Effect of intramammary injection of RbIL-8 on milk levels of somatic cell count, chemiluminescence activity and shedding patterns of total bacteria and S. aureus in Holstein cows with naturally infected-subclinical mastitis.

Summary The effect of intramammary injection of recombinant bovine interleukin-8 (rbIL-8, 1 mg/10 ml of saline) on quarter milk levels of somatic cell count (SCC), chemiluminescence (CL) activity and counts of total bacteria and Staphylococcus aureus (S. aureus) was investigated, using 10 Holstein cows with an early stage or a late stage of subclinical mastitis naturally infected with S. aureus. In the late-stage group, milk SCC and CL activity had significant rises with maximum levels at 6 h, following maintained high levels thereafter post-cytokine injection. The counts in milk total bacteria and S. aureus were insignificantly decreased, being increased back on day 7 post-cytokine injection. Thus, the cytokine was inefficient for the late-stage subclinical mastitis. However, in the early-stage group milk SCC and CL activity declined to under pre-injection levels on day 7 after marked and significant rises at 6 h and day 1 post-cytokine injection. The milk total bacterial count decreased significantly on days 0.25 and 2. Furthermore, the milk S. aureus count was decreased significantly on days 1, 2, 3 and 7 by the cytokine injection. These results suggest that the rbIL-8 has a potential as a therapeutic agent of the subclinical mastitis of dairy cows, if the cytokine is applied at an initial stage of infection.

Effects of dexamethasone on the pathogenesis of porcine circovirus type 2 infection in piglets.

To investigate the effect of immunosuppression on porcine circovirus type 2 (PCV2) infection, hysterectomy-produced, colostrum-deprived piglets were inoculated with the virus by the intranasal or intraperitoneal route, with or without dexamethasone (DEX) treatment. Eleven piglets aged 8 days were divided into four groups, namely group A (four animals given PCV2), B (three given PCV2 with DEX), C (two given sterile medium with DEX) and D (two given sterile medium). No significant clinical signs were observed. Histopathological and immunohistochemical examination revealed granulomatous inflammation and PCV2 antigen in the lymphoid tissues of group B piglets, but not in the other three groups. Flow cytometric analysis of peripheral blood lymphocytes showed a reduced number of CD4+ T cells in DEX-treated piglets (groups A and C). No differences between groups were observed in respect of the number of B cells, serum IgG concentration, or PCV2 antibody titre. These results indicate that DEX influenced the pathogenic effects of PCV2 infection in lymphoid organs, and that suppression of cell-mediated immunity may play a role in the aetiology of postweaning multisystemic wasting syndrome.

Predominance of G3B and G14 equine group A rotaviruses of a single VP4 serotype in Japan.

A total of 65 equine group A rotaviruses (GAR) isolated from diarrheal foals at 48 farms in Hokkaido, Japan, between 1996 (29 isolates) and 1997 (36 isolates) were characterized for their VP7 and VP4 serotypes by PCR, nucleotide sequencing, and virus neutralization (VN) tests. By PCR VP7 typing, all isolates were classified as G3 or G 14, and the predominant serotype in each year was G3 (86%) in 1996 and G14 (53%) in 1997. VN tests with these 20 isolates randomly selected confirmed the specificity of PCR on the bases of complete agreement of the results in these methods (9 G3 and 11 G14), and revealed that all 9 G3 isolates were subtype G3B. There were five differing amino acid residues in three VP7 antigenic regions between subtypes G3A and G3B. Antiserum to a baculovirus recombinant that expressed P[12] VP4 neutralized all isolates and P[12] reference strains. These results suggest that genotype P[12] GAR belong to a single VP4 serotype, and that one VP4 and two VP7 serotypes (G3B and G14) of GAR were predominant in the equine population in Japan.

Experimental transmission of sheep-associated malignant catarrhal fever from sheep to Japanese deer (Cervus nippon) and cattle.

