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Genetics and pathogenesis of feline infectious peritonitis virus.

Brown MA, Troyer JL, Pecon-Slattery J, Roelke ME, O'Brien SJ - Emerging Infect. Dis. (2009)

Bottom Line: Uncertainty remains regarding whether genetically distinctive avirulent and virulent forms coexist or whether an avirulent form mutates in vivo, causing FIP.These data demonstrate distinctive circulating virulent and avirulent strains in natural populations.These findings may have potential as diagnostic markers for virulent FIP-associated FCoV.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Genomic Diversity, National Cancer Institute, Frederick, Maryland 21702, USA. brownmer@gmail.com

ABSTRACT
Feline coronavirus (FCoV) is endemic in feral cat populations and cat colonies, frequently preceding outbreaks of fatal feline infectious peritonitis (FIP). FCoV exhibits 2 biotypes: the pathogenic disease and a benign infection with feline enteric coronavirus (FECV). Uncertainty remains regarding whether genetically distinctive avirulent and virulent forms coexist or whether an avirulent form mutates in vivo, causing FIP. To resolve these alternative hypotheses, we isolated viral sequences from FCoV-infected clinically healthy and sick cats (8 FIP cases and 48 FECV-asymptomatic animals); 735 sequences from 4 gene segments were generated and subjected to phylogenetic analyses. Viral sequences from healthy cats were distinct from sick cats on the basis of genetic distances observed in the membrane and nonstructural protein 7b genes. These data demonstrate distinctive circulating virulent and avirulent strains in natural populations. In addition, 5 membrane protein amino acid residues with functional potential differentiated healthy cats from cats with FIP. These findings may have potential as diagnostic markers for virulent FIP-associated FCoV.

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Related in: MedlinePlus

Maximum-likelihood (ML) phylogenetic tree of unique sequences from 3 feline coronavirus (FCoV) genes membrane, nonstructural protein 7b (NSP 7b), and spike-NPS3 (see Figure 3) gene sequences showing monophyly correlating to disease status. Cloned sequences from feline infectious peritonitis (FIP) cases are shown in red; feline enteric coronavirus (FECV) asymptomatic cats are shown in blue, and FCoV virulent strain from Aju-92 (cheetah) is in green. Number of cats and number of clones assessed are listed in Figure 3, panel B. A) membrane 575-bp sequences (ML –ln L = 3086.20787 best tree found by maximum parsimony [MP]: length = 493, confidence interval [CI] = 0.551724, retention index [RI] = 0.0926505); B) NSP 7b 736-bp sequences (ML –ln L = 4556.60497 best tree found by MP: length = 452, CI = 0.608, RI = 0.942; C) spike-NSP3 1017-bp sequences (ML –ln L = 2804.53198 best tree found by MP: length = 280, CI = 0.800, RI = 0.954). The number of FIP cases and FECV asymptomatic cats and number of cloned sequences is indicated in parenthesis in the key. Each sequence is labeled as follows: first letter indicates source farm (W, Weller Farm; F, Frederick Animal Shelter; S, Seymour Farm; M, Mount Airy Shelter; A, Ambrose Farm), 4-digit cat identification number, tissue source (fe, feces; af, ascites fluid; co, colon; li, liver; sp, spleen; in, intestine; je, jejunum; ln, lymph node), 2-digit year (e.g., 04 = 2004), and the number of clones for each sequence. Bootstrap values are shown (maximum parsimony/minimum evolution/maximum likelihood) above branches. Where maximum likelihood tree was congruent with maximum parsimony tree, branch lengths are indicated below branches; the number of homoplasies is in parenthesis after the branch length. Virus sequence obtained from cat no. 4590 in May 2004 and at the time of death due to FIP in December 2004 is indicated by box. Scale bars indicate substitutions/site.
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Figure 4: Maximum-likelihood (ML) phylogenetic tree of unique sequences from 3 feline coronavirus (FCoV) genes membrane, nonstructural protein 7b (NSP 7b), and spike-NPS3 (see Figure 3) gene sequences showing monophyly correlating to disease status. Cloned sequences from feline infectious peritonitis (FIP) cases are shown in red; feline enteric coronavirus (FECV) asymptomatic cats are shown in blue, and FCoV virulent strain from Aju-92 (cheetah) is in green. Number of cats and number of clones assessed are listed in Figure 3, panel B. A) membrane 575-bp sequences (ML –ln L = 3086.20787 best tree found by maximum parsimony [MP]: length = 493, confidence interval [CI] = 0.551724, retention index [RI] = 0.0926505); B) NSP 7b 736-bp sequences (ML –ln L = 4556.60497 best tree found by MP: length = 452, CI = 0.608, RI = 0.942; C) spike-NSP3 1017-bp sequences (ML –ln L = 2804.53198 best tree found by MP: length = 280, CI = 0.800, RI = 0.954). The number of FIP cases and FECV asymptomatic cats and number of cloned sequences is indicated in parenthesis in the key. Each sequence is labeled as follows: first letter indicates source farm (W, Weller Farm; F, Frederick Animal Shelter; S, Seymour Farm; M, Mount Airy Shelter; A, Ambrose Farm), 4-digit cat identification number, tissue source (fe, feces; af, ascites fluid; co, colon; li, liver; sp, spleen; in, intestine; je, jejunum; ln, lymph node), 2-digit year (e.g., 04 = 2004), and the number of clones for each sequence. Bootstrap values are shown (maximum parsimony/minimum evolution/maximum likelihood) above branches. Where maximum likelihood tree was congruent with maximum parsimony tree, branch lengths are indicated below branches; the number of homoplasies is in parenthesis after the branch length. Virus sequence obtained from cat no. 4590 in May 2004 and at the time of death due to FIP in December 2004 is indicated by box. Scale bars indicate substitutions/site.

