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. Sera from chickens infused with low doses (10(5) EID50) of the virus only showed marginal haemagglutination inhibiting activity. Trypsin levels as high as 0.35 mg ml-1 were detected from duodenal secretions and are assumed to be responsible in part for viral inactivation. Fasting (no food and water) the chickens beyond 12 h did not appear to increase antibody response to low titre virus.

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. Immunity was waning at 16 weeks after a single vaccination with CT strain.

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. This sudden late appearance of HI antibody, to titres higher than those observed with V4 chickens, was explained by V4 virus being introduced to the AVL NDV-1 group of chickens. When groups of these chickens were challenged with Roakin virus (mesogenic NDV) at 3 weeks and Fontana 1083 virus (viscerotropic velogenic NDV) and Texas GB virus (neutrotropic NDV) at 3, 5, 10 and 21 weeks only three chickens developed clinical illness one of which died. These chickens were one AVL NDV-1 chicken contact challenged with Fontana 1083 virus at 3 weeks, one V4 chicken oronasally challenged with Texas GB virus at 5 weeks and one V4 chicken challenged oronasally with Fontana 1083 virus at 10 weeks. Susceptible non-vaccinated chickens died soon after challenge. Challenge by oronasal infection with 10(7.0) ELD50 of virus or contact with susceptible infected chickens enabled virulent virus to be isolated from most chickens and was accompanied by a large anamnestic increase in serum HI antibody.

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 heterogeneity characteristic of the Aust-V4 strain and NI-Ulster strain could not be demonstrated in B1, NJ-LaSota, and ENG-F, lentogenic strains commonly used in vaccines. The question is discussed of whether standard vaccine strains are also hetrogeneous if a technique for separating stock populations is found, and the significance of possible heterogeneity to the effectivenss of the vaccines.

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. Virulence appeared to be very host specific in that only strain M56 among the six chlamydiae tested was highly lethal for the snowshoe hare.

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 64.8%. Virus was demonstrated most readily in chickens challenged when antibody was decreasing, about 9 weeks after vaccination. The observation that virus in blood may be contained within a cellular component and be readily demonstrable only if the cells are separated and washed is significant both to an understanding of the immunological responsiveness of vaccinated chickens exposed to field challenge and to an understanding of epizootiological events.

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. The transmissibility of B1 and V4 strains for chickens 1, 4, 8, and 16 weeks old was assessed by within-cage contact infection, exposure to contaminated food and water containers, and exposure to air from infected chickens. Serology and immunity to challenge with virulent virus were used as criteria. Differences in transmissibility were observed for the strain of virus used, route of exposure, and age of chickens. Care must be used in interpreting the significance of strain differences until the effect of variables can be minimized by further improvements in design of the test procedure.

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. Inapparent disease usually resulted, and only 1/13 cases were fatal. Goose embryos responded differently to inoculation with selected NDV strains than did chicken embryos of comparative developmental stages. Some goslings that hatched from inoculated embryos died and were found to have virus, whereas others survived and developed active antibodies. Four strains of virus isolated from migratory ducks of the Pacific flyway were characterized. All 4 strains were lentogenic but differed from lentogenic strains prevalent in chickens by being thermostable. It is proposed that wild waterfowl neither receive their ND infection from domestic poultry nor pass their disease to poultry. The virus reservoir probably exists in nature.

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. Antigenic differences among these viruses distinguished them from older, well characterized Newcastle disease viruses.

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. Ocular lesions accompanied the chlamydial infection in the rabbits. Bilateral anterior uveitis, a common occurrence, began on the second or third day and subsided by the tenth day whereas keratoconjunctivitis was observed infrequently. After 15 days the most prominent microscopic lesion was iritis. Accumulations of inflammatory cells, mainly plasma cells, were observed in the iris and ciliary body and elementary bodies were found infrequently in macrophages. Chlamydiae were recovered consistently by conjunctival swabbing from the fifth to the twenty-fourth day. The agent was present within the eye (viz. iris-ciliary body) in three of four rabbits killed at 15 days and in five of ten rabbits killed 60 days after inoculation. Chlamydiae had persisted in the cerebrum and joints as well. Although neutralizing antibody was consistently present in sera at 60 days none of the samples of aqueous humor were capable of neutralizing the agent. It is suggested that systemic chlamydial infections in the rabbit provide a model for the study of endogenous uveitis, a common ophthalmological problem.