

The prevalence of ovine herpesvirus-2 in 4 sheep breeds from different regions in South Africa

About 90% of bovine malignant catarrhal fever (BMCF) PCR-positive cases in South Africa are caused by alcelaphine herpesvirus-1 (AlHV-1) and the other 10% by ovine herpesvirus-2 (OvHV-2). The prevalence of OvHV-2 in different sheep breeds in South Africa was determined in order to investigate whether the lower incidence of BMCF caused by OvHV-2 in comparison with AlHV-1 can be ascribed to a low incidence of the virus in sheep. A single-tube hemi-nested PCR was developed, evaluated and applied to detect OvHV-2 DNA. The prevalence of the virus in 4 sheep breeds from various regions in South Africa was shown to be 77%. No statistically significant difference was found amongst the sheep breeds tested.     

Molecular detection and characterization of ovine herpesvirus-2 using heminested PCR in Pakistan

BackgroundMalignant catarrhal fever (MCF) is a highly fatal lymphoproliferative disease of cattle, deer, bison, water buffalo, and pigs caused by the gamma-herpesviruses alcelaphine herpesvirus-1 (AlHV-1) and ovine herpesvirus-2 (OvHV-2).ObjectivesThis study aimed to determine the prevalence of OvHV-2 in sheep, goats, cattle, and buffalo in Rawalpindi and Islamabad, Pakistan, by applying molecular and phylogenetic methods.MethodsBlood samples were aspirated from sheep (n = 54), goat (n = 50), cattle (n = 46) and buffalo (n= 50) at a slaughterhouse and several farms. The samples were subjected to heminested polymerase chain reaction (PCR), followed by sequencing and phylogenetic analysis of the OvHV-2 POL gene and the OvHV-2 ORF75 tegument protein gene.ResultsThe highest percentage of MCF positive samples was in sheep (13%), whereas goat, cattle, and buffalo had lower positive percentages, 11%, 9%, and 6.5%, respectively. Four OvHV-2-positive PCR products obtained from sheep samples were sequenced. The sequences obtained were submitted to the NCBI GenBank database ({"type":"entrez-nucleotide","attrs":{"text":"MK852173","term_id":"1694854431","term_text":"MK852173"}}MK852173 for the POL gene; {"type":"entrez-nucleotide","attrs":{"text":"MK840962","term_id":"1686143390","term_text":"MK840962"}}MK840962, {"type":"entrez-nucleotide","attrs":{"text":"MK852171","term_id":"1694854427","term_text":"MK852171"}}MK852171, and {"type":"entrez-nucleotide","attrs":{"text":"MK852172","term_id":"1694854429","term_text":"MK852172"}}MK852172 for the ORF75 tegument protein gene). Phylogenetic analysis revealed a close similarity of study sequences with those of worldwide samples.ConclusionsThis study is the first cross-sectional study on the prevalence and molecular detection of OvHV-2 in apparently healthy cattle and buffalo that could be carrying OvHV-2 acquired from OvHV-2-positive sheep and goats. The results indicate that OvHV-2 is circulating in Pakistan. Further studies are needed to characterize OvHV-2 and elucidate further its prevalence.     

Transmission of ovine herpesvirus 2 among adult sheep

Previous studies from this laboratory have defined the pattern of acquisition of ovine herpesvirus 2 (OHV-2) in lambs under natural flock conditions. This study examined the question of whether OHV-2 could be transmitted between adult sheep. Two potential routes of transmission were examined: (1) direct inoculation of either viable leukocytes or whole blood from OHV-2 positive sheep, and (2) horizontal transmission through natural contact with OHV-2 positive sheep. Two groups of OHV-2 negative adult sheep were inoculated with material from infected sheep, one with 5x10(8) viable peripheral blood leukocytes (PBL), and the other with 100 ml of whole peripheral blood. No PCR signals were detected in any of the three sheep inoculated with the PBL during the 20 weeks following inoculation. In the group of five sheep inoculated with whole blood, two became PCR-positive at 7 and 8 weeks post-inoculation, respectively, and the remaining three sheep maintained their negative status until termination of the experiment at 20 weeks post-inoculation. In two experiments conducted in different flocks, a total of 20 adult sheep were used to examine horizontal transmission by contact; all animals became PCR-positive within 12 months of mixing the uninfected and infected animals. The results of these experiments support two conclusions. First, the susceptibility to OHV-2 is not limited to young lambs; adult sheep remain fully susceptible. Second, the fact that whole blood, but not PBL, from infected sheep was able to transmit the infection to only two of five inoculated sheep suggests that the infection in peripheral blood cells may be largely non-productive.     

