Experimental viral myocarditis: parvoviral infection of neonatal pups

Case report: Long-term survival in puppies assessed with echocardiography, electrocardiography and cardiac troponin I after acute death in littermates due to parvoviral myocarditis

Positive clinical outcomes of a group of surviving puppies from a litter affected by parvoviral myocarditis are detailed in this case report. Past reports focus on the negative outcomes of littermates of puppies who have died of parvoviral myocarditis. In this case, two puppies in a shelter setting, from a litter exposed to parvovirus, died suddenly with parvoviral myocarditis diagnosed at necropsy. The other seven puppies were screened for cardiac health with echocardiogram, electrocardiogram, and cardiac troponin I prior to adoption. All seven puppies had normal echocardiograms, electrocardiograms, and normal initial and recheck cardiac troponin I results. At recheck 2 years after the initial round of testing, two of the puppies were screened and continue to have normal cardiac diagnostics. All seven dogs are alive and thriving at 5 years old in homes with adopters who were given a complete medical history on the dogs prior to adoption. In summary, the outcomes for puppies in litters affected by parvoviral myocarditis are variable but they do not have to be grave. The use of cardiac diagnostics including echocardiogram, electrocardiogram and cardiac troponin I may serve as a prognostic basis for assessing the potential outcomes for the surviving puppies in affected litters.

Small but mighty: old and new parvoviruses of veterinary significance

In line with the Latin expression "sed parva forti" meaning "small but mighty," the family Parvoviridae contains many of the smallest known viruses, some of which result in fatal or debilitating infections. In recent years, advances in metagenomic viral discovery techniques have dramatically increased the identification of novel parvoviruses in both diseased and healthy individuals. While some of these discoveries have solved etiologic mysteries of well-described diseases in animals, many of the newly discovered parvoviruses appear to cause mild or no disease, or disease associations remain to be established. With the increased use of animal parvoviruses as vectors for gene therapy and oncolytic treatments in humans, it becomes all the more important to understand the diversity, pathogenic potential, and evolution of this diverse family of viruses. In this review, we discuss parvoviruses infecting vertebrate animals, with a special focus on pathogens of veterinary significance and viruses discovered within the last four years.

Systolic dysfunction by two-dimensional speckle tracking echocardiography in dogs with parvoviral enteritis

INTRODUCTION/OBJECTIVES

Parvoviral enteritis (PVE) can cause either primary or secondary myocardial injury; the latter is associated with systemic inflammatory response syndrome and sepsis. Strain (St) and strain rate (SR) are relatively new speckle tracking echocardiographic (STE) variables used to assess myocardial function and are less influenced by preload and volume status than are conventional variables. The aim of this study was to evaluate systolic function in dogs with PVE using two-dimensional STE.

ANIMALS

Forty-five client-owned dogs were included.

MATERIALS AND METHODS

Dogs were classified into four groups: healthy (n = 9), PVE-mild (n = 15), PVE-severe (n = 13) and PVE-died (n = 8). Left ventricular global and segmental myocardial St and SR were assessed in radial, circumferential and longitudinal axes in the right parasternal transverse and apical 4-chamber views. In the circumferential and longitudinal axes, the value of each segment was determined separately at the endocardial and epicardial levels.

RESULTS

Compared to healthy animals, all dogs with PVE showed significantly impaired St and SR values, mainly for PVE-severe and PVE-died groups. Moreover, the lowest SR value was observed in the circumferential axis at the mid-septal epicardial segment in the PVE-died group. For this variable, a cut-off value of 0.95 s^-1 demonstrated 100% sensitivity and specificity for distinguishing between PVE-severe and PVE-died groups.

CONCLUSIONS

In the present study, all dogs with PVE developed systolic dysfunction, which was more severe in non-survivors. Assessment of St and SR in dogs with PVE might be clinically useful for evaluating haemodynamic status and developing suitable therapeutic strategies to improve prognosis.

