Detection of turkey rhinotracheitis virus from chickens with swollen head syndrome by reverse transcriptase-polymerase chain reaction (RT-PCR)

Development of a real-time RT-PCR assay for the simultaneous identification, quantitation and differentiation of avian metapneumovirus subtypes A and B

In recent years, special attention has been paid to real-time polymerase chain reaction (PCR) for avian metapneumovirus (AMPV) diagnosis, due to its numerous advantages over classical PCR. A new multiplex quantitative real-time reverse transcription-PCR (qRT-PCR) with molecular beacon probe assay, designed to target the SH gene, was developed. The test was evaluated in terms of specificity, sensitivity and repeatability, and compared with conventional RT nested-PCR based on the G gene. All of the AMPV subtype A and B strains tested were amplified and specifically detected while no amplification occurred with other non-target bird respiratory pathogens. The detection limit of the assay was 10(-0.41) median infectious dose/ml and 10(1.15) median infectious dose/ml when the AMPV-B strain IT/Ty/B/Vr240/87 and the AMPV-A strain IT/Ty/A/259-01/03 were used, respectively, as templates. In all cases, the amplification efficiency was approximately 2 and the error values were <0.2. Standard curves, generated either using the serial dilution of an RNA suspension or RNA extracted from the serial dilution of titrated viral suspensions as templates, exhibited good linearity (R (2)>0.9375) between crossing point values and virus quantities, making the assay herein designed reliable for quantification. When the newly developed qRT-PCR was compared with a conventional RT nested-PCR, it showed greater sensitivity with RNA extracted from both positive controls and from experimentally infected birds. This assay can be effectively used for the detection, identification, differentiation and quantitation of AMPV subtype A or subtype B to assist in disease diagnosis and to carry out rapid surveillance with high levels of sensitivity and specificity.

Swollen head syndrome in broiler chickens in Japan: Its pathology, microbiology and biochemistry

Four-to-seven-week-old broilers with swollen head syndrome (SHS) from 4 different districts of Japan were examined for pathological, microbiological and biochemical findings. Periocular and mandibular subcutaneous swelling, sometimes accompanied by ocular, hepatic and cardiac lesions were observed. Histologically, diffuse fibrinopurulent inflammation with focal granulomatous lesions was characteristic of subcutaneous tissue of the head, especially periocular tissue. The air spaces of the cranial bones and middle ear showed fibrinopurulent inflammation. Upper respiratory lesions (rhinitis, sinusitis and tracheitis) were always present in chickens with SHS. The characteristic lesions of chicken colibacillosis, i.e. fibrinopurulent serositis, panophthalmitis, fibrinous thrombi in sinusoids of the liver and fibrinous exudation in the ellipsoids and lymphoid follicles of the spleen, were occasionally seen. No virological agents could be isolated. Turkey rhinotracheitis (TRT) virus gene was detected in tracheas from two flocks by reverse transcriptase polymerase chain reaction and serum antibodies against TRT virus were present. Escherichia coli and Staphylococcus aureus were isolated from subcutaneous lesions. Serum alpha(1)-acid glyco-protein, an acute phase protein, was present at high concentration in chickens with SHS. This study suggests that upper respiratory lesions induce E. coli invasion into subcutaneous connective tissue adjacent to the infraorbital sinus and nasal cavity, and SHS in this study may possibly be a local infection of E. coli in facial subcutaneous connective tissue.

Attempts to reproduce swollen head syndrome in specific pathogen-free chickens by inoculating with Escherichia coli and/or turkey rhinotracheitis virus

Attempts to reproduce swollen head syndrome (SHS) lesions were carried out in specific pathogen-free (SPF) chickens. In Experiment 1, chickens inoculated into the submucosal tissue of the nasal membrane or subcutaneous tissue of eyelids with four different strains of Escherichia coli, developed typical SHS lesions; purulent and necrotic lesions of facial subcutis (especially around their eyelids), periocular connective tissue, infraorbital sinus, air spaces, middle ears and eyeballs. The lesions elsewhere included splenic necrosis with fibrinous exudation, fibrin thrombi in hepatic sinusoids, and fibrinopurulent epicardi-tis and perihepatitis which occasionally accompanied lesions in SHS cases. In Experiment 2, SPF chickens inoculated intranasally with turkey rhinotracheitis (TRT) virus and/or E. coli showed no significant lesions in the facial skin, upper respiratory tract or other organs. However, the presence of TRT antibodies demonstrated that the virus infected the chickens. This study suggests that E. coli may play a significant role in the pathogenesis of SHS, but that the significance of TRT virus in the pathogenesis is still to be clarified.

