Canine parvoviral disease: experimental reproduction of the enteric form with a parvovirus isolated from a case of myocarditis

Development of an accurate and rapid method for whole genome characterization of canine parvovirus

Canine parvovirus is a highly contagious pathogen affecting domestic dogs and other carnivores globally. Monitoring CPV through continuous genomic surveillance is crucial for mapping variability and developing effective control measures. Here, we developed a method using multiplex-PCR-next-generation sequencing to obtain full-length CPV genomes directly from clinical samples. This approach utilizes tiling and tailed amplicons to amplify overlapping fragments of roughly 250 base pairs. This enables the creation of Illumina libraries by conducting two PCR reaction runs. We tested the assay in 10 fecal samples from dogs diagnosed with CPV and one CPV-2 vaccine strain. Furthermore, we applied it to a feline sample previously diagnosed with the feline panleukopenia virus. The assay provided 100 % genome coverage and high sequencing depth across all 12 samples. It successfully provided the sequence of the coding regions and the left and right non-translated regions, including tandem and terminal repeats. The assay effectively amplified viral variants from divergent evolutionary groups, including the antigenic variants (2a, 2b, and 2c) and the ancestral CPV-2 strain included in vaccine formulations. Moreover, it successfully amplified the entire genome of the feline panleukopenia virus found in cat feces. This method is cost-effective, time-efficient, and does not require lab expertise in Illumina library preparation. The multiplex-PCR-next-generation methodology facilitates large-scale genomic sequencing, expanding the limited number of complete genomes currently available in databases and enabling real-time genomic surveillance. Furthermore, the method helps identify and track emerging CPV viral variants, facilitating molecular epidemiology and control. Adopting this approach can enhance our understanding of the evolution and genetic diversity of Protoparvovirus carnivoran1.

Isolation, cloning and analysis of parvovirus-specific canine antibodies from peripheral blood B cells

B-cell cloning methods enable the analysis of antibody responses against target antigens and can be used to reveal the host antibody repertoire, antigenic sites (epitopes), and details of protective immunity against pathogens. Here, we describe improved methods for isolation of canine peripheral blood B cells producing antibodies against canine parvovirus (CPV) capsids by fluorescence-activated cell sorting, followed by cell cloning. We cultured sorted B cells from an immunized dog in vitro and screened for CPV-specific antibody production. Updated canine-specific primer sets were used to amplify and clone the heavy and light chain immunoglobulin sequences directly from the B cells by reverse transcription and PCR. Monoclonal canine IgGs were produced by cloning heavy and light chain sequences into antibody expression vectors, which were screened for CPV binding. Three different canine monoclonal antibodies were analyzed, including two that shared the same heavy chain, and one that had distinct heavy and light chains. The antibodies showed broad binding to CPV variants, and epitopes were mapped to antigenic sites on the capsid. The methods described here are applicable for the isolation of canine B cells and monoclonal antibodies against many antigens.

Cryo EM structures map a post vaccination polyclonal antibody response to canine parvovirus

Canine parvovirus (CPV) is an important pathogen that emerged by cross-species transmission to cause severe disease in dogs. To understand the host immune response to vaccination, sera from dogs immunized with parvovirus are obtained, the polyclonal antibodies are purified and used to solve the high resolution cryo EM structures of the polyclonal Fab-virus complexes. We use a custom software, Icosahedral Subparticle Extraction and Correlated Classification (ISECC) to perform subparticle analysis and reconstruct polyclonal Fab-virus complexes from two different dogs eight and twelve weeks post vaccination. In the resulting polyclonal Fab-virus complexes there are a total of five distinct Fabs identified. In both cases, any of the five antibodies identified would interfere with receptor binding. This polyclonal mapping approach identifies a specific, limited immune response to the live vaccine virus and allows us to investigate the binding of multiple different antibodies or ligands to virus capsids.

A history of canine parvovirus in Australia: what can we learn?

