Feline Panleukopenia. I. Pathogenesis in germfree and specific pathogen-free cats

Effect of vaccination on parvovirus antigen testing in kittens

OBJECTIVE

To determine the frequency and duration of feline panleukopenia virus (FPV) vaccine-induced interference with fecal parvovirus diagnostic testing in cats.

DESIGN

Prospective controlled study.

ANIMALS

Sixty-four 8- to 10-week-old specific-pathogen-free kittens.

PROCEDURES

Kittens were inoculated once with 1 of 8 commercial multivalent vaccines containing modified-live virus (MLV) or inactivated FPV by the SC or intranasal routes. Feces were tested for parvovirus antigen immediately prior to vaccination, then daily for 14 days with 3 tests designed for detection of canine parvovirus. Serum anti-FPV antibody titers were determined by use of hemagglutination inhibition prior to vaccination and 14 days later.

RESULTS

All fecal parvovirus test results were negative prior to vaccination. After vaccination, 1 kitten had positive test results with test 1, 4 kittens had positive results with test 2, and 13 kittens had positive results with test 3. Only 1 kitten had positive results with all 3 tests, and only 2 of those tests were subjectively considered to have strongly positive results. At 14 days after vaccination, 31% of kittens receiving inactivated vaccines had protective FPV titers, whereas 85% of kittens receiving MLV vaccines had protective titers.

CONCLUSIONS AND CLINICAL RELEVANCE

Animal shelter veterinarians should select fecal tests for parvovirus detection that have high sensitivity for FPV and low frequency of vaccine-related test interference. Positive parvovirus test results should be interpreted in light of clinical signs, vaccination history, and results of confirmatory testing. Despite the possibility of test interference, the benefit provided by universal MLV FPV vaccination of cats in high-risk environments such as shelters outweighs the impact on diagnostic test accuracy.

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.

Comparative examination of cats with feline leukemia virus-associated enteritis and other relevant forms of feline enteritis

Cats with feline leukemia virus (FeLV)-associated enteritis (FAE), enteritis of other known viral etiology (parvovirus [PV], enteric coronavirus [CoV]), and enteritis of unknown etiology with histologic features similar to those of FAE and PV enteritis (EUE) and FeLV-negative and FeLV-positive cats without enterocyte alterations were examined. Amount and types of infiltrating leukocytes in the jejunum and activity and cellular constituents of mesenteric lymph nodes, spleen, and bone marrow were determined. PV and CoV infections were confirmed by immunohistologic demonstration of PV and CoV antigen, ultrastructural demonstration of viral particles in the intestinal content, and in situ hybridization for PV genome. FeLV infection was detected by immunohistology for gp70, p27, and p15E. Latent FeLV infection was excluded by polymerase chain reaction methods for exogenous FeLV DNA. Enterocyte lesions involved the crypts in cats with PV enteritis, FAE, and EUE and the villous tips in cats with CoV enteritis. Inflammatory infiltration was generally dominated by mononuclear cells and was moderate in the unaltered intestine and in cats with PV enteritis and marked in cats with FAE, CoV enteritis, and EUE. In cats with EUE, myeloid/histiocyte antigen-positive macrophages were relatively numerous, suggesting recruitment of peripheral blood monocytes. Lymphoid tissues were depleted in cats with PV enteritis and with EUE but were normal or hyperplastic in cats with FAE. Bone marrow activity was decreased in cats with PV enteritis; in cats with FAE or EUE and in FeLV-positive cats without enterocyte alterations, activity was slightly increased. In cats with FAE and PV enteritis, a T-cell-dominated response prevailed. EUE showed some parallels to human inflammatory bowel disease, indicating a potential harmful effect of infiltrating macrophages on the intestinal epithelium.

Apoptosis in feline panleukopenia and canine parvovirus enteritis

Tissue samples of cats and dogs with panleukopenia and parvovirus enteritis, respectively, were examined for the presence of viral antigen-positive cells and apoptotic cells by immunohistochemistry and by TUNEL assay (Terminal Transferase-Mediated dUTP Nick End Labelling). Compared to control animals, infected cats and dogs generally had more TUNEL-positive cells. Cell types positive for parvovirus antigen, for example digestive tract epithelial and mesenchymal cells, and lymphocytes and macrophages in lymphoid tissues were also positive for TUNEL signals. Occasionally, TUNEL signal and viral antigen were present in the same tissue areas, suggesting a direct viral trigger of apoptosis. More frequently, however, there was no complete overlap of antigen and TUNEL-positive areas. The results of this study indicate that apoptotic cell death contributes significantly to the widespread tissue damage of parvovirus infection in cats and dogs.

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.

The relationship between capsid protein (VP2) sequence and pathogenicity of Aleutian mink disease parvovirus (ADV): a possible role for raccoons in the transmission of ADV infections

Aleutian mink disease parvovirus (ADV) DNA was identified by PCR in samples from mink and raccoons on commercial ranches during an outbreak of Aleutian disease (AD). Comparison of DNA sequences of the hypervariable portion of VP2, the major capsid protein of ADV, indicated that both mink and raccoons were infected by a new isolate of ADV, designated ADV-TR. Because the capsid proteins of other parvoviruses play a prominent role in the determination of viral pathogenicity and host range, we decided to examine the relationship between the capsid protein sequences and pathogenicity of ADV. Comparison of the ADV-TR hypervariable region sequence with sequences of other isolates of ADV revealed that ADV-TR was 94 to 100% related to the nonpathogenic type 1 ADV-G at both the DNA and amino acid levels but less than 90% related to other pathogenic ADVs like the type 2 ADV-Utah, the type 3 ADV-ZK8, or ADV-Pullman. This finding indicated that a virus with a type 1 hypervariable region could be pathogenic. To perform a more comprehensive analysis, the complete VP2 sequence of ADV-TR was obtained and compared with that of the 647-amino-acid VP2 of ADV-G and the corresponding VP2 sequences of the pathogenic ADV-Utah, ADV-Pullman, and ADV-ZK8. Although the hypervariable region amino acid sequence of ADV-TR was identical to that of ADV-G, there were 12 amino acid differences between ADV-G and ADV-TR. Each of these differences was at a position where other pathogenic isolates also differed from ADV-G. Thus, although ADV-TR had the hypervariable sequence of the nonpathogenic type 1 ADV-G, the remainder of the VP2 sequence resembled sequences of other pathogenic ADVs. Under experimental conditions, ADV-TR and ADV-Utah were highly pathogenic and induced typical AD in trios of both Aleutian and non-Aleutian mink, whereas ADV-Pullman was pathogenic only for Aleutian mink and ADV-G was noninfectious. Trios of raccoons experimentally inoculated with ADV-TR and ADV-Utah all became infected with ADV, but only a single ADV-Pullman-inoculated raccoon showed evidence of infection. Furthermore, none of the ADV isolates induced pathological findings of AD in raccoons. Finally, when a preparation of ADV-TR prepared from infected raccoon lymph nodes was inoculated into mink and raccoons, typical AD was induced in Aleutian and non-Aleutian mink, but raccoons failed to show serological or pathological evidence of infection. These results indicated that raccoons can become infected with ADV and may have a role in the transmission of virus to mink but that raccoon-to-raccoon transmission of ADV is unlikely.

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.

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.

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.

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.

Molecular cloning of the Aleutian disease virus genome: expression of Aleutian disease virus antigens by a recombinant plasmid