Clinical presentation, cardiovascular findings, etiology, and outcome of myocarditis in dogs: 64 cases with presumptive antemortem diagnosis (26 confirmed postmortem) and 137 cases with postmortem diagnosis only (2004-2017)

INTRODUCTION

This study describes presentation, cardiovascular abnormalities, etiology, and outcome of canine myocarditis in geographic areas not endemic for Trypanosoma or Leishmania.

ANIMALS

Sixty-four (presumed antemortem diagnosis) and 137 (postmortem diagnosis only) client-owned dogs at two tertiary care facilities were included.

MATERIALS AND METHODS

Medical records of dogs with clinical or histopathological diagnosis of myocarditis were reviewed retrospectively.

RESULTS

Common examination findings in dogs with a presumed antemortem diagnosis included fever (21%) and heart murmur (19%). Median cardiac troponin I was 12.2 ng/mL (range: 0.2-808.0 ng/mL), and troponin exceeded 1.0 ng/mL in 26 of 29 (90%) dogs. Ventricular ectopy was the most common arrhythmia (54%), whereas decreased left ventricular systolic function was the most common echocardiographic abnormality (56%). An infectious etiology was diagnosed in 35 of 64 (55%) dogs. Confirmed infectious etiologies included bacterial sepsis (n = 9) or extension of endocarditis (3), toxoplasmosis or neosporosis (3), parvovirus (2), and one case each of bartonellosis, trypanosomiasis, leptospirosis, and dirofilariasis. Median survival time was 4 days (range: 0-828 days) for all dogs vs. 82 days for dogs who survived at least 2 weeks after diagnosis. Presence of pericardial effusion or azotemia was a significant predictor of non-survival. The most common inflammatory infiltrate on histopathology was neutrophilic (47%), and 20 of 137 (14.5%) dogs had concurrent bacterial endocarditis on postmortem.

CONCLUSIONS

Bacterial infection was the most common confirmed etiology of myocarditis in this study. Prognosis for canine myocarditis is guarded and similar to that reported for infective endocarditis. Criteria for the antemortem diagnosis of canine myocarditis are suggested.

Review of canine dilated cardiomyopathy in the wake of diet-associated concerns

Dilated cardiomyopathy (DCM) has been in the literature and news because of the recent opinion-based journal articles and public releases by regulatory agencies. DCM is commonly associated with a genetic predisposition in certain dog breeds and can also occur secondary to other diseases and nutritional deficiencies. Recent communications in veterinary journals have discussed a potential relationship between grain-free and/or novel protein diets to DCM, citing a subjective increase in DCM in dog breeds that are not known to have a genetic predisposition for the disease. This literature review describes clinical presentations of DCM, common sequelae, treatment and preventative measures, histopathologic features, and a discussion of the varied etiological origins of the disease. In addition, current literature limitations are addressed, in order to ascertain multiple variables leading to the development of DCM. Future studies are needed to evaluate one variable at a time and to minimize confounding variables and speculation. Furthermore, to prevent sampling bias with the current FDA reports, the veterinary community should be asked to provide information for all cases of DCM in dogs. This should include cases during the same time period, regardless of the practitioner's proposed etiology, due to no definitive association between diets with specific characteristics, such as, but not limited to, grain-free diets and those containing legumes, novel protein diets, and those produced by small manufacturers to DCM in dogs. In summary, in order to determine if certain ingredients, categories of diets, or manufacturing processes are related to an increased risk of DCM, further studies investigating these variables are necessary.

