Isolation of feline herpesvirus-1 and feline calicivirus from healthy cats in Swedish breeding catteries

An efficient method for the selective isolation of feline herpesvirus 1(FHV-1) in feline calicivirus (FCV) coinfected specimens

BACKGROUND

Feline herpesvirus 1 (FHV-1) and feline calicivirus (FCV) are the most common viral pathogens of feline respiratory disease and are highly prevalent in cats worldwide. Coinfection with these viruses is frequent in cats with feline respiratory disease complex (FRDC). It is difficult to isolate pure FHV-1 by conventional laboratory cell culture methods from specimens with FRDC, which brings great trouble to the epidemiological investigation of FHV-1.

METHODS

FCV polyclonal antibodies were obtained by immunizing rabbits, and the coinfected specimens were neutralized with FCV polyclonal antibodies. Then, virus isolation was performed. After several rounds of neutralization, FHV-1 was finally obtained.

RESULTS

The FCV polyclonal antibody was successfully obtained with neutralizing activities of 1:128, 1:537, and 1:91. After virus neutralization, the FHV-1 was successfully isolated from the coinfected cell culture suspension and confirmed by immunofluorescence and QRT-PCR.

CONCLUSION

In this study, all FHV-1 present in the coinfection samples were isolated, without any cross-contamination. This method is also theoretically suitable for the isolation and purification of other FCV coinfections or contaminating disease substances.

The Latest Prevalence, Isolation, and Molecular Characteristics of Feline Herpesvirus Type 1 in Yanji City, China

Epidemiological surveys revealed that 33 of the 93 samples were positive for FHV-1, with the gD gene of these 33 samples exhibiting low variation, high homology, and no critical amino acid mutation. Feline herpesvirus type 1 (FHV-1), also known as feline viral rhinotracheitis (FVR) virus, is one of the main causes of URT disease in cats. All cats can become hosts of FHV-1, and the spread of this disease affects the protection of rare feline animals. Nasal swabs from cats with URT disease were collected at five veterinary clinics in Yanji City from 2022 to 2024. The purpose of this study was to isolate and investigate the epidemiology of FHV-1. The gD gene of the FHV-1 strain was cloned and inserted into the pMD-18T vector and transformed into a competent Escherichia coli strain. Subsequently, the gD gene of the positive samples was sequenced and phylogenetic analysis was performed to determine the genetic evolution relationship between the strains. We successfully isolated the FHV-1 strain YBYJ-1 in Yanji City for the first time. The diameter of the virus is approximately 150-160 nm. After 48 h of virus inoculation, the cells were round, isolated, and formed grape-like clusters. The gD gene of the virus was sequenced, and the length was 1125 bp, which proved the isolate was FHV-1. This study found that the genetic evolution of the FHV-1 gD gene was stable, expanding the molecular epidemiological data on FHV-1 in cats in Yanji City.

First report of molecular epidemiology and phylogenetic characteristics of feline herpesvirus (FHV-1) from naturally infected cats in Kunshan, China

BACKGROUND

Feline herpesvirus type 1 (FHV-1) is a life threatening highly contagious virus in cats and typically causes upper respiratory tract infections as well as conjunctival and corneal ulcers. Genetic variability could alter the severity of diseases and clinical signs. Despite regular vaccine practices against FHV-1 in China, new FHV-1 cases still commonly occur. The genetic and phylogenetic characteristics of FHV-1 in Kunshan city of China has not been studied yet. Therefore, this study was planned to investigate the prevalence, molecular characteristics of circulating strains, and phylogenetic analyses of FHV-1. This is the first report of molecular epidemiology and phylogenetic characteristics of FHV-1 from naturally infected cats in Kunshan, China.