Canine parvovirus (CPV) has been reported throughout the world since the late 1970s. Published information was reviewed to draw insights into the epidemiology, pathogenesis, diagnosis, treatment and outcomes of CPV disease in Australia and the role of scientific research on CPV occurrence, with key research discoveries and knowledge gaps identified. Australian researchers contributed substantially to early findings, including the first reported cases of parvoviral myocarditis, investigations into disease aetiopathogenesis, host and environmental risk factors and links between CPV and feline panleukopenia. Two of the world's first CPV serological surveys were conducted in Australia and a 1980 national veterinary survey of Australian and New Zealand dogs revealed 6824 suspected CPV cases and 1058 deaths. In 2010, an Australian national disease surveillance system was launched; 4940 CPV cases were reported between 2009 and 2014, although underreporting was likely. A 2017 study estimated national incidence to be 4.12 cases per 1000 dogs, and an annual case load of 20,110 based on 4219 CPV case reports in a survey of all Australian veterinary clinics, with a 23.5% response rate. CPV disease risk factors identified included socioeconomic disadvantage, geographical location (rural/remote), season (summer) and rainfall (recent rain and longer dry periods both increasing risk). Age <16 weeks was identified as a risk factor for vaccination failure. Important knowledge gaps exist regarding national canine and feline demographic and CPV case data, vaccination coverage and population immunity, CPV transmission between owned dogs and other carnivore populations in Australia and the most effective methods to control epizootics.

Limited Intrahost Diversity and Background Evolution Accompany 40 Years of Canine Parvovirus Host Adaptation and Spread

Canine parvovirus (CPV) is a highly successful pathogen that has sustained pandemic circulation in dogs for more than 40 years. Here, integrating full-genome and deep-sequencing analyses, structural information, and in vitro experimentation, we describe the macro- and microscale features that accompany CPV's evolutionary success. Despite 40 years of viral evolution, all CPV variants are more than ∼99% identical in nucleotide sequence, with only a limited number (<40) of substitutions becoming fixed or widespread during this time. Notably, most substitutions in the major capsid protein (VP2) gene are nonsynonymous, altering amino acid residues that fall within, or adjacent to, the overlapping receptor footprint or antigenic regions, suggesting that natural selection has channeled much of CPV evolution. Among the limited number of variable sites, CPV genomes exhibit complex patterns of variation that include parallel evolution, reversion, and recombination, compromising phylogenetic inference. At the intrahost level, deep sequencing of viral DNA in original clinical samples from dogs and other host species sampled between 1978 and 2018 revealed few subconsensus single nucleotide variants (SNVs) above ∼0.5%, and experimental passages demonstrate that substantial preexisting genetic variation is not necessarily required for rapid host receptor-driven adaptation. Together, these findings suggest that although CPV is capable of rapid host adaptation, a relatively low mutation rate, pleiotropy, and/or a lack of selective challenges since its initial emergence have inhibited the long-term accumulation of genetic diversity. Hence, continuously high levels of inter- and intrahost diversity are not necessarily required for virus host adaptation.IMPORTANCE Rapid mutation rates and correspondingly high levels of intra- and interhost diversity are often cited as key features of viruses with the capacity for emergence and sustained transmission in a new host species. However, most of this information comes from studies of RNA viruses, with relatively little known about evolutionary processes in viruses with single-stranded DNA (ssDNA) genomes. Here, we provide a unique model of virus evolution, integrating both long-term global-scale and short-term intrahost evolutionary processes of an ssDNA virus that emerged to cause a pandemic in a new host animal. Our analysis reveals that successful host jumping and sustained transmission does not necessarily depend on a high level of intrahost diversity nor result in the continued accumulation of high levels of long-term evolution change. These findings indicate that all aspects of the biology and ecology of a virus are relevant when considering their adaptability.

Parvovirus Infection Is Associated With Myocarditis and Myocardial Fibrosis in Young Dogs

Perinatal parvoviral infection causes necrotizing myocarditis in puppies, which results in acute high mortality or progressive cardiac injury. While widespread vaccination has dramatically curtailed the epidemic of canine parvoviral myocarditis, we hypothesized that canine parvovirus 2 (CPV-2) myocardial infection is an underrecognized cause of myocarditis, cardiac damage, and/or repair by fibrosis in young dogs. In this retrospective study, DNA was extracted from formalin-fixed, paraffin-embedded tissues from 40 cases and 41 control dogs under 2 years of age from 2007 to 2015. Cases had a diagnosis of myocardial necrosis, inflammation, or fibrosis, while age-matched controls lacked myocardial lesions. Conventional polymerase chain reaction (PCR) and sequencing targeting the VP1 to VP2 region detected CPV-2 in 12 of 40 cases (30%; 95% confidence interval [CI], 18%-45%) and 2 of 41 controls (5%; 95% CI, 0.1%-16%). Detection of CPV-2 DNA in the myocardium was significantly associated with myocardial lesions ( P = .003). Reverse transcription quantitative PCR amplifying VP2 identified viral messenger RNA in 12 of 12 PCR-positive cases and 2 of 2 controls. PCR results were confirmed by in situ hybridization, which identified parvoviral DNA in cardiomyocytes and occasionally macrophages of juvenile and young adult dogs (median age 61 days). Myocardial CPV-2 was identified in juveniles with minimal myocarditis and CPV-2 enteritis, which may indicate a longer window of cardiac susceptibility to myocarditis than previously reported. CPV-2 was also detected in dogs with severe myocardial fibrosis with in situ hybridization signal localized to cardiomyocytes, suggesting prior myocardial damage by CPV-2. Despite the frequency of vaccination, these findings suggest that CPV-2 remains an important cause of myocardial damage in dogs.

