Isolation and propagation of coronaviruses in embryonated eggs

The embryonated egg is a complex structure comprising an embryo and its supporting membranes (chorioallantoic, amniotic, yolk). The developing embryo and its membranes provide the diversity of cell types that are needed for successful replication of a wide variety of different viruses. Within the family Coronaviridae, the embryonated egg has been used as a host system primarily for two group 3 coronaviruses, infectious bronchitis virus (IBV) and turkey coronavirus (TCoV), but it also has been shown to be suitable for pheasant coronavirus. IBV replicates well in the embryonated chicken egg, regardless of the inoculation route; however, the allantoic route is favored as the virus replicates extensively in chorioallantoic membrane and high titers are found in allantoic fluid. TCoV replicates only in embryo tissues, within epithelium of the intestines and bursa of Fabricius; thus amniotic inoculation is required for isolation and propagation of this virus. Embryonated eggs also provide a potential host system for studies aimed at identifying other, novel coronavirus species.

Detection of turkey coronavirus in commercial turkey poults in Brazil

Poult enteritis complex has been incriminated as a major cause of loss among turkey poults in other countries. We have observed this in Brazil, associated with diarrhoea, loss of weight gain and, commonly, high mortality. In this study, we have used the reverse transcriptase polymerase chain reaction (RT-PCR) to detect turkey coronavirus (TCoV) in sick poults 30 to 120 days of age from a particular producer region in Brazil. The RT-PCR was applied to extracts of intestine tissue suspensions, and the respective intestinal contents, bursa of Fabrícius, faecal droppings and cloacal swabs. Primers were used to amplify the conserved 3' untranslated region of the genome, and the nucleocapsid protein gene of TCoV. Histopathological and direct immunohistochemical examinations were performed to detect TCoV antigen in infected intestine and bursa slides. All the results from stained tissues revealed lesions as described previously for TCoV infection. The direct immunohistochemical positive signal was present in all intestine slides. However, all bursa of Fabrícius tissues analysed were negative. RT-PCR findings were positive for TCoV in all faecal droppings samples, and in 27% of cloacal swabs. Finally, the best field material for TCoV diagnosis was faecal droppings and/or intestine suspensions.

Comparison of 3'-end encoding regions of turkey coronavirus isolates from Indiana, North Carolina, and Minnesota with chicken infectious bronchitis coronavirus strains

Objective

To analyze the 3′-end structural protein-encoding region of turkey coronavirus (TCoV) isolates associated with outbreaks of acute enteritis in Indiana, North Carolina, or Minnesota.

Methods

Four isolates of TCoV were sequenced over the entire 3′-end structural protein-encoding region and compared phylogenetically along with the corresponding sequences of infectious bronchitis virus (IBV) strains.

Results

The sequence similarity between TCoV and IBV was lower than that among TCoV isolates or that among IBV strains. The variation of sequences between TCoV and IBV was mainly contributed by the S protein gene. The sequence similarity of S gene between TCoV and IBV was lower than that among TCoV isolates or that among IBV strains. The phylogenetic tree based on the S protein region was similar to that based on the entire 3′-end structural protein-encoding region with TCoV isolates and IBV strains grouped in two separate clusters. The phylogenetic tree based on other genes had a very different topology with TCoV isolates randomly forming groups with different IBV strains.

Conclusions

These results suggested that TCoV probably shared the same origin with that of IBV and acquired sequences of S gene for turkey intestine tropism during the process of evolution in a separate environment.

