Antigenic diversity of Chlamydia psittaci of mammalian origin determined by microimmunofluorescence

A group of twenty-five isolates of Chlamydia psittaci representing at least seven different biotypes of bovine, ovine, caprine, equine, feline, porcine, and guinea pig origin were immunotyped by an indirect microimmunofluorescence test. Different groups of chlamydia-free BALB/c mice received two weekly intravenous inoculations with chicken embryo-propagated, partially purified elementary bodies of each strain. Antisera for immunotyping were collected 4 days after the first inoculation and 3 to 4 days after the second inoculation and tested for antichlamydial immunoglobulin M and immunoglobulin G antibodies by the indirect microimmunofluorescence test with cell culture-propagated, partially purified homologous and heterologous antigens. Nine immunotypes of C. psittaci were distinguished. The correlation between immunotypes and biotypes was close, and a pattern of either disease or host specificity could be associated with each immunotype. Most immunotypes identified induced cross-reacting antibodies against each other, but no significant cross-reactions were observed with elementary bodies of the mouse pneumonitis strain of C. trachomatis. Findings from this study should provide the necessary background for the rational selection of prototype strains of C. psittaci for further antigenic analysis at the molecular level.

Persistent infection of L cells with an ovine abortion strain of Chlamydia psittaci

L cells inoculated at multiplicities of infection greater than or equal to 1 inclusion-forming unit of the abortigenic chlamydial strain B577 were destroyed within 10 to 15 days. Upon continued incubation in fresh medium, a few surviving cells repopulated the flasks, and the reemerging cultures remained persistently infected. The persistent state was characterized by cycles of repopulation with a low ratio of infected cells and cycles of extensive cytopathic changes in which greater than 90% of the cells had chlamydial inclusions and which could be delayed or even terminated by penicillin treatment. Immunofluorescence and superinfection during the period of repopulation revealed that the persistently infected cells could adsorb chlamydiae but their multiplication was arrested. This nonpermissive state could be terminated by the specific action of cycloheximide. L cells spontaneously cured from a persistent infection exhibited no change in susceptibility to chlamydiae when compared with normal L cells. However, chlamydiae derived from L cells after 7.5 months of persistence destroyed L-cell monolayers more rapidly and at lower multiplicities of infection than the wild type. This state of chlamydia-host cell interaction could not be established with the arthropathogenic strain LW613 because chlamydial infectivity was lost after the first cytolytic burst of infection in the cell cultures. The persistence described for the strain B577-L-cell system appears to differ from previously described models involving other chlamydial strains.

Bovine cytomegaloviruses: identification and differential properties

Biological properties and restriction enzyme patterns of the slowly replicating herpesviruses isolated from cattle affected with different diseases in North America and Europe were analysed. These virus isolates induced identical plaques that developed within 7 to 9 days in bovine foetal spleen cells and within 5 days in actively growing Georgia bovine kidney cells. These virus isolates were found to be antigenically related when tested in the indirect immunofluorescence test, and antigenic relationships with bovine herpesvirus 1 (BHV-1), BHV-2, BHV-3 or BHV-6 were not detected. The genomes of these strains were shown to have virtually identical cleavage sites when treated with restriction enzymes EcoRI, BamHI, SstII, SphI and HindIII. The resulting restriction enzyme patterns differed strikingly from those of BHV-1, BHV-2, BHV-3 and BHV-6. Because the herpesviruses tested become enveloped on the nuclear as well as on endoplasmic membranes, a process through which they induce cytoplasmic vesicles filled with enveloped viral particles, and because of the unique cytoplasmic inclusions that are induced, we classify them tentatively as bovine cytomegaloviruses.

Morphogenesis of a cytomegalovirus from an American bison affected with malignant catarrhal fever

A herpesvirus isolated from several organs of an American bison affected with malignant catarrhal fever was cultured in bovine foetal spleen cells and studied by electron microscopy. The fine structural features of the mature virion and the mode of virus morphogenesis were found to be similar to herpesviruses classified in the subgroup cytomegalovirus. The capsids were granular, hexagonal in shape and contained pleomorphic cores in thin sections. Envelopment of the capsids occurred primarily by budding on cytoplasmic membranes which appeared to be formed as extended vesicles of the Golgi apparatus; budding on nuclear membranes was only rarely observed. Cytoplasmic inclusions consisting of granular threads and amorphous electron-dense material were found in association with virions during the late stages of infection. The formation of cytoplasmic inclusions, the morphogenesis and ultrastructure of the virus are all consistent with classification of this virus as a cytomegalovirus.

Antigenicity of bovine parvovirus in fetal infections

The humoral immune response of bovine fetuses to bovine parvovirus (BPV) infection during the 2nd and 3rd trimesters was studied by the single radial immunodiffusion, hemagglutination-inhibition (HI), indirect immunofluorescence (IFA), microneutralization (MN), plaque-neutralization, and double immunodiffusion (DID) tests. Serum samples collected from 23 BPV-inoculated and several control fetuses were tested. The immunoglobulin (Ig) M concentrations reached 355 mg/100 ml at 10 days after fetal inoculations were done and then decreased. The IgG concentration increased 10 days after inoculation and was maximal 142 days later. A correlation between Ig concentrations and antibodies reacting in the HI, IFA, MN, DID, and plaque-neutralization tests existed in all samples. Neutralizing and HI antibodies were detected 10 days after fetal inoculations. The highest MN titer of 4,096 was detected in a fetus 10 days after the inoculation done during the 3rd trimester. Six serum samples were positive in the IFA test. These samples, collected 10 to 60 days after fetuses were inoculated, had IgG concentrations of 615 mg/100 ml or higher, and had titers of 16 to 64. Treatment of BPV with carbonate-bicarbonate buffer (pH 10.5) disrupted the virus and liberated antigens reacting in the DID test. Electron microscopic examination of the negatively stained antigen preparation revealed loss of structural integrity of the viral particles. This suspension of disrupted BPV was reactive with some of the fetal serum samples in the DID test, inducing 1 or 2 precipitin lines.

