Typing of feline calicivirus isolates from different clinical groups by virus neutralisation tests

One hundred and thirteen isolates of feline calicivirus originating from seven different clinical groups were typed by virus neutralisation tests using eight different cat antisera. The clinical groups comprised 'healthy' cats, cases of acute oral/respiratory disease, chronic stomatitis, acute febrile lameness syndrome, vaccine reactions (clinical disease seen within 21 days of vaccination) and vaccine breakdowns (clinical disease seen more than 21 days after but within one year of vaccination). Isolates from the vaccine reaction cases were grouped into those associated with acute oral/respiratory disease alone and those associated with the lameness syndrome, and the latter group was further subdivided according to the vaccine used. Two groups appeared significantly different from others with some of the antisera. Thus the lameness vaccine reaction isolates associated with vaccine B were significantly different from the isolates from all the other clinical groups, including other lameness isolates, with a number of the antisera. In addition, the chronic stomatitis isolates were significantly different from those from the 'healthy' and the acute oral/respiratory disease groups with one or two of the antisera. Eighty-five to 88 per cent of the isolates were neutralised by antisera raised against F9 or F9-like vaccine strains at a dilution of 1 in 2. Twenty antibody units of such antisera neutralised 42 to 80 per cent of the isolates. A bivalent antiserum raised against a vaccine F9 strain and field strain LS015 neutralised 96 per cent of the isolates at a dilution of 1 in 2, and 20 antibody units neutralised 68 per cent of isolates. Antisera to field strain F65 neutralised all the remaining isolates at a dilution of 1 in 2 and 44 per cent of the remaining isolates at a dilution of 20 antibody units. Therefore, strains LS015 and F65 may be of use in the production of a polyvalent feline calicivirus vaccine, together with the widely used strain F9.