Feline coronavirus serotypes 1 and 2: seroprevalence and association with disease in Switzerland

Abstract

To determine the prevalence of antibodies to feline coronavirus (FCoV) serotypes 1 and 2 in Switzerland and their association with different disease manifestations, a serological study based on immunofluorescence tests was conducted with Swiss field cats using transmissible gastroenteritis virus (TGEV), FCoV type 1 and FCoV type 2 as antigens. A total of 639 serum samples collected in the context of different studies from naturally infected cats were tested. The current study revealed that, with an apparent prevalence of 83%, FCoV serotype 1 is the most prevalent serotype in Switzerland. FCoV type 1 viruses induced higher antibody titers than FCoV type 2, and were more frequently associated with clinical signs and/or feline infectious peritonitis. The antibody development in seven cats experimentally infected with FCoV type 1 revealed that, with progressing duration of infection, antibodies to FCoV type 1 significantly increased over those to FCoV type 2. There was a significant relationship between antibody titers against TGEV, FCoV 1, and FCoV 2 and TGEV antigen detected the highest proportion of seropositive cats. We conclude that a vaccine against FCoV should be based on FCoV type 1-related antigens and that for serodiagnosis of FCoV infection TGEV should be used to attain the highest diagnostic efficiency. When serology is used in addition to clinical signs, hematology, and clinical chemistry results as an aid to diagnose clinical FIP, TGEV shows a diagnostic efficiency equal to that of a FCoV antigen.

FIG. 1.

Course of mean titers of antibodies to both FCoV 1 and 2 serotypes in cats experimentally infected with FCoV serotype 1. A statistically relevant specification of the immune system to the FCoV serotype of infection can be seen 40/42 weeks after infection (ANOVA with repeated measures, P = 0.038).

FIG. 2.

Prevalence of FCoV serotypes in different Swiss cat groups. Numbers on bars indicate the percentage of samples within the according group (A through D) referring to the four categories on the x axis. Categories are defined as follows: neg, antibody titers to both FCoV serotypes below detectable level; FCoV 1, antibody titers to FCoV 1 greater than antibody titers to FCoV 2; FCoV 2, antibody titers to FCoV 2 greater than antibody titers to FCoV 1; FCoV 1 = FCoV 2, antibody titers to FCoV equal to antibody titers to FCoV 2.

FIG. 3.

Box-plot distribution of titers to FCoV types 1 and 2. In cats with antibodies to FCoV type 1 (1 > 2), the titers were significantly higher than in cats with antibodies to FCoV type 2 (2 > 1) and equal titers (1 = 2; Kruskal-Wallis, P < 0.0001).

FIG. 4.

Box plot distribution of FCoV (serotype 1 and 2) and TGEV antibody titers of FIP (group C) and non-FIP cases (group D). FIP cases show significantly higher FCoV/TGEV antibody titers than non-FIP cases (Mann-Whitney U test, P < 0.0001 for both FCoV and TGEV). The ratio of median titers of FIP and non-FIP cases was identical for both FCoV and TGEV antigens.

FIG. 5.

Immunological relationship between FCoV types 1 and 2 and TGEV displayed as intersections. Of a total of 500 serum samples, 140 tested negative for coronavirus while the remaining 360 samples within the circles depicted with broken lines tested positive on at least one of the three types of immunofluorescence slides. A total of 210 samples tested positive on all three types of test slides, while 88 samples were detected positive on TGEV slides and 3 on FCoV 1 only.