The Causes of Canine Myocarditis and Myocardial Fibrosis Are Elusive by Targeted Molecular Testing: Retrospective Analysis and Literature Review

Myocarditis can cause death or permanent heart damage. As epidemiologic and etiopathologic data for canine myocarditis are lacking, we performed a retrospective study using nucleic acid extracted from archived (2007 to 2015) tissues from myocarditis cases and control dogs without myocardial lesions. Heart tissue from pediatric/juvenile and adult dogs was tested with a comprehensive panel of conventional and real-time polymerase chain reaction (PCR) assays targeting recognized agents of canine myocarditis based on a literature review and informed by the comparative epidemiology of human myocarditis. The PCR screen, which included canine parvovirus 2 (CPV-2), canine distemper virus, canine herpesvirus, Borrelia spp, West Nile virus, adenovirus, parainfluenza virus, pneumovirus, respiratory coronavirus, influenza virus, Bartonella spp, Rickettsia spp, Mycoplasma spp, and Neospora caninum, did not detect agents in 35 of 66 cases (53%; 95% confidence interval [CI], 41%-65%) and was frequently negative in adults (21/26); by comparison, agents were not detected in 27 of 57 controls (47%; 95% CI, 35%-60%). Canine distemper virus, herpesvirus, adenovirus, coronavirus, parainfluenza virus, Mycoplasma haemocanis, and N. caninum were occasionally detected in both cases and controls; thus, PCR detection was not considered to indicate causation. We previously reported that CPV-2 continues to be associated with myocarditis in young dogs despite widespread vaccination; in adults, CPV-2 was detected in 2 of 26 cases and 4 of 22 controls. As several agents were similarly detected in cases and controls, it is unclear if these are cardiopathogenic, incidental, or latent. West Nile virus was detected at the analytic limit in 1 adult case. We did not detect Borrelia spp, Bartonella spp, Rickettsia spp, or influenza A virus in the myocarditis cases. These data demonstrate the limitations of current targeted diagnostic tests and the need for additional research to identify unknown agents and develop testing strategies for canine myocarditis.

Long-term effects of canine parvovirus infection in dogs

BACKGROUND

Canine parvovirus (CPV) is the most important viral cause of acute canine enteritis leading to severe damage of the intestinal barrier. It has been speculated that dogs might develop chronic disorders after surviving CPV infection. However, no studies regarding the long-term implications of CPV infection have been published to date. The aim of this study was to evaluate whether dogs that have survived CPV infection will have an increased risk for developing chronic gastroenteritis, atopic dermatitis, or cardiac disease.

METHODOLOGY/PRINCIPAL FINDINGS

Dogs that had been treated at the Clinic of Small Animal Medicine, LMU Munich, for CPV infection for which a follow-up of at least 12 months was available, were included in the study. Owners completed a questionnaire on the presence of chronic gastrointestinal and cutaneous signs, cardiac disease, and other potential disorders. An identical questionnaire was sent to owners of matched control dogs during the same time period. Seventy-one questionnaires of dogs with CPV infection and 67 of control dogs were analyzed. Significantly more CPV-infected dogs (30/71) compared to control dogs (8/67) had developed chronic gastrointestinal signs later in their lives (P < 0.001). No significant differences were observed regarding skin diseases (P = 1), cardiac problems (P = 0.160), or any other diseases (P = 0.173) later in life.

CONCLUSIONS

Results of this study suggest that dogs that survive CPV infection have a significantly higher risk (odds ratio = 5.33) for developing a chronic gastrointestinal disease. Further prospective studies to identify the trigger for the development of chronic diarrhoea and possible targeted treatment strategies are needed.

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.

Canine parvovirus: the worldwide occurrence of antigenic variants

The most important enteric virus infecting canids is canine parvovirus type 2 (CPV-2). CPV is the aetiologic agent of a contagious disease, mainly characterized by clinical gastroenteritis signs in younger dogs. CPV-2 emerged as a new virus in the late 1970s, which could infect domestic dogs, and became distributed in the global dog population within 2 years. A few years later, the virus's original type was replaced by a new genetic and antigenic variant, called CPV-2a. Around 1984 and 2000, virus variants with the single change to Asp or Glu in the VP2 residue 426 were detected (sometimes termed CPV-2b and -2c). The genetic and antigenic changes in the variants have also been correlated with changes in their host range; in particular, in the ability to replicate in cats and also host range differences in canine and other tissue culture cells. CPV-2 variants have been circulating among wild carnivores and have been well-documented in several countries around the world. Here, we have reviewed and summarized the current information about the worldwide distribution and evolution of CPV-2 variants since they emerged, as well as the host ranges they are associated with.

