Canine parvovirus: strain difference in haemagglutination activity and antigenicity

[Parvovirus infections in cats in animal shelters]

Due to widespread vaccination programs against feline panleukopenia virus (FPV), the disease associated with this virus infection, feline panleukopenia, is rarely seen in privately owned cats in Germany. In contrast, the situation in animal shelters differs due to the constant intake of new cats that are often unprotected. In such facilities, panleukopenia outbreaks are common and often accompanied by a high number of fatalities. Due to the high contagiosity of the virus, some shelters do not accept cats with clinical signs suspicious for panleukopenia, since these animals can pose a risk to the shelter population. However, not only cats with panleukopenia shed parvovirus, but also healthy, asymptomatic cats can and thus contribute to risk of infection. Nevertheless, the risk for panleukopenia outbreaks in animal shelters can be reduced by rigorous outbreak management. This includes hygiene measures using correctly applied cleaning and disinfection protocols, quarantine measures, separate isolation units, as well as specific prophylactic measures, such as identification of infected animals and immunization of susceptible groups.

Molecular analysis of carnivore Protoparvovirus detected in white blood cells of naturally infected cats

Background

Cats are susceptible to feline panleukopenia virus (FPV) and canine parvovirus (CPV) variants 2a, 2b and 2c. Detection of FPV and CPV variants in apparently healthy cats and their persistence in white blood cells (WBC) and other tissues when neutralising antibodies are simultaneously present, suggest that parvovirus may persist long-term in the tissues of cats post-infection without causing clinical signs. The aim of this study was to screen a population of 54 cats from Sardinia (Italy) for the presence of both FPV and CPV DNA within buffy coat samples using polymerase chain reaction (PCR). The DNA viral load, genetic diversity, phylogeny and antibody titres against parvoviruses were investigated in the positive cats.

Results

Carnivore protoparvovirus 1 DNA was detected in nine cats (16.7%). Viral DNA was reassembled to FPV in four cats and to CPV (CPV-2b and 2c) in four cats; one subject showed an unusually high genetic complexity with mixed infection involving FPV and CPV-2c. Antibodies against parvovirus were detected in all subjects which tested positive to DNA parvoviruses.

Conclusions

The identification of FPV and CPV DNA in the WBC of asymptomatic cats, despite the presence of specific antibodies against parvoviruses, and the high genetic heterogeneity detected in one sample, confirmed the relevant epidemiological role of cats in parvovirus infection.

Seroprevalence of Canine Parvovirus in Dogs in Lusaka District, Zambia

Canine parvovirus (CPV) enteritis is a highly contagious enteric disease of young dogs. Limited studies have been done in Zambia to investigate the prevalence of CPV in dogs. Blood was collected from dogs from three veterinary clinics (clinic samples, n = 174) and one township of Lusaka (field samples, n = 56). Each dog's age, sex, breed, and vaccination status were recorded. A haemagglutination assay using pig erythrocytes and modified live parvovirus vaccine as the antigen was used. Antibodies to CPV were detected in 100% of dogs (unvaccinated or vaccinated). The titres ranged from 160 to 10240 with a median of 1280. Vaccinated dogs had significantly higher antibody titres compared to unvaccinated (p < 0.001). There was a significant difference in titres of clinic samples compared to field samples (p < 0.0001) but not within breed (p = 0.098) or sex (p = 0.572). Multiple regression analysis showed that only age and vaccination status were significant predictors of antibody titres. The presence of antibody in all dogs suggests that the CPV infection is ubiquitous and the disease is endemic, hence the need for research to determine the protection conferred by vaccination and natural exposure to the virus under local conditions.