Complete sequences of 3' end coding region for structural protein genes of turkey coronavirus

Overlapping fragments of genomic RNA spanning 6963 nucleotides from 5′ end of spike (S) protein gene to 3′ end of nucleocapsid (N) protein gene of turkey coronavirus (TCoV) were amplified by reverse-transcription-polymerase chain reaction (RT-PCR). The primers were derived from the corresponding sequences of infectious bronchitis virus (IBV). The PCR products were cloned and sequenced and their nucleic acid structure and similarity to published sequences of other coronaviruses were analyzed. Sequencing and subsequent analysis revealed 9 open reading frames (ORFs) representing the entire S protein gene, tricistronic gene 3, membrane (M) protein gene, bicistronic gene 5, and N protein gene in the order of 5′–3′. The overall nucleic acid structures of these encoding regions of TCoV were very similar to the homologous regions of IBV. The consensus transcription-regulating sequence (TRS) of IBV, CT(T/G)AACAA, was highly conserved in TCoV genome at the levels of nucleotide sequence and location in regarding to the initiation codon of individual genes. Pair-wise comparison of gene 3, M gene, gene 5, or N gene sequences with their counterparts of IBV revealed high levels (82.1–92.0%) of similarity. Phylogenetic analysis based on the deduced amino acid sequences of S, M, or N protein demonstrated that TCoV was clustered within the same genomic lineage as the IBV strains while all the other mammalian coronaviruses were grouped into separate clusters corresponding to antigenic groups I or II. There were substantial differences of S protein sequence between TCoV and IBV with only 33.8–33.9% of similarity.

Expression and purification of turkey coronavirus nucleocapsid protein in Escherichia coli

Purification of turkey coronavirus (TCoV) nucleocapsid (N) protein, expressed in a prokaryotic expression system as histidine-tagged fusion protein is demonstrated in the present study. Turkey coronavirus was partially purified from infected intestine of turkey embryo by sucrose gradient ultracentrifugation and RNA was extracted. The N protein gene was amplified from the extracted RNA by reverse transcription-polymerase chain reaction and cloned. The recombinant expression construct (pTri-N) was identified by polymerase chain reaction and sequencing analysis. Expression of histidine-tagged fusion N protein with a molecular mass of 57 kd was determined by Western blotting analysis. By chromatography on nickel-agarose column, the expressed N protein was purified to near homogeneity as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. The protein recovery could be 2.5 mg from 100 ml of bacterial culture. The purified N protein was recognized by antibody to TCoV in Western blotting assay. The capability of the recombinant N protein to differentiate positive serum of turkey infected with TCoV from normal turkey serum was evident in enzyme-linked immunosorbent assays (ELISA). These results indicated that the expressed N protein is a superior source of TCoV antigen for development of antibody-capture ELISA for detection of antibodies to TCoV.

Existence of gene 5 indicates close genomic relationship of Turkey coronavirus to infectious bronchitis virus

A segment of genomic RNA extending from the 3'-end of the membrane (M) protein gene to the 5'-end of the nucleocapsid (N) protein gene of Turkey coronavirus (TCV) was amplified by reverse transcription-polymerase chain reaction (RT-PCR). The primers were derived from the corresponding sequences of Infectious bronchitis virus (IBV). The PCR products were cloned and sequenced and their nucleic acid structure and similarity to the published sequences of IBV were analyzed. Gene 5 containing two overlapping open reading frames (ORFs), 5a and 5b, was localized between M and N genes of TCV. The overall nucleotide sequences of the amplified regions from TCV isolates shared 88.4% to 91.8% similarity to the corresponding region of IBV strains. The consensus transcription-associated sequence of IBV, CTTAACAA, was highly conserved in the TCV genome with regard to nucleotide sequence and location in terms of the initiation codons of the genes 5 and N. The similarities between the predicted amino acid sequences of ORFs 5a and 5b of TCV isolates and the homologous genes of IBV strains were 85.4% to 94.0%. The results indicate the existence of gene 5 in the genome of TCV and a close relatedness of the TCV gene 5 to the IBV gene 5 in location and nucleotide sequence.