Three nonoverlapping segments representing approximately 80% of the 4.8-kilobase pair Aleutian disease virus (ADV-G) duplex genome were molecularly cloned into either bacteriophage M13mp9 (M13bm2 = 0.07 to 0.15 map unit; M13bm1 = 0.15 to 0.54 map unit) or plasmid pUC8 (pBM1 = 0.54 to 0.88 map units). In addition the 0.54- to 0.88-map unit segment of a Danish isolate of ADV (DK ADV) was also cloned into pUC8 (pBM2). The recombinant plasmids pBM1 and pBM2 induced expression of several polypeptides in Escherichia coli JM103 that were specifically recognized by sera from mink infected with ADV. The same three proteins with approximate molecular weights of 55,000, 34,000, and 27,000 were detected both by immune blotting and by immunoprecipitation of [35S]methionine-labeled JM103 (pBM1). None of these proteins were recognized in JM103 or JM103 (pUC8), nor were they detected by sera from normal mink. Purified pBM1 and pBM2 DNA appeared identical in size by gel analysis and contour length measurement, and electron microscopic heteroduplex mapping revealed no visible areas of heterology. However, restriction endonuclease mapping showed that pBM2 was different from pBM1, indicating that this segment of the ADV genome was similar but not identical for two strains of ADV (ADV-G and DK ADV). Furthermore, when cloned DNA from ADV-G was labeled with [32P]dCTP by nick translation, DNA relatedness to several field strains of ADV (Utah I, Pullman, and DK), but not to mink enteritis virus or cellular DNA, was shown by Southern blot hybridization.

Isospora suis infection in piglets. A review

Recently several reports have been published on the association of Isospora suis with diarrhea in piglets. A review is given of I. suis infection in piglets, in which the taxonomy, life cycle, pathogenicity, immunity, and treatment of I. suis and related organisms are discussed.

Canine parvovirus infections in a colony of dogs

A serological study of canine parvovirus (CPV) infections in a colony of dogs was conducted over a period of 8 months. Twenty-two of 24 adults samples initially had significant antibody titres to CPV. Nine litters of puppies were bled at fortnightly intervals and the sera tested for antibodies to CPV. Twenty-nine of 35 naturally PV infections observed were subclinical. A puppy in one litter developed vomiting and diarrhoea during the same period as seroconversion to CPV. Four puppies from a further litter developed histologically confirmed myocarditis. Serological testing of this latter litter indicated that the virus infections occurred between 2 weeks prior to and 1 week post whelping, and that clinical disease developed 20-40 days after viral infection. The mean half life of the decline of passively derived immunity to CPV was 8.3 days.

Feline panleukopenia. III. Development of lesions in the lymphoid tissues

Germfree and specific pathogen-free cats were inoculated with feline panleukopenia virus. Cats were necropsied 2 to 6 days after inoculation and tissues from the thymus, lymph nodes and spleen taken for histological and immunofluorescence studies. Necrosis of lymphoid cells in the thymic cortex began 3 days after inoculation and continued for 5 to 6 days after inoculation when the thymus was nearly depleted of lymphocytes. Immunofluorescence studies showed the lesions to be caused by virus. There was gross and histological involution of the thymus in both germfree and specific pathogen-free cats. The lymph nodes and spleen of uninoculated germfree cats looked "inactive" and lacked well developed lymphoid follicles and paracortical areas. In both germfree and specific pathogen-free cats there was necrosis in both follicular and paracortical areas of the lymph nodes and follicular and periarteriolar areas of the spleen 3 to 4 days after inoculation. Immunofluorescence showed these areas had virus infection. By 5 to 6 days after inoculation, these areas were populated by many lymphoblastoic cells. Even though significant destruction of lymphoid cells occurred, subsequently, in cats that develop mild clinical illness, these lymphoid tissues seemed stimulated rather than depleted of lymphocytes.

Light and ultrastructural pathologic changes in intestinal coronavirus infection of newborn calves

Summary

Seven conventional newborn calves were inoculated orally with the coronavirus strain LY‐138, originally recovered from naturally‐infected diarrheic calves. All calves developed diarrhea during the first 24 h after inoculation. The presence and excretion of virus was monitored by electron microscopy.

Grossly, the changes were subtle and not striking. The intestinal tract was distended and contained a yellow clear fluid. The small intestinal wall was thin and transparent.