Glycoprotein gene truncation in avian metapneumovirus subtype C isolates from the United States

The length of the published glycoprotein (G) gene sequences of avian metapneumovirus subtype-C (aMPV-C) isolated from domestic turkeys and wild birds in the United States (1996–2003) remains controversial. To explore the G gene size variation in aMPV-C by the year of isolation and cell culture passage levels, we examined 21 turkey isolates of aMPV-C at different cell culture passages. The early domestic turkey isolates of aMPV-C (aMPV/CO/1996, aMPV/MN/1a-b, and 2a-b/97) had a G gene of 1,798 nucleotides (nt) that coded for a predicted protein of 585 amino acids (aa) and showed >97% nt similarity with that of aMPV-C isolated from Canada geese. This large G gene got truncated upon serial passages in Vero cell cultures by deletion of 1,015 nt near the end of the open reading frame. The recent domestic turkey isolates of aMPV-C lacked the large G gene but instead had a small G gene of 783 nt, irrespective of cell culture passage levels. In some cultures, both large and small genes were detected, indicating the existence of a mixed population of the virus. Apparently, serial passage of aMPV-C in cell cultures and natural passage in turkeys in the field led to truncation of the G gene, which may be a mechanism of virus evolution for survival in a new host or environment.

Emergence of a virulent type C avian metapneumovirus in turkeys in Minnesota

The objectives of the present study were to investigate the pathogenesis of a recent isolate of avian metapneumovirus (aMPV) in turkeys and to evaluate the quantitative distribution of the virus in various tissues during the course of infection. Seventy 2-week-old turkey poults were divided equally into two groups. One group was inoculated with aMPV (MN 19) with a titer of 10(5.5) TCID50 oculonasally. Birds in the second group were maintained as sham-inoculated controls. Birds showed severe clinical signs in the form of copious nasal discharge, swollen sinus, conjunctivitis, and depression from 4 days postinoculation (PI) to 12 days PI. Samples from nasal turbinates, trachea, conjunctiva, Harderian gland, infraorbital sinus, lungs, liver, and spleen were collected at 1, 3, 5, 7, 9, 11, and 14 days PI. Histopathologic lesions such as a multifocal loss of cilia were prominent in nasal turbinate and were seen from 3 to 11 days PI. Immunohistochemistry revealed the presence of aMPV from 3 to 9 days PI in nasal turbinate and trachea. Viral RNA could be detected for 14 days PI from nasal turbinate and for 9 days from trachea. In situ hybridization demonstrated the presence of aMPV from 1 to 11 days PI in nasal turbinates and from 3 to 9 days PI in the trachea. Quantitative real-time polymerase chain reaction data showed the presence of a maximum amount of virus at 3 days PI in nasal turbinate and trachea. Clinically and histopathologically, the new isolate appears to be more virulent compared to the early isolates of aMPV in the United States.

Development and evaluation of a blocking enzyme-linked immunosorbent assay for detection of avian metapneumovirus type C-specific antibodies in multiple domestic avian species

The first cases of infection caused by avian metapneumoviruses (aMPVs) were described in turkeys with respiratory disease in South Africa during 1978. The causative agent was isolated and identified as a pneumovirus in 1986. aMPVs have been detected in domestic nonpoultry species in Europe, but tests for the detection of these viruses are not available in the United States. To begin to understand the potential role of domestic ducks and geese and wild waterfowl in the epidemiology of aMPV, we have developed and evaluated a blocking enzyme-linked immunosorbent assay (bELISA) for the detection of aMPV type C (aMPV-C)-specific antibodies. This assay method overcomes the species-specific platform of indirect ELISAs to allow detection of aMPV-C-specific antibodies from potentially any avian species. The bELISA was initially tested with experimental turkey serum samples, and the results were found to correlate with those of virus neutralization assays and indirect enzyme-linked immunosorbent assay (iELISA). One thousand serum samples from turkey flocks in Minnesota were evaluated by our bELISA, and the level of agreement of the results of the bELISA and those of the iELISA was 94.9%. In addition, we were able to show that the bELISA could detect aMPV-C-specific antibodies from experimentally infected ducks, indicating its usefulness for the screening of serum samples from multiple avian species. This is the first diagnostic assay for the detection of aMPV-C-specific antibodies from multiple avian species in the United States.

Presence of avian pneumovirus subtypes A and B in Japan

Four avian pneumovirus (APV) isolates from chickens clinically diagnosed with swollen head syndrome were genetically characterized as to the subtypes of the virus in Japan. The results of reverse transcriptase-polymerase chain reactions based on subtype-specific primers and direct sequence analysis of G genes indicated subtypes A and B but not C or D of APV were present in Japan. Several routes or sources are conceivable for APV to invade into Japan.

Characterization of avian metapneumoviruses isolated in the USA

Avian pneumovirus (APV; officially known as turkey rhinotracheitis virus) is an emergent pathogen of birds in the USA that results in upper respiratory tract disease in turkeys. Six years after the first outbreak in the USA, the disease continues to ravage turkey flocks, primarily in the state of Minnesota. From 1997 to 2000, the industry recorded losses estimated at 15 million US dollars per annum. Researchers have developed sensitive diagnostic techniques, including the enzyme-linked immunosorbent assay and the reverse transcriptase-polymerase chain reaction. which, when used together, are highly sensitive in detecting APV outbreaks in commercial turkey flocks. Phylogenetic analysis of the nucleotide and predicted amino acid sequence of 15 US viruses isolated between 1996 and 2000 demonstrated that the US viruses are relatively homogenous but different from the European APV subgroups A and B, resulting in the classification of US isolates into subgroup C. Infectious APV was isolated from sentinel waterfowls placed close to an infected commercial turkey farm and from wild Canada geese captured in Minnesota, suggesting that free-ranging birds may be involved in the spread of APV. Current efforts to prevent and control the infection include improving management and biosecurity practices and developing attenuated live and deletion mutant vaccines capable of conferring protection.