Mechanical transmission of turkey coronavirus by domestic houseflies (Musca domestica Linnaeaus)

Domestic houseflies (Musca domestica Linnaeaus) were examined for their ability to harbor and transmit turkey coronavirus (TCV). Laboratory-reared flies were experimentally exposed to TCV by allowing flies to imbibe an inoculum comprised of turkey embryo-propagated virus (NC95 strain). TCV was detected in dissected crops from exposed flies for up to 9 hr postexposure; no virus was detected in crops of sham-exposed flies. TCV was not detected in dissected intestinal tissues collected from exposed or sham-exposed flies at any time postexposure. The potential of the housefly to directly transmit TCV to live turkey poults was examined by placing 7-day-old turkey poults in contact with TCV-exposed houseflies 3 hr after flies consumed TCV inoculum. TCV infection was detected in turkeys placed in contact with TCV-exposed flies at densities as low as one fly/bird (TCV antigens detected at 3 days post fly contact in tissues of 3/12 turkeys); however, increased rates of infection were observed with higher fly densities (TCV antigens detected in 9/12 turkeys after contact with 10 flies/bird). This study demonstrates the potential of the housefly to serve as a mechanical vector of TCV.

Purification of turkey coronavirus by Sephacryl size-exclusion chromatography

Sephacryl S-1000 size-exclusion chromatography was used to purify turkey coronavirus (TCoV) from infected turkey embryo. TCoV was propagated in the 22-day-old turkey embryos. Intestines and intestinal contents of infected embryos were harvested and homogenized. After low speed centrifugation, the supernatant was concentrated by ultracentrifugation through a cushion of 30 or 60% sucrose solution, or by ammonium sulfate precipitation. The purification methods included sucrose gradient and Sephacryl S-1000 size-exclusion chromatography. Ultracentrifugation through a cushion of 60% sucrose solution was better than the other two methods for concentration of TCoV from intestinal homogenate. The most effective method for purifying TCoV and removing extraneous materials was size-exclusion chromatography as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. More spike-rich particles were observed in the sample purified by chromatography than those purified by sucrose gradient as examined by electron microscopy. Differentiation of turkey anti-TCoV antiserum from normal turkey serum was better achieved by ELISA plates coated with TCoV preparation purified by size-exclusion chromatography than that purified by sucrose density gradient. The results indicated that Sephacryl S-1000 chromatography was useful for purification of TCoV.

Development of a competitive enzyme-linked immunosorbent assay for detection of turkey coronavirus antibodies

A competitive enzyme-linked immunosorbent assay (cELISA) was developed for detection of turkey coronavirus (TCV) antibodies. The cELISA utilized a recombinant baculovirus (Autographa californica nuclear polyhedrosis virus)-expressed TCV nucleocapsid (N) protein and biotin-labeled TCV N protein-specific monoclonal antibody. Sensitivity and specificity of the cELISA for detection of TCV antibodies were determined by comparison with the indirect fluorescent antibody test (IFAT) with 1269 reference, experimentally derived, and field-origin sera. Sera with discordant cELISA and IFAT results were further evaluated by western immunoblot analyses. The cELISA detected antibodies specific for TCV and infectious bronchitis virus, a closely related coronavirus, but did not detect antibodies specific for other avian viruses. A high degree of concordance was observed between the cELISA and IFAT; sensitivity and specificity of the cELISA relative to IFAT were 92.9% and 96.2%, respectively. Western immunoblot analyses provided additional evidence of cELISA specificity. The findings indicate that the cELISA is a rapid, sensitive, and specific serologic test for detection of TCV antibodies in turkeys.

