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

The role of goblet cells in viral pathogenesis

Goblet cells are specialized epithelial cells that are essential to the formation of the mucus barriers in the airways and intestines. Armed with an arsenal of defenses, goblet cells can rapidly respond to infection but must balance this response with maintaining homeostasis. Whereas goblet cell defenses against bacterial and parasitic infections have been characterized, we are just beginning to understand their responses to viral infections. Here, we outline what is known about the enteric and respiratory viruses that target goblet cells, the direct and bystander effects caused by viral infection and how viral interactions with the mucus barrier can alter the course of infection. Together, these factors can play a significant role in driving viral pathogenesis and disease outcomes.

Infection of calves with bovine norovirus GIII.1 strain Jena virus: an experimental model to study the pathogenesis of norovirus infection

The experimental infection of newborn calves with bovine norovirus was used as a homologous large animal model to study the pathogenesis of norovirus infection and to determine target cells for viral replication. Six newborn calves were inoculated orally with Jena virus (JV), a bovine norovirus GIII.1 strain, and six calves served as mock-inoculated controls. Following infection, calves were euthanized before the onset of diarrhea (12 h postinoculation [hpi]), shortly after the onset of diarrhea (18 to 21 hpi), and postconvalescence (4 days pi [dpi]). Calves inoculated with JV developed severe watery diarrhea at 14 to 16 hpi, and this symptom lasted for 53.5 to 67.0 h. Intestinal lesions were characterized by severe villus atrophy together with loss and attenuation of villus epithelium. Viral capsid antigen (JV antigen) was detected by immunohistochemistry in the cytoplasm of epithelial cells on villi. In addition, granular material positive for JV antigen was detected in the lamina propria of villi. Lesions first appeared at 12 hpi and were most extensive at 18 to 19 hpi, extending from midjejunum to ileum. The intestinal mucosa had completely recovered at 4 dpi. There was no indication of systemic infection as described for norovirus infection in mice. JV was found in intestinal contents by reverse transcription-PCR (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) as early as 12 hpi. Fecal shedding of the virus started at 13 hpi and stopped at 23 hpi or at necropsy (4 dpi), respectively. Throughout the trial, none of the control calves tested positive for JV by ELISA or RT-PCR.

Coronavirus infection of polarized epithelial cells

Epithelial cells are the first host cells to be infected by incoming c oronaviruses. Recent observations in vitro show that coronaviruses are released from a specific side of these polarized cells, and this polarized release might be important for the spread of the infection in vivo. Mechanisms for the directional sorting of coronaviruses might be similar to those governing the polar release of secretory proteins.

Comparison of the S genes and the biological properties of respiratory and enteropathogenic bovine coronaviruses

The nucleotide sequence of the S gene of the bovine respiratory coronavirus (BRCV) strain G95, which was isolated from nasal swabs of a calf suffering from respiratory disorders, was determined and compared with the S gene of the enteropathogenic bovine coronavirus (BECV) strain LY138. Sequence analysis revealed 98.7% nucleotide and 98.3% deduced amino acid identities between the S genes of BRCV-G95 and BECV-LY138 without any deletions or insertions. Nucleotide substitutions were distributed randomly throughout the gene. Five monoclonal antibodies specific for the S protein distinguished BRCV-G95 from BECV-L9, but failed to differentiate it from BECV-LY138 in Western blots under denatured and native conditions. BRCV-G95 induced cytopathic changes in cell cultures that were similar to BECV-LY138 but different from BECV-L9. These results suggest that strain BRCV-G95 is more closely related to the virulent strain BECV-LY138 than to the avirulent, cell culture-adapted strain BECV-L9.

Virus infection of polarized epithelial cells

This chapter focuses on the interaction of viruses with epithelial cells. The role of specific pathways of virus entry and release in the pathogenesis of viral infection is examined together with the mechanisms utilized by viruses to circumvent the epithelial barrier. Polarized epithelial cells in culture, which can be grown on permeable supports, provide excellent systems for investigating the events in virus entry and release at the cellular level, and much information is being obtained using such systems. Much remains to be learned about the precise routes by which many viruses traverse the epithelial barrier to initiate their natural infection processes, although important information has been obtained in some systems. Another area of great interest for future investigation is the process of virus entry and release from other polarized cell types, including neuronal cells.

