Use of a related ELISA antigen for efficient TRT serological testing following live vaccination

Avian Metapneumovirus Infection in Poultry Flocks: A Review of Current Knowledge

Avian metapneumovirus (aMPV) is one of the respiratory viruses that cause global economic losses in poultry production systems. Therefore, it was important to design a comprehensive review article that gives more information about aMPV infection regarding the distribution, susceptibility, transmission, pathogenesis, pathology, diagnosis, and prevention. The aMPV infection is characterized by respiratory and reproductive disorders in turkeys and chickens. The disease condition is turkey rhinotracheitis in turkeys and swollen head syndrome in chickens. Infection with aMPV is associated with worldwide economic losses, especially in complications with other infections or poor environmental conditions. The genus Metapneumovirus is a single-stranded enveloped RNA virus and contains A, B, C, and D subtypes. Meat and egg-type birds are susceptible to aMPV infection. The virus can transmit through aerosol, direct contact, mechanical, and vertical routes. The disease condition is characterized by respiratory manifestations, a decrease in egg production, growth retardation, increasing morbidity rate, and sometimes nervous signs and a high mortality rate, particularly in concurrent infections. Definitive diagnosis of aMPV is based mainly on isolation and identification methods, detection of the viral DNA, as well as seroconversion. Prevention of aMPV infection depends on adopting biosecurity measures and vaccination using inactivated, live attenuated, and recombinant or DNA vaccines.

RESEARCH NOTE: Evaluation of the cross protective efficacy of a subtype B aMPV vaccine against virulent subtype A aMPV by different administration routes

Avian metapneumovirus (aMPV) causes respiratory and reproductive diseases in birds, including chickens. In the chicken industry, live vaccines against aMPV subtypes A and B, which are the major aMPV subtypes, are widely used to control disease caused by aMPV. In this study, we evaluated the cross protective efficacy of a live aMPV subtype B vaccine administered via 3 different routes (nasal, spray, and oral) against virulent aMPV subtype A in chickens. At 3 wk after vaccination of 1-wk-old specific-pathogen-free chickens, we measured the serological responses. On the same day, we challenged the birds with aMPV subtype A. Protection was evaluated by viral gene detection and histopathological examination at 3 and 5 days postchallenge. Although there were differences in the serological responses according to administration route, all vaccinated birds showed complete protection at 5 days postchallenge. Regardless of administration route, genome of challenge virus was not detected in vaccinated group, and there were significant differences between vaccinated birds and control group. Overall, our results demonstrated that a subtype B aMPV vaccine can provide cross protection against virulent subtype A aMPV in chickens.

Evaluation of Five Different Antigens in Enzyme-Linked Immunosorbent Assay for the Detection of Avian Pneumovirus Antibodies

Five different antigens were evaluated in enzyme-linked immunosorbent assay (ELISA) tests for the detection of avian pneumovirus (APV) antibodies. Two of the 5 antigens were prepared from recent APV isolates from Minnesota. The 2 older isolates were passage 63 of a strain currently used as a live, attenuated vaccine and a Colorado strain isolated for the first time in the United States and currently used in an ELISA test. The fifth antigen is based on an APV recombinant N-protein. Basic parameters and positive-negative threshold of the assays were established for all 5 antigens on the basis of data obtained by testing 46 known negative and 46 known positive serum samples. Subsequently, 449 field samples were tested by all 5 ELISAs. The optical density difference (ODD) was calculated by subtracting optical density of the sample in the negative antigen well from that in the positive antigen well. In the current ELISA test based on the Colorado strain, an ODD of 0.2 is considered to be the cutoff value to classify samples as negative or positive. In this study, however, use of different cutoffs, based on ODD of negative control plus 3 SD or values estimated from Receiver operating characteristic analysis, was considered to be more appropriate for the various antigens used. Overall person-to-person and day-to-day variability was found to be large for all tests using either ODD or sample to positive ratio to report results. In addition, results suggest that antigenicity of the APV isolates in the United States has not changed between 1997 and 2000.

Deletion of the SH gene from avian metapneumovirus has a greater impact on virus production and immunogenicity in turkeys than deletion of the G gene or M2-2 open reading frame

Subgroup A avian metapneumoviruses lacking either the SH or G gene or the M2-2 open reading frame were generated by using a reverse-genetics approach. The growth properties of these viruses were studied in vitro and in vivo in their natural host. Deletion of the SH gene alone resulted in the generation of a syncytial-plaque phenotype and this was reversed by the introduction of the SH gene from a subgroup B, