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.

Morphology and morphogenesis of a coronavirus infecting intestinal epithelial cells of newborn calves

The morphology and morphogenesis of virus strain LY-138 recovered from neonatal diarrheic calves were investigated by electron microscopy using negativestaining techniques and ultrathin sectioning. Purified viral particles were spherical in shape and measured 90 nm in average diameter in negatively stained preparations. Pleomorphic forms were also present. The virions had envelopes with petal-shaped projections characteristic of coronaviruses. In ultrathin sections, cores in viral factories were round with a diameter of 50–60 nm. Most of these cores were electron dense but some had an electron-lucent center. In cytoplasmic vacuoles, Golgi vesicles, and on the apical plasmalemma of intestinal epithelial cells, the virions were round or ellipsoidal in shape, measuring 70–80 nm in diameter, and had fine thread-like projections on their surfaces. Uptake of virus occurred through fusion of viral envelopes with the plasmalemma of the microvillous border or by entry into intercellular spaces and interaction with the lateral cell membranes of adjacent intestinal epithelial cells. As a result of this interaction, the lateral cell membranes became altered and ill-defined. During the early stage of infection, the rough andasmooth elements of the endoplasmic reticulum became distended with electron-dense granulofibrillar material. This material accumulated subsequently as well-defined, smooth membrane-bound areas mainly in the apical cytoplasm of infected cells. These structures were considered to be viral factories. The morphogenesis of virus occurred mainly through condensation of the electron-dense, granulo-fibrillar material into viral cores in cytoplasmic viral factories or within the distended cisternes of the rough endoplasmic reticulum. Viral envelopment occurred on membranes of cytoplasmic vacuoles, Golgi vesicles, or in association with membranes of viral factories. Release of virus from infected cells occurred by lysis and fragmentation of the apical plasmalemma and flow of the cytoplasm with its contents into the gut lumen. Release also occurred by digestion and lysis of extruded infected cells or by fusion of virus-containing cytoplasmic vacuoles with the apical plasmalemma and liberation of their contents.

Ultrastructural changes in host cellular organelles in the course of the chlamydial developmental cycle

Different stages in the chlamydial developmental cycle were correlated with cytopathic changes in host cellular organelles by ultrastructural analysis of infected cultured cells and cells of the intestinal mucosa of newborn calves. Four distinct morphologic forms of chlamydial development can be distinguished: elementary bodies, dispersing forms, reticulate bodies and condensing forms which proceed to form elementary bodies. From the stage of elementary body uptake through formation and multiplication of reticulate bodies, the host cellular changes consisted mainly of displacement of cellular organelles by the enlarging chlamydial inclusions in the cytoplasm of infected cells. Beginning with the formation of condensing forms and elementary bodies from 20 to 30 hours after infection, cellular organelles became altered and progressively damaged. The damage was initially degenerative and then necrotic. It consisted of loss of free ribosomes and polysomes, dilation and vesiculation of the endoplasmic reticulum network and vesiculation and loss of microvilli. The specific granules of enterochromaffin cells and the mucous droplets of goblet cells were reduced in number. The mitochondria and nuclei were affected last. The mitochondria became swollen and their cristae became fragmented. The nuclei of infected cells lost their normal chromatin pattern and proceeded to pyknosis and karyolysis. Rupture and lysis of cytoplasmic and inclusion membranes liberated the different chlamydial developmental forms. After release the elementary bodies remained ultrastructurally intact.

Virologic studies on cattle with naturally occurring and experimentally induced malignant catarrhal fever