Bovine coronavirus antigen in the host cell plasmalemma

Expression of bovine coronavirus (BCV) antigen in the plasmalemma of epithelioid human rectal tumor (HRT-18) and fibroblastic bovine fetal spleen (BFS) cell lines was traced by immunofluorescence and immunoelectron microscopy facilitated by colloidal gold. Cytoplasmic fluorescence was first observed at 12 hr postinfection (h.p.i) in infected HRT-18 cultures. This fluorescence coincided with the appearance of cell surface antigen reacting with colloidal gold-labeled antibodies to BCV antigens. At 24 h.p.i the amount of viral antigens at the surface of HRT-18 had increased, although cytoplasmic fluorescence remained constant. Infected BFS cells but not HRT-18 cells formed polykaryons when incubated in the presence of trypsin. One viral antigen in the plasma membrane of BFS cells was thus identified as the S glycoprotein with a fusion domain. In contrast to HRT-18 cells, the overall amount of BCV antigens at the surface of BFS cells remained constant after the onset of fusion. Analysis of the labeling characteristics established that the gold-marked-sites represented de novo expression of BCV antigen in the plasma membrane of infected cells.

Scanning electron microscopic characterization of bovine coronavirus plaques in HRT cells

The ecology of cytopathic expression of bovine coronavirus (BCV) in HRT-18 cells was analyzed within virus-induced plaques by scanning electron microscopy. Virus replication was cytocidal for many HRT-18 cells, a function enhanced in the presence of trypsin. A monolayer of cells remained that imparted a characteristic turbidity to the plaque. These structurally normal, lysis-resistant cells did not stain with fluorescent antibodies specific for BCV antigens, failed to adsorb virus particles or mouse erythrocytes in contrast to the susceptible cells. The survival of cells in the plaque interior reflects a non-productively infected population with evidence of viral persistence.

Development of nasal, fecal and serum isotype-specific antibodies in calves challenged with bovine coronavirus or rotavirus

Unsuckled specific pathogen free calves were inoculated at 3-4 weeks of age, either intranasally (IN) or orally (O) with bovine coronavirus or O plus IN (O/IN) or O with bovine rotavirus. Shedding of virus in nasal or fecal samples, and virus-infected nasal epithelial cells were detected using immunofluorescent staining (IF), ELISA or immune electron microscopy (IEM). Isotype-specific antibody titers in sera, nasal and fecal samples were determined by ELISA. Calves inoculated with coronavirus shed virus in feces and virus was detected in nasal epithelial cells. Nasal shedding persisted longer in IN-inoculated calves than in O-inoculated calves and longer than fecal shedding in both IN and O-inoculated calves. Diarrhea occurred in all calves, but there were no signs of respiratory disease. Calves inoculated with rotavirus had similar patterns of diarrhea and fecal shedding, but generally of shorter duration than in coronavirus-inoculated calves. No nasal shedding of rotavirus was detected. Peak IgM antibody responses, in most calves, were detected in fecal and nasal speciments at 7-10 days post-exposure (DPE), preceeding peak IgA responses which occurred at 10-14 DPE. The nasal antibody responses occurred in all virus-inoculated calves even in the absence of nasal shedding of virus in rotavirus-inoculated calves. Calves inoculated with coronavirus had higher titers of IgM and IgA antibodies in fecal and nasal samples than rotavirus-inoculated calves. In most inoculated calves, maximal titers of IgM or IgA antibodies correlated with the cessation of fecal or nasal virus shedding. A similar sequence of appearance of IgM and IgA antibodies occurred in serum, but IgA antibodies persisted for a shorter period than in fecal or nasal samples. Serum IgG1 antibody responses generally preceeded IgG2 responses and were predominant in most calves after 14-21 DPE.

Studies on the relationship between coronaviruses from the intestinal and respiratory tracts of calves

An immunofluorescence test on smears of nasal epithelial cells was used to detect coronavirus infection in the respiratory tract of calves. Thirteen gnotobiotic calves were infected with coronavirus isolates derived from faeces or respiratory material: virus was detected in faeces and nasal swabs from all animals. In 115 calves from a field survey, there was a significant association between coronavirus excretion from both respiratory and enteric routes in calves with diarrhoea. In a further 12 calves, at necropsy, the predilection sites for coronavirus growth were the distal small intestine, large intestine and the epithelia of the nasal cavity and trachea. Antigen was not found in lung tissue by immunofluorescence or immunoperoxidase staining. Infection with enteric coronavirus induced immunity to reinfection and to heterologous challenge with two coronavirus isolates derived from the respiratory tract. Nine coronaviruses were cultivated, cloned and antisera to three were prepared in pigs. There was complete virus neutralisation in tests with homologous sera and significant cross reactions with the eight other isolates which were of intestinal and respiratory origin. Thus, these bovine coronavirus isolates belonged to the same serotype despite the source of virus.