METHODS

The occulo-nasal swabs were collected from diseased cats showing respiratory distress, conjunctivitis, and corneal ulcers at different veterinary clinics in Kunshan from 2022 to 2023. Clinical data and general information were recorded. Swab samples were processed for preliminary detection of FHV-1. Thymidine kinase (TK), glycoprotein B (gB) and glycoprotein D (gD) genes were sequenced and analyzed to investigate genetic diversity and evolution of FHV-1.

RESULTS

The FHV-1 genome was detected in 43 (43/200, 21.5%) samples using RT-PCR targeting the TK gene. Statistical analysis showed a significant correlation between age, vaccination status and living environment (p < 0.05) with FHV-1 positivity, while a non-significant correlation was observed for FHV-1 positivity and sex of cats (p > 0.05). Additionally, eight FHV-1 positive cats were co-infected with feline calicivirus (8/43,18.6%). FHV-1 identified in the present study was confirmed as FHV-1 based on phylogenetic analyses. The sequence analyses revealed that 43 FHV-1 strains identified in the present study did not differ much with reference strains within China and worldwide. A nucleotide homology of 99-100% was determined among gB, TK and gD genes nucleotide sequences when compared with standard strain C-27 and vaccine strains. Amino acid analysis showed some amino acid substitutions in TK, gB and gD protein sequences. A potential N-linked glycosylation site was observed in all TK protein sequences. Phylogenetic analyses revealed minor variations and short evolutionary distance among FHV-1 strains detected in this study.

CONCLUSIONS

Our findings indicate that genomes of 43 FHV-1 strains are highly homogenous and antigenically similar, and the degree of variation in major envelope proteins between strains is low. This study demonstrated some useful data about prevalence, genetic characteristics, and evolution of FHV-1 in Kunshan, which may aid in future vaccine development.

First Report of Isolation and Molecular Characterization of Felid Herpesvirus-1 from Symptomatic Domestic Cats in Egypt

Feline herpesvirus 1 (FHV-1) is one of the main causes of upper respiratory tract infection in cats. Despite its veterinary importance, no previous studies investigated the occurrence of this virus in Egypt. In the present work, a total number of one hundred forty (N = 140) conjunctival and/or oropharyngeal swabs were collected from symptomatic cats during veterinary clinic visits located in two Egyptian provinces. Virus isolation was performed in the Chorioallantoic membranes (CAMs) of 12-days-old SPF eggs. Interestingly, the embryos showed stunting growth and abnormal feathering and infected CAMs showed edematous thickening and cloudiness with characteristic white opaque pock lesions. Polymerase chain reaction (PCR) amplification of the thymidine kinase gene (TK) was successful in 16/140 (11.4%) of the suspected cases. Two of the amplified genes were sequenced and the TK gene sequences of the FHV-1 isolates were highly similar to other reference strains in the GenBank database. Given the above information, the present study represents the first report of feline herpesvirus type 1 (FHV-1) in domestic cats in Egypt. Further studies on the causes of upper respiratory tract infections in cats as well as vaccine efficacy are needed.

Development of a novel reverse transcription PCR and its application to field sample testing for feline calicivirus prevalence in healthy stray cats in Korea

Background

Feline calicivirus (FCV) is a major and highly infectious pathogen in cats worldwide. However, there have been limited studies about the status of FCV infections in Korea.

Objectives

To investigate the current status of FCV infections in stray cats in Korea.

Methods

A novel reverse transcription polymerase chain reaction (RT-PCR) assay was developed based on the conserved nucleotide sequences of reported FCV strains. Field swab samples were collected from 122 cats (2 hospital admitted cats and 120 stray cats) in 2016 and 2017. All the samples were tested by virus isolation and 2 different RT-PCRs, including the novel RT-PCR, for the detection of FCV.

Results

The novel RT-PCR assay showed no cross-reactivity to the nucleic acids of the other feline pathogens tested, and the limit of detection was calculated as 10⁰ TCID₅₀/mL based on an in vitro assessment. The novel RT-PCR assay detected 5 positive samples from the 122 field samples, which showed perfect agreement with the results of the virus isolation method. In contrast, another RT-PCR assay used in a previous study in Korea detected no positive samples. The prevalence of FCV infection in stray cats was 2.5% (3/120) based on the results of virus isolation and the novel RT-PCR assays.

