Abstract
Feline parvovirus (FPV) or feline panleukopenia virus is a highly contagious, life-threatening infectious virus in cats. Although FPV vaccination is routinely practiced in China, clinical diseases continue to occur. The investigation of genotypes and viral evolution can contribute to the prevention, diagnosis, and treatment of FPV. Therefore, this study aimed to provide an up-to-date understanding of the epidemiological, genotypic, and phylogenetic characteristics of FPV. In total, 152 rectal swabs were collected from diseased cats. All swab samples were tested for FPV using molecular methods. Amplification of the complete viral protein 2 (VP2) gene was performed for further analysis and to infer the genotypic and evolutionary characteristics of FPV. Of the 152 samples, FPV DNA was detected in 17 (17/152, 11.18%). Cats with FPV showed variable clinical signs such as dehydration, anorexia, fever, vomiting, and blood-stained diarrhea. Furthermore, VP2 sequences were identified in 17 PCR-positive cats, confirming the presence of FPV. Phylogenetic and nucleotide pairwise identity analyses revealed high genetic similarity among FPV sequences (99.6–100%) and clustered them into the FPV-G1 group. Amino acid analysis indicated a novel mutation (Ala91Ser) in all VP2 gene sequences amplified in this study. Our study provides baseline epidemiological data for the better prevention of FPV with respect to vaccination strategies. Genotypic and phylogenetic analyses confirm that FPV-G1 was the predominant FPV group in infected cats in Kunshan. Therefore, a rigorous countrywide investigation of the genotypic and evolutionary characteristics of FPV is warranted.
Keywords: China, evolution, feline parvovirus, genotyping
Feline parvovirus infection, also known as feline panleukopenia, is a highly contagious, life-threatening virus infecting cats which spreads quickly from one infected cat to another [5, 13, 31]. Kittens and non-vaccinated cats are usually affected by feline panleukopenia, leading to high morbidity and mortality rates, especially in young cats or kittens. Although vaccination against feline panleukopenia is routinely practiced in China, disease cases are still observed. Feline panleukopenia can spread directly or indirectly through infected cats, contaminated objects, and bedding materials [22]. Diarrhea, vomiting, fever, and significant decrease in white blood cells are the main characteristics of Feline panleukopenia in cats [5]. The etiology of feline panleukopenia is a small single-stranded DNA virus known as feline parvovirus (FPV). Notably, FPV was first identified in 1928 and later isolated from tissue culture in 1964 [9]. Researchers believe that canine parvovirus (CPV-2) that infects canines originated from FPV and acquired two key substitution mutations (Lys93Asn and Asp323Asn) in the capsid protein (VP2) [8, 27]. Although the original CPV-2 does not infect cats, new variants of CPV-2 (CPV-2a, CPV-2b, and CPV-2c) can. Amino acid substitution mutations at six key positions (87, 297,300, 305,426, 555) in the VP2 protein have been associated with infection in cats. The pathogenicity of CPV-2 variants (CPV-2a, CPV-2b, and CPV-2c) is apparently mild; however, they can induce severe disease in immunocompromised or co-infected cats. Primarily, FPV targets rapidly dividing cells such as those lining the intestinal mucosa, bone marrow, and lymphoid tissues, leading to a significant reduction in white blood cells (leukopenia) and subsequent immunosuppression [26]. This makes infected cats prone to secondary infections.
Carnivore protoparvovirus 1 is a unique species of viruses in the family Parvoviridae which also includes FPV, CPV-2, mink enteritis virus, and raccoon parvovirus [7]. This icosahedral virion has a size of approximately 25 nm and a genome length of approximately 5,000 bases, and mainly encodes two non-structural proteins, NS1 and NS2, as well as two structural proteins, VP1 and VP2 [17]. Notably, VP2 is a key and predominant capsid protein and a major target of neutralizing antibodies against FPV. The VP2 gene plays key roles in viral replication and pathogenesis. It encodes the viral capsid protein that facilitates viral entry into host cells and is a major target of host immunity [17, 18]. The host ranges of FPV and CPV-2 are determined by specific amino acids in the VP2 protein, including 80 (L to R), 93 (L to N), 103 (V to A), 232 (V to I), 323 (E to N), 564 (N to S), and 568 (A to G). The antigenicity of FVP or CPV-2 depends on the VP2 protein. Random genetic drift is the main driver of FPV evolution. In addition, genetic recombination has played a crucial role in FPV evolution. Alterations in VP2 amino acids can lead to viral evolution and the generation of different antigenic variants, making it difficult to prevent and treat feline panleukopenia [12, 15, 28].