Characterization of turkey coronavirus from turkey poults with acute enteritis

The present study was to characterize turkey coronavirus associated with turkey poult enteritis and mortality. Intestinal contents or intestines from affected turkey poults and inoculated turkey embryos contained coronaviruses as revealed by electron microscopy or were positive for turkey coronavirus by immunofluorescent antibody assay. Sucrose density gradient ultracentrifugation of the virus-containing intestinal homogenate yielded two opalescent bands corresponding to the buoyant densities of 1.14-1.15 and 1.18-1.20 g/ml, respectively. Coronaviral particles from intestinal contents or the sucrose density gradient preparation were mainly spherical in shape and had envelope and central depression. They were surrounded by a fringe of regularly spaced petal-shaped projections attached to the particles by a short stalk. Purified viruses hemagglutinated rabbit erythrocytes with a titer of 16. Major protein bands of purified viruses analyzed by SDS-PAGE were located at 200, 100-110, 50-60, and 30-35 kDa. The patterns of protein bands were consistent with those of Minnesota or Quebec turkey coronavirus isolates. A 568 bp nucleotide fragment of turkey coronavirus spike protein gene was amplified from RNA of inoculated turkey embryo intestine or purified virus. Sequence analysis of the 568 bp PCR product revealed high degree of identity with the corresponding spike protein gene sequence of human and bovine coronaviruses. The results indicated that turkey coronavirus was associated with turkey poults with acute enteritis.

Comparison of virus isolation, immunohistochemistry, and reverse transcriptase-polymerase chain reaction procedures for detection of turkey coronavirus

A reverse transcriptase-polymerase chain reaction (RT-PCR) procedure and two monoclonal antibody (MAb)-based immunohistochemical procedures were developed for detection of turkey coronavirus (TCV) in tissues and intestinal contents/dropping samples. The RT-PCR, MAb-based fluorescent antibody (FA), and MAb-based immunoperoxidase (IP) procedures were compared with virus isolation (VI) for detection of TCV in experimentally infected turkeys. TCV was detected in experimentally infected turkeys as early as day 1 postexposure (PE) by each of the four detection procedures. TCV was detected as late as day 35 PE by FA or IP and days 42 and 49 PE by VI and RT-PCR, respectively. With VI as a reference, sensitivity and specificity of RT-PCR were 93% and 92%, respectively; specificity of both FA and IP was 96%, and sensitivities were 69% and 61%, respectively. Each of the examined procedures was highly specific, but the RT-PCR procedure was also highly sensitive. These findings demonstrate the utility of both immunohistochemistry and RT-PCR for detection of TCV. In addition, the findings indicate that RT-PCR is a highly sensitive and specific alternative to conventional diagnostic procedures.

Detection of antibody to turkey coronavirus by antibody-capture enzyme-linked immunosorbent assay utilizing infectious bronchitis virus antigen

An antibody-capture enzyme-linked immunosorbent assay (ELISA) for detection of antibody to turkey coronavirus (TCV) utilizing infectious bronchitis virus (IBV) antigen was developed. Anti-TCV hyperimmune turkey serum and normal turkey serum were used as positive or negative control serum for optimization of the ELISA system. Goat anti-turkey immunoglobulin G (light plus heavy chains) conjugated with horseradish peroxidase was used as detector antibody. The performance of the ELISA system was evaluated with 45 normal turkey sera and 325 turkey sera from the field and the cutoff point was determined. Serum samples of turkeys experimentally infected with TCV collected sequentially from 1 to 63 days postinfection were applied to the established antibody-capture ELISA using IBV antigens. The optimum conditions for differentiation between anti-TCV hyperimmune serum and normal turkey serum were serum dilution at 1:40 and conjugate dilution at 1:1600. Of the 325 sera from the field, 175 were positive for TCV by immunofluorescent antibody (IFA) assay. The sensitivity and specificity of the ELISA relative to IFA test were 93.1% and 96.7%, respectively, based on the results of serum samples from the field turkey flocks using the optimum cutoff point of 0.18 as determined by the logistic regression method. The ELISA values of all 45 normal turkey sera were completely separated from that of IFA-positive sera. The ELISA results of serum samples collected from turkeys experimentally infected with TCV were comparable to that of the IFA assay. Reactivity of anti-rotavirus, anti-reovirus, anti-adenovirus, or anti-enterovirus antibodies with the IBV antigens coated in the commercially available ELISA plates coated with IBV antigens could be utilized for detection of antibodies to TCV in antibody-capture ELISA.

