Genetic diversity and correlation with feline infectious peritonitis of feline coronavirus type I and II: a 5-year study in Taiwan

Abstract

The outcomes of feline coronavirus (FCoV) infection vary greatly from asymptomatic or mild enteric infection to fatal feline infectious peritonitis (FIP). On the basis of in vitro neutralization tests, FCoVs can be divided into two serotypes. To explore the correlation between different types of FCoV and FIP, clinical specimens collected from 363 naturally infected cats during 2003-2007 were analyzed. Amplification of a portion of the S gene from the FCoV was performed and a total of 222 cases were differentiated. Among them, 197 (88.7%) cats were type I-positive, 13 (5.9%) were type II-positive, and 12 (5.4%) were positive for both types. Irrespective of the predominance of type I FCoV infection in Taiwan, type II FCoV demonstrated a significantly higher correlation with FIP (p<0.01). Analysis of partial S gene sequences of the local type I and II FCoVs strains revealed that type I viruses were more genetically divergent (6.2-11.7%) than type II viruses (0.6-3.2%) within the 5-year study period. The higher genetic diversity of type I FCoVs might be due to the larger infected cat population and to the long period of viral persistence in asymptomatic cats in comparison to type II viruses.

Fig. 1

Multiple nucleotide sequence alignment of the 168 bp fragment of the S gene from 12 type I FCoVs and 3 type I CCoVs. Only those nucleotides differing from the overall majority sequence are shown. The Taiwanese FCoV and CCoV GenBank accession numbers are EU513381–EU513384 and EU513390–EU513391, respectively. The reference strains include FCoV F13-27 (EF408013), FCoV Ku-2 (D32400), FCoV 99LVIPortugal_05A (EU327752), FCoV Black (DQ122859), FCoV UCD1 (AB088222), FCoV J10_0998 (AY159748), FCoV C1Je (DQ848678), and CCoV C15-60 (EF407998).

Fig. 2

Multiple nucleotide sequence alignment of the 168 bp fragment of the S gene from 11 type II FCoVs, 2 type II CCoVs and 2 wild animal CoVs. The Taiwanese FCoV GenBank accession number is EU513385–EU513389. The reference strains include FCoV F21-1 (EF408020), FCoV F20-54-II (EF408022), FCoV HABER (DQ122859), FCoV DF-2 (DQ286389), FCoV 79-1146 (DQ010921), FCoV 79-1683 (X80799), CCoV C8-45 (EF408003), CCoV Chiba-40 (EF408004), RDCoV/GZ43/2003 (EF192155), and CFBCoV/DM95/2003 (EF192156).

Fig. 3

Phylogenetic relationships determined by the S gene sequences of the local FCoV and CCoV strains and reference FCoV, CCoV and wild animal CoVs strains. The phylogenetic trees were generated using the DNASTAR MegAlign program. The number of branches were calculated using bootstrapped values from 1000 replicates. The scale beneath the tree provides a key for the distance between sequences and the units at the bottom of the tree indicate the number of substitution events. Light grey underlay: local FCoV strains; dark grey underlay: local CCoV strains.