Mentions: Phylogenetic analysis of the cloned virus sequences from 3 Maryland locales sampled during 2004–2006 showed specific patterns of viral dynamics. First, gene sequences from healthy cats infected with FECV displayed a monophyletic cluster pattern that was generally distinctive from cats diagnosed with FIP in the membrane, NSP 7b, and spike-NSP3 gene segments (Figure 4). For example, every FCoV gene sequence for the membrane gene from FIP cases fell within a major cluster consisting of 3 principal clades (Figure 4). By contrast, 127/154 (82%) virus gene sequences from FECV-asymptomatic cats sorted in 2 separate clades that were distinct (100 bootstrap statistical support) from the viral gene sequences of FIP cases (Figure 4). Similar reciprocal monophyly of 140 NSP7b sequences was obtained for FIP cases versus FECV-asymptomatic cats (Figure 4). A consistent disease driven phylogeographic sorting was also observed for the 1,017-bp sequence spanning the spike-NSP3 genes, albeit with less statistical resolution, likely because of evolutionary constraints on gene divergence in this region (Figure 4). Together the remarkable reciprocal monophyly in these 3 genes supports the predictions of the circulating virulent-avirulent strain hypothesis illustrated in Figure 1.


Genetics and pathogenesis of feline infectious peritonitis virus.

Brown MA, Troyer JL, Pecon-Slattery J, Roelke ME, O'Brien SJ - Emerging Infect. Dis. (2009)

Maximum-likelihood (ML) phylogenetic tree of unique sequences from 3 feline coronavirus (FCoV) genes membrane, nonstructural protein 7b (NSP 7b), and spike-NPS3 (see Figure 3) gene sequences showing monophyly correlating to disease status. Cloned sequences from feline infectious peritonitis (FIP) cases are shown in red; feline enteric coronavirus (FECV) asymptomatic cats are shown in blue, and FCoV virulent strain from Aju-92 (cheetah) is in green. Number of cats and number of clones assessed are listed in Figure 3, panel B. A) membrane 575-bp sequences (ML –ln L = 3086.20787 best tree found by maximum parsimony [MP]: length = 493, confidence interval [CI] = 0.551724, retention index [RI] = 0.0926505); B) NSP 7b 736-bp sequences (ML –ln L = 4556.60497 best tree found by MP: length = 452, CI = 0.608, RI = 0.942; C) spike-NSP3 1017-bp sequences (ML –ln L = 2804.53198 best tree found by MP: length = 280, CI = 0.800, RI = 0.954). The number of FIP cases and FECV asymptomatic cats and number of cloned sequences is indicated in parenthesis in the key. Each sequence is labeled as follows: first letter indicates source farm (W, Weller Farm; F, Frederick Animal Shelter; S, Seymour Farm; M, Mount Airy Shelter; A, Ambrose Farm), 4-digit cat identification number, tissue source (fe, feces; af, ascites fluid; co, colon; li, liver; sp, spleen; in, intestine; je, jejunum; ln, lymph node), 2-digit year (e.g., 04 = 2004), and the number of clones for each sequence. Bootstrap values are shown (maximum parsimony/minimum evolution/maximum likelihood) above branches. Where maximum likelihood tree was congruent with maximum parsimony tree, branch lengths are indicated below branches; the number of homoplasies is in parenthesis after the branch length. Virus sequence obtained from cat no. 4590 in May 2004 and at the time of death due to FIP in December 2004 is indicated by box. Scale bars indicate substitutions/site.
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Related In: Results  -  Collection