Limited transmission of turkey coronavirus in young turkeys by adult Alphitobius diaperinus (Coleoptera: Tenebrionidae)

We examined the role of lesser mealworm, Alphitobius diaperinus (Panzer), in the transmission of an enteric disease of turkeys caused by a coronavirus. Turkey coronavirus (TCV) from two sources was studied, one isolate (NC95) was embryo propagated, the second was TCV infected material from turkeys diagnosed with poult enteritis mortality syndrome (PEMS). Beetles were fed virus-infected feces mixed with chicken feed. Transmission of virus was effectively halted by surface sterilization of the beetles. Turkey poults administered beetle homogenates infected with TCV+ PEMS that had not been surface sterilized had reduced weight gains and 50% mortality. Mortality and weight gains were not effected in the NC95 group. Virus isolation procedures were performed to determine NC95 viability at varying time intervals. Beetles were dissected and the guts removed 1, 12, and 24 h after the initial viral feeding. Whole beetles were also examined for comparison. Whole beetles and beetle guts were homogenized and injected into turkey eggs for embryo propagation. Direct immunofluorescence was used to determine the presence of TCV. A. diaperinus were capable of mechanical transmission of TCV. However, only turkey embryos receiving whole beetle and beetle gut homogenates within 1 h of feeding on the virus were positive for TCV. Laboratory studies demonstrating PEMS transmission by A. diaperinus are continuing.

Viral agents associated with poult enteritis and mortality syndrome: the role of a small round virus and a turkey coronavirus

Intestinal samples from turkey poults affected with poult enteritis and mortality syndrome (PEMS) were examined for viruses by immune electron microscopy and double-stranded RNA virus genome electropherotyping. Turkey coronavirus (TCV), avian rotaviruses, reovirus, and a yet undefined small round virus (SRV) were detected. The SRV and TCV were isolated and propagated in turkey embryos. Challenge of specific-pathogen-free turkey poults with SRV, TCV, or both resulted in mortality and clinical responses similar to those of natural PEMS. Our experiments indicate that SRV and TCV are possibly important agents in the etiology of PEMS and the combination of these infections might result in outbreaks with high mortality. The severity of clinical signs and mortality of PEMS are postulated to be partly related to the virus agents involved in individual outbreaks.

PCR for specific detection of haemorrhagic enteritis virus of turkeys, an avian adenovirus

A hexon gene based PCR was developed for specific amplification of DNA sequences from the haemorrhagic enteritis virus (HEV) of turkeys. The hexon genes of different avian adenoviruses were compared for primer construction. Two regions with low sequence homology between HEV and fowl adenovirus (FAV) hexon genes were selected for primer localisation. In correlation with the known sequence data a fragment of 1647 bp was amplified from a live vaccine and spleens of turkeys suffering from haemorrhagic enteritis (HE). All other avian adenoviruses which are able to infect turkeys, i.e. FAV and turkey adenoviruses (TAV), were negative. This is the first PCR for specific detection of HEV DNA which should be useful for rapid diagnosis and epidemiological investigations of HEV infections in turkeys.

Comparative pathogenesis of haemorrhagic enteritis virus (HEV) infection in turkeys and chickens

The pathogenesis of haemorrhagic enteritis virus (HEV) infection in chickens 3-4 days post-infection was compared with that in turkeys. As expected, infected turkeys showed HEV-specific lesions that included enlargement and mottling of the spleen, as well as haemorrhagic enteritis. In infected chickens, only splenomegaly was observed. The number of HEV-infected cells in the spleen was significantly (P < 0.05) higher in the turkey than in the chicken. In both species, the immunohistochemical labelling of B-cell surface determinants was diminished and the splenic B-cell areas were undetectable after HEV infection. Infection with HEV resulted in an increase in nitric oxide production by macrophages in chickens but not in turkeys.