The molecular biology of coronaviruses

Coronaviruses have recently emerged as an important group of animal and human pathogens that share a distinctive replicative cycle. Some of the unique characteristics in the replication of coronaviruses include generation of a 3' coterminal-nested set of five or six subgenomic mRNAs, each of which appears to direct the synthesis of one protein. Two virus-specific RNA polymerase activities have been identified. Many of the distinctive features of coronavirus infection and coronavirus-induced diseases may result from the properties of the two coronavirus glycoproteins. The intracellular budding site, which may be important in the establishment and maintenance of persistent infections, appears to be due to the restricted intracytoplasmic migration of the E1 glycoprotein, which acts as a matrix-like transmembrane glycoprotein. E1 also exhibits distinctive behavior by self-aggregating on heating at 100°C in sodium dodecyl sulfate (SDS) and by its interaction with RNA in the viral nucleocapsid. The E1 of mouse hepatitis virus (MHV) is an O -linked glycoprotein, unlike most other viral glycoproteins. Thus, the coronavirus system may be a useful model for the study of synthesis, glycosylation, and transport of O -linked cellular glycoproteins.

Pathology of experimental CV777 coronavirus enteritis in piglets. II. Electron microscopic study

Sixteen cesarean-derived, colostrum-deprived piglets were infected oronasally with CV777 coronavirus on the second or third day of life. Two uninfected piglets were controls. After an incubation period of 22 hours to 36 hours, all principals showed severe diarrhea. The piglets were killed at different time intervals. Viral particles were found in the jejunal villous epithelial cells from 18 hours after infection until four days after the beginning of diarrhea. In the colonic epithelial cells, viral particles and degenerative lesions were found only in the piglet killed 36 hours after onset of diarrhea. Degenerative lesions in the enterocytes began at 18 hours after infection and were most pronounced in the jejunum at the onset of clinical signs. From 24 hours on after the onset of clinical signs, three cell types were found: degenerated virus-containing enterocytes; cuboidal cells; and columnar, highly vacuolated cells containing lipid droplets.

Pathology of experimental CV777 coronavirus enteritis in piglets. I. Histological and histochemical study

Sixteen cesarean-derived colostrum-deprived piglets were infected oronasally with CV777 coronavirus on the second or third day of life. Two uninfected piglets were controls. They were killed at 96 and 120 hours after birth. After an incubation period of 22 to 36 hours, all principals showed severe diarrhea. The principals were killed between 12 and 120 hours after infection. Exfoliation of enterocytes were seen first in the piglet killed 24 hours after infection (two hours after the diarrhea began). From that time on, shortening and fusion of villi was present in all small intestinal parts. Affected cells showed vacuolation. The histochemical study showed that infected piglets had decreased activity of all four enzymes studied. The light microscope showed no lesions in the absorptive colonic epithelium. The significance of the lesions in relation to intestinal dysfunction is discussed, and lesions are compared to those of transmissible gastroenteritis and porcine rotavirus infection.

[Calf coronavirus neonatal diarrhea. A literature review (author's transl)]

Calf coronavirus neonatal diarrhea. A literature reviewThe importance of the calf coronavirus in the etiology of neonatal diarrhea of calves has been reported many times from various countries. A literature review concerning this virus is presented in this paper. A detailed description of the pathogenesis, clinical signs and lesions of the disease, as well as the morphological, physicochemical, biological and antigenic characteristics of the virus are presented. The immunity of the calf against this virus and the principal diagnosis technics are also discussed.

Enhancement of plaque formation and cell fusion of an enteropathogenic coronavirus by trypsin treatment

Plaque formation, replication, and related cytopathic functions of the enteropathogenic bovine coronavirus strain L9 in bovine fetal thyroid (BFTy) and bovine fetal brain (BFB) cells were investigated in the presence and absence of trypsin. Plaque formation was enhanced in both cell types. Plaques reached a size with an average diameter of 5 mm within 4 days with trypsin in the overlay, whereas their diameter remained less than 1 mm at this time after plating without trypsin in the overlay. Fusion of both cell types was observed 12 to 18 h after infection when trypsin was present in the medium. Fusion was not observed in infected BFB cell cultures and was rarely observed 48 h after infection of BFTy cells maintained with the trypsin-free medium. The largest polycaryons formed had 15 to 22 nuclei. They then lysed and detached. Cell fusion depended on de novo synthesis of hemagglutinin and infectivity. Fusion from without was not observed. Virus produced under trypsin-enhancing conditions accompanied by cell fusion did not lyse mouse erythrocytes that reacted with L9 coronavirus hemagglutinin. Trypsin-treated, infected BFTy cultures produced coronaviral particles that excluded stain from the envelope confinement. These virions had uniformly shorter surface projections than did the viral forms generated by trypsin-free cell cultures.

