Viral encephalomyelitis of pigeons. IV. Growth of the virus in tissue cultures.

Growth and cytopathogenicity of pigeon herpes encephalomyelitis virus (PHEV) in avian and mammalian cell cultures were investigated. The virus was cytopathogenic to all avian primary cell cultures tested and produced large syncytia with intranuclear inclusions. Viral antigen was detected in the nuclei of infected cells 6 hr postinoculation. Infective virus, however, was obtained 8 hr post-inoculation. Maximum virus yields in avian cell cultures were reached 72 hr postinoculation. In mammalian cell lines tested, the virus proved to be cytopathogenic except in swine embryo kidney cell lines. The cytopathic effect in mammalian cell lines was characterized by the rounding and clumping of cells., Moderate virus yields were obtained with lamb kidney and bovine embryo thymus cell lines, but not with other cell lines tested. Growth behavior of the virus in cell cultures in comparison with other human and avian herpesviruses is discussed.

Role of Coccidia in the occurrence of necrotic enteritis of chickens.

Clostridium perfringens type A, Eimeria acervulina, and Eimeria necatrix were used to produce necrotic enteritis in chickens. The disease was produced in all groups of birds that received feed contaminated with C. perfringens. Mortality due to necrotic enteritis was highest (53%) in birds infected with E. acervulina before infection with clostridia. There was a significant difference in mortality rates between birds infected with E. acervulina and birds infected with E. necatrix before infection with C. perfringens. Mortality rates also differed significantly between the group infected with E. necatrix and the group that received only feed contaminated with C. perfringens. It was concluded that under field conditions, coccidia can play a significant role in the occurrence of necrotic enteritis when a sufficient number of toxigenic strain of C. perfringens type A is present. The pathological changes induced by clostridia and coccidia are described.

Viral encephalomyelitis of pigeons. V. Comparative studies of virulent and cell-culture-adapted virus.

Two strains of pigeon herpes encephalomyelitis virus BVC 78, a virulent field strain, and BVC 78 T7, a cell-culture-adapted strain, were assayed in embryonated chicken eggs and in chicken-embryo-fibroblast (CEF) cell culture to investigate their cytopathogenicity, growth kinetics, plaque characters, and virulence. In CEF the BVC 78 induced syncytia 24-48 hr postinoculation (PI), while the BVC 78 T7 induced only cell rounding 72 hr PI. The strains differed in growth patterns in CEF. The BVC 78 and BVC 78 T7 strains had respective logarithmic phases at 24 and 72 hr PI and maximum virus yields at 36 and 120 hr PI. The BVC 78 T7 was more cell-associated than the BVC 78, the ratio of cell-bound to cell-free virus was about 2 for the former and near unity for the latter. In CEF the BVC 78 induced plaques 1-2 mm in diameter by the third day PI, while the BVC 78 T7 produced small plaques 0.3-0.5 mm in diameter by the 5th day PI. The BVC T7 strain was of low killing capacity for chicken embryos, in contrast to the high killing capacity of the BVC 78. Pigeons inoculated subcutaneously with the former strain and challenged 21 days later with the virulent strain proved resistant.

Viral encephalomyelitis of pigeons: pathology and virus isolation.

A previously unrecorded nervous disease in pigeons was investigated. The disease, characterized by paresis, paralysis of the extremities, head-shaking, and torticollis, is contagious and spreads slowly. The mortality rate of affected pigeons was very high. The disease appeared to spread among pigeon flocks in spring and summer. The predominant gross change in most cases examined was congestion of the visceral organs. Some cases had grayish spots on the pancreas and kidneys. The histologic changes are characterized by neuronal and myelin degeneration with mononuclear cell infiltration and perivascular cuffing. Degeneration of the parenchyma and marked congestion are prominent in the visceral organs. The causal agent, found to be a virus, produced pock lesions on chorioallantoic membranes of developing chick embryos and failed to aagglutinate chicken RBCs. Antisera against Newcastle disease virus and avian encephalomyelitis virus did not neutralize the isolated virus. The virus produced typical signs in experimentally inoculated pigeons.

Inclusion body hepatitis in broiler chickens in Iraq.