Observations on the indirect transmission of virulent ovine footrot in sheep yards and its spread in sheep on unimproved pasture

SUMMARY: Virulent ovine footrot was transmitted accidentally to a group of 23 adult Merino sheep (flock B) after holding for 1 hour in sheep yards, which earlier the same day had contained another flock (flock A) with < 1% prevalence of sheep with footrot lesions. Sheep in flock B were rendered susceptible to virulent footrot by grazing 600 mm high unimproved pasture dominated by paspalum ( Paspalum dilatatum ) and kangaroo grass ( Themeda australis ) during warm, humid and wet weather. In addition to moisture, interdigital abrasions caused by the pasture might have predisposed the interdigital skin to infection with Dichelobacter nodosus .     

Experimental transmission of jaagsiekte (ovine pulmonary adenomatosis) to goats

Jaagsiekte was successfully transmitted to at least 2 out of 6 goats inoculated intratracheally with partially purified jaagsiekte retrovirus. Multiple, small, well circumscribed nodules found in the lungs consisted of typical papilliform proliferations of neoplastic Type II epithelial cells. Histological evidence of a mild interstitial pneumonia in 4 of the experimental animals can probably be attributed to a contaminating lentivirus in the jaagsiekte retrovirus preparation, as suggested by the seroconversion of the animals.     

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

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

Ovine interleukin-2: partial purification and assay in normal sheep and sheep with ovine progressive pneumonia

Interleukin-2 (IL-2), a T cell derived lymphokine, acts in nonspecific hormone-like fashion to maintain proliferation of activated lymphocytes in vitro and is believed to play a key role in cell-mediated immune function in vivo. The parameters of induction and assay of factors with IL-2 activity were examined in a group of clinically normal sheep seronegative for antibodies to ovine progressive pneumonia virus (OPPV-). Supernatants from cultures of Concanavalin A (Con A) stimulated mononuclear leukocytes (ML) derived from peripheral blood and lymph nodes contained factors with the capacity to maintain continued proliferation in Con A stimulated lymphoblasts. This activity was localized by gel chromatography to fractions containing proteins of 17,000-20,000 daltons. In a group of sheep seropositive for antibodies to OPPV (OPPV+), decreased levels of IL-2 activity were found in ML culture supernatants derived from the posterior mediastinal lymph nodes of sheep with clinical and pathological evidence of OPP, when compared to OPPV+ sheep with no lesions and sheep with visceral caseous lymphadenitis. This decrease in IL-2 activity appeared not to be associated directly with levels of prostaglandin E2 in these supernatants. These findings may correlate with virus induced alterations in cell mediated immune function in lymphoproliferative lesions of OPP.     

Experimental T-2 toxicosis in sheep.

Lambs received T-2 toxin at a rate of 0.6 or 0.3 mg/kg body weight per day in a protein reduced diet for 21 days to study the immunological and pathological effects of T-2 toxin in sheep. Blood was collected before T-2 treatment and on days 7, 14 and 21 of the trial for hematological and biochemical examination and for the separation of peripheral blood lymphocytes for the mitogen assay. Myeloid:erythroid ratios were determined from sternal bone marrow samples taken a day before T-2 treatment began, on day 12 and at death (day 22). Lambs treated with 0.6 mg/kg body weight of T-2 toxin daily were leukopenic on day 7 and lymphopenic on days 7 and 14. Also, on day 7, the mitogenic responses of these lambs to the B-cell mitogen, lipopolysaccharide, were significantly depressed and prothrombin times were prolonged. At necropsy, lymphoid atrophy of mesenteric lymph nodes and spleens was most marked in lambs treated with 0.6 mg/kg body weight of T-2 toxin per day. To the authors' knowledge, this is the first report of leukopenia, lymphopenia and lymphoid depletion in ruminants fed T-2 toxin.     

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

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