Isolation And Identification Of Feline Calicivirus And Establishment Of Infection Model

Feline calicivirus(FCV),belonging to the genus Vesivirus of the family Caliciviridae,is one of the main pathogenic pathogens causing upper respiratory tract diseases in cats.FCV cause great harm to pet cats and serious threat to the free-ranging wild felid populations around the world.FCV has only one serotype.FCV can mutation quickly under immune pressure,and lead to diversity of strains in different areas of the cat population,because the low fidelity and the High error rate of RNA polymerase lead to a higher mutation rate during replication of FCV.Cats infected with different strains of FCV were observed different clinical signs.The typical clinical signs including upper respiratory symptoms such as oral ulcers and sneezing.And the symptoms of lower respiratory tract(severe pneumonia),lameness,or systemic disease can also be observed with the mutates of different strains.The immunologic escape caused by genetic mutation of FCV is the main factor for immunity failure of vaccine.In recent years,the pet industry has been booming in China,and the number of cats is increasing by 10?15%every year.In 2020,the number of pet cats in cities and towns is 48.62 million in China[1].With the increase of pets population,the cases of upper respiratory disease of cats is increasing.Prevention of feline viral diseases entirely relies on the imported cat triplet inactivated vaccine,which was studied in last century.There are many reports that vaccinated cats infected with feline calicivirus[2-4].At present,there are few epidemiological studies,and lack of large-scale and systematic epidemiological data on FCV in China.Thus,1739 samples were collected from 61 pet hospital cooperation of 20 cities to study the epidemic of FCV.And 11 strains of FCV was isolated and identified form FCV positive samples.The FCV infection model was established by the strain F2019TJ3,which is of great importance for the development of products for prevention,diagnosis and treatment of FCV,and for the prevention and control of the spread of FCV.I Epidemic Survey on Feline Calicivirus of Some Areas in ChinaIn this study,1739 samples of cats from 61 pet hospitals in 20 cities including Tianjin,Beijing,Luoyang,Haikou and Shenyang from 2019 to 2020 were identified by RT-PCR.The results showed that the positive rate of FCV was 13.00%(226/1739).The positive rate of FCV infection in different cities ranged from 2.63%to 28.21%.FCV infection has a certain seasonality,and the prevalence of FCV was high(15.49%-17.18%)in winter and spring.Some cats vaccinated with imported cat triple vaccine showed FCV positive,while kittens unvaccinated with imported cat triple vaccine were more susceptible to FCV.The gene VP1 of 20 strains of FCV form different cities was sequenced.The 20 strains shared 73.3%?96.6%nucleotide identity and 82.4%?98.4%amino acids identity,and showed 73.2%?86.1%nucleotide identity and 82.2%?93.6%amino acids identity with domestic endemic strains and vaccine strains.These results indicated that the gene of FCV was diversity and similarity was low,and it makes the prevention and control of FCV more difficult.? Isolation And Identification of Feline CalicivirusEye and nose swab from 15 FCV infected cat were collected and cultured in F81 cells line.Cytopathic effect(CPE)including cell crumpled,rounded,clustered into grape-like cell lesions were observed in 11 samples infected F81.The cell culture were identified as FCV by electron microscopy,VP1 gene sequence analysis and indirect immunofluorescence.The strain F2019TJ3,isolated from deae cat with higer titer and purity,was kept for investigation for pathogenicity in cats.The infected cats displayed clinical signs,such as fever,coughs,rales,eye and nasal discharge,loss of appetite and depression.The mortality rate was 25%and the infected cats shed virus on 4 to 10 days after infection,which indicated that F2019TJ3 has high pathogencity.? Establishment of Feline Calicivirus Infection ModelThe kittens were infected with strain F2019TJ3 with does of 107.00 TCID50/mL,106.00 TCID50/mL and 105.00 TCID50/mL through nasal transmission.All the groups with different doses of infection was observed typical clinical symptoms of FCV,and the incidence rates were 100%,100%,and 25%,respectively.The cats infected with does of 106 00 TCID50/mL was observed loss of appetite,depression,oral and nasal discharge and oral ulcers.The infected cats shed virus on 6 to 8 days after infection.The histopathological results showed that local alveolar septum widening and lymphocyte infiltration.These results showed that the cats was infected strain F2019TJ3 with does of 106.00 TCID50/mL through nasal transmission was observed typical clinical signs of FCV.