Therefore, genetic analysis of the VP2 gene can help identify, characterize different FPV strains and provide valuable insights into the evolution, epidemiology, and possible virulence factors associated with the virus [30]. Several studies have analyzed the full-length VP2 gene of FPV and identified several genetic variations that can be used to track the evolution and spread of the virus. Genetic variations in the VP2 gene can be used to track the origin and spread of the virus, as well as to develop effective vaccines and treatments for the disease [30].
Several epidemiological studies on FPVs have been conducted in China. Between 2021 and 2022, a study conducted in Yanji, China isolated and examined the FPV strain and found that 27 of 80 samples tested positive for the virus [31]. Furthermore, a study performed in Beijing, China, found that cats were predominantly infected with FPV strains, with CPV-2b and CPV-2c variants circulating in the population [24]. The CPV-2c strain has been identified as the dominant antigenic variant prevalent among cats in Beijing. Other studies have identified FPV-like viruses in dogs in Southwest China, with 28/113 (24.8%) strains identified based on amino acid residues in VP2 [29]. The treatment of feline panleukopenia typically involves supportive care such as fluid therapy and antibiotics to prevent secondary infections. Vaccination is the most effective way to prevent this disease, and all cats should be vaccinated against FPV. Furthermore, isolating infected cats and disinfecting any areas they have visited is important to prevent the spread of the virus to other cats.
As FPV has evolved over time, multiple strains have been identified. Genotypic and viral evolution analyses have contributed to the prevention, diagnosis, and treatment of viral infections. Data on FPV in cats in China is limited. To the best of our knowledge, no published data regarding FPV epidemiology and genotypic and phylogenetic characteristics are available from Kunshan City, indicating the need for epidemiological studies focused on the molecular evolution and genetic characteristics of FPV. Therefore, this study aimed to provide an up-to-date understanding of the epidemiology, genotype, and phylogenetic characteristics of FPV in Kunshan City, Jiangsu Province, China. By investigating the genetic variations and phylogenetic relationships among FPV strains circulating in this specific region and period, we aimed to contribute to the understanding of the molecular epidemiology, evolution, and potential effects on feline health. This information is essential for the development of effective preventive measures, including vaccines and antiviral therapies, and for the implementation of appropriate control strategies to mitigate the spread of FPV in domestic cat populations.
MATERIALS AND METHODS
Ethical approval
The Institutional Animal Care and Use Committee (IACUC) was not required for this non-invasive study; however, the international ethical standards for animal handling and sample collection were strictly followed.
Cat population and sample collection
During the feline disease surveillance program, 152 rectal swabs were collected from cats with diarrhea and other health problems at animal clinics in Kunshan City, China, between January 2022 and September 2023 (Fig. 1). Clinical staff recorded data on the breed, age, sex, clinical symptoms, residence, and vaccination status of all cats sampled. Sterile anal swabs (Copan Diagnostics Inc., Brescia, Italy) were used to collect samples from the rectum of the infected cats. Subsequently, the anal swabs were immersed in a vial containing sterile saline solution. The sample tubes were centrifuged for 10 min to separate undigested feed particles from the swab samples. The supernatant was collected and kept at −80°C for DNA extraction.
Fig. 1.
Maps of the study area and sampling locations. Rectal swabs were collected from cats between 2022 and 2023 from veterinary clinics in Kunshan City, Jiangsu Province, China.
DNA extraction and molecular detection of FPV
All samples were processed for DNA extraction and tested for FPV identification using molecular methods. DNA was extracted from all samples using a TaKaRa MiniBEST Viral RNA/DNA Extraction Kit (Cat#9766, Takara, Dalian, China). Molecular screening was conducted by PCR amplification of a 428 bp fragment of the VP2 gene using the primers and thermocycling conditions given in Supplementary Table 1 [1]. PCR was performed using Rapid Taq master mix (Vazyme, Nanjing, China) on a thermocycler (LifeEco TC 96, Bioer, Hangzhou, China). PCR amplicons of approximately 428 bp in length were analyzed by 1.5% agarose gel electrophoresis using a gel imaging analysis system (GenoSens 1880, Clinx, Shanghai, China).
