Studies on the development of pelleted Newcastle disease virus (NDV) vaccine.

White leghorn chickens (7-10 weeks old) were orally infused with varied doses of lentogenic and mesogenic strains of Newcastle disease virus. The antibody response of the chickens was monitored by haemagglutination inhibition tests weekly for 4 weeks postinfusion. A high dose of virus (10(9) EID50) was necessary to induce a serological response typical of chickens that resist challenge.

Thermostability of the hemagglutinin of Newcastle disease virus as a strain marker in epizootiologic studies.

The recent isolation of viscerotropic velogenic strains of Newcastle disease virus having a thermosensitive hemagglutinin and of a lentogenic strain with an unusually thermostable hemagglutinin confirmed that virulence for chickens was not related to the thermostability and could be used as a marker for strains in epizootiologic investigations.

Immunogenicity of Australian lentogenic strains of Newcastle disease virus.

Seven-week-old chickens vaccinated oronasally with V4 and CT strains of Australian lentogenic strains of NDV were immune to intramuscular challenge with Herts 33 and Texas GB strains of virulent NDV. Vaccination of 1- and 3-week-old chickens with V4 strain by oronasal, conjunctival and drinking water routes using various doses of virus demonstrated that chickens were immune to oronasal challenge with Fontana 1083 strain of virulent NDV except where low doses of vaccine virus were administered. One 6- and 36-week-old chickens vaccinated oronasally with CT strain of virus remained immune to oronasal challenge with Fontana 1083 strain for 9 weeks after vaccination.

Simulated natural infection of chickens with Australian lentogenic newcastle disease virus and subsequent challenge with virulent virus.

A total of 291 eight-week-old chickens were exposed to chickens infected with either of two Australian lentogenic strains (V4 and AVL NDV-1) of Newcastle disease virus (NDV). At 3 weeks after exposure, all chickens exposed to V4 infected chickens had developed haemagglutination-inhibition (HI) antibody. All chickens exposed to AVL NDV-1 virus infected chickens had developed HI antibody 5 weeks later.

Evidence of genetic heterogeneity of some lentogenic Newcastle disease virus strains.

Two distinguishable subpopulations were recovered from chickens infected with lentogenic strains of Newcastle disease virus originally ioslated from chickens in Australia and Ireland. In both instances, a subpopulation that rapidly eluted from chicken erythrocytes was recovered predominantly from tracheal swabs, and a slow-eluting subpopulation from cloacal swabs. The two subpopulations differed in thermostability of the hemagglutinatin and mean survival time of infected chicken embryos, as well as in elution pattern.

The occurrence of virus in leukocytes of vaccinated chickens following challenge with virulent Newcastle disease virus.

Chickens that had been vaccinated with a lentogenic strain 2 to 9 weeks before challenge with a virulent virus remained clinically normal following challenge and circulated virus within leukocytes for as long as ten days. The virulent virus was detected by inoculating embryonating eggs with leukocytes separated from blood shortly after drawing. Freezing the leukocytes before inoculating the eggs reduced isolation 64.

Observations on the transmissibility of lentogenic strains of Newcastle disease virus: significance of variables.

Virus strain and age of chicken influenced the transmissibility of lentogenic strains of Newcastle disease virus (NDV). The ability of LaSota, B1, V4, CT, F, and Ulster strains to spread from cages of oronasally inoculated chickens to adjacent cages of susceptible chickens was assessed by virus isolation, serology, and immunity to challenge with virulent NDV. Although all inoculated chickens were immune to challenge, the immunity of contact chickens ranged from 100% for LaSota and CT strains to 0% for Ulster strain.

Experimental chlamydiosis in wild and domestic lagomorphs.

Chlamydia psittaci (strain M56, the agent of epizootic chlamydiosis of muskrats and hares) was highly lethal for the snowshoe hare (Lepus americans) following intravenous inoculation, whereas the agent was much less virulent for cottontail (Sylvilagus floridanus) and albino domestic rabbits (Oryctolagus cuniculus). Tissue titres of strain M56 were generally higher after 96 hr in the snowshoe hare than in tissues of the other lagomorphs. Spleen, liver and bone marrow were apparently the chief sites of primary multiplication of strain M56 in the hare.

Epizootiology of Newcastle disease in waterfowl.

Antibodies to Newcastle disease virus (NDV) as measured by hemagglutination-inhibition and virus-neutralization tests were detected in 40/236 Canada geese captured while in their southward migration or in their wintering grounds. Antibodies were also found in 37/267 wild ducks and in 20/31 domestic geese. Adult geese were readily infected by several routes.

Newcastle disease virus antigens and strain variations.

Study of antigenic differences among strains of Newcastle disease virus is complicated by the presence in most field isolates and strains of several genetically distinct plaque populations, and by differences in avidity (reactions to antibody) among Newcastle disease viruses. Kinetic neutralization tests were used to demonstrate antigenic differences among 3 plaque clones of velogenic viscerotropic Newcastle disease viruses recently isolated from 3 avian species. The 3 viruses could be distinguished on the basis of plaque structure and hemagglutinin and neuraminidase activity.

Ocular involvement with Chlamydia psittaci (strain M56) in rabbits inoculated intravenously.

Fourteen albino rabbits were inoculated intravenously with 10(3.5)-10(4.0) mouse ICLD(50) of Chlamydia psittaci (strain M56) of mammalian origin.

Isolation of a bunyamwera group arbovirus from a naturally infected caribou.

A Bunyamwera group arbovirus was isolated from the blood and from the brain of a female caribou parasitized with meningeal worms. The virus passed through a 0.45 micron filter; was ether sensitive; possessed no hemagglutination properties; could be propagated in suckling mice, 6-day old chick embryos, and BHK-21 tissue culture; and produced plaques in chick embryo fibroblast tissue culture.

The susceptibility of muskrats and snowshoe hares to experimental infection with a chlamydial agent.

Muskrats (Ondatra zibethicus) and snowshoe hares (Lepus americanus) were exposed experimentally by various routes to a chlamydial agent (designated strain M56) originally isolated during a die-off of muskrats and snowshoe hares which occurred in Saskatchewan during 1961. Both species were susceptible to experimental infection. Whereas M56 was highly lethal for snowshoe hares (18 deaths/19 exposed), it was less virulent for muskrats (6 deaths/20 exposed).