Serological Survey of Feline Calicivirus and Felid Herpesvirus in Rio Grande do Sul, Brazil

Background: Feline calicivirus (FCV) and felid herpesvirus type 1 (FeHV-1) are widely distributed in the feline population. These viruses are the main cause of upper respiratory tract disease in this species, and FCV can also causes oral disease characterized by stomatitis and ulcers. Furthermore, FCV has been associated with a systemic hemorrhagic syndrome named FCV-associated virulent systemic disease (FCV-VSD), which has not yet been reported in Brazil. The aim of the present study was to investigate the presence of antibodies against FCV and FeHV-1 in the population of domestic felines from some counties of the Rio Grande do Sul State (RS), using a virus neutralizing (VN) assay. Materials, Methods & Results: A total of 630 feline serum samples collected between the years 2007 and 2011 were analyzed to detect antibodies against FCV and FeHV-1 by a VN assay. The serum samples came from cats admitted in veterinary clinics, household cats and cats examined in veterinary hospitals at three universities from Rio Grande do Sul State (RS) [UFRGS, UFSM and UPF]. The serum samples were classifi ed according to the origin, gender, age and vaccination status of the cat. All animal handling procedures were performed under veterinary supervision and following the recommendations of the Brazilian Committee on Animal Experimentation. The feline cell line CRFK (Crandell-Rees feline kidney) was used for viral amplifi cation and for the VN assay. The viruses used in the assay were the isolate SV65/90 of FCV, and the isolate SV534/00 of FeHV-1, from the Setor de Virologia/ UFSM; which were well characterized in a previous study by our group. The serum samples were tested against 100-200 TCID 50/mL (tissue cellular infection dose 50/mL) of both viruses in the VN assay, and a serial dilution of the serum was performed, starting at 1:5 up to > 1:1280 for FCV and at 1:2 to > 1:256 for FeHV-1 in 96 wells plates. Neutralization titers were calculated as the reciprocal of the highest serum dilution able to inhibit the cytopathic effect. Concerning to the results obtained, the groups with the highest number of collected samples were the group of the male cats (44%, 277/630), the group of the cats with ages among one to fi ve years old (36.3%, 229/630) and the group of non-vaccinated cats (94%, 592/630). Neutralizing antibodies against one or both viruses were detected in 53.6% (338/630) of the 630 cats sampled; 23% (145/630) of the cats were seropositive only to FCV, 14.4% (91/630) were seropositive only to FeHV-1 and 16.2% (102/630) were seropositive for both, FCV and FeHV1. Regarding the groups, a higher percentage of positive samples was found for the group of female cats (85.6%) and the group of cats over fi ve years old for both viruses (82.3%). Considering vaccination status, only 6% of the cats were vaccinated against FCV and/or FeHV-1, however not all vaccinated cats had neutralizing antibodies against the viruses, since only 50% of the vaccinated population were seropositive against FCV and 42.1% of them were seropositive for FeHV-1. Discussion: The data showed in the present study demonstrated that both viruses are circulating in the feline population sampled; and, it also revealed that FCV seems to be more prevalent among this population since the presence of antibodies against FCV were detected more frequently than antibodies against FeHV-1. The high number of non-reagent serum and non-vaccinated cats indicates that there is yet a large percentage of the cat population that is susceptible to infection. The application of vaccination programs according of the recommendations could help to prevent the infection and change the situation among the feline population sampled.