Parvoviral myocarditis in a 5-week-old Dachshund

OBJECTIVE

To describe a case of myocarditis associated with naturally occurring canine parvovirus type 2 (CPV-2).

CASE SUMMARY

A 5-week-old male intact Dachshund dog presented for acute respiratory distress. Limited diagnostic tests prior to the dog experiencing cardiopulmonary arrest included a lateral thoracic radiograph, which indicated cardiomegaly and diffuse unstructured pulmonary infiltrate. Necropsy was performed and results identified a lymphoplasmacytic myocarditis with positive CPV-2 immunohistochemistry within the myocardium.

UNIQUE INFORMATION PROVIDED

This report describes the natural occurrence of CPV-2-associated myocarditis. In addition to highlighting this rare form of canine parvovirus, cardiomyopathy in survivors of the acute viral myocarditis phase is reviewed.

Tei index (myocardial performance index) and cardiac biomarkers in dogs with parvoviral enteritis

Tei index (myocardial performance) and cardiac biomarkers were evaluated in dogs with parvoviral enteritis (PVE). Tei index was calculated as isovolumic contraction time plus isovolumic relaxation time divided by ejection time. Myocardial and skeletal muscle damages were assessed by serum levels of cardiac troponin I (cTnI), creatine (phospho) kinase, lactate dehydrogenase and aspartate aminotransferase. Serum magnesium level was also determined. According to treatment response, dogs were divided into the survivor (n=20) and non-survivor groups (n=23). Seven healthy dogs served as controls. The mean value of the Tei index was higher in non-survivors, compared with survivors (p<0.02) and healthy controls (p<0.01). Serum level of cTnI in non-survivors was higher than that of survivors and controls (p<0.05). Tei index showed the highest sensitivity and specificity to predict mortality. The findings of an elevated Tei index and an increase in serum cTnI are factors associated with a poor prognosis in cases of canine parvovirosis.

Molecular screening by polymerase chain reaction detects panleukopenia virus DNA in formalin-fixed hearts from cats with idiopathic cardiomyopathy and myocarditis

Viral myocarditis has been suggested as an etiology for cardiomyopathy in several mammalian species. Myocarditis and idiopathic cardiomyopathy have been reported in the domestic cat, although a viral etiology has not been demonstrated. Because of the continuing interest in the potential relationship between viral myocarditis and cardiomyopathy, we evaluated hearts from cats with spontaneous, idiopathic cardiomyopathy for viral genomic material within myocytes by polymerase chain reaction, and for the presence of myocarditis by light microscopy. Thirty-one (31) formalin-fixed hearts from domestic cats who died of idiopathic cardiomyopathy were randomly selected from pathology archives. Seventeen (17) formalin-fixed hearts from healthy cats were similarly selected as normal controls. The polymerase chain reaction (PCR) was used to evaluate myocardial tissue for the presence of viral genome from feline panleukopenia virus, herpes virus, calici virus, and corona virus. Hearts were examined using light microscopy for histologic evidence of myocarditis according to the Dallas criteria. Panleukopenia virus was identified by PCR in 10 of 31 cats with cardiomyopathy but in none of the controls. Neither cardiomyopathic or control cats tested positive by PCR for herpes virus, calici virus, and corona virus. Myocarditis was detected by histologic examination in 18 of 31 cardiomyopathic cats and in none of 17 control cats. Myocarditis and or feline panleukopenia virus genome was detected in felines with idiopathic hypertrophic, dilated, and restrictive cardiomyopathy, suggesting a possible role of viral infection and inflammation in the pathogenesis of cardiomyopathy in this species.