Malignant catarrhal fever is an important disease of cattle and certain wild ruminants. It occurs in sporadic and epizootic forms in Colorado cattle. Specimens from 15 cattle with naturally occurring malignant catarrhal fever and 5 cattle with induced disease were examined for cell-free and cell-associated viruses. Enteroviruses were isolated from leukocytes of 2 cattle with field cases of the disease. A herpesvirus with characteristics of the "Movar"-type, isolated from the spleen of another steer with a field case could be propagated optimally in bovine fetal spleen cells. A cell-associated virus, forming polykaryons, was isolated in adrenal and thyroid cells from 3 cattle with experimentally induced malignant catarrhal fever. It was cultured from leukocytes, ependymal tissue, spleen, lymph node, kidney and thyroid and adrenal glands of affected cattle and remained cell-associated in 48 subsequent passages. It was inactivated by freezing and thawing and by treatment with ultrasound; its polykaryon-forming activity was inhibited by 25 mug of 5 fluoro-2' deoxyuridine/ml. This viral agent replicated in bovine fetal adrenal, thyroid, and spleen cells, but not in primary kidney cells or in MDBK, HeLa, or L cells. A representative isolate was identified electronmicroscopically as an enveloped virus, 120 to 150 nm in diameter. Structural analysis indicated that it had properties of the bovine syncytial viruses. Attempts to induce MCF in cattle with 1 of the isolates failed. A parvovirus was isolated from the jejunal lymph node of calf 72-P-293, which had the experimentally induced disease and was also infected with the syncytial virus.

Urogenital infection and seminal excretion after inoculation of bulls and rams with chlamydiae

Five mature rams and 4 bulls were inoculated parenterally with bovine or ovine chlamydial strains of type 1 and 2. One to 3 days later, all animals developed a chlamydemia lasting 4 to 8 days. Chlamydial agents were isolated from the semen near the end of the chlamydemic phase. All rams and 3 of 4 inoculated bulls excreted chlamydiae in the semen for 22 to 29 days. From 8 to 39 days after inoculation, selected rams or bulls were killed to test for chlamydial infection in the urogenital tract and other organs. Chlamydiae were isolated in developing chicken embryos from testis, epididymis, and accessory sex glands. Bulls examined 29 and 39 days after inoculation did not harbor chlamydiae. Chlamydiae were also not isolated from 3 control bulls which were from the same herd as the principal bulls. All inoculated bulls and rams had a group-specific chlamydial antibody response within 7 days. The titers reached maximal levels of 128 to 512 at 14 days after inoculation. Subsequently, the antibody titers decreased gradually. Seminal plasma collected at different times after animals were inoculated did not fix complement in the presence of chlamydial group antigen. The number of polymorphonuclear leukocytes in the semen increased during the experiment. The semen was grossly purulent in 2 rams inoculated with the type 2 chlamydial strain of polyarthritis.

Ultrastructural cytochemical evidence for the activation of lysosomes in the cytocidal effect of Chlamydia psittaci

The cytopathic effect of the polyarthritis strain of Chlamydia psittaci was studied in cultured bovine fetal spleen cells and found to be mediated by the release of lysosomal enzymes into the host cytoplasm during the late stages of chlamydial development. Ultrastructural cytochemical analysis and cell fractionation studies of infected cells revealed a close relationship between the stage of chlamydial development, fine structural features of the host, and localization of lysosomal enzyme activities. After adsorption, chlamydiae entered the host cells by endocytosis. The endocytic vacuoles containing individual chlamydiae and later the inclusion vacuoles containing the different chlamydial developmental forms were always free from lysosomal enzyme activity. Even after extensive multiplication of chlamydiae, lysosomal enzymes remained localized within lysosomes or their precursors in the host cell. Coincident with the process of chlamydial maturation, lysosomal enzymes were released into the host cytoplasm and were always associated with disintegration of host cell constituents and lysis. The chlamydiae appeared to be protected from this lysosomal enzyme activity by the inclusion membrane. After release from the inclusion, elementary bodies maintained their fine structural features, whereas all other chlamydial developmental forms lost their ultrasturctural integrity.

Protein profiles of dense-centered forms of five chlamydial strains of animal origin