Spiking mortality of turkey poults: 2. Effect of six different in vitro disinfection techniques on organ homogenates capable of reproducing SMT

Spiking mortality of turkeys (SMT) is an infectious disease of 5-to-25-day-old turkey poults characterized by acute enteritis and bursal and thymic atrophy. It is reproducible by exposure to organ homogenates or contaminated litter. We studied methods potentially useful for decontamination of turkey houses contaminated with SMT. Organ homogenates capable of producing SMT and containing turkey intestinal coronavirus were exposed in vitro for 5 hr to either 5.0% NaCl, pH 2.0, pH 12, 1.0% formaldehyde, 57 C, or lyophilization. Results were assessed by oral gavage of treated inocula into 1-day-old turkeys and measurement of subsequent coronavirus shedding, growth rate, feed conversion, and mortality from 1 to 21 days of age. Formaldehyde treatment rendered the inoculum nonpathogenic, whereas other treatments failed to ameliorate its negative effects.

Spiking mortality of turkey poults: 1. Experimental reproduction in isolation facilities

Spiking mortality of turkeys (SMT) is an infectious disease of 5-to-25-day-old turkey poults characterized by acute enteritis and bursal and thymic atrophy. Brooding 1-day-old poults on litter taken from naturally occurring cases successfully reproduced SMT 5 days postexposure. Oral exposure to an organ homogenate made of tissue samples from naturally occurring cases successfully reproduced SMT 5 days postinoculation. Coronaviruses were present in intestinal and bursal contents taken from poults with naturally occurring SMT. They were also present 5 days after exposure in the experimentally reproduced disease. Severe intestinal villus atrophy, bursal follicular lymphoid depletion, and thymic cortical atrophy were present histologically in naturally occurring SMT and in SMT reproduced by either experimental method.

Antigenic characterization of a turkey coronavirus identified in poult enteritis- and mortality syndrome-affected turkeys

A turkey coronavirus (TCV [NC95]) was characterized by antigenic comparison with other avian and mammalian coronaviruses using immunofluorescence (FA) and immunoperoxidase (IP) procedures. Based on FA and IP procedures, TCV (NC95) was determined to be antigenically indistinguishable from turkey enteric (bluecomb) coronavirus (TECV). In addition, TCV (NC95) and TECV were found to be closely related to infectious bronchitis virus (IBV); a one-way antigenic relationship was demonstrated. Polyclonal antibodies specific for TECV and IBV reacted strongly against TCV (NC95), as determined by FA procedures. Monoclonal antibodies (MAbs) specific for IBV matrix protein (MAb 919) reacted strongly against TCV (NC95) and TECV as determined by FA and IP procedures; an IBV peplomer protein-specific MAb (MAb 94) did not recognize the two viruses. These studies suggest an identification of TCV (NC95) as a strain of TECV, and provide evidence of a close antigenic relationship between these viruses and IBV.

Preliminary studies of primary ostrich fibroblasts for the isolation of ratite viruses

An ostrich egg at 21 days of development was used to propagate primary embryo cell cultures. Primary cultures of skeletal muscle cells (for fibroblasts) were prepared by routine typsinization techniques. The ostrich embryo fibroblasts were tested for their ability to propagate stock avian viruses of infectious bronchitis virus, paramyxiovirus-1 (PMV-1), PMV-2, PMV-3, infectious bursal disease virus, quail bronchitis virus, avian reovirus, turkey coronavirus, and two ostrich-originating specimens (one of which was a possible coronavirus identified by electron microscopy). Cytopathic effects were seen by light microscopy in cell cultures inoculated with PMV-1, turkey coronavirus, and the two ostrich specimens. Hemaglutinating titers of 4 or more were determined for PMV-1, turkey coronavrius, and the two ostrich specimens after inoculation onto monolayers of ostrich embryo fibroblasts. Hemagglutination-inhibition tests confirmed the identification of PMV-1 when homologous antisera were used as the specific inhibitor. Bovine coronavirus antisera inhibited the hemagglutination of one of the cultured ostrich specimens.

