Hooper Pt

The lesions of experimental equine morbillivirus disease in cats and guinea pigs.

Nine cats and four guinea pigs became affected with severe disease during experiments on the infectivity of equine morbillivirus, a newly recognized cause of respiratory disease in horses and humans. Four of the cats were challenged by subcutaneous inoculation, two by intranasal installation, two by oral dosage, and one by direct contact with a cat previously infected by subcutaneous inoculation. All four guinea pigs were inoculated subcutaneously. Gross pathology seen in all affected cats was characterized by hydrothorax and dark, heavy, wet, congested and/or hemorrhagic lungs with froth sometimes found in the respiratory passages. Pulmonary lymph nodes were enlarged and edematous. Six cats also had congested ceca with accompanying edema of mesenteric lymph nodes. Histologically, the lesions in the lungs of the cats were those of severe interstitial pneumonia characterized by serofibrinous alveolar edema, alveolar macrophages, intra-alveolar hemorrhage, thrombosis of small veins, alveolar wall necrosis, and syncytial cells. Clearly defined vascular lesions included intramural hemorrhage, edema, and necrosis and syncytial cells in the endothelium of pulmonary arteries and veins, 20-80 μm in diameter. Vascular lesions accompanied by parenchymal degeneration were also seen in the gastrointestinal and lymphoid organs. Syncytial cells were also visible in the lymphoid tissues of lymph nodes, spleen, and Peyers patches. At necropsy, all guinea pigs were cyanosed and had congestion and edema in the gastrointestinal tract. Histologically, there was widespread vascular disease in arteries and veins, 20-80 μm in diameter, in many organs such as the lungs, kidneys, spleens, lymph nodes, gastrointestinal tracts, and skeletal and intercostal muscles, but there was no severe pulmonary edema as seen in horses and cats. Sections of tissues of the cats and guinea pigs, examined by indirect immunocytochemical stains, confirmed that the vascular damage was associated with the presence of equine morbillivirus antigen. The syncytia in small blood vessels in the lungs and other organs of both cats and guinea pigs were similar to those seen in horses, and their presence was interpreted as an important characteristic of the disease consistent with a reaction to a morbillivirus.

Lesions of Experimental Equine Morbillivirus Pneumonia in Horses

Laboratory examinations of equine morbillivirus included experimental reproductions of the disease caused by the virus by transmission of mixed lung and spleen taken from two field equine cases into two horses and by inoculating tissue culture virus into a further two horses. The most distinctive gross lesions of the diseases that developed in three of the horses was that of pulmonary edema characterized by gelatinous distension of subpleural lymphatics. Histologically, the lesions in the lungs were those of serofibrinous alveolar edema, alveolar macrophages, hemorrhage, thrombosis of capillaries, and syncytial cells. Clearly defined vascular lesions in three horses that became clinically affected within 8 days of inoculation of virus included intramural hemorrhage, edema, and necrosis and syncytial cells in the endothelium of pulmonary vessels (∼40-70 μm in diameter). Vascular lesions accompanied by parenchymal degeneration were also seen in the heart, kidney, brain, spleen, lymph node, and stomach. A fourth horse, which survived for 12 days, had detectable lesions only in the lungs, which were more chronic than those in the other three horses, a greater degree of cellular infiltration, and fewer well-defined vascular lesions. Sections stained by an indirect immunocytochemical method showed equine morbillivirus antigen was present in the vascular lesions and along alveolar walls. When endothelial cells were examined by electron microscope, cytoplasmic virus inclusion bodies containing filamentous structures were seen that reacted to an immunogold test to equine morbillivirus antigen. The presence of the syncytia in the small blood vessels in the lungs and other organs was interpreted as an important characteristic of the disease and consistent with a reaction to a morbillivirus.

Epidemic of blindness in kangaroos--evidence of a viral aetiology.

Objective To determine the cause of an epidemic of blindness in kangaroos. Design and procedures Laboratory examinations were made of eyes and brains of a large number of kangaroos using serological, virological, histopathological, electron microscopical, immunohistochemical methods, and PCR with cDNA sequencing. In addition, potential insect viral vectors identified during the disease outbreak were examined for specific viral genomic sequences. Sample population For histopathological analysis, 55 apparently blind and 18 apparently normal wild kangaroos and wallabies were obtained from New South Wales, Victoria, South Australia, and Western Australia. A total of 437 wild kangaroos and wallabies (including 23 animals with apparent blindness) were examined serologically. Results Orbiviruses of the Wallal and Warrego serogroups were isolated from kangaroos affected with blindness in a major epidemic in south-eastern Australia in 1994 and 1995 and extending to Western Australia in 1995/96. Histopathological examinations showed severe degeneration and inflammation in the eyes, and mild inflammation in the brains. In affected retinas, Wallal virus antigen was detected by immunohistochemical analysis and orbiviruses were seen in electron microscopy. There was serological variation in the newly isolated Wallal virus from archival Wallal virus that had been isolated in northern Australia. There were also variations of up to 20% in genotype sequence from the reference archival virus. Polymerase chain reactions showed that Wallal virus was present during the epidemic in three species of midges, Culicoides austropalpalis, C dycei and C marksi. Wallal virus nucleic acid was also detected by PCR in a paraffin-embedded retina taken from a blind kangaroo in 1975. Conclusion Wallal virus and perhaps also Warrego virus are the cause of the outbreak of blindness in kangaroos. Other viruses may also be involved, but the evidence in this paper indicates a variant of Wallal virus, an orbivirus transmitted by midges, has the strongest aetiological association, and immunohistochemical analysis implicates it as the most damaging factor in the affected eyes.

Immunohistochemistry in the identification of a number of new diseases in Australia.

Immunohistochemistry plays an important part in the diagnosis of some viral diseases. Demonstration of viral antigen in a lesion is an important contribution to diagnosis, either at the time of investigation or retrospectively. At the CSIRO Australian Animal Health Laboratory, the most frequent use of immunohistochemistry has been in the diagnosis of the important avian diseases, highly pathogenic avian influenza and Newcastle disease. The technology took key roles in the diagnoses of Hendra virus infections, and, later, an immunoperoxidase test gave the first indication of the existence of Australian bat lyssavirus. The test can often confirm that a virus isolated in an animal is the actual virus causing disease and not a coincidental isolation. Good examples of that in some more new diseases were the association of Wallal virus with blindness in kangaroos, and of the new porcine Menangle virus in natural and experimental cerebral disease in foetal piglets.