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Figure 4: Maximum-likelihood (ML) phylogenetic tree of unique sequences from 3 feline coronavirus (FCoV) genes membrane, nonstructural protein 7b (NSP 7b), and spike-NPS3 (see Figure 3) gene sequences showing monophyly correlating to disease status. Cloned sequences from feline infectious peritonitis (FIP) cases are shown in red; feline enteric coronavirus (FECV) asymptomatic cats are shown in blue, and FCoV virulent strain from Aju-92 (cheetah) is in green. Number of cats and number of clones assessed are listed in Figure 3, panel B. A) membrane 575-bp sequences (ML –ln L = 3086.20787 best tree found by maximum parsimony [MP]: length = 493, confidence interval [CI] = 0.551724, retention index [RI] = 0.0926505); B) NSP 7b 736-bp sequences (ML –ln L = 4556.60497 best tree found by MP: length = 452, CI = 0.608, RI = 0.942; C) spike-NSP3 1017-bp sequences (ML –ln L = 2804.53198 best tree found by MP: length = 280, CI = 0.800, RI = 0.954). The number of FIP cases and FECV asymptomatic cats and number of cloned sequences is indicated in parenthesis in the key. Each sequence is labeled as follows: first letter indicates source farm (W, Weller Farm; F, Frederick Animal Shelter; S, Seymour Farm; M, Mount Airy Shelter; A, Ambrose Farm), 4-digit cat identification number, tissue source (fe, feces; af, ascites fluid; co, colon; li, liver; sp, spleen; in, intestine; je, jejunum; ln, lymph node), 2-digit year (e.g., 04 = 2004), and the number of clones for each sequence. Bootstrap values are shown (maximum parsimony/minimum evolution/maximum likelihood) above branches. Where maximum likelihood tree was congruent with maximum parsimony tree, branch lengths are indicated below branches; the number of homoplasies is in parenthesis after the branch length. Virus sequence obtained from cat no. 4590 in May 2004 and at the time of death due to FIP in December 2004 is indicated by box. Scale bars indicate substitutions/site.
Mentions: Phylogenetic analysis of the cloned virus sequences from 3 Maryland locales sampled during 2004–2006 showed specific patterns of viral dynamics. First, gene sequences from healthy cats infected with FECV displayed a monophyletic cluster pattern that was generally distinctive from cats diagnosed with FIP in the membrane, NSP 7b, and spike-NSP3 gene segments (Figure 4). For example, every FCoV gene sequence for the membrane gene from FIP cases fell within a major cluster consisting of 3 principal clades (Figure 4). By contrast, 127/154 (82%) virus gene sequences from FECV-asymptomatic cats sorted in 2 separate clades that were distinct (100 bootstrap statistical support) from the viral gene sequences of FIP cases (Figure 4). Similar reciprocal monophyly of 140 NSP7b sequences was obtained for FIP cases versus FECV-asymptomatic cats (Figure 4). A consistent disease driven phylogeographic sorting was also observed for the 1,017-bp sequence spanning the spike-NSP3 genes, albeit with less statistical resolution, likely because of evolutionary constraints on gene divergence in this region (Figure 4). Together the remarkable reciprocal monophyly in these 3 genes supports the predictions of the circulating virulent-avirulent strain hypothesis illustrated in Figure 1.

Bottom Line: Uncertainty remains regarding whether genetically distinctive avirulent and virulent forms coexist or whether an avirulent form mutates in vivo, causing FIP.These data demonstrate distinctive circulating virulent and avirulent strains in natural populations.These findings may have potential as diagnostic markers for virulent FIP-associated FCoV.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Genomic Diversity, National Cancer Institute, Frederick, Maryland 21702, USA. brownmer@gmail.com

ABSTRACT
Feline coronavirus (FCoV) is endemic in feral cat populations and cat colonies, frequently preceding outbreaks of fatal feline infectious peritonitis (FIP). FCoV exhibits 2 biotypes: the pathogenic disease and a benign infection with feline enteric coronavirus (FECV). Uncertainty remains regarding whether genetically distinctive avirulent and virulent forms coexist or whether an avirulent form mutates in vivo, causing FIP. To resolve these alternative hypotheses, we isolated viral sequences from FCoV-infected clinically healthy and sick cats (8 FIP cases and 48 FECV-asymptomatic animals); 735 sequences from 4 gene segments were generated and subjected to phylogenetic analyses. Viral sequences from healthy cats were distinct from sick cats on the basis of genetic distances observed in the membrane and nonstructural protein 7b genes. These data demonstrate distinctive circulating virulent and avirulent strains in natural populations. In addition, 5 membrane protein amino acid residues with functional potential differentiated healthy cats from cats with FIP. These findings may have potential as diagnostic markers for virulent FIP-associated FCoV.

Show MeSH
Related in: MedlinePlus