A monoclonal antibody-based immunoperoxidase method for rapid detection of haemorrhagic enteritis virus of turkeys

An indirect immunoperoxidase (IP) technique involving avidin-biotin peroxidase complex, using a monoclonal antibody was developed for the detection of haemorrhagic enteritis (HE) virus antigen in frozen and formalin-fixed paraffin-embedded tissue sections. This IP procedure was compared with an indirect immunofluorescence antibody technique (IFAT) and an agar gel precipitation test (AGPT). Spleens from turkeys experimentally infected with HE virus were collected and examined for the presence of viral antigen. The IP staining procedure detected HE viral antigen as early as 48 hours after infection and continued to demonstrate the presence of viral antigen for up to 11 days after infection at which time the experiment was terminated. The antigen was detected from three to seven days and from two to nine days after infection by the AGPT and IFAT, respectively. The IFAT and AGPT had sensitivities of 74.19 and 48 per cent, respectively, compared with IP. Because of its high sensitivity and specificity, the IP technique could be useful for studying the pathogenesis and rapid laboratory detection of HE virus.

Genomic relationship between turkey and bovine enteric coronaviruses identified by hybridization with BCV or TCV specific cDNA probes

Genomic relationships between turkey and bovine coronavirus (TCV and BCV), which are currently placed in distinct antigenic groups, were demonstrated by hybridization using specific cDNA probes. BCV-specific recombinant plasmid probes p 52, p 27, and p 247, holding inserts derived from (probably nonstructural) genes, and plasmids pN 17 and pN 9 holding the N and M gene, respectively, permitted the detection of isolates of both BCV and TCV with similar sensitivities. Similarly, probing supernatants of cell cultures infected with several isolates of TCV, using probes pN 17 and pM 78, respectively holding the N gene of BCV and TCV, resulted in equally intense detection signals. Only a slight detection of MHV-3, which is antigenically related to BCV, was observed, whereas the probes did not allow the detection of IBV, TGEV, and HCV-229E, which are placed in antigenic groups separate from those of BCV and TCV. Detection of TCV was improved by hybridization with BCV-specific single-stranded (ss) probes holding sequences of the N and M genes and synthesized by the polymerase chain reaction. Diagnosis of TCV in 134 clinical samples by hybridization was better with PCR-produced ss BCV-specific probes than with ds PCR-produced probes or a combination of six recombinant plasmid probes holding non-overlapping BCV-specific cDNA sequences. Detection signals were absent when probing clinical samples with 32P-labelled pUC-DNA.

Detection of turkey enteric coronavirus by enzyme-linked immunosorbent assay and differentiation from other coronaviruses

A double-antibody ELISA for the detection of coronaviruses in intestinal contents from turkey poults with diarrhea was developed. Antibodies were raised in rabbits and guinea pigs against a Minnesota isolate of turkey enteric coronavirus (TCV) propagated in embryonating turkey eggs and were purified by density-gradient centrifugation. The specificity of antisera was confirmed by hemagglutination-inhibition and immunoelectron microscopy. Absorption of anti-TCV hyperimmune sera with egg extracts or egg ovalbumin and the use of different dilution and blocking buffers influenced the sensitivity and specificity of the ELISA. Reciprocal cross-reactivity was detected among turkey, chicken, bovine, and murine coronaviruses. Antisera to the transmissible gastroenteritis virus of swine, the rabbit enteric coronavirus, or the human coronavirus strain 299E failed to react with TCV. The TCV cross-reacted only moderately with the avian infectious bronchitis virus and the hemagglutinating encephalomyelitis virus of swine. Investigations with samples from 47 commercial turkey flocks in Quebec with episodes of transmissible enteritis revealed that the ELISA was more sensitive than was electron microscopy for detection of TCV.

