The gene encoding the fusogenic spike protein of the coronavirus causing feline infectious peritonitis was recombined into the genome of vaccinia virus. The recombinant induced spike-protein-specific, in vitro neutralizing antibodies in mice. When kittens were immunized with the recombinant, low titers of neutralizing antibodies were obtained. After challenge with feline infectious peritonitis virus, these animals succumbed earlier than did the control group immunized with wild-type vaccinia virus (early death syndrome).

Blood samples from 426 healthy and sick cats in the UK were tested in a PCR assay for 'Candidatus Mycoplasma haemominutum' and Mycoplasma haemofelis (basonym Haemobartonella felis). Seventy-two of the cats (16.9 per cent) were positive for 'Candidatus M. haemominutum' alone, six (1.4 per cent) were positive for M. haemofelis alone and one (0.2 per cent) was positive for both. Logistic regression analysis indicated that older male cats were significantly more likely to be infected with 'Candidatus M. haemominutum', but there was no significant association between it and any of the haematological variables measured. M. haemofelis infection was uncommon in the anaemic cats sampled, and there were too few positive cases for multivariable analysis to be performed for M. haemofelis-positive status.

A full history of the management practices and the prevalence of upper respiratory tract disease (URTD) at 218 rescue shelters, breeding establishments and private households with five or more cats was recorded. Oropharyngeal and conjunctival swabs and blood samples were taken from 1748 cats. The prevalences of feline herpesvirus (FHV), feline calicivirus (FCV), Chlamydophila felis and Bordetella bronchiseptica were determined by PCR on swab samples. An ELISA was applied to determine the prevalence of antibodies to B bronchiseptica. The rates of detection by PCR of each pathogen in the cats in catteries with and without ongoing URTD were, respectively, FHV 16 per cent and 8 per cent; FCV 47 per cent and 29 per cent; C felis 10 per cent and 3 per cent; and B bronchiseptica 5 per cent and 1·3 per cent; the seroprevalences of B bronchiseptica were 61 per cent and 41 per cent, respectively. There was evidence that FHV, FCV and B bronchiseptica played a role in URTD. The risk factors associated with the disease were less than excellent hygiene, contact with dogs with URTD, and larger numbers of cats in the cattery or household.

In 65 natural cases of feline infectious peritonitis (FIP) the common clinicopathological changes included lymphopenia (77 per cent), neutrophilia (45 per cent), anaemia (37 per cent), hyperproteinaemia (39 per cent) and hyperglobulinaemia (39 per cent). There was no difference in the frequency of these abnormalities between the 38 cases of effusive disease and the 27 cases of non-effusive disease. The most consistent changes shown by serum protein electrophoresis were increases in alpha 2- and gamma-globulins. The protein content of the effusions ranged from 39 to 98 g/litre with the globulins comprising 50 to 82 per cent. Coronavirus serology showed a wide variation in antibody titres (0 to 2560) with 320 the modal titre. The diagnostic value of this information was evaluated by comparing it with data from 65 cats in which FIP was considered as a differential diagnosis, but another disease was diagnosed. None of the laboratory tests, including coronavirus serology, had good sensitivity and specificity for the diagnosis of the disease. The presence of multiple abnormalities compatible with the disease increased the specificity but decreased the sensitivity of the diagnosis.

A reverse transcriptase-polymerase chain reaction (RT-PCR) assay for the detection of the feline coronavirus (FCoV) genome and a co-cultivation method for the isolation of field strains of FCoV are described. Using the RT-PCR assay to assess blood samples from cats with feline infectious peritonitis (FIP) (n = 47) and healthy cats from households with endemic FCoV (n = 69) it was shown that approximately 80% of the cats were viraemic, irrespective of their health status. It was also shown that, over a 12-month period, a similar percentage of healthy cats remained viraemic, and that the presence of viraemia did not appear to predispose the cats to the development of FIP. The co-cultivation system proved to be a suitable method for the culture of field strains of FCoV from blood samples, so long as the cultures were maintained for at least 4 weeks. Using this system, followed by the RT-PCR, viraemia was detected as frequently as by RT-PCR on RNA extracted directly from peripheral blood mononuclear cells.