[Diagnostic tools for canine parvovirus infection]

Canine parvovirus (CPV) infection is one of the most important and common infectious diseases in dogs, in particular affecting young puppies when maternal antibodies have waned and vaccine-induced antibodies have not yet developed. The mortality rate remains high. Therefore, a rapid and safe diagnostic tool is essential to diagnose the disease to 1) provide intensive care treatment and 2) to identify virus-shedding animals and thus prevent virus spread. Whilst the detection of antibodies against CPV is considered unsuitable to diagnose the disease, there are several different methods to directly detect complete virus, virus antigen or DNA. Additionally, to test in commercial laboratories, rapid in-house tests based on ELISA are available worldwide. The specificity of the ELISA rapid in-house tests is reported to be excellent. However, results on sensitivity vary and high numbers of false-negative results are commonly reported, which potentially leads to misdiagnosis. Polymerase chain reaction (PCR) is a very sensitive and specific diagnostic tool. It also provides the opportunity to differentiate vaccine strains from natural infection when sequencing is performed after PCR.

Evidence of feline panleukopenia infection in cats in India

The samples collected from cats showing clinical signs suspected for feline panleukopenia infection were confirmed using various molecular techniques and virus isolation. The suspected samples were confirmed using feline parvovirus specific primers. The partial VP2 gene was submitted to GenBank for the first time in India (Accession number JQ684660.1). The PCR positive samples were further amplified using full length FPV VP2 gene specific primers and sequenced. The blast analysis revealed that the local field isolates of FPV showed 99 % homology with other FPV sequences available in the GenBank. The evidence for occurrence of feline panleukopenia infection in cats in Tamil Nadu, India was further confirmed by host specific nucleotides present in the VP2 gene region as well as virus isolation in A72 cell line.

Characterization of parvoviruses from domestic cats in Brazil

To characterize Feline parvovirus (FPV) circulating in domestic cats in Brazil, 51 fecal samples from unvaccinated domestic cats were collected during 2004-2005. Six parvoviruses were characterized by hemagglutination (HA) assay at different pH values and temperatures and by polymerase chain reaction (PCR) using different pairs of primers. However, data obtained from HA and PCR did not allow the discrimination between FPV and Canine parvovirus (CPV). Two regions of the VP2 capsid gene (1,171-bp fragment) involved in controlling canine and feline host range were sequenced; 9 synonymous and 10 non-synonymous nucleotide substitutions were detected. All samples were confirmed as FPV by nucleotide sequencing, but 3 feline samples had amino acid changes at residues 93, 375, and 426, which are present in canine strains. The phylogenetic tree built based on nucleotide sequences showed that Brazilian feline samples form a cluster distinct from other parvoviruses deposited in GenBank. Taken together, the findings reinforce the importance of monitoring the continuous evolution of CPV and FPV in the feline population in Brazil.

Molecular typing of canine parvovirus variants by polymerase chain reaction and restriction enzyme analysis

Canine parvovirus type 2 (CPV-2) is a pathogen of dogs, which causes acute gastroenteritis and lymphopenia mostly in young pups. This paper reports the incidence of CPV-2 infection in diarrhoeic dogs with an aim to define the involvement of various variants of canine parvovirus circulating in India. CPV-2a, a variant of CPV-2 was differentiated from CPV-2b by polymerase chain reaction (PCR). The samples positive for CPV-2b were further analysed by PCR and restriction endonuclease (RE) analysis using Mbo II to detect the CPV-2c variant. Of 129 faecal samples studied, 78 were found positive for canine parvovirus by PCR. Among the 78 samples, 27 were of CPV-2a, 39 of CPV-2b and 12 of CPV-2c type, respectively. This study also showed that CPV-2c, anew variant, is circulating in India. The CPV-2c could be successfully detected by PCR and RE analysis while CPV-2b is the major antigenic type prevalent in this region followed by CPV-2a.