Reactivity of antibodies in human serum with antigens of an enteropathogenic bovine coronavirus

Antibodies in human serum against an enteropathogenic bovine coronavirus were detected by double immunodiffusion (DID), neutralization of infectivity, indirect immunofluorescence, and immune electron microscopy. Human sera reacting in the DID test neutralized the infectivity of the bovine coronaviruses to indices of 2.5 to greater than 5. Nineteen of 40 DID-negative, heat-inactivated sera had neutralizing indices of 1 to 3.0. Human serum with neutralizing and DID antibodies produced juxtanuclear and cytoplasmic fluorescence identical to that of bovine immune serum in cells infected with the bovine coronavirus. Antibodies in human and bovine sera interacted with the peplomeres of the bovine coronavirus, matting and bridging them, when present in excess, and facilitated formation of large viral aggregates when present in equivalent concentrations. Complement added to the virus-antibody complexes did not alter specifically the morphology of single, antibody-laden viral particles or viral particles in aggregates. Evidence of the transmission of coronavirus from experimentally inoculated calves to man, with ensuing gastroenteritis, was found by electron microscopic tracing of the coronavirus and its virus-antibody complexes.

Immunoglobulin levels in non-aborted and aborted fetuses from Danish herds of cattle

The applicability of serological tests in the diagnosis of intrauterine infections in Danish cattle was investigated. Fetuses from slaughter animals, experimentally infected and spontaneously aborted fetuses, premature and stillborn calves, were subjected to necropsy and histological studies, and to microbiological and serological examinations. The latter comprised rocket immunoelectrophoresis and radial immunodiffusion. In sera of the fetuses from slaughter animals, immunoglobulins were either not detectable or only present in very small quantities, whereas sera of fetuses and calves with pathological changes and/or verified infection contained considerable amounts of IgM and IgG. IgA was also detected in the latter group. The results corroborate the diagnostic importance of immunoglobulin determination in aborted fetuses and stillborn calves.

Viral diarrhea of young animals: a review

A brief presentation is given of the enteric viral infections of young animals. The general characteristics of rotaviruses, coronaviruses and parvoviruses are reported, and the different aspects of the diseases associated with these viruses are discussed. Certain suggestions are made regarding the prevention of these diseases.

Structural polypeptides of the enteropathogenic bovine coronavirus strain LY-138

The bovine coronavirus strain LY-138 was purified by differential as well as velocity and isopycnic centrifugation in sucrose or CsCl gradients. The substrate for purification was contents of the small intestine of experimentally inoculated calves. This strain is highly enteropathogenic, but it could not yet be propagated in cultured cells. Intact virions had a density of 1.245 g/cm3 in CsCl and 1.185 g/cm3 in sucrose. A spherical core-like structure with an average diameter of 82 nm remaining after treatment with chloroform had a density of 1.299 g/cm3 in CsCl and 1.201 g/cm3 in sucrose. Seven distinct bands of polypeptides and 4 shoulders were detected after electrophoresis of SDS-solubilized virions in polyacrylamide gels. The approximate molecular weights ranged from 110,000 to 36,000. Four of the bands gave a PAS positive reaction. These 4 glycoproteins and an additional protein with an approximate molecular weight of 70,000 were removed by chloroform treatment. The remaining core-like structure contained the 2 polypeptides VP3 and VP7.

The rate of development of postmortem artefact in the small intestine of neonatal calves

The rate of development of postmortem artefacts was investigated in the mucosa of the small intestine of a calf dually infected with an enteropathogenic strain of Esch. coli and rotavirus, and an uninfected control calf. Samples were removed under general anaesthesia from the proximal, middle and distal small intestine and compared with those taken from adjacent sites 1-30 min after severing the major blood vessels of the neck. In the challenged calf, changes occurred in the villous mucosa by 3 min after severance, whilst in the control calf good fixation was obtained until 10 min after severance.