Purified dense-centered form of 1 bovine strain (LW613) and 3 ovine strains (B577, 034-EYE, and 047-EYE) of Chlamydia psittaci and 1 murine strain of Chlamydia trachomatis (MoPn) were dissociated in the presence of sodium dodecyl sulfate (SDS) and 2-mercaptoethanol. The number of polypeptides detected in the 5 strains varied between 17 and 20, with a molecular weight range of 29,000 to 120,000. Two polypeptides predominated and comprised approximately a third of the total protein in each of the 5 strains. The average molecular weights of the 2 polypeptides were 89,000 and 85,250 for 4 of the strains, and the polypeptide molecular weights were 100,000 and 98,000 for the ovine abortion strain (B577). Molecular weights and proportional composition of the polypeptides permitted differentiation of the chlamydial strains. The 3 strains from naturally occurring conjunctivitis or polyarthritis (LW613, 034-EYE, and 047-EYE) had similar polypeptide profile in the 75,000 to 100,000 molecular weight range. The polypeptides of the ovine abortion strain (B577) differed significantly from these 3 strains. Eight of the polypeptides of this strain had a molecular weight of 100,000 or greater, and 3 of the predominant polypeptides were in excess of 100,000. In contrast, some of the polypeptides of the murine strain had lower molecular weights than the 4 other strains. Three predominant polypeptides had molecular weights below 50,000.

Serotyping of Chlamydia: isolates of bovine origin

Chlamydial isolates of bovine origin were serotyped by a plaque reduction method. Of the two major serotypes observed, type 1 included isolates from bovine abortion and enteric infections, whereas type 2 isolates were associated with polyarthritis or encephalomyelitis. These two serotypes were identical to those with a similar disease distribution previously observed in isolates of ovine origin. The two groups did not cross-react and they were serologically unrelated to chlamydiae of avian origin. Thus, it appears that many chlamydial isolates causing intestinal infections or abortion in sheep or cattle are closely related antigenically, as are those producing polyarthritis, encephalomyelitis, and conjunctivitis, and that the two groups are distinct.

Serotyping of Chlamydia. I. Isolates of ovine origin

Eight chlamydial isolates of ovine origin were tested in a plaque reduction system using homologous and heterologous rooster antisera. The eight isolates could be separated into two separate immunotypes. Type 1 included isolates associated with ovine abortion and one agent recovered from the feces of an apparently normal sheep. Type 2 isolates were associated with polyarthritis and conjunctivitis. These two serotypes were not cross-reactive with several chlamydiae of avian origin. Further application of the plaque reduction test may provide a useful means of typing chlamydiae.

Ultrastructural changes in the chlamydia-infected ileal mucosa of newborn calves

Ultrastructural changes induced by chlamydial infection of mucosal cells of the ileum of newborn calves after oral inoculation were investigated. Depending on the stage of chlamydial development, the organelles of all infected cells became damaged. The damage was degenerative and included vesiculation of microvilli and swelling of the terminal web of absorptive epithelial cells. The mitochondria were swollen and had fragmented cristae. The endoplasmie reticulum was dilated and vesiculated, and infected cells gradually lost their ribosomes. The lateral junctional complex between infected cells became occasionally dislocated and fragmented. The basal lamina was thrown into folds, became discontinuous and separated from the basal border of the epithelial cells. The nuclei of infected cells were affected last, lost their chromatin pattern, and ultimately became pyknotic.

Chlamydiae as agents of human and animal diseases

A brief review is given of the properties, occurrence, and public health significance of chlamydiae in man and animals and of the diagnosis and control of chlamydial infections. Chlamydiae occur naturally in a large number of avian and mammalian species. Man is the primary host of chlamydiae causing trachoma, inclusion conjunctivitis, genito-urinary tract infection, and lymphogranuloma venereum. In animals chlamydial infections have been recognized as a cause of pneumonia, encephalitis, abortion, arthritis, diarrhoea, and conjunctivitis. Chlamydial infections have been recognized in a wide range of avian hosts. Sporadic psittacosis/ornithosis in man is associated with close exposure to birds and may occur as an occupational disease. Transmission studies suggest that mammalian chlamydial strains are not very host-specific and that diseases and even chains of infection may develop in secondary hosts. There are a few well-documented cases of human infection with chlamydiae of mammalian origin. Although various chlamydial isolates have specific antigenic components, no routine test for identifying different serotypes has been generally accepted. Further investigation of the host range of chlamydiae and of their antigenic properties is essential for a more accurate assessment of the potential danger of chlamydia-infected animals to human health. The frequent occurrence of inapparent or latent infections makes it imperative to establish adequate laboratory facilities for the effective surveillance and control of chlamydial infections.