The maintenance of challenge strains used in the potency test for canine leptospira vaccines.

The challenge test for leptospira vaccines required by most licensing authorities is difficult to standardise and unreliable. One of the main contributory factors to this, is the difficulty in maintaining the virulence of the challenge strain. This paper describes work carried out to assess the practicality of storing challenge strains of Leptospira canicola and Leptospira icterohaemorrhagiae in liquid nitrogen. The effects of different concentrations of glycerol and dimethyl sulphoxide on the recovery of virulent and avirulent strains of Leptospira canicola and Leptospira icterohaemorrhagiae were investigated. Concentrations of cryopreservant above 5% increased the time taken for the leptospires to grow after recovery from vials stored in liquid nitrogen. In addition, the virulence of five challenge strains were shown to be little affected after 18 passages in vitro.

Vaccination of commercial layer chicks against infectious bursal disease with maternally derived antibodies.

Day-old commercial layer chicks with maternally derived antibody to infectious bursal disease (IBD) were reared in four pens on a commercial farm, and chicks from the same flock were reared at the laboratory and examined for the decay of the maternal antibody and the development of susceptibility to IBD. The chicks in the pens on the farm were vaccinated with different combinations of commercial inactivated and live vaccines against IBD, transferred to the laboratory, and challenged with virulent IBD virus to assess the efficacy of the vaccination programmes. The chicks from one pen, given a live IBD vaccine only, did not develop antibodies and were fully susceptible to challenge by seven weeks old; only one to two weeks later than the unvaccinated control chicks reared at the laboratory. The chicks in the other three pens were inoculated with an inactivated vaccine, and the chicks in two of these pens were inoculated later with a live vaccine. All these chicks developed IBD antibodies and were protected by between 91 and 100 per cent against challenge. There was no demonstrable benefit in administering a live vaccine either alone or in addition to an inactivated oil emulsion vaccine.

Use of an inactivated infectious bursal disease oil emulsion vaccine in commercial layer chicks.

Commercial layer chicks of different ages were inoculated with either one-fifth, two-fifths or a full dose of an inactivated infectious bursal disease oil emulsion vaccine and then challenged with virulent virus. The partial doses given at seven or 10 days old gave only partial protection. A full dose given at 10, 14 or 28 days old failed to give full protection but a full dose administered at seven days old protected all the chicks after each challenge.

A comparison of serum neutralisation, immunofluorescence and immunoperoxidase tests for the detection of antibodies to chicken anaemia agent.

A comparison was made of the serum neutralisation, immunofluorescent antibody and immunoperoxidase tests for the detection of antibodies to chicken anaemia agent. Serum samples from groups of chicks with and without maternally derived antibody to the agent were tested and the response of chicks after inoculation with the agent was also measured. The serum neutralisation test was reliable and sensitive, but expensive and could take up to three weeks to obtain a result. The immunofluorescent antibody test was cheaper and required only one day to obtain a result, but it was not as sensitive in detecting low levels of antibody to the chicken anaemia agent. The immunoperoxidase test was also cheaper but took two days to obtain a result and required one more manipulation than the immunofluorescence test. It was comparable to the serum neutralisation test in its ability to detect low levels of antibody.

Use of infectious bursal disease vaccines in chicks with maternally derived antibodies.

Day-old chicks with maternally derived infectious bursal disease (IBD) antibodies were inoculated with IBD oil emulsion vaccine. The vaccine protected at least 85 per cent of the chicks when they were challenged at four weeks old with virulent IBD virus and at least 90 per cent of those challenged at seven weeks of age. There was no benefit in using a combination of the oil emulsion vaccine and a live IBD vaccine.

Observations on swollen head syndrome in broiler and broiler breeder chickens.

Chickens on 14 broiler breeder farms were examined at various times throughout their laying cycle. Antibodies to the turkey rhinotracheitis virus were common although they were not always accompanied by clinical signs of the swollen head syndrome. Ninety-nine broiler flocks were tested of which only 20 were serologically positive to the virus. Some of these infections were subclinical. On nine farms where swollen head syndrome occurred several successive flocks were sampled; the syndrome occurred intermittently.

An outbreak of disease due to chicken anaemia agent in broiler chickens in England.

Outbreaks of clinical chicken anaemia in four broiler chicken flocks affected chicks which were all the progeny of the same parent flock. Three of the flocks were reared on farms in the south-east of England and in these flocks clinical disease did not occur in other chicks of the same age. The fourth flock was reared in a positive-pressure isolator and clinical disease appeared at 10 days of age. Chicken anaemia agent was isolated from three of the flocks. The clinical signs, post mortem lesions and histopathological changes were similar to those reported in outbreaks of the disease in other countries. The parent flock seroconverted to chicken anaemia agent, as determined by fluorescent antibody tests, during the course of the outbreaks.

Failure of maternally derived infectious bursal disease antibodies to serotypes 1 and 2 to protect against heterologous virus.

Chicks with maternally derived infectious bursal disease antibodies to either serotype 1 or 2 were challenged at intervals between day-old and 7 weeks of age using the homologous and the heterologous viruses. With both serotypes good protection was demonstrated against the homologous challenge, but not against the heterologous virus.

Infectious stunting syndrome: evidence of vertical transmission.

Day-old broiler chicks were collected while in transit from a hatchery to a farm and reared in isolation. These chicks did not develop clinical signs of infectious stunting syndrome. When they were 14 days old, susceptible day-old chicks were placed in contact with them and these subsequently developed typical signs and lesions of the disease.

Antibody responses and virus reisolation in turkeys experimentally infected with an infectious bursal disease isolate.

Following the infection of turkey poults with a field isolate of infectious bursal disease virus, antibody levels were examined and reisolation of the virus was attempted. After inoculation at 36 days of age, peak titres in both the inoculated and a contact-exposed group were obtained after 13 days. The titres fell slightly during the next week and then remained level until the experiment was terminated at 91 days of age. Virus was reisolated from faeces from day 3 until day 8 after inoculation in the inoculated group and from day 4 until day 9 in the contact-exposed group. In the inoculated group, virus was recovered from the bursae, spleens and intestines on both days 4 and 6 after inoculation, but the thymuses on day 6 only. No clinical signs were observed.