Histologic changes were characterized by atrophy and fusion of the villi, decreased height and vacuolation of the intestinal epithelial cells, by a reduced number of goblet cells, crypt hypertrophy and dilatation, and by edema and increased cellularity of the lamina propria mucosae.

Ultrastructurally the viral agent infected the intestinal absorptive epithelial cells, undifferentiated epithelial cells and goblet cells of the villi, and occasionally fibroblasts and endothelial cells of the lamina propria mucosae. Morphologic evidence indicated that virus multiplication occurred only in the cytoplasm of infected cells. The rough and smooth endoplasmic reticulum became dilated, and electron‐dense, granulo‐fibrillar material filled their cysternae to form smooth membrane‐bounded viral factories in the supranuclear cytoplasm of infected intestinal epithelial cells. Ultrastructural cytologic changes in this viral infection consisted of dilation of the endoplasmic reticulum network, cellular ribosome depletion, extensive endoplasmic vacuolation and vesiculation of Golgi elements of intestinal epithelial cells, swelling and degeneration of mitochondria, loss of normal nuclear polarity with pyknosis and karyolysis of the nuclei, loss of cytoplasmic matrix, and a broad spectrum of pathologic changes involving the microvilli and terminal web.

Zusammenfassung

Lichtmikroskopische und Ultrastrukturelle pathologische Veränderungen bei intestinaler Coronavirusinfektion neugeborener Kälber

Sieben konventionelle neugeborene Kälber wurden oral mit dem Coronavirus‐Stamm LY‐138, der ursprünglich von natürlich infizierten Kälbern mit Diarrhoe stammt, infiziert. Alle Kälber entwickelten Durchfall während der ersten 24 Stunden nach Inokulation. Vorhandensein und die Ausscheidung des Virus wurden elektronenoptisch verfolgt.

Sichtbare Veränderungen waren gering und wenig auffallend. Der Darmtrakt war erweitert und enthielt eine gelbe, klare Flüssigkeit. Die Dünndarmwand war dünn und durchscheinend.

Histologische Veränderungen waren charakterisiert durch Atrophie und Verschmelzung der Zotten, verminderte Höhe und Vakuolisierung der intestinalen Epithelzellen, durch eine reduzierte Anzahl von Gobletzellen, Kryptenhypertrophie und ‐erweiterung, sowie Ödematisierung und erhöhte Zellularität der lamina propria mucusae. Ultrastrukturell infizierte das Virus die intestinalen absorptiven Epithelzellen, nichtdifferenzierte Epithelzellen und Gobletzellen der Zotten, und gelegentlich Fibroblasten sowie Endothelzellen der Lamina propria mucosae. Die morphologischen Veränderungen weisen darauf hin, daß die Virusvermehrung nur im Zytoplasma infizierter Zellen stattfand. Das rauhe und glatte endoplasmatische Retikulum war erweitert, und elektronendichtes, granulo‐fibrilläres Material füllte die Zisternen aus, die feine Membran‐gebundene Virusvermehrungsfabriken in dem supranukleären Zytoplasmabereich infizierter intestinaler Epithelzellen bildeten. Ultrastrukturelle zytologische Veränderungen bestanden bei dieser Virusinfektion aus Erweiterung des endoplasmatischen Retikulumnetzwerks, zellulärem Ribosomenverlust, extensiver endoplasmatischer Vakuolisierung der Golgielemente der intestinalen Epithelzellen, Schwellung und Degeneration von Mitochondrien, Verlust der normalen nukleären Polarität mit Pyknose und Karyolyse der Zellkerne, Verlust der Zytoplasmamatrix, und aus einem breiten Spektrum pathologischer Veränderungen an den Mikrozotten und der terminalen Netzstruktur.

Résumé

Lésions pathologiques ultrastructurelles et au microscope optique lors d'infection intestinale à Coronavirus chez des veaux nouveau‐nés

Sept veaux nouveau‐nés conventionnels ont été infectés oralement par la souche LY‐138 de Coronavirus, isolée précédement chez des veaux naturellement infectés présentant une diarrhée. Tous les veaux développèrent une diarrhée durant les premières 24 heures suivant l'inovulation. La présence et la sécrétion du virus ont été suivies au microscope électronique.