Infectivity of Chlamydia psittaci of bovine and ovine origins for cultured cells

The infectivity of 2 strains of Chlamydia psittaci of mammalian origin were studied in mouse L cells. Infectivity was enhanced by centrifuging the chlamydial inoculum onto the cell monolayer. Infectivity increased as force of centrifugation increased. The enhanced infectivity was not caused by centrifugal sedimentation of chlamydiae, since centrifugation longer than 10 minutes and an inoculum dose larger than 0.4 ml did not further enhance infectivity. Centrifuge-enhanced adsorption was temperature dependent, because infection was not detected when stationary or centrifuge-assisted adsorption occurred at less than 15 C. Infectivity was higher in cultures centrifuged at 37 degrees C than in cultures centrifuged at room temperature. Treatments of cells with cycloheximide, colchicine, and hydrocortisone enhanced infectivity of chlamydiae above that of untreated cells. In addition, developing chlamydial inclusions were larger and easier to observe in colchicine-treated cells. Infectivity was thought to be enhanced in colchicine-treated cells, because cells with depolymerized microtubules provided favorable conditions for the early phases of chlamydial multiplication. Treatment of cells with cytochalasin B, carbachol, cGMP, lumicolchicine, or vinblastine did not significantly alter chlamydial infectivity.

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.

Chlamydia psittaci: growth characteristics and enumeration of serotypes 1 and 2 in cultured cells

The growth characteristics of Chlamydia psittaci serotypes 1 and 2 (ovine and bovine origin) were studed in mouse L cells. Formation of inclusions and yield of infectious progeny for serotype 1 were maximal when host cells were treated with cycloheximide and the pH in the cell culture medium was 7.2-7.4. The number of cells that contained inclusions and the infectivity yield for serotype 2 were maximal when the pH was 6.6-7.0. Treatments with diethylaminoethyl dextran and cycloheximide increased inclusion formation in serotype 2 but decreased the yield per infected cell. For both serotypes, centrifugation of the chlamydiae onto monolayers infected 50-1,200 times the number of cells infected with use of stationary adsorption. An enumeration method for L-cell infectious units was developed that gave higher titers than the chicken embryo 50% lethal dose after yolk sac inoculation.

Biotyping of Chlamydia psittaci based on inclusion morphology and response to diethylaminoethyl-dextran and cycloheximide

Strains of Chlamydia psittaci from cattle, sheep, pigs, mice, guinea pigs, rabbits, cats, and parrots were subdivided based on their biological characteristics. Chlamydiae grown in the yolk sac of chicken embryos were used to infect L cell monolayers. The host cells were infected without further treatment or treated with diethylaminoethyl-dextran, cycloheximide, or both. The following criteria were used for biotyping the strains: the morphology of the inclusions and time after infection at which they appeared, the effect of chlamydial multiplication on the host cell cytoskeleton, and the change in the number of cells infected in response to diethylaminoethyl-dextran and cycloheximide. These properties were determined for 29 strains of C. psittaci. Based on the results, the strains were placed into eight biotypes.

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.

Pathogenesis of chlamydial polyarthritis in domestic animals: characteristics of causative agent

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Clinical and clinicopathologic observations in induced malignant catarrhal fever of cattle

In an epizootic of malignant catarrhal fever in 1976/1977 in southern California, 166 cows (17%) died. Blood from one of those cows was used in transmission studies involving 8- to 14-month-old steers. In 17 (74%) of 23 inoculated steers, the disease was reproduced. The clinical signs in 8 of the diseased steers were characterized by an initially mild intestinal form of the disease, which suddenly fulminated and terminated in death within 1 to 3 days. No lesions or only mild oral or ocular lesions were noticed in this group, but in the other steers, such lesions predominated. It was concluded that a subtle form of the disease can terminate in acute fatal indigestion.

Experimental transmission of malignant catarrhal fever in cattle: gross and histopathologic changes

Bovine malignant catarrhal fever (MCF) was serially transmitted from a spontaneous case to 19 cattle through 12 passages during a 12-month period. Seventeen of 23 cattle (74%) injected with whole blood and 2 of 5 cattle (40%) injected with blood mononuclear cells developed clinical signs of MCF after a mean incubation period of 30.2 days. A previously unreported nonsuppurative polyarthritis is described. Large numbers of lymphoid cells were found in synovial fluid and in cerebrospinal fluid. Histopathologic changes of lymphoid infiltration and proliferation, necrosis of epithelial tissues, and nonsuppurative vasculitis were found in almost all organs of the body. The possibility that MCF may be a viral-induced, cell-mediated immunopathologic disease with pansystemic lymphoreactivity and necrosis is discussed.