Eighteen outbreaks of inclusion body hepatitis (IBH) were identified in broiler chickens in Baghdad in 1977 and 1978. The disease was seen mainly in 4-to-6-week-old broiler chickens. The mortality rate did not exceed 1% in any outbreak investigated. The most common gross findings were stellate or punctiform hemorrhagic areas in markedly fatty livers. Noticed in many cases were enlarged and pale kidneys, hemorrhagic lesions in the skeletal muscles, and pale fattened bone marrow. Histological examination of tissues revealed fat droplets and intranuclear inclusion bodies in degenerated liver cells. Eosinophilic inclusion bodies were seen in all cases. Only five cases had basophilic inclusions along with the eosinophilic ones. The etiologic agent was isolated on chorioallantoic membrane (CAM) of 12-day-old embryonated chicken eggs. The disease was produced experimentally in 4-week-old chicks using infected CAM suspension.

Reproduction and treatment of necrotic enteritis in broilers.

A change in ration from one containing 50% fish meal to a standard chick starter containing 10(8) Clostridium perfringens/g of feed resulted in the production of necrotic enteritis in 2-week-old broiler chicks. Lincomycin added to the inoculated ration at a concentration of 20 g/907.2 kg significantly reduced mortality in the chicks. Inoculation of broth cultures of C perfringens directly into the duodenum, using a surgically inserted tetrafluoroethylene resin tube, indicated a relationship existed between the number of C perfringens inoculated and the gross lesions. The disease could be consistently produced by this technique.

The pathology of necrotic enteritis of chickens following infusion of crude toxins of Clostridium perfringens into the duodenum.

Necrotic enteritis was produced in 4-week-old chickens with bacteria-free crude toxins of Clostridium perfringens. Typical gross lesions could be seen as early as 3 hr after intraduodenal infusion of toxin was begun. Early microscopic lesions were observed at 20 minutes, progressing with time to involve most of the mucosa. Death was related to the amount of toxin administered. Because systemic absorption of toxin is likely, acutely affected birds may die from toxemia.

The pathology of necrotic enteritis of chickens following infusion of broth cultures of Clostridium perfringens into the duodenum.

Necrotic enteritis was consistently reproduced when enough active broth culture of Clostridium perfringens type A was infused intraduodenally. Typical lesions of necrotic enteritis were seen as early as 5 hr after infusion was begun. The histologic lesions observed at 1 hr were characterized by edema in the lamina propria and desquamation of epithelial cells. Large numbers of clostridia were seen among these sloughed cells. Coagulation necrosis of the tips of villi became evident at 3 hr and was marked at 5 hr. Many clumps of clostridia were obvious among the necrotic tissue. At 8 and 12 hr the necrotic lesions extended to involve most of the villus structures. Morphologically abnormal erythrocytes were evident in the visceral organs at 12 hr.

The interaction of Clostridium perfringens and its toxins in the production of necrotic enteritis of chickens.

The intraduodenal administration of large numbers of Clostridium perfringens cells harvested from broth cultures and resuspended in PBS or fresh sterile thioglycollate broth produced a very mild form of necrotic enteritis. Administering an appropriate number of cells in culture supernatant, however, produced typical field-type disease. Alpha toxin was shown to be the significant toxin recoverable from broth-culture supernatant fluids. Requirements to produce the disease are minor intestinal damage and sufficient numbers of toxigenic C. perfringens in the intestine.

Pathology of velogenic Newcastle Disease virus infection in turkeys.

Twenty-four 4-week-old poults, free from Mycoplasma meleagridis and M. gallisepticum, were inoculated with a velogenic viscerotropic strain of Newcastle disease virus. Clinical signs (gasping, coughing, and dyspnea) developed 4-5 days postinoculation, continued until nervous derangement appeared, and then (usually 3 days after initial clinical signs appeared) declined in severity. Prominent nervous signs were paresis and paralysis of the extremities, with pronounced head-shaking. The most constant gross lesions detected involved the airsacs. The abdominal sacs of a few poults contained a large accumulation of yellowish, cheesy exudate and there was cloudiness of the thoracic airsacs of all inoculated poults. A few turkeys had tracheitis with some catarrhal exudates and casts in the lower part of the tracheal lumen. Congestion of lepto-meningeal vessels usually correlated with the severity of the nervous signs. The histologic lesions were characterized by both degenerative and proliferative changes with predominantly mononuclear cell and heterophil infiltrations throughout the body. The obvious lesion seen in the recovery stage of the disease was proliferation of lymphofollicular nodules in the parenchymatous organs.