Les lésions apparentes furent faibles et peu apparentes. Le tractus digestif fut élargi et contenait un liquide jaune et clair. La paroi de l'intestin grêle était mince et transparente.

Les lésions histologiques furent caractérisées par une atrophie et une fusion des villi, une hauteur diminuée et une vacuolisation des cellules épithéliales de l'intestin, par un nombre réduit des cellules caliciformes, une hypertrophie et un élargissement des cryptes ainsi qu'un oedème et un nombre de cellules augmenté de Lamina propria mucosae.

Le virus a infecté ultrastructurellement les cellules épithéliales absorbantes de l'intestin, des cellules épithéliales non différenciées et des cellules caliciformes des villi, de temps en temps des fibroblastes et des cellules endothéliales de Lamina propria mucosae. Les lésions morphologiques ont montré que la multiplication du virus n'avait lieu que dans le cytoplasme des cellules infectées. Le Reticulum endoplasmique grossier et fin fut élargi et un matériel granuleux et fibrillaire remplissait les citernes qui formaient de fines régions de réplication virale liées à la membrane dans le voisinage cytoplasmique supranucléaire des cellules épithéliales infectées de l'intestin. Les lésions cytologiques ultrastructurelles lors de cette infection virale consistèrent en un élargissement du réseau endoplasmique, une perte des ribosomes cellulaires, une vacuolisation endoplasmique extensive des éléments de Golgi dans les cellules épithéliales de l'intestin, une enflure et une dégénérescence des mitochondries, une perte de la polarité nucléaire normale avec une picnose et une carylolyse des noyaux cellulaires, une perte de la matrice cytoplasmique et un large éventail de lésions pathologiques des microvilli et des tissus terminaux.

Resumen

Modificaciones patológicas fotomicroscópicas y ultraestructurales en la infección intestinal de terneros recién nacidos por virus Corona

Se infectaron por vía oral siete terneros convencionales con la estirpe de virus Corona LY‐138, la cual es originaria de terneros, infectados naturalmente, con diarrea. Todos los terneros manifestaban diarrea durante las 24 horas primeras después de la inoculación. Se seguía electrónicoópticamente la presencia y eliminación de virus.

Las modificaciones visibles eran escasas y se destacaban poco. El tracto intestinal se hallaba dilatado, conteniendo un líquido amarillo claro. La pared del intestino delgado era tenue y translúcida.

Las modificaciones histopatológicas se caracterizaban por atrofia y soldadura de las villosidades, altura reducida y vacuolización de las células epiteliales intestinales, por una cantidad reducida de células caliciformes, hipertrofia y ensanchamiento de las criptas, y por edematización y celularidad aumentada de la lámina propia mucosa. El virus infectaba ultraestructuralmente las células epiteliales intestinales absortivas, células epiteliales no diferenciadas y células caliciformes de las villosidades, y, en ocasiones fibroblastos y células endoteliales de la lámina propia mucosa. Las modificaciones morfológicas señalan que la multiplicación de virus solo tuvo lugar en el citoplasma de las células infectadas. El retículo endoplasmático basto y fino se hallaba dilatado y material granulosofibrilar, opaco a los electrones, ocupaba las cisternas, las cuales formaban lugares finos de replicación antiviral, ligados a las membranas en el ámbito citoplasmático supranuclear de células epiteliales intestinales infectadas. Las modificaciones citológicas ultraestructurales consistían en esta infección a virus en dilatación del retículo endoplasmático, pérdida celular de ribosomas, vacuolización endoplasmática extensiva de los elementos de Golgi de las células epiteliales intestinales, tumefacción y degeneración de mitocondrias, pérdida de la polaridad nuclear normal con picnosis y cariolisis de los núcleos celulares, pérdida de la matriz citoplasmática, y en un espectro amplio de modificaciones patológicas en las microvillosidades y tejidos terminales.