Conclusions

The current study is the first report of the detection and prevalence of FCV in stray cats in Korea. The novel RT-PCR assay developed in this study showed high sensitivity and specificity, which indicates a useful diagnostic assay to identify FCV infection in cats.

Ability of vaccine strain induced antibodies to neutralize field isolates of caliciviruses from Swedish cats

Background

Feline calicivirus (FCV) is a common cause of upper respiratory tract disease in cats worldwide. Its characteristically high mutation rate leads to escape from the humoral immune response induced by natural infection and/or vaccination and consequently vaccines are not always effective against field isolates. Thus, there is a need to continuously investigate the ability of FCV vaccine strain-induced antibodies to neutralize field isolates.

Methods

Seventy-eight field isolates of FCV isolated during the years 2008–2012 from Swedish cats displaying clinical signs of upper respiratory tract disease were examined in this study. The field isolates were tested for cross-neutralization using a panel of eight anti-sera raised in four pairs of cats following infection with four vaccine strains (F9, 255, G1 and 431).

Results

The anti-sera raised against F9 and 255 neutralised 20.5 and 11.5 %, and 47.4 and 64.1 % of field isolates tested, respectively. The anti-sera against the more recently introduced vaccine strains G1 and 431 neutralized 33.3 and 70.5 % and 69.2 and 89.7 %, respectively. Dual vaccine strains displayed a higher cross-neutralization.

Conclusions

This study confirms previous observations that more recently introduced vaccine strains induce antibodies with a higher neutralizing capacity compared to vaccine strains that have been used extensively over a long period of time. This study also suggests that dual FCV vaccine strains might neutralize more field isolates compared to single vaccine strains. Vaccine strains should ideally be selected based on updated knowledge on the antigenic properties of field isolates in the local setting, and there is thus a need for continuously studying the evolution of FCV together with the neutralizing capacity of vaccine strain induced antibodies against field isolates at a national and/or regional level.

Electronic supplementary material

The online version of this article (doi:10.1186/s13028-015-0178-z) contains supplementary material, which is available to authorized users.

Feline calicivirus: a neglected cause of feline ocular surface infections?

OBJECTIVE

To investigate the prevalence of feline calicivirus (FCV) infection in relation to ocular surface lesions in cats with upper respiratory tract diseases (URTD).

ANIMALS STUDIED

Ninety-nine cats with ocular surface infection and symptoms or recent history of URTD were examined at various rescue shelters and hospitals.

PROCEDURE

A complete general and ophthalmic examination was performed including Schirmer tear test, slit-lamp biomicroscopy, fluorescein and lissamine green staining. Clinical and ocular symptoms were scored and recorded. Conjunctival samples were collected using a cytobrush, and nucleic acid extraction using RT-PCR was carried out to analyze for the presence of various infectious agents.

RESULTS

RT-PCR detected either FCV, feline herpes virus type 1 (FHV-1), Chlamydophila felis or Mycoplasma spp. in 63/99 samples. 30/63 samples were positive for FCV, 23/63 for C. felis, 21/63 for Mycoplasma spp., and 16/63 for FHV-1. Out of the 30 FCV-positive samples, 11 were positive only for FCV and in 19 samples FCV was seen in combination with other agents. FCV infection was highest in animals examined at the rescue centers and in the age group of 0-2 months. Erosive conjunctivitis was an important ocular finding. Oral ulcers were detected in all FCV-infected cats.

CONCLUSION

Results indicate that FCV is highly prevalent in cats with URTD either as a sole infectious agent or in combination with other pathogens and therefore is a potential cause for ocular surface lesions during the URTD.