Neutralizing antibodies against feline parvoviruses in nondomestic felids inoculated with commercial inactivated polyvalent vaccines

The virus neutralization (VN) antibody titers of serum samples from 18 individuals representing 8 carnivore species vaccinated with commercial polyvalent vaccines optimized for domestic cats containing inactivated feline panleukopenia virus (FPLV) were evaluated against canine parvovirus type 2 (CPV2). In addition, the titers among 5 individuals from 4 carnivore were evaluated against antigenic variants of feline parvoviruses; FPLV, CPV2, CPV2a, CPV2b, CPV2c, mink enteritis virus type 1 (MEV1) and MEV2. The polyvalent vaccines induced cross-reactive VN titers against antigenic variants of feline parvoviruses in nondomestic felids. However, we observed very low cross-reactive VN antibody in lions and Siberian tigers, therefore we should pay attention to CPV infections in these animals even if they were vaccinated with inactivated FPLV vaccines.

Monoclonal antibodies that distinguish antigenic variants of canine parvovirus

Canine parvovirus (CPV) is classified as a member of the feline parvovirus (FPV) subgroup. CPV isolates are divided into three antigenic types: CPV type 2 (CPV-2), CPV-2a, and CPV-2b. Recently, new antigenic types of CPV were isolated from Vietnamese leopard cats and designated CPV-2c(a) or CPV-2c(b). CPV-2c viruses were distinguished from the other antigenic types of the FPV subgroup by the absence of reactivity with several monoclonal antibodies (MAbs). To characterize the antigenicity of CPV-2c, a panel of MAbs against CPV-2c was generated and epitopes recognized by these MAbs were examined by selection of escape mutants. Four MAbs were established and classified into three groups on the basis of their reactivities: MAbs which recognize CPV-2a, CPV-2b, and CPV-2c (MAbs 2G5 and 20G4); an MAb which reacts with only CPV-2b and CPV-2c(b) (MAb 21C3); and an MAb which recognizes all types of the FPV subgroup viruses (MAb 19D7). The reactivity of MAb 20G4 with CPV-2c was higher than its reactivities with CPV-2a and CPV-2b. These types of specificities of MAbs have not been reported previously. A mapping study by analysis of neutralization-resistant mutants showed that epitopes recognized by MAbs 21C3 and 19D7 belonged to antigenic site A. Substitution of the residues in site B and the other antigenic site influenced the epitope recognized by MAb 2G5. It was suggested that the epitope recognized by MAb 20G4 was related to antigenic site B. These MAbs are expected to be useful for the detection and classification of FPV subgroup isolates.

Differences in the evolutionary pattern of feline panleukopenia virus and canine parvovirus

Canine parvovirus (CPV) suddenly appeared in the late 1970s after which it showed continuous antigenic changes. Virological and molecular genetic analyses mainly focused on feline panleukopenia virus (FPLV) were conducted in this study because FPLV is the suspected ancestor of CPV; the way in which FPLV evolves may help to explain the emergence of CPV. Analysis of escape mutants against FPLV-specific monoclonal antibody showed that viruses possessing CPV-like properties were not easily detected in FPLV virus stocks. Phylogenetic analysis revealed that the nonstructural protein 1 (NS1) and capsid protein 2 (VP2) genes of FPLV changed with time. A similar tendency, however, was not observed in the FPLV VP2 proteins. In contrast, the topology of the phylogenetic tree of VP2 proteins of CPV basically concurred with that of the VP2 genes. Analysis of the ratio of nonsynonymous and synonymous substitutions revealed that synonymous substitutions exceeded nonsynonymous substitutions in both the NS1 and VP2 genes of FPLV, even when the analysis focused on specific regions in the VP2 gene that are known to be located on the capsid surface. Comparison of the CPV VP2 genes revealed that nonsynonymous substitution was found to dominate over synonymous substitution in one specific region in the VP2 gene. These results suggested that FPLV has changed mainly by random genetic drift. In contrast, after the appearance of CPV, changes in the CPV VP2 gene appear to be partly selected by certain positive selection forces. CPV and FPLV are known to be closely related viruses genetically and biologically, but the evolutionary mechanisms of the two viruses appeared to be different.