Further studies on in vitro and in vivo assays of hemorrhagic enteritis virus (HEV)

Isolation of hemorrhagic enteritis virus (HEV) from spleens of infected turkeys in the MDTC-RP19 lymphoblastoid cell line was compared with detection of HEV antigen in the same spleens using the agar gel precipitation (AGP) test. A concordance of 80% was found between the two assays. Virus isolation had a sensitivity of 84% and a specificity of 88% compared with the AGP test. RP19 cells were also susceptible to infection with several other avian adenoviruses, but such infection was easily differentiated from that of HEV by a fluorescent-antibody (FA) test. Turkeys required 10(2) tissue-culture-infectious doses (TCID) to develop HE-specific lesions and 10(5) TCID to be killed. On the other hand, as little as 10 TCID of apathogenic HEV protected the poults against challenge with virulent HEV. The enzyme-linked immunosorbent assay (ELISA) for detection of HEV antibody was improved by using virus-infected RP19 cells as antigen. The ELISA appears to be more sensitive than the serum-neutralization test.

Coronaviruses associated with outbreaks of transmissible enteritis of turkeys in Quebec: hemagglutination properties and cell cultivation

Coronaviruses were observed by electron microscopy in the intestinal contents of turkeys in Quebec flocks where repeated outbreaks of enteritis occurred. Three isolates could be serially propagated in turkey embryos inoculated by the amniotic route with clarified intestinal contents. Purification and concentration of viral particles contained in intestinal contents of infected embryos were achieved by precipitation with polyethylene glycol and ultracentrifugation on sucrose density gradients. Three particle types were demonstrated: intact virions with a density of 1.18 to 1.20 g/ml and incomplete particles with densities of 1.14 and 1.24 g/ml. Hemagglutination of rabbit and guinea pig erythrocytes was demonstrated with the intact viral particles; the hemagglutinin was not dependent on incubation temperature. All the isolates were antigenically related, as shown by hemagglutination-inhibition. The turkey coronaviruses did not cross-react with antisera against coronaviruses of avian infectious bronchitis, porcine transmissible enteritis, bovine neonatal calf diarrhea, or mouse hepatitis. One of the Quebec isolates was shown to induce syncytia formation on its third passage in primary chicken-embryo kidney cell cultures. Electron-microscopic examination of infected cell-culture fluids revealed characteristics coronavirus particles identical to those found in intestinal contents of infected turkeys.

Field outbreaks of colibacillosis of turkeys associated with hemorrhagic enteritis virus

In a study of field material and a survey conducted by the authors, typical signs of colibacillosis of 6-to-12-week-old poults included sudden onset, listlessness, rales, and high mortality. Signs persisted for about 2 weeks and were often followed by a low incidence of lameness caused by Escherichia coli. Gross lesions included enlarged and congested spleens and livers, and dilated discolored black or purple duodenal loops. Microscopic lesions included splenic and hepatic congestion. In some birds (freshly killed and fixed immediately), the epithelium at the tips of the duodenal villi was sloughing, but in other birds the villi were intact and normal in appearance. Splenic enlargement, the presence of intranuclear splenic inclusions similar to those found in hemorrhagic enteritis (HE), and the isolation of HE virus from some of the field spleens all indicated that inapparent HE infection often occurs at approximately the same time as this type of colibacillosis. It is therefore believed that HE infection often exacerbates colibacillosis of older poults.

Hemorrhagic enteritis in turkeys: purification and quantification of the virus

Two methods for purifying the virus of hemorrhagic enteritis from infected turkey spleens are described. One procedure utilized precipitation with polyethylene glycol, and the other consisted of trichlorotrifluoroethane extraction. Both procedures included sucrose-cesium chloride gradient centrifugation in the final purification step. The buoyant density of the viral fraction was 1.34 g/cm3, typical for adenoviral particles, and the size and morphologic characteristics of the virions observed by transmission electron microscopy suggested that the purified virus belongs to the family Adenoviridae. The biologic activity of the purified virus was titrated by inoculating 10-fold dilutions of the viral suspension into turkey poults. Mortality and hemorrhagic diarrhea proved to be inconsistent parameters of infection, and the degree of splenomegaly was proportional to the virus dose. The body/spleen ratio was the parameter selected for measuring viral activity, and the body/spleen ratio 50% was adopted as the unit for the titration of the virus. By using the same system it was demonstrated that the infectivity of the virus could be neutralized with antiserum produced in turkeys.