Subacute massive necrotizing myocarditis by canine parvovirus type 2 infection with diffuse leukoencephalomalacia in a puppy

Severe necrotizing myocarditis associated with canine parvovirus type 2 (CPV-2) infection and diffuse leukoencephalomalacia was recognized in a 4-week-old mongrel puppy. The cardiac lesions were characterized by severe diffuse myocardial degeneration and necrosis with occasional massive mineralization and distinct intranuclear inclusion bodies. Immunohistochemical examination revealed the presence of CPV-2 antigens in both the cytoplasm and nuclei of the myocytes. In the white matter of the cerebrum, moderate to severe diffuse necrosis with diffuse infiltration of gitter cells and occasional diffuse mineral deposits were recognized symmetrically and bilaterally. In the meningocortical area of the cerebellum, there was mild focal hemorrhage and accumulation of hemosiderin-laden histiocytes. In addition to the absence of viral antigen (as judged by immunohistochemistry), neither viral inclusions nor other vascular lesions were identified in examined sections of brain. These findings suggest that the brain lesions were not induced by direct CPV-2 infection but were related to severe myocardial lesions producing prolonged hypoxia and/or ischemia.

Non-suppurative myocarditis in piglets associated with porcine parvovirus infection

The involvement of porcine parvovirus (PPV) in the aetiology of non-suppurative myocarditis in sucking piglets was investigated by a polymerase chain reaction (PCR), designed to assess the presence of viral genome in formalin-fixed paraffin wax-embedded tissue of diseased animals. Myocardium and lung of stillborn piglets with a confirmed PPV infection were used to set up the PCR amplification method. Subsequently, 20 myocardia with inflammatory lesions were examined in parallel with 20 myocardia without lesions, from age-matched control piglets. Tissues were first tested for the presence and the integrity of porcine DNA by amplifying a sequence encoding the highly conserved nuclear protein histone H4. Tissue from 15 out of 20 animals with myocarditis contained amplifiable histone H4 DNA and in 12 of the 15 histone H4-positive samples, PPV DNA was detected. It proved possible to amplify histone H4 DNA in all 20 negative controls (without myocarditis), and PPV DNA was detected in three cases. In-situ hybridization with a digoxigenin-labelled probe homologous to PPV was performed in four PCR-positive cases of non-suppurative myocarditis. In two animals several positively stained nuclei were observed in the myocardium, within or close to the mild inflammatory cellular infiltrates. These results strongly suggest that PPV can cause non-suppurative myocarditis in sucking piglets.

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.

Canine parvovirus

Canine parvovirus is a truly new pathogen of dogs that emerged in the late 1970s. Initially seen as epidemic disease in all dogs, parvoviral enteritis is now primarily a disease of 1- to 6-month-old dogs. Maternal antibody interference with immunization accounts for the vast majority of vaccine "breaks." Molecular virologic methods have revealed continued evolution of the virus, but this appears to be of greater academic than practical interest. Clinical diagnosis can be definitive in fulminant cases but requires laboratory support--usually demonstration of virus in the feces--in less clear-cut cases. Treatment remains symptomatic, based simply on principles of good supportive care. As the virus is firmly entrenched in both the wild and domestic canine population, elimination of the virus is impossible, and CPV-2 will remain a concern for the small animal practitioner indefinitely.

Retrospective study of myocardial canine parvovirus infection by in situ hybridization

The diagnosis of myocardial canine parvovirus (CPV) infection used to depend on the presence of pathognomonic intranuclear inclusion bodies. The in situ hybridization technique, however, allowed to detect CPV specific nucleic acid in myocardial tissue where no inclusion bodies were found. Hence, we applied this technique to check formalin-fixed paraffin-embedded myocardial tissue from puppies with heart lesions for the presence of CPV. The tissues had been collected between 1977 and 1989. A biotinylated probe was used for in situ hybridization. This way CPV specific nucleic acid was detected in 3 dogs where CPV myocarditis had not been diagnosed on routinely stained slides because of the lack of intranuclear inclusion bodies. However, in spite of the application of the in situ hybridization technique no further myocardial CPV infection was detected in puppies with heart lesions from after 1979, confirming that the number of puppies with myocardial CPV infection declined after that year.

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.

Analysis of parvovirus infections using strand-specific hybridization probes

The autonomous parvoviruses cause a broad spectrum of acute and chronic infections of animals and man. The discrimination of sites of viral replication from sites of viral sequestration is an important goal in elucidating the pathogenesis of these diseases. It is possible to employ strand-specific RNA hybridization probes in such analyses because a 'plus' sense probe will react with single stranded virion DNA and duplex replicative form DNA, but a 'minus' sense probe will react preferentially with obligate replicative intermediates (duplex replicative form DNA and mRNA). Strand-specific RNA hybridization probes were developed for the Aleutian mink disease parvovirus (ADV) and were used to study acute and chronic infections of mink. Such probes were capable of differentiating replicative intermediates (duplex replicative form DNA and mRNA) from single-stranded virion DNA in Southern blot analysis and in strand-specific in situ hybridization. ADV infection of seronegative newborn mink kits causes an acute, cytopathic infection of type II alveolar cells. Replication in these cells is highly permissive and is characterized by high levels of replicative intermediates and virion DNA. A fatal respiratory distress syndrome and hyaline membrane formation result from impaired surfactant production by the infected type II cells. On the other hand, ADV infection of adult mink is associated with a persistent infection and a disorder of the immune regulation. The target cells for viral replication in adult mink are confined to the lymphoid system and the bone marrow. Replication in these cells, which are probably lymphocytes, is restricted, and characterized by greatly reduced levels of replicative intermediates and virion DNA. It, therefore, seems that disease in the infected adult mink results from a restricted infection by ADV. Large amounts of virion DNA can also be demonstrated in locations where replication cannot be detected and apparently represents sequestration of virion particles by elements of the reticuloendothelial system. Thus, replication and sequestration can, in fact, be distinguished by the strand-specific in situ hybridization. These studies indicate that strand-specific in situ hybridization is a potentially valuable method for studying the pathogenesis of parvovirus infections.

Clinical and experimental aspects of viral myocarditis

Picornaviruses are frequently implicated as the etiological agents of acute myocarditis. This association is based historically on serological evidence of rising antibody titers to specific pathogens and more recently on identification of viral genomic material in endocardial biopsy specimens through in situ hybridization. Only rarely is infectious virus isolated from either the patient or the heart during periods of maximum myocardial inflammation and injury. Thus, despite a probable viral etiology, much interest centers on the role of the immune system in cardiac damage and the likelihood that the infection triggers an autoimmune response to heart-specific antigens. Heart-reactive antibodies and T cells are found in most myocarditis patients, and immunosuppressive therapy has proven beneficial in many, though not all, cases. Furthermore, murine models of coxsackievirus group B type 3-induced myocarditis also demonstrate that virus infection initiates autoimmunity and that these autoimmune effectors are predominately responsible for tissue injury. How virus-host interactions overcome presumed self-tolerance to heart antigens is discussed, and evidence supporting various theories of virus-initiated autoimmunity and disease pathogenesis are delineated.

Myocarditis and cardiomyopathy in the dog and cat

Myocarditis and cardiomyopathy were diagnosed in 36 dogs from 11 litters, and myoendocarditis and restrictive cardiomyopathy were diagnosed in 51 cats. Most of the dogs and cats died unexpectedly. Spontaneous parvoviral infection in the dogs caused acute (myocytolysis with presence of intranuclear inclusion bodies in the myocytes), subacute (inflammatory reaction and myocytolysis), and chronic (fibrosis and myocytolysis) myocarditis, which led to extensive myocardial fibrosis and abnormality of the myocytes, similar to dilated cardiomyopathy in man. Spontaneous acute, subacute, and chronic myoendocarditis in the cats led to granulation, extensive fibrosis, and necrosis of the myoendocardium, i.e., like restrictive cardiomyopathy which occurs in man without eosinophilia. Thus, the dog and cat are important animal models of primary myocardial disease.

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.