Occurrence of conjunctivitis, sinusitis and upper region tracheitis in Japanese quail (Coturnix coturnix japonica), possibly caused by Mycoplasma gallisepticum accompanied by Cryptosporidium sp. infection

On a farm raising approximately 75,000 Japanese quail (Coturnix coturnix japonica) for egg production, the diseased quail showed clinical signs of swelling of the head, nasal discharge, increased lacrimation, and decreased egg production. The flock experienced a mortality rate of 5.7% per day. Macroscopic observation revealed large, gelatinous masses of caseous exudate in the sinuses, egg peritonitis, and airsacculitis. Microscopically, non-purulent or purulent inflammation accompanied by lymphoid hyperplastic tissue with germinal centers was observed in the oculofacial respiratory mucosa. The developing stage of the lesions was abscess formation. In the investigation of pathogens, antigens to Mycoplasma gallisepticum and Pasteurella multocida serotype D were immunolabeled on and demonstrated in the mucosal membranes. In addition, P. multocida, Escherichia coli, Staphylococcus sp., and Streptococcus sp. were isolated from the infraorbital sinuses, and Mycoplasma isolated from a diseased bird was confirmed as M. gallisepticum by polymerase chain reaction (PCR). Furthermore, Cryptosporidium sp. was frequently found in the brush border. Serological, bacteriological and PCR examinations, some with negative outcomes, were carried out concerning microbes that are known to cause swollen heads in birds (Haemophilus paragallinarum, Newcastle disease virus and turkey rhinotracheitis virus). The average concentration of ammonia fumes in the cages was 30.6 parts/106, which suggests that the high levels of ammonia fumes promoted infection and multiplication of M. gallisepticum in the quail, and that the clinical disease then worsened due to mixed infection with M. gallisepticum and Cryptosporidium sp. or other bacteria.

PCR-based detection of an emerging avian pneumovirus in US turkey flocks

Avian pneumovirus (APV) or turkey rhinotracheitis virus (TRTV) is an important respiratory pathogen of domesticated poultry in many countries in Europe, Africa, and Asia. Until recently, the United States was considered free of APV. In late 1996, an atypical upper respiratory tract infection appeared in turkey flocks in Colorado and shortly thereafter in turkey flocks in Minnesota. An avian pneumovirus (APV-US) that was serologically distinct from the previously described TRTV was isolated as the primary cause of the new syndrome. The nucleotide sequence of a fragment of the APV-US fusion gene was determined and used to develop a polymerase chain reaction-based assay that specifically detects APV-US viral nucleic acid sequences in RNA extracts of tracheal swabs and turbinate homogenates. The assay is highly sensitive in that it can detect <0.01 TCID50 of APV. The availability of this assay enables the rapid and accurate determination of APV-US in infected poultry flocks.

Avian pneumovirus infections of turkeys and chickens

Avian pneumoviruses (APVs) cause major disease and welfare problems in many areas of the world. In turkeys the respiratory disease and the effect on egg laying performance are clearly defined. However, in chickens, the role of APV as a primary pathogen is less clear, although it is widely believed to be one of the factors involved in Swollen Head Syndrome. The mechanisms of virus transmission over large distances are not understood, but wild birds have been implicated. APV has recently been reported in the USA for the first time and the virus isolated was a different type or possibly a different serotype from the APVs found elsewhere. Good biosecurity is crucial for controlling infection and highly effective vaccines are available for prophylaxis. Although different subtypes and possibly different serotypes exist, there is good cross protection between them. Diagnosis is usually based on serology using ELISAs, but the available kits give variable results, interpretation is difficult and improved diagnostic tests are required.

Molecular characterization of Brazilian avian pneumovirus isolates: comparison between immunochemiluminescent Southern blot and nested PCR

Avian pneumovirus (APV) causes acute respiratory tract infection both in turkeys (turkey rhinotracheitis) and chickens (swollen head syndrome (SHS)) with sudden onset and rapid spread through the flocks. In this study, an immunochemiluminescent Southern blot RT-PCR assay was employed to detect a F gene transcript of the APV in two European turkey isolates and two Brazilian chicken isolates. Limiting dilution PCR was carried out to compare the sensitivity of immunochemiluminescent Southern blot assay and nested PCR assay (nPCR). The sensitivity and specificity of immunochemiluminescent Southern blot RT-PCR assay were comparable to that of nPCR, and at least 100 fold more sensitive than a single PCR amplification. Sequence analysis of the 175 bp product of the F gene revealed 100% identity with APV sequences described earlier.