Feline Panleukopenia Virus Is Not Associated With Myocarditis or Endomyocardial Restrictive Cardiomyopathy in Cats

Canine parvovirus-2 (CPV-2) is nearly indistinguishable from feline panleukopenia virus (FPV) and is a well-known cause of viral myocarditis in young puppies; however, it is not known whether either FPV or CPV-2 naturally infects feline cardiomyocytes and causes myocarditis. Endomyocarditis (EMC) and left ventricular endomyocardial fibrosis (LVEF), clinically known as "endomyocardial restrictive cardiomyopathy," are important feline heart diseases suspected to have an infectious etiology. A continuum is suggested with EMC representing the acute reaction to an unknown infectious agent and LVEF the chronic manifestation of repair. The purpose of this study was to determine (1) whether there is natural parvovirus infection of the feline myocardium and (2) whether parvoviral infection is associated with feline EMC and/or LVEF. In a retrospective study, polymerase chain reaction and sequencing for the parvovirus VP1/2 gene was performed on archived heart tissue from cats with endomyocardial disease and controls. Similar methods were used prospectively on myocardial tissues from shelter-source kittens. Although 8 of 36 (22%; 95% confidence interval [CI], 11%-40%) shelter kittens had parvoviral DNA in myocardial tissue, VP1/2 DNA was not detected in 33 adult cases or 34 controls (95% CI, 0% to ∼11%). These findings were confirmed by in situ hybridization: adult cats did not have detectable parvovirus DNA, although rare intranuclear signal was confirmed in 7 of 8 shelter-source kittens. In kittens, parvovirus was not significantly associated with myocarditis, and in situ hybridization signal did not colocalize with inflammation. Although infection of cardiomyocytes was demonstrated in kittens, these data do not support a role for parvovirus in EMC-LVEF.

The widely distributed hard tick, Haemaphysalis longicornis, can retain canine parvovirus, but not be infected in laboratory condition

ABSTRACT. Ticks are known to transmit various pathogens, radically threatening humans and animals. Despite the close contact between ticks and viruses, our understanding on their interaction and biology is still lacking. The aim of this study was to experimentally assess the interaction between canine parvovirus (CPV) and a widely distributed hard tick, Haemaphysalis longicornis, in laboratory condition. After inoculation of CPV into the hemocoel of the ticks, polymerase chain reaction assay revealed that CPV persisted in inoculated unfed adult female ticks for 28 days. Canine parvovirus was recovered from the inoculated ticks using a cell culture, indicating that the virus retained intact in the ticks after inoculation, but significant positive reaction indicating virus infection was not detected in the tick organs by immunofluorescence antibody test using a monoclonal antibody. In the case of ticks inoculated with feline leukemia virus, the virus had shorter persistence in the ticks compared to CPV. These findings provide significant important information on the characteristic interaction of tick with non-tick-borne virus.