Complete VP2 gene amplification and sequencing
The complete VP2 gene was amplified using PCR for genotypic and evolutionary analyses. The complete VP2 gene was amplified with a predicted length of 1932 bp using previously reported primers and conditions [31]. The sequencing primers and conditions are listed in Table 1. Positive and negative controls were added to each reaction to optimize and validate the assays. All PCR products were sequenced by GeneWiz (Suzhou, China).
Table 1. Correlation between clinical signs and feline panleukopenia virus-positive samples in this study.
| Specimen ID | Age (months) | Clinical sign | Vaccine history | GenBank ID |
|---|---|---|---|---|
| 13 | 4 | Vomiting, diarrhea | - | OR399559 |
| 19 | 9 | Anorexia, lethargy | + | OR399560 |
| 34 | 7 | Fever, anorexia | - | OR399561 |
| 41 | 12 | Vomiting, fever, anorexia | - | OR399562 |
| 42 | 6 | Anorexia, vomiting | +- | OR399563 |
| 56 | 5 | Dehydration, fever, diarrhea | - | OR399564 |
| 59 | 9 | Diarrhea, anorexia | + | OR399565 |
| 73 | 13 | Fever, diarrhea, anorexia | - | OR399566 |
| 77 | 16 | No clinical sign | + | OR399567 |
| 89 | 8 | Vomiting, sticky feces | - | OR399568 |
| 109 | 2 | Vomiting, fever | - | OR399569 |
| 111 | 5 | Vomiting, anorexia | - | OR399570 |
| 122 | 3 | Dehydration, fever | + | OR399571 |
| 133 | 9 | Sticky feces, anorexia | - | OR399572 |
| 141 | 4 | Vomiting, anorexia | - | OR399573 |
| 143 | 2 | Anorexia, lethargy | - | OR399574 |
| 149 | 5 | Dehydration, fever, diarrhea | - | OR399575 |
+, Vaccinated; -, non vaccinated; +-, incomplete vaccination.
Genetic and evolutionary analysis
For comparative genetic analysis, we retrieved the reference VP2 gene sequences of FPV and CPV-2 from the National Center for Biotechnology Information (NCBI) GenBank nucleotide database (http://www.ncbi.nlm.nih.gov). A total of 110 global reference sequences were downloaded for comparative analysis. The VP2 sequences from this study were aligned using the ClustalW algorithm with 118 reference sequences, followed by manual editing in BioEdit (Ibis Biosciences, Carlsbad, CA, USA). Phylogenetic relationships were calculated by the neighbor-joining method (500 bootstrap replicates), and evolutionary distances were computed using the maximum composite likelihood method in the MEGA11 software package [23]. The sequences obtained in the present study were compared with the reference sequences of FPV using phylogenetic and nucleotide pairwise identity analyses. The FPV sequences found in the present study were deposited in the NCBI GenBank database (accession numbers OR399559-OR399575).
Recombination analysis in VP2 gene
The complete VP2 gene sequences of FPV found in this study were aligned using MEGA 11 software. Screening was performed to detect any possible recombination among sequences using the RDP4 recombination detection software containing various recombination detection methods (RDP, GENECONV, Bootscan, MaxChi, Chimaera, SiScan, and 3Seq). The highest acceptable P value was set at 0.05 [24, 27].
RESULTS
Preliminary detection of FPV in samples
Of the 152 samples, we detected FPV DNA in 17 (17/152, 11.18%) using PCR assays. A 428 bp DNA segment of the VP2 gene was targeted for the preliminary detection of FPV in samples. Our results were verified using a positive control by amplifying PCR products of similar size in all reactions. Cats with FPV exhibited various clinical signs (Table 1). No clinical signs were observed in one FPV-positive cat. Among the 17 positive cats, anorexia (10/17, 58.8%), vomiting (7/17, 41.17%), fever (7/10, 41.17%), and diarrhea (5/17, 29.4%) were the prominent clinical signs. Of the 152 cats sampled, nine showed clinical signs of diarrhea. Among these, only four cats with diarrhea tested positive for FPV, whereas five cats with diarrhea tested negative for FPV. All samples from cats with diarrhea were retested for confirmation. Four fully vaccinated cats tested positive for FPV. Three of the vaccinated cats showed mild clinical signs (anorexia, lethargy, diarrhea, dehydration, and fever), whereas one cat was asymptomatic (Table 1). The samples were not tested for other enteric pathogens.
Nucleotide homology analysis and phylogeny
Genotypic and phylogenetic analyses were performed using the complete VP2 gene sequences to infer the genotyping and evolutionary characteristics of FPV in Kunshan. Reference sequences were categorized into three main groups (FPV-G1, FPV-G2, and FPV-G3) and eight subgroups (FPV-G3A, FPV–G3B, FPV–G3C, FPV–G3D, FPV–G3E, FPV–G3F, FPV–G3G, and FPV–G3H) as previously described [30]. Seventeen complete VP2 gene sequences confirmed the presence of FPV. Phylogenetic and nucleotide pairwise identity analyses revealed higher genetic similarity among FPV sequences (99.6–100%) and showed a close relationship with the FPV-G1 group (Fig. 2). None of the sequences from the present study clustered with FPV-G2 or FPV-G3. The VP2 sequences were genetically similar and revealed a close evolutionary association with sequences reported from China (Beijing, Nanjing, Yanji, Yangzhou, Chengdu, Changchun, Jilin, and Nanyang), South Korea, and Argentina. Although the VP2 sequences were more similar to each other, they showed distant relationships with the reference sequences of FPV reported from other countries, including the US, Japan, Turkey, France, Germany, Vietnam, Italy, and Brazil, and clustered separately in the phylogenetic tree.
Fig. 2.
Complete VP2 gene-based phylogenetic tree of feline parvovirus (FPV) strains circulating in Kunshan. Phylogenetic relationships were calculated by the neighbor-joining method (500 bootstrap replicates). The evolutionary distances were computed using the maximum composite likelihood method and are in the units of the number of base substitutions per site. Evolutionary analyses were conducted in MEGA11. FPV isolates collected in the present study have been marked with “red” circles.
Deduced amino acid analysis
The key amino acid positions in the VP2 protein (positions 5, 80, 87,91,101, 103,297, 300, 305, 323, 426, 564, and 568) were analyzed by deduced amino acid analysis. The VP2 protein sequences in this study were typed as FPV after analysis of key amino acids. Amino acid analysis indicated a novel mutation (Ala91Ser) in all VP2 sequences in this study. Since 2019, mutations at amino acid position 91 (A91S) have become predominant among the Chinese FPV strains. Only OR399569 showed an amino acid substitution (glycine instead of aspartic acid) at position 305 compared to the FPV reference strains (M24004 and M38246). Marked amino acid variations were observed among CPV-2 and FPV reference strains and FPV strains observed in this study. Table 2 shows the variations in amino acids among the FPV sequences observed in this study and the reference FPV strains.
Table 2. Variation of amino acids among Feline parvovirus (FPV) sequences observed in the present study and reference FPV strains.
| Accession number | type | Origin | amino-acid positions A
|
||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 5 | 80 | 87 | 91 | 93 | 101 | 103 | 262 | 267 | 297 | 300 | 305 | 323 | 324 | 370 | 375 | 426 | 440 | 555 | 564 | 568 | |||
| M24004 | FPV | Reference | A | K | M | A | K | T | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| M38246 | FPV | Vaccine | A | K | M | A | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| M38245 | CPV2 | Reference | A | R | M | A | N | I | A | A | F | S | A | D | N | Y | Q | D | N | T | V | S | G |
| EU659118 | CPV2a | Reference | A | R | L | A | N | I | A | A | F | S | G | Y | N | Y | Q | D | N | T | V | S | G |
| M74849 | CPV2b | Reference | A | R | L | A | N | I | A | A | F | S | G | Y | N | Y | Q | D | D | T | V | S | G |
| FJ222821 | CPV2c | Reference | A | R | L | A | N | I | A | A | F | A | G | Y | N | Y | Q | D | E | T | V | S | G |
| AB054214 | New CPV2a | Reference | A | R | L | A | N | I | A | A | F | A | G | Y | N | Y | Q | D | N | T | V | S | G |
| GQ379042 | New CPV2b | Reference | A | R | L | A | N | I | A | A | F | A | G | Y | N | I | Q | D | N | T | V | S | G |
| OR399559 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399560 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399561 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399562 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399563 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399564 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399565 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399566 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399567 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399568 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399569 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | G | D | Y | Q | D | N | T | V | N | A |
| OR399570 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399571 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399572 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399573 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399574 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
| OR399575 | FPV | Cat | A | K | M | S | K | I | V | A | F | S | A | D | D | Y | Q | D | N | T | V | N | A |
a amino-acid positions refer to the prototype FPV (M24004). FPV, feline panleukopenia virus; CPV, canine parvovirus; A, Ala; D, Asp; E, Glu; G, Gly; K, Lys; L, Leu; M, Met; N, Asn; R, Arg; S, Ser; V, Val; Y, Tyr.
Recombination analysis of VP2 gene
Based on the RDP4 results, no potential recombination events were found within the 17 complete VP2 gene sequences of FPV. This finding suggests that the FPV sequences in this study were not the products of recombination events in other parvoviruses.
DISCUSSION
Feline panleukopenia is a highly contagious disease, characterized by fever, vomiting, diarrhea, severe leukopenia, and abdominal pain. The feline panleukopenia virus is commonly responsible for acute gastroenteritis and leukemia in cats [5]. In addition to domestic cats, FPV has been reported in racoons, minks, and a few wild cat species, including tigers, lions, leopard cats, civets, and wild fishing cats [11]. FPV causes immunosuppression in cats by damaging immune cells, bone marrow, and the gut epithelium, providing an opportunity for coinfection with other enteric viruses. Genetic variations in FPV and differences in host immune responses can alter the severity of disease and clinical signs. Despite the regular practice of vaccination against FPV in China, new cases continue to occur. The genetic and evolutionary characteristics of FPV in Kunshan City, China, have not yet been studied. Therefore, this study aimed to investigate the prevalence, molecular and phylogenetic characteristics of circulating FPV strains. This is the first report of the genetic and evolutionary analyses of FPV strains in Kunshan, China.
In this study, 152 rectal swabs were collected from cats in Kunshan and analyzed for the presence of FPV DNA. Overall, the FPV detection rate was 11.18%, which was higher than that reported in previous studies conducted in China [24]. In contrast to our findings, higher detection rates have been previously reported [1, 3, 30]. Recently, Wang et al. (2024) reported a prevalence of 41.2% in cats in Shandong Province, China. Similarly, Awad et al. (2018) and Abdel Baky et al. (2023) reported prevalence rates of 45% and 43%, respectively, among cats in Egypt. A better vaccination program could explain the lower prevalence of FPV in Kunshan. Interestingly, one FPV-positive cat in this study did not show any clinical signs. Among the 17 FPV-positive cats, anorexia (10/17; 58.8%), vomiting (7/17; 41.17%), fever (7/10; 41.17%), and diarrhea (5/17; 29.4%) were prominent clinical signs. These clinical signs are similar to those reported in previous studies [1, 18, 19]. However, in this study, four vaccinated cats were also found to be positive for FPV, which could be the result of vaccine failure or insufficient protection provided by current FPV vaccines. Most of the infected cats in the present study were below six months of age (58.8%), whereas 76.47% (13/17) of the infected cats were non-vaccinated, indicating that kittens and non-vaccinated cats can be easily infected with FPV from the environment [16, 18]. Notably, FPV mostly infects cats below 6 months of age, whereas older cats often exhibit mild or no clinical signs [2]. Vaccine failure may be due to improper administration or neutralization of vaccines by maternal antibodies [25]. Viral evolution and crucial mutations in the capsid gene of FPV can also contribute to vaccine insufficiency [16, 18].
Notably, FPV has a conserved genome relative to other feline viruses, which explains the absence of genotypic subgrouping [6, 14, 18, 30]. However, some studies have used different groups for genetic analysis of FPV [24, 30]. For the genotypic and phylogenetic analyses, 110 reference sequences were retrieved from the NCBI GenBank sequence database. A phylogenetic tree was constructed to study the evolutionary relationship between the FVP reference sequences and the FPV sequences obtained in this study. Reference sequences were categorized into three main groups (FPV-G1, FPV-G2, and FPV-G3) and eight subgroups (FPV-G3A, FPV–G3B, FPV–G3C, FPV–G3D, FPV–G3E, FPV–G3F, FPV–G3G, and FPV–G3H). Seventeen complete VP2 gene sequences confirmed the presence of FPV. Phylogenetic and nucleotide pairwise identity analyses revealed higher genetic similarity among FPV sequences (99.6–100%) and showed a close relationship with the FPV-G1 group (Fig. 2). None of the sequences from the present study clustered into FPV-G2 or FPV-G3 and diverged from internationally published sequences. These findings are consistent with the findings of Wang et al. (2024) and Chen et al. (2022) who reported the predominance of FPV-G1 in China. In contrast to other countries, only one inactivated vaccine (FPV-Cu4) is used in China. Inoculation with this inactivated vaccine could be one of the reasons for the absence of FPV-G2 in China [30].
The VP2 gene sequences obtained in this study were genetically similar and revealed close evolutionary associations with sequences reported from China, including Beijing, Nanjing, Yanji, Yangzhou, Chengdu, Changchun, Jilin, and Nanyang. Amino acid analysis indicated a novel mutation (Ala91Ser) in all VP2 gene sequences detected in this study. This finding is consistent with previous studies from China [6, 30]. Since 2019, mutations at amino acid position 91 (A91S) have become predominant among the Chinese FPV strains. A mutation at position 91 has been reported to alter the biological activities of FPV and its receptor binding [6, 30]. Interestingly, we observed an amino acid substitution (glycine instead of aspartic acid) in OR399569 compared to other sequences, including the FPV reference sequences. Similar findings have been reported for the FPV sequence (OR194125) from Nanjing, China (unpublished data, sequences published in NCBI GenBank).
Based on the RDP4 results, no potential recombination breakpoints were found within the 17 complete VP2 gene sequences of FPV observed in this study, suggesting that these FPV sequences were not a result of recombination events from other parvoviruses. These findings are similar to those reported by Liu et al. (2023) in China, who reported no signs of recombination between FPV sequences. Previously, recombination events were observed within FPV and reference sequences [10, 20, 24]. Tang et al. (2022) reported recombination events in only one FPV sequence, indicating that recombination events among FPV sequences are rare in China. Random genetic drift is the main driver of FPV evolution. In addition, genetic recombination plays a crucial role in FPV evolution and is recognized as a crucial evolutionary force in several viral families, leading to better replication and survival [4, 15, 21]. To track the spread of FPV and identify potential risk factors for disease outbreaks, epidemiological studies are necessary, in addition to genetic analyses. Furthermore, understanding the transmission routes and reservoir hosts of FPV in China remains crucial to implement effective control measures and prevent future outbreaks.
This study has some limitations such as a small sample size and lack of information on the correlation between antibody responses to vaccination and infection. Future studies should include a larger number of FPV isolates from diverse geographical locations in China for genetic analysis. Second, we could not study co-infecting viruses within these samples. Co-infection with enteric viruses could have a serious additive effect on the health of cats with FPV. Finally, the risk factors associated with FPV infection in cats were not studied. Regardless of these limitations, further studies are necessary and should be conducted regularly to better understand FPV evolution.
Conclusion
Our study provides baseline epidemiological data for policymakers to improve the prevention of FPV with respect to vaccination strategies. This study confirms that FPV-G1 carries a novel mutation (A91S) and is the predominant group of FPV infecting cats in Kunshan. Therefore, we urge careful screening of cats for the VP2 gene of FPV during routine diagnosis to determine the genotypes. In addition, a rigorous countrywide investigation of the genotypic and evolutionary characteristics of FPV is warranted.
CONFLICT OF INTEREST
The authors declare no conflicts of interest.
Supplementary
Acknowledgments
We thank all staff, technicians, and veterinary doctors for collecting specimens and clinical data from infected cats at veterinary clinics in Kunshan. This research was supported in part by the Start-up Fund of the Division of Natural and Applied Sciences at Duke Kunshan University (00AKUG0105).
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