Pathologic features of horses given avirulent equine arteritis virus intramuscularly

Twenty horses that were seronegative for equine arteritis virus antibodies were inoculated IM with live equine arteritis virus vaccine. The inoculation did not cause clinical signs of disease. A mild, transient febrile reaction developed in 6 horses, 3 of which were in poor condition before inoculation. Six horses, 2 of which were in poor condition before inoculation, experienced mild lymphopenia. Necropsy revealed mild lesions in the lymph nodes of 6 horses (3 of which were in poor condition before inoculation). Maximum concentrations of virus were detected in the lymph nodes and were consistently present from postvaccination day 3 through 8. Lesser concentrations of virus were detected in the spleen of 5 horses, liver and kidney of 4, abdominal fluid of 3, pleural fluid of 2, and lungs and urine of 1, between postvaccination days 3 and 7. Virus was not detected in the brain, nasal tract, or serum of any of the horses.     

Seroprevalence of antibodies against equine arteritis virus in horses residing in the United States and imported horses

OBJECTIVE: To compare seroprevalence of antibodies against equine arteritis virus (EAV) in horses residing in the United States with that of imported horses. DESIGN: Serologic survey. SAMPLE POPULATION: Serum samples from 364 horses on 44 equine operations in California and 226 horses imported from various countries. PROCEDURE: Serum samples were collected from each imported horse and from up to 20 horses on each operation. For resident horses, the number of sampled horses on each operation was determined on the basis of the number of horses on the operation. Samples were tested for antibodies against EAV by use of a serum neutralization test. RESULTS: 1.9% of resident horses and 18.6% of imported horses were seropositive to EAV, including 16.1% of imported stallions. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that the EAV seroprevalence of horses residing in California is considerably lower than that of imported horses, including imported stallions.     

Differentiation of strains of equine arteritis virus of differing virulence to horses by growth in equine endothelial cells

OBJECTIVE: To compare growth characteristics of strains of equine arteritis virus (EAV) of differing virulence to horses in rabbit kidney (RK)-13 cells and equine endothelial cells (EECs) cultured from the pulmonary artery of a foal. SAMPLE POPULATION: 13 strains of EAV, including 11 field isolates of differing virulence to horses; the highly virulent, horse-adapted Bucyrus strain; and the modified-live virus (MLV) vaccine derived from it. PROCEDURE: The growth characteristics of the 13 strains were compared in EECs and RK-13 cells. Viral nucleoprotein expression, cytopathogenicity, and plaque size were compared to determine whether growth characteristics of the 13 strains were predictive of their virulence to horses. RESULTS: Cytopathogenicity, viral nucleoprotein expression, and plaque size induced by all 13 viruses were similar in RK-13 cells, whereas virulent strains of EAV caused significantly larger plaques in EECs than did the avirulent strains of EAV. Paradoxically, the highly attenuated MLV vaccine and 1 field isolate of EAV caused plaques in EECs that were larger than those caused by any of the other viruses, and sequence analysis confirmed the field isolate of EAV to be indistinguishable from the MLV vaccine. CONCLUSIONS AND CLINICAL RELEVANCE: With the notable exception of the MLV vaccine, growth of the various strains of EAV in EECs was predictive of their individual virulence to horses. Thus, EECs provide a relevant and useful model to further characterize determinants of virulence and attenuation amongst strains of EAV.     

Serological studies of the recent infections of Austrian horses with the equine arteritis virus]

944 serum samples of horses, collected in 1988 and 1989, were examined for the occurrence of antibodies against equine arteritis virus by a microneutralizations test. In 10.9% of all sera reactors could be found. The distribution of seropositive horses varied from 4.6% (Salzburg) to 15.7% (Lower Austria). From Tyrol and Vorarlberg no samples could be obtained. It was not possible, to correlate clinical symptoms (infertility, respiratory symptoms, fever and edema) with the infection. It is assumed, that the disease appears in Austria only in a clinical inapparent form.     

The occurrence of equine arteritis virus in Australia

This paper reports the first isolation of equine arteritis virus (EAV) in Australia and serological evidence of exposure to EAV in Australian horses. Twelve Standardbred stallions imported from North America were found to shed EAV in semen. One hundred and seven stallions were tested for serum antibodies to EAV and 73% of Standardbred stallions tested were seropositive as compared to 8% of Thoroughbred stallions. Serum antibody was detected in 71% of Standardbred mares, 6% of Standardbred racehorses and 1% of Thoroughbred mares and racehorses. Examination of stored serums demonstrated that EAV had been present in Australia since at least 1975.     

Diagnosis of equine arteritis virus infection in two horses by using monoclonal antibody immunoperoxidase histochemistry on skin biopsies

Two 5-year-old grade male horses presented with epiphora, rhinorrhea, conjunctival and nasal mucosal hyperemia, and dorsal and thoracic macropapular rash. Skin biopsies were collected from the affected areas, and serial sections were evaluated following hematoxylin and eosin and immunoperoxidase histochemistry staining by using a murine monoclonal antibody of the immunoglobulin G2A isotype recognizing the 30-kDa membrane protein of equine arteritis virus (EAV). In both horses, lesions consisted of mild to moderate diffuse superficial dermal edema and vasculitis with mild perivascular lymphocytic infiltrates, occasional endothelial hypertrophy, and single-cell necrosis of tunica media myocytes. Immunohistochemically, a few endothelial cells, myocytes, and pericytes containing intracytoplasmic EAV antigen were identified. Immunoperoxidase histochemistry of skin biopsies can be used as an ancillary test for the clinical diagnosis of equine viral arteritis in horses, especially when a cutaneous macropapular rash is evident.     

马动脉炎病毒进化分析及DNA条形码的确定

从GenBank数据库下载马动脉炎病毒所有基因组全序列和同属的其他病毒基因组序列,对其进行多重比对,绘制系统进化树,并根据序列比对筛选保守序列作为马动脉炎病毒的DNA条形码。结界发现马动脉炎病毒分为两个分枝,即欧洲型和美洲型,两者同源性在85%以上,而与同属其他病毒同源性低于40%,亲缘关系较远;对马动脉炎病毒基因组序列进行分析,筛选出9条基因序列作为马动脉炎病毒的DNA条形码,可用于马动脉炎病毒的鉴别诊断。     

Molecular epizootiology of equine arteritis virus isolates from Poland

Phylogenetic analysis was performed on the sequences of 44 Polish isolates of equine arteritis virus that were isolated from the semen of stallions from national and private studs, collected during 2001--2005. These sequences were also compared with 41 reference strains previously described and commonly used in phylogenesis. On the basis of the nucleotide sequence analysis of the ORF5 gene, encoding the glycoprotein GP5, it was demonstrated that the Polish EAV isolates belonged to two subgroups and showed the closest relationship to the European strains. Similar results were obtained using the nucleotide sequences of the ORF7 gene. The nucleotide identity between the ORF5 and ORF7 sequences of all Polish isolates was in the range of 80.1-99.0% and 93.6-100%, respectively. The analysis of genetic diversity within the ORF5 sequences enabled a retrospective epizootic investigation. This study suggested that some of the EAV shedding stallions were probably infected before they were moved to Poland.