Canine parvovirus: current perspective

Canine parvovirus 2 (CPV-2) has been considered to be an important pathogen of domestic and wild canids and has spread worldwide since its emergence in 1978. It has been reported from Asia, Australia, New Zealand, the Americas and Europe. Two distinct parvoviruses are now known to infect dogs-the pathogenic CPV-2 and CPV-1 or the minute virus of canine (MVC). CPV-2, the causative agent of acute hemorrhagic enteritis and myocarditis in dogs, is one of the most important pathogenic viruses with high morbidity (100%) and frequent mortality up to 10% in adult dogs and 91% in pups. The disease condition has been complicated further due to emergence of a number of variants namely CPV-2a, CPV-2b and CPV-2c over the years and involvement of domestic and wild canines. There are a number of different serological and molecular tests available for prompt, specific and accurate diagnosis of the disease. Further, both live attenuated and inactivated vaccines are available to control the disease in animals. Besides, new generation vaccines namely recombinant vaccine, peptide vaccine and DNA vaccine are in different stages of development and offer hope for better management of the disease in canines. However, new generation vaccines have not been issued license to be used in the field condition. Again, the presence of maternal antibodies often interferes with the active immunization with live attenuated vaccine and there always exists a window of susceptibility in spite of following proper immunization regimen. Lastly, judicious use of the vaccines in pet dogs, stray dogs and wild canids keeping in mind the new variants of the CPV-2 along with the proper sanitation and disinfection practices must be implemented for the successful control the disease.

An Annotated Historical Account of Canine Parvovirus

A brief annotated history of canine parvovirus-type 2 (CPV-2) and its variants is summarized with emphasis on the most significant contributions of individuals involved in the initial recognition of CPV-2 and subsequent discoveries that have advanced our knowledge of the nature and evolution of this novel canine virus. Time has obscured the observations of many veterinary clinicians and researchers throughout the world who sensed the presence of a new disease when CPV-2 first made its appearance in 1978 and then, within 1-2 years, spread worldwide. Since 1979, nearly 600 articles, papers, numerous text chapters and monographs have been published on the subject of CPV-2. The early history is well known by veterinary infectious diseases specialists and noteworthy publications are recorded on the National Library of Medicine (USA) website, PubMed and in review articles. Because of the great number of publications, it is not practicable to cite them individually; however, reference is made to certain individuals, reviews and selected papers that I consider particularly relevant to the history of progress in the understanding of CPV-2 and the disease it causes. The clinical disease caused by CPV-2 and its variants, the immune response to infection or vaccines, host range and the development of practical diagnostic assays are noted in historical context. The basic biological properties and the physical, molecular and antigenic structure of CPV-2 and its variants are also discussed briefly. Finally, key players who have contributed to the antigenic and DNA sequence (evolutionary) relationships between CPV-2 and the other autonomous parvoviruses of carnivores are noted and hypotheses regarding the origin and evolution of CPV-2 and its variants are mentioned.

Feline host range of canine parvovirus: recent emergence of new antigenic types in cats

Since the emergence of Canine parvovirus (CPV-2) in the late 1970s, CPV-2 has evolved consecutively new antigenic types, CPV-2a and 2b. Although CPV-2 did not have a feline host range, CPV-2a and 2b appear to have gained the ability to replicate in cats. Recent investigations demonstrate the prevalence of CPV-2a and 2b infection in a wide range of cat populations. We illustrate the pathogenic potential of CPV in cats and assess the risk caused by CPV variants.

Characterization of mouse parvovirus infection by in situ hybridization

Infection of young adult BALB/cByJ mice with mouse parvovirus-1, a newly recognized, lymphocytotropic, nonpathogenic parvovirus, was examined by in situ hybridization. Virus appeared to enter through the small intestine and was disseminated to the liver and lymphoid tissues. Strand-specific probes detected virion DNA in a consistently larger number of cells than replicative forms of viral DNA and/or viral mRNA. The number of signal-positive cells in the intestinal mucosa, lymph nodes, spleen, and thymus increased through day 10 after oral inoculation but decreased after seroconversion. Positive cells were still detected, however, in peripheral lymphoid tissues of mice examined at 9 weeks postinoculation. The results underscore the need to assess potential effects of persistent mouse parvovirus-1 infection on immune function in mice.

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.

Infection of peripancreatic lymph nodes but not islets precedes Kilham rat virus-induced diabetes in BB/Wor rats

A parvovirus serologically identified as Kilham rat virus (KRV) reproducibly induces acute type I diabetes in diabetes-resistant BB/Wor rats. The tissue tropism of KRV was investigated by in situ hybridization with a digoxigenin-labelled plasmid DNA probe containing approximately 1.6 kb of the genome of the UMass isolate of KRV. Partial sequencing of the KRV probe revealed high levels of homology to the sequence of minute virus of mice (89%) and to the sequence of H1 (99%), a parvovirus capable of infecting rats and humans. Of the 444 bases sequenced, 440 were shared by H1. KRV mRNA and DNA were readily detected in lymphoid tissues 5 days postinfection but were seldom seen in the pancreas. High levels of viral nucleic acids were observed in the thymus, spleen, and peripancreatic and cervical lymph nodes. The low levels of infection observed in the pancreas involved essentially only endothelial and interstitial cells. Beta cells of the pancreas were not infected with KRV. These findings suggest that widespread infection of peripancreatic and other lymphoid tissues but not pancreatic beta cells by KRV triggers autoimmune diabetes by perturbing the immune system of genetically predisposed BB/Wor rats.

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.

Immunodeficient dwarfism in dogs: a model for neuroimmunomodulation

This paper discusses the use of dogs as experimental models for neuroimmunomodulation and compares immunodeficient dwarfism in dogs to that in rodents. Immunodeficient dwarfism in dogs is reviewed including description of the clinical syndrome, immunologic characteristics, neuroendocrine abnormalities, thymus histopathology, and therapy.

Possible association of thymus dysfunction with fading syndromes in puppies and kittens

"Wasting" or "fading" syndromes are common causes of puppy and kitten mortality. Numerous infectious and toxic, metabolic, or nutritional factors could potentially be responsible for wasting and death in young animals. Evidence has been presented that infectious canine hepatitis virus infection, beta-hemolytic streptococcus infection, and feline infectious peritonitis virus infection are responsible for a significant number of deaths due to wasting syndrome. However, many cases of wasting syndrome cannot be attributed to infectious agents or other specific etiologies. The thymus gland warrants special attention when one is evaluating an animal with a wasting syndrome because it is known that, in some species, neonatal thymectomy results in wasting and death. Unfortunately, most reports describing fading syndromes in puppies and kittens do not mention the gross or histologic appearance of the thymus gland at postmortem examination. When examining the thymus gland, one must keep in mind that the thymus may be hypoplastic owing to a congenital or genetic defect in its structure and function or it may be atrophic secondary to whatever is causing the fading syndrome. If a thorough history, clinical examination, and/or postmortem examination do not reveal a cause for the fading syndrome, then defective thymus function should be considered as a possible causative or contributing factor to the fading syndrome. In these cases, therapy designed to replace or improve the defective thymus function should be considered. At least one form of wasting syndrome in puppies (immunodeficient dwarfism) has been found to respond to short-term therapy with a thymus hormone (thymosin fraction 5) or with bovine growth hormone (which is thymotropic) in limited clinical trials. It is possible that other forms of wasting or fading syndromes would also respond to therapy with thymus hormone or growth hormone. Certain thymus hormones (thymopoietin pentapeptide, thymosin alpha 1, facteur thymique serique, and rabbit thymus acetone powder) and bovine growth hormone are commercially available. Before initiating therapy, one should consider that if the cause of the wasting syndrome is genetic, then successful treatment may perpetuate a genetic defect. More research (both basic and clinical) is needed to determine the role of thymus gland dysfunction in fading syndromes of puppies and kittens and if therapy with one or several of the thymus hormones or with growth hormone could reverse the symptoms of wasting.

Pathogenesis of canine parvovirus enteritis: sequential virus distribution and passive immunization studies

After oral inoculation, the sequential distribution of canine parvovirus was studied in 14 nine-week-old seronegative beagle dogs. Two or three dogs were necropsied on days 1 through 6 after inoculation. Tissues were collected for virus isolation, immunofluorescence testing, and light microscopy. Virus was isolated from, and fluorescent cells were seen in the tonsil, retropharyngeal and mesenteric lymph nodes one and two days after inoculation. Virus infection of systemic and intestinal lymphoid tissues occurred as early as three days after inoculation and was associated with viremia. Intestinal epithelial infection was first seen four days after oral inoculation. All dogs were viremic before intestinal epithelial infection was found. Fecal virus excretion first occurred four days after oral virus inoculation. Intestinal virus infection and lesions became progressively more severe between four and six days after inoculation. The severity of intestinal lesions was variable and related to the severity of systemic lymphoid tissue lesions and the magnitude and duration of viremia. Four littermates of virus-infected dogs were passively immunized against canine parvovirus with convalescent canine serum 24 hours after oral virus inoculation. Neither clinical signs, lymphopenia, nor fecal virus excretion occurred in passively immunized dogs. Intestinal epithelial infection was not demonstrable by immunofluorescence testing when passively immunized dogs were necropsied four, five, and six days after virus inoculation.

Pathogenesis of canine parvovirus enteritis: the importance of viremia

The clinical signs, hematologic changes, serum and fecal virus titers, specific antibody production and the occurrence of histologic lesions were studied in 22 nine-week-old seronegative beagle dogs inoculated by the oral and intravenous route with canine parvovirus. Approximately 30% of the dogs had clinical signs of pyrexia, depression, vomiting, and diarrhea irrespective of the route of inoculation. Events in the dogs inoculated intravenously preceded those in dogs inoculated orally by approximately two days. Only one dog died. Lymphopenia was the most consistent hematologic change. Viremia always preceded the initiation of fecal virus shedding. Viral titers in the serum and feces were significantly greater in symptomatic dogs compared to asymptomatic dogs. Termination of the plasma viremia coincided with the onset of the humoral immune response, but viremia persisted one day longer in symptomatic dogs. The severity of lymphoid tissue and intestinal infection, assessed by tissue immunofluorescence and histology, was also greater in symptomatic dogs. The severity of intestinal disease was highly correlated with the magnitude and duration of viremia.

Experimental viral myocarditis: parvoviral infection of neonatal pups

Myocarditis was produced in seronegative five-day-old pups by oral and by intraperitoneal inoculation of canine parvovirus. The disease was subclinical. Histologic lesions were compatible with, but less extensive than, those seen in naturally occurring canine parvoviral myocarditis. In pups necropsied 23 days after inoculation, scattered cardiac myocytes contained intranuclear inclusion bodies, and virus-infected myocytes were demonstrated by immunofluorescence. Degeneration and loss of cardiac myocytes usually was not associated with a cellular infiltrate. At 51 days after inoculation, the myocardium contained an extensive lymphocytic infiltrate which was sometimes associated with fragmented myocytes, and was often contiguous with areas of interstitial fibrosis. At 108 days after inoculation, inflammatory lesions had regressed, and there were multifocal areas of myocardial fibrosis.

Experimentally induced severe canine parvoviral enteritis

Severe enteritis was produced in recently weaned, 8-week old pups 3 to 9 days after being given parvovirus by mouth. The most severe manifestations of disease were observed 7 days after infection, when one pup died. Viraemia was detected on days 4 and 5 and a severe leucopenia was present 6 to 8 days after infection. Antibody was demonstrated in serum 4 days after infection, high titres being present 3 days later. Sequential pathological studies revealed necrosis of Peyer's patches on day 3. Between days 5 and 7 typical lesions of the disease became widespread with necrosis of tonsil and thymus being prominent. By the fifth day after infection viral inclusion bodies were numerous. Virus isolation from tissues was greatest at this stage and had diminished by the seventh day. Although tissue repair was well advanced by the tenth day thymic necrosis remained prominent and villous atrophy was still present on day 13. Based on these findings a possible pathogenesis is discussed.

Maternal antibody, vaccination and reproductive failure in dogs with parvovirus infection

The maternal antibody (MAb) titre to canine parvovirus (CPV) was determined on consecutive serums from 39 puppies in 7 litters. Vaccination with inactivated CPV was performed at a variety of ages and the response of the puppies determined. Transfer of MAb was demonstrated in 71% (5/7) of the litters and persisted for up to 10 weeks in some litters. MAb titres of greater than 20 precluded a vaccination response by puppies. Sixty- one per cent (8/13) of puppies responded to vaccination when the MAb titre was less than 20. However, no anamestic response occurred and in some cases a decrease in antibody titre was observed following a second vaccination. During an outbreak of canine parvovirus enteritis (CPE) in the kennel, 33 puppies developed clinical signs of enteritis. Of these puppies 85% (28) had MAb titres of less than 80 at the onset of clinical signs. Fifty per cent (4/8) of the puppies which responded to vaccination developed CPE, whereas 100% (5/5) of those that did not respond to vaccination developed CPE. The results indicate that MAb may persist for up to 10 weeks and puppies with MAb in the titre range greater than 20 to less than 80 do not respond to vaccination but are still susceptible to infection. It is also apparent that a significant minority of puppies with MAb less than 20 do not respond to vaccination. An examination of the breeding records of the kennel for the 7 year period 1973-1981 demonstrated a sudden decrease in reproductive efficiency during and subsequent to 1978. This coincided with the recognition of cases of CPV infection in the kennel. It is suggested that further investigation is required into the possible role of CPV in reproductive failure.