Duck virus hepatitis: the effect of attenuation on virus stability in ducklings.

The effect of further attenuation by serial passage in specific pathogen free embryonated hens' eggs, on the stability of the H strain of duck hepatitis virus (DHV) when serially passaged in ducklings was investigated. The 65th, 75th, 86th and 94th passage viruses (H65, H75, H86 and H94) which were considered to be potential vaccines all reverted to virulence on serial passage in ducklings. The virulent Q strain of DHV was similarly attenuated and tested for vaccine potential and stability. Virus passaged serially 10 times was still pathogenic. The 20th and 30th passage virus was apathogenic but did not protect as well as the 40th, 50th, 60th, 70th and 80th passage virus. The 90th passage virus was less protective. All these potential vaccines reverted to virulence on serial passage in ducklings.

Duck virus hepatitis: serial passage of attenuated virus in ducklings.

The safety of three attenuated virus vaccines of proven efficacy against duck virus hepatitis was assessed by controlled laboratory studies which involved the serial transmission of the virus through groups of two-day-old ducklings known to be susceptible to the disease. Each vaccine was initially derived from a different source. Enhancement of virulence which resulted in deaths from the disease in test groups of ducklings occurred in each instance.

Antigens associated with canine spontaneous mammary carcinoma.

Soluble proteins were prepared from canine spontaneous mammary carcinoma (CSMC) cells by extraction with 3M KCl or limited hydrolysis of isolated cell membranes with papain. These preparations were assayed for tumour-associated antigens by inhibition of fully absorbed rabbit antisera. Organ-specific reactivity was demonstrated and antigenic specificity indicated the possible involvement of fetal components. Exclusion chromatography showed that antigenic activity was associated with macromolecules of different sizes in each of the protein preparations which allowed partial purification of tumour-associated antigens. Antigens were also prepared from circulating immune complexes in the serum of tumour-bearing animals. These studies provide a basis for the development of serological markers of malignancy in CSMC.

Active immunisation of ducklings against duck virus hepatitis.

Egg-attenuated duck hepatitis type (Rispens H55) was exhaustively tested as a potential vaccine under controlled conditions in ducklings fully susceptible to the disease at day 2 after hatching. Data are presented which indicate that this vaccine fulfils essential criteria of efficacy in terms of (a) the optimal age at which successful vaccination is practicable (day 2 or earlier), (b) the rapidity of onset of immunity (in 48 to 72 hours), (c) the high level of immunity induced (88.0 to 94.0 per cent), (d) the persistence of this degree of immunity in the individual bird throughout the period when it would otherwise be at risk (until the end of the fourth week of life) and (e) the consistency of the effects of the vaccine in successive groups of ducklings hatched over a four year period. Employed as a vaccine. H55 was completely innocuous to the vaccinated ducklings under laboratory conditions.