Infectious causes for feline upper respiratory tract disease--a case-control study

The aim of this case-control study was to investigate the prevalence of microorganisms in group-living cats with clinical signs of upper respiratory tract disease (URTD), in in-contact cats and in cats in groups without URTD problems. Samples were taken from the ventral conjunctival fornix for analysis of feline herpesvirus-1 (FHV), Mycoplasma felis and Chlamydiaceae using a real-time polymerase chain reaction technique. The oropharynx was sampled for bacteriological culture and viral isolation. Specific infectious agents were identified in 11/20 (55%) of the case households, in 7/20 (35%) of the cats with clinical signs and in 3/20 (15%) of the control households, in 3/40 (7.5%) of the cats. Chlamydiae and M felis were only detected from case households, both from cats with URTD and from in-contact cats. The difference in prevalence between case and control households was statistically significant for M felis (P=0.047). The presence of M felis in cat groups was thus associated with clinical signs of URTD.

Feline herpesvirus 1 and feline calicivirus infections in a heterogeneous cat population of a rescue shelter

Feline herpesvirus 1 (FeHV-1) and feline calicivirus (FCV), associated with upper respiratory tract disease, are highly prevalent in cats worldwide. With the aim to investigate the importance of feline respiratory viruses in a heterogeneous population of cats, samples were taken in a rescue shelter in Liège, Belgium, between March 2005 and August 2006. Reverse transcription polymerase chain reaction (RT-PCR) and polymerase chain reaction (PCR) were performed to diagnose FCV and FeHV-1 infection in the sampled cats. The prevalence rate (33.1%) was higher for FCV than for FeHV-1 (20.1%) whereas prevalence rate of co-infection with both viruses was 10%. Gingivitis was more common in FCV infections (odds ratio (OR)=2.83) whereas respiratory signs were more often observed with FeHV-1 infections. The average age was significantly higher in FCV positive cats (38 months) than in FeHV-1 positive cats (29.9 months). The second and the fourth quarters of the year and the two first quarters were significantly more at risk than the others in the case of FeHV-1 and FCV infection, respectively. Age was found to be a confounding factor. High prevalence of both infections strengthens the importance of applying hygienic and preventive measures in rescue shelters where cats with an unknown status of vaccination are introduced.

Prevalence of feline herpesvirus 1, feline calicivirus and Chlamydophila felis in clinically normal cats at a Korean animal shelter

The prevalence of feline herpesvirus-1 (FHV-1), feline calicivirus (FCV), and Chlamydophila (C.) felis was studied in cats of an animal shelter in Korea. Total 78 cats without ocular and upper respiratory tract disease were examined. Specimens were obtained from ocular conjunctiva and oropharynx. Using multiplex polymerase chain reaction (PCR) and reverse transcription PCR, three pathogens were simultaneously detected. In examined 78 cats, 49 (63%) cats were positive for FHV-1. However, all specimens were negative for C. felis and FCV. In conclusion, many cats recovered from FHV-1 infection remain subclinical carriers in shelter environment.

Comparison of the ability of feline calicivirus (FCV) vaccines to neutralise a panel of current UK FCV isolates

Feline calicivirus (FCV) comprises a large number of strains which are related antigenically to varying degrees. The antigenic variability creates problems for choosing antigens to include in vaccines. Historically, these have been selected for use based on their cross-reactivity with a high proportion of field strains. However, it is important to determine the current level of cross-reactivity of vaccines and whether or not this may be decreasing owing to widespread vaccine use. In this in vitro study, we have compared the ability of antisera to two vaccine viruses (FCV strain F9 and FCV strain 255) to neutralise a panel of 40 recent UK field isolates. These 40 isolates were obtained by randomised, cross-sectional sampling of veterinary practices in different geographical regions of the UK so as to ensure they were representative of viruses circulating in the veterinary-visiting population of cats in the UK. Virus neutralisation assays showed that both vaccine strains are still broadly cross-reactive, with F9 antiserum neutralising 87.5% and 255 antiserum 75% of isolates tested with antiserum dilutions of 1 in 2 or greater. However, when antibody units were used, in order to take account of differences in homologous titres between antisera, fewer isolates were neutralised, with F9 antiserum showing a slightly higher proportion of isolates neutralised than 255. Multivariable analysis of the sample population of 1206 cats from which the 40 isolates were derived found that vaccinated cats were at a decreased risk of being positive for FCV, whereas cats from households with more than one cat, and cats with mouth ulcers were at increased risk. In addition as cats became older their risk of shedding FCV decreased.