Detection and genomic analysis of canine parvovirus by the polymerase chain reaction

Prevalence of canine parvovirus type 2 (CPV-2) in Japanese dogs and genomic variations among the virus strains were examined. Two-step polymerase chain reaction with double-nested primer pairs designed in the NS and VP1/VP2 genes of CPV-2 was developed for the detection of the viral genome in faecal samples. A total of 74 samples obtained from diarrhoeal house dogs between 1993 and 1995 were tested by the PCR. The virus-positive rate was 54.1%, showing that CPV-2 is still involved in many cases of acute infectious diarrhoea in Japanese dogs. The VP1/VP2 gene of the positive samples was subjected to restriction fragment length polymorphism (RFLP) analysis and nucleotide sequencing. RFLP patterns of the samples were almost identical to those of one CPV-2 strain (TDKet-91-42) isolated in 1991, but different from those of the CPV-2 in the late 1970s and 1980s. The results suggest that a new genotype of CPV-2 appeared and spread among Japanese dogs in the early 1990s.

Differentiation of wild- and vaccine-type canine parvoviruses by PCR and restriction-enzyme analysis

The polymerase-chain reaction (PCR) and restriction-fragment-length-polymorphism (RFLP) analysis were used to differentiate the wild- and vaccine-type of canine parvovirus (CPV) in Japan. The entire coding region of the CPV genome was enzymatically amplified, and the PCR products of three wild strains and four vaccine strains were analysed using RFLP assay. Then, two polymorphic regions in the VP1/VP2 gene were selected to generate strain-specific RFLP patterns. By using four restriction enzymes, wild and vaccine strains were clearly differentiated; only two vaccine strains, probably of the same origin, were indistinguishable from each other. The wild strains retained strain-specific RFLP patterns throughout in vitro passage, and there was no diversity of RFLP patterns among the different lots of vaccine strains. A total of 21 recent field samples were tested, showing RFLP patterns identical to those of a wild strain isolated in 1991. These results suggest that the PCR-RFLP analysis is a practical and reliable method of differentiating wild- and vaccine-type CPVs.

Evolution of the feline-subgroup parvoviruses and the control of canine host range in vivo

A related group of parvoviruses infects members of many different carnivore families. Some of those viruses differ in host range or antigenic properties, but the true relationships are poorly understood. We examined 24 VP1/VP2 and 8 NS1 gene sequences from various parvovirus isolates to determine the phylogenetic relationships between viruses isolated from cats, dogs, Asiatic raccoon dogs, mink, raccoons, and foxes. There were about 1.3% pairwise sequence differences between the VP1/VP2 genes of viruses collected up to four decades apart. Viruses from cats, mink, foxes, and raccoons were not distinguished from each other phylogenetically, but the canine or Asiatic raccoon dog isolates formed a distinct clade. Characteristic antigenic, tissue culture host range, and other properties of the canine isolates have previously been shown to be determined by differences in the VP1/VP2 gene, and we show here that there are at least 10 nucleotide sequence differences which distinguish all canine isolates from any other virus. The VP1/VP2 gene sequences grouped roughly according to the time of virus isolation, and there were similar rates of sequence divergence among the canine isolates and those from the other species. A smaller number of differences were present in the NS1 gene sequences, but a similar phylogeny was revealed. Inoculation of mutants of a feline virus isolate into dogs showed that three or four CPV-specific differences in the VP1/VP2 gene controlled the in vivo canine host range.

Pathogenesis of feline panleukopenia virus and canine parvovirus

Feline panleukopenia virus (FPV) and canine parvovirus (CPV) are autonomous parvoviruses which infect cats or dogs, respectively. Both viruses cause an acute disease, with virus replicating for less than seven days before being cleared by the developing immune responses. The viruses have a broad tropism for mitotically active cells. In neonatal animals the viruses replicate in a large number of tissues, and FPV infection of the germinal epithelium of the cerebellum leads to cerebellar hypoplasia, while CPV may infect the hearts of neonatal pups, causing myocarditis. In older animals the virus replicates systemically, primarily in the primary and secondary lymphoid tissues, and also in the rapidly replicating cells of the small intestinal epithelial crypts. A transient panleukopenia or relative lymphopenia is often observed after FPV or CPV infection, respectively. Whether the reduction in cell numbers in vivo is due to virus replicating in and killing cells, or due to other indirect effects, is not known. However, FPV kills both erythroid and myeloid colony progenitors in in vitro bone marrow cultures, and it has been suggested that virus replication in the myeloid cells in vivo could lead to the reduced neutrophil levels seen after FPV infection of cats.