The assumption that sheep carry ovine herpesvirus-2 (OvHV-2), the causative agent of sheep-associated malignant catarrhal fever (SA-MCF), is widely accepted, albeit OvHV-2 has not been isolated. We attempted experimental contact transmission of MCF from Japanese sheep persistently infected with OvHV-2 to Japanese deer (Cervus nippon) and cattle. In Experiment 1, a deer was kept in close quarters with an infected ewe. In Experiment 2, a second deer was kept with the same ewe. In Experiment 3, two cows were each kept with two infected wethers. In Experiment 1, the deer developed clinical signs at 138 days after first contact and then died. OvHV-2 genes by polymerase chain reaction (PCR) and fluorescent antibodies to Alcelaphine herpesvirus-1 were detected in the affected deer. Moreover, sequences of PCR products (423bp), obtained by amplification of materials from the sheep and from the affected deer, coincided. These results clearly confirmed that the sheep was a carrier of OvHV-2, and that this virus had induced SA-MCF in a deer. In other experiments, no OvHV-2 infection occurred in deer and cattle during the 6-18 months periods of contact, though viral genes were detected in the nasal swabs and white blood cells of the sheep. To our knowledge, this is the first report on successful experimental transmission of MCF from OvHV-2-infected sheep to deer.

Effects of in vitro atmospheric ammonia exposure on recovery rate and luminol-dependent chemiluminescence of bovine neutrophils and bronchoalveolar macrophages.

The effects of atmospheric ammonia, a major pollutant in animal confinement facilities, on bovine neutrophils and bronchoalveolar macrophages were evaluated in vitro. Ammonia exposure at concentrations 50, 100 and 200 ppm for one hour impaired recovery rates of neutrophils dose-dependently but enhanced their chemiluminescence activity per cell at lower concentrations (50 and 100 ppm). Macrophages were resistant to the exposure. Their recovery rates and chemiluminescence remained unaffected even at 200 ppm exposure. The present results suggest that ammonia exposure is unfavorable for bovine neutrophils in vitro, and probably in vivo also, in light of causing cell damage and triggering wider inflammatory responses.

Biochemical and pathological findings on sheep and calves dying of experimental cerebrocortical necrosis.

For observing biochemical and morphopathological changes in experimental cerebrocortical necrosis, 6 sheep and 6 calves were given amprolium (600 mg/kg/day). All of the amprolium-dosed animals showed neurological signs and died on days 35 to 57 after the onset of daily administration. They were pathologically confirmed as cerebrocortical necrosis. Total thiamine levels in blood and tissues were markedly reduced at death. Blood total thiamine level decreased significantly on day 7 of amprolium administration, and reached to the level as low as that seen at death about 2 weeks before the onset of abnormal electroencephalograms. Significant decrease in a thiamine-dependent enzyme, erythrocyte transketolase activity, and increase in thiamine pyrophosphate effect were detected about 2 weeks before the onset of abnormal electroencephalograms. Pathological changes and cerebral autofluorescence observed under ultraviolet light were also examined at death.

Biochemical and pathological observations on sheep showing various clinical manifestations of experimental cerebrocortical necrosis.

For observing chronological changes of biochemical and pathological aspects in experimental cerebrocortical necrosis, 14 sheep were given amprolium (600 mg/kg/day), and killed at various clinical stages. At the onset of abnormal electroencephalograms, total thiamine concentrations in the cerebrum, liver, heart and blood were reduced significantly. After anorexia was noted, total thiamine concentrations in them did not decrease further as symptoms developed severely. Autofluorescence and necrotic lesions in the cerebral cortex were observed in animals killed one day after the onset of abnormal electroencephalograms.

Electroencephalographic observation on sheep and cattle with experimental cerebrocortical necrosis.

Nine Suffolk sheep and 4 Holstein cattle were employed to observe electroencephalographic changes in experimental cerebrocortical necrosis. Amprolium (600 mg/kg/day) alone was given intraruminally 6 sheep and 4 cattle, all of which showed neurological signs and abnormal electroencephalograms. Both amprolium and thiamine (200 mg/day) and thiamine (50 mg/day) alone were given 2 and 1 sheep, respectively, as controls, which did not show any abnormal signs. Abnormal electroencephalograms included continuous slow waves and long-lasting spindles, both of which appeared diffusely and were seen subclinically or with neurological signs. The spindles consisted of slow waves or sharp- (or spike-) and-slow-wave complexes with or without convulsive seizures even during the convulsion stage. Conversely, the seizures occurred with the spindles or slow waves.