Detection of virulent feline herpesvirus-1 in the corneas of clinically normal cats

To evaluate the clinically normal feline cornea for the presence of virulent feline herpesvirus-1 (FHV-1), corneas from 31 cats (25 with normal eyes and six with active disease or corneal scarring) euthanased at a shelter were collected. Corneas from two specific pathogen-free cats were included as negative controls. Virus isolation (VI), fluorescent antibody (FA) staining and real-time polymerase chain reaction (rt-PCR) were performed on all samples. The presence or absence of dexamethasone in the media was evaluated for its effect on VI. VI was positive for FHV-1 in six corneas from five cats, all with clinically normal eyes. One cornea was positive for feline calicivirus (FCV) in addition to FHV-1, but only in media that included dexamethasone. Eight corneas were positive on rt-PCR for FHV-1, all from cats with clinically normal eyes. All positive VI samples were confirmed with FA staining. VI and rt-PCR were negative for FHV-1 and FCV in cats with active disease or corneal scarring. Data from this study indicate that virulent FHV-1 and FCV can be present in feline corneas that are clinically normal. Dexamethasone may enhance viral spread through a cell receptor mechanism.

Feline calicivirus

Feline calicivirus (FCV) is an important and highly prevalent pathogen of cats. It belongs to the family Caliciviridae which includes other significant pathogens of man and animals. As an RNA virus, high polymerase error rates convey upon FCV a high genome plasticity, and allow the virus to respond rapidly to environmental selection pressures. This makes the virus very adaptable and has important implications for clinical disease and its control. Being genetically diverse, FCV is associated with a range of clinical syndromes from inapparent infections to relatively mild oral and upper respiratory tract disease with or without acute lameness. More recently, highly virulent forms of the virus have emerged associated with a systemic infection that is frequently fatal. A proportion of FCV infected cats that recover from acute disease, remain persistently infected. In such cats, virus evolution is believed to help the virus to evade the host immune response. Such long-term carriers may only represent a minority of the feline population but are likely to be crucial to the epidemiology of the virus. Vaccination against FCV has been available for many years and has effectively reduced the incidence of clinical disease. However, the vaccines do not prevent infection and vaccinated cats can still become persistently infected. In addition, FCV strain variability means that not all strains are protected against equally. Much progress has been made in understanding the biology and pathogenesis of this important feline virus. Challenges for the future will necessarily focus on how to control the variability of this virus particularly in relation to emerging virulent strains and vaccination.

Real-time reverse transcription polymerase chain reaction assay to detect a broad range of feline calicivirus isolates

This report describes a real-time reverse transcription polymerase chain reaction (RT-PCR) assay with SYBR Green targeting the VP2 (ORF 3) of feline caliciviruses. All of the 44 feline calicivirus isolates tested were detected, whereas neither feline herpesvirus, feline panleukopenia virus, feline immunodeficiency virus and feline leukemia virus nor other calicivirus like rabbit hemorrhagic disease virus and a canine calicivirus isolate showed specific amplification products. The sensitivity of the SYBR Green reaction was shown to be equivalent to 5 x 10(1) to 5 x 10(2) copies/reaction and the overall sensitivity equivalent to a feline calicivirus titer of 10(0.6) TCID(50)/100 microl in Crandell Reese Feline Kidney (CRFK) cells.