Detection by PCR of wild-type canine parvovirus which contaminates dog vaccines

A method for detecting wild-type canine parvovirus (CPV) strains which contaminate vaccines for dogs has been developed by PCR. PCR primers which distinguish vaccine strains from the most common, recent strains of wild-type CPV in many countries, including Japan and the United States, were developed. This PCR is based on the differences in nucleotide sequences which determine the two antigenic types of this virus. CPV vaccine strains derived from antigenically old-type virus prevalent in former times were not detected by PCR with differential primers. Detection sensitivity of PCR was 100- to 10,000-fold higher than that of the culture method in Crandell feline kidney cells.

Antigenic and genomic variabilities among recently prevalent parvoviruses of canine and feline origin in Japan

Canine parvovirus type 2 (CPV-2) and feline panleukopenia (FLP) virus (FPLV) are well known and ubiquitous diarrhea-causing pantropic viruses. A "new" antigenic variant of CPV-2 (designated as CPV-2a) has been also prevalent among dogs in Japan. In the present study, 24 canine and 8 feline isolates collected during 1987-1991 were compared with 17 CPV-2 or CPV-2a and 7 FPLV strains that had been characterized previously. Genomic properties were determined by the restriction cleavage patterns of amplified genes encoding the capsid proteins VP1 and VP2 by the polymerase chain reaction. Antigenic properties were determined by hemagglutination-inhibition assay with monoclonal antibodies against an FPLV strain. Growth characteristics in feline CRFK and canine MDCK cells were also examined. Genomic and antigenic properties of the canine isolates were relatively invariable with one exceptional isolate, C27, which was recovered from a typical clinical case of parvovirus infection but possessed properties similar to FPLV rather than CPV-2 and CPV-2a. All isolates from FPL cases possessed the same genomic and antigenic properties as those of reference FPLVs isolated in the 1970s, but three of five strains isolated from the feces of clinically healthy cats were likely to be of canine origin because they possessed very similar properties to CPV-2a. Although species-specificity of these novel isolates could not be determined definitely, the results indicate a possibility that transmission of parvovirus has occurred between these two animal species.

Multiple amino acids in the capsid structure of canine parvovirus coordinately determine the canine host range and specific antigenic and hemagglutination properties

Canine parvovirus (CPV) and feline panleukopenia virus (FPV) are over 98% similar in DNA sequence but have specific host range, antigenic, and hemagglutination (HA) properties which were located within the capsid protein gene. In vitro mutagenesis and recombination were used to prepare 16 different recombinant genomic clones, and viruses derived from those clones were analyzed for their in vitro host range, antigenic, and HA properties. The region of CPV from 59 to 91 map units determined the ability to replicate in canine cells. A complex series of interactions was observed among the individual sequence differences between 59 and 73 map units. The canine host range required that VP2 amino acids (aa) 93 and 323 both be the CPV sequence, and those two CPV sequences introduced alone into FPV greatly increased viral replication in canine cells. Changing any one of aa 93, 103, or 323 of CPV to the FPV sequence either greatly decreased replication in canine cells or resulted in an inviable plasmid. The Asn-Lys difference of aa 93 alone was responsible for the CPV-specific epitope recognized by monoclonal antibodies. An FPV-specific epitope was affected by aa 323. Amino acids 323 and 375 together determined the pH dependence of HA. Amino acids involved in the various specific properties were all around the threefold spikes of the viral particle.

