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H W Yoder

Publications and source records attributed to H W Yoder.

29 records · Page 2Linked to original sources
PubMedDate not supplied

Reversion to virulence of chicken-passaged infectious bronchitis vaccine virus.

Serial passage of two infectious bronchitis virus (IBV) vaccine strains in chickens enhanced their capacity to increase the incidence and severity of Mycoplasma synoviae (MS) airsacculitis. Included in this report were the mild Massachusetts-type Connaught strain and the Arkansas 99 vaccine strain of IBV. The Connaught strain and one of two Ark 99 vaccine strains passaged in chickens increased the incidence of airsacculitis markedly compared with nonpassaged virus. The other Ark 99 vaccine virus already exacerbated MS airsacculitis, before passage in chickens, and its influence did not increase on passage. All IBV strains studied to date have either possessed this trait or reacquired it on passage in the natural host.

Air Sacs↗
PubMedDate not supplied

A historical account of the diagnosis and characterization of strains of Mycoplasma gallisepticum of low virulence.

Numerous chicken flocks were studied beginning in 1970 because of questionable results on their serologic tests for Mycoplasma gallisepticum (MG). Typically a low number of hens in the flocks were positive reactors to the rapid serum plate test and rarely had hemagglutination-inhibition (HI) titers over 1:80. Usually no clinical signs were observed. Isolates of MG eventually were cultured from most of the flocks that exhibited that type of marginal serologic pattern. In the laboratory, the MG isolates were frequently less virulent and less pathogenic than the typical field isolates recovered in previous years. Most isolates produced airsacculitis of varying severity when broilers were exposed to the MG cultures as aerosols following exposure to infectious bronchitis virus. They became positive on the rapid serum plate test and developed moderate to high HI titers. Egg-transmission appeared to be the most likely means of transmission, even though the infected progeny rarely showed clinical signs of disease.

Animals↗
PubMedDate not supplied

Identification of avian mycoplasma isolates by the agar-gel precipitin test.

Recent isolates of Mycoplasma gallisepticum and Mycoplasma synoviae were readily typed by the agar-gel precipitin test with antigens prepared by freezing and thawing, sonic vibration, or sodium dodecyl sulfate. Specific antisera prepared in rabbits or in foot-pad-inoculated chickens were adequate for culture typing. Relatively few sera from chickens and turkeys in naturally infected flocks reacted positively. The precipitin reaction was highly specific, however.

Animals↗
PubMedDate not supplied

Influence of infectious bronchitis strains and vaccines on the incidence of Mycoplasma synoviae airsacculitis.

A model system was used to study infectious bronchitis virus (IBV) and Mycoplasma synoviae (MS) interaction. The system involved exposure of chickens to IBV, followed by exposure to MS 2-5 days later. The chickens were subjected to a cold environment (10 +/- 2 C) for 3 weeks starting one day before MS exposure. Under these conditions, differences in the capacity of various strains of IBV to exacerbate MS airsacculitis was demonstrated. Exposure to IBV field isolates generally resulted in more air-sac lesions than did higher-egg-passaged laboratory strains and vaccine strains. Use of lower-egg-passaged vaccines resulted in a higher incidence of airsacculitis than did higher-egg-passaged vaccines. When chickens were IBV-vaccinated before being used in the model system, the incidence of airsacculitis was lowered, even though the chickens became infected by the challenge virus. Vaccination of MS-free chickens with IBV had no effect on airsacculitis incidence when MS exposure occurred after the vaccine reaction was past.

Air Sacs↗
PubMedDate not supplied

Increased incidence of airsacculitis in broilers infected with mycoplasma synoviae and chicken-passaged infectious bronchitis vaccine virus.

Infectious bronchitis vaccine virus is thought to cycle (i.e., pass from vaccine-virus-infected to susceptible chickens) in commercial broiler and pullet flocks. To simulate the effect of this cycling, mild infectious bronchitis vaccine virus was passaged in chickens serially six times. This sixth passage virus was used to infect chickens, which were then exposed to a moderately cold environment of 10 +/- 2 C and to Mycoplasma synoviae. In two separate experiments, the chicken-passaged vaccine virus resulted in a marked increase in the incidence of airsacculitis compared with nonpassaged vaccine virus. Intermediate passage levels also increased airsacculitis incidence but not as much as the sixth passage virus. In another experiment, virus chicken-passaged by contact transmission also caused increased airsacculitis incidence.

Air Sacs↗
PubMedDate not supplied

Evaluation of inactivated Mycoplasma gallisepticum oil-emulsion bacterins for protection against airsacculitis in broilers.

Broiler chicks were vaccinated subcutaneously in the neck at various ages with a single 0.5-ml dose of beta-propiolactone-inactivated Mycoplasma gallisepticum (MG) oil-emulsion bacterin. Four weeks later, vaccinated and control chicks were placed in cold environmental cabinets, infected with infectious bronchitis virus intratracheally, and 2 days later challenged by aerosol exposure to live MG broth culture. All chicks were killed 21 days later and scored postmortem for the rate and severity of airsacculitis produced in each group. Broiler chicks vaccinated at 1 day of age had only slight protection against the development of airsacculitis. Results were variable when chicks were vaccinated at 7 days of age, with little evidence of resistance to airsacculitis. However, when broiler chicks were vaccinated with MG bacterins at 11 to 15 days of age, they acquired significant protection against airsacculitis compared with controls. Viable MG organisms were readily isolated from most of the sampled tracheas and air-sac lesions cultured 21 days post-challenge, indicating a lack of protection against infection of the respiratory tract. MG-vaccinated chicks generally produced antibodies readily detectable by the rapid serum-plate test, tube-agglutination, and hemagglutination-inhibition (HI) tests. Some of the vaccinated chicks, but none of the unvaccinated control chicks, developed positive reactions to agar-gel-precipitin tests following challenge. Low HI titers at challenge were not necessarily indicative of lack of protection against the development of airsacculitis, since good protection was often observed in chickens with low to moderate HI titers.

Aging↗