Rapid antigenic-type replacement and DNA sequence evolution of canine parvovirus

Analysis of canine parvovirus (CPV) isolates with a panel of monoclonal antibodies showed that after 1986, most viruses isolated from dogs in many parts of the United States differed antigenically from the viruses isolated prior to that date. The new antigenic type (designated CPV type 2b) has largely replaced the previous antigenic type (CPV type 2a) among virus isolates from the United States. This represents the second occurrence of a new antigenic type of this DNA virus since its emergence in 1978, as the original CPV type (CPV type 2) had previously been replaced between 1979 and 1981 by the CPV type 2a strain. DNA sequence comparisons showed that CPV types 2b and 2a differed by as few as two nonsynonymous (amino acid-changing) nucleotide substitutions in the VP-1 and VP-2 capsid protein genes. One mutation, resulting in an Asn-Asp difference at residue 426 in the VP-2 sequence, was shown by comparison with a neutralization-escape mutant selected with a non-CPV type 2b-reactive monoclonal antibody to determine the antigenic change. The mutation selected by that monoclonal antibody, a His-Tyr difference in VP-2 amino acid 222, was immediately adjacent to residue 426 in the three-dimensional structure of the CPV capsid. The CPV type 2b isolates are phylogenetically closely related to the CPV type 2a isolates and are probably derived from a common ancestor. Phylogenetic analysis showed a progressive evolution away from the original CPV type. This pattern of viral evolution appears most similar to that seen in some influenza A viruses.

Antigenic and genomic comparisons of some feline parvovirus subspecies strains

Fourteen feline parvovirus (FPV) strains isolated from cats, mink and dogs were comparatively examined on their antigenic and genetic diversities by using monoclonal antibodies against feline panleukopenia virus (FPLV) and restriction enzyme analysis of viral DNA. Mink enteritis virus (MEV) strains recently isolated in the northeastern area of the People's Republic of China were found to possess more similar antigenic and genetic properties to the antigenic variant virus of canine parvovirus (CPV) ("new" antigenic type CPV), than to FPLV strains and MEV Abashiri strain of Japan. A feline isolate detected in normal cat feces was considered to be rather CPV because of its antigenic and genetic characteristics. An early isolate of "new" antigenic type CPV strains showed a similar cleavage pattern to those of "old" antigenic type CPV strains when digested with HinfI. The results including some features above-mentioned suggest the presence of antigenic heterogeneities and genomic polymorphisms among FPV subspecies viruses.

Characterization of newly isolated rat viruses from asymptomatic laboratory rats

We surveyed the extent of rat virus (RV) infections in Japan and isolated new RV strains. The new strains were similar to the prototype RV strain in stability, morphology in electron microscopy and structural polypeptides. There were slight differences, however, in hemagglutination activity and the antigenicity.

Emergence, natural history, and variation of canine, mink, and feline parvoviruses

This chapter discusses the emergence of canine parvovirus (CPV), the evidence concerning the previous emergence of mink enteritis virus (MEV) as the cause of a new disease in minks in the 1940s, and the mechanisms that determine the host ranges and other specific properties of the viruses of cats, minks, and dogs. The viruses are classified as the feline parvovirus subgroup of the genus Parvovirus, within the family Parvoviridae. Feline panleukopenia virus (FPV), MEV, and CPV are classified as “host range variants.” In addition to the viruses of cats, minks, and dogs, similar viruses naturally infect many species within the families Felidae, Canidae, Procyonidae, Mustelidae, and possibly the Viverridae. The differences in virulence for minks observed after inoculation of MEV or FPV suggests that there are subtle differences between FPV and MEV that have yet to be defined. Genetic mapping studies indicate that only three or four sequence differences between the FPV and CPV-2 isolates within the VP-1 lVP-2 gene determine all of the specific properties of CPV that have been defined: the pH dependence of hemagglutination, the CPV-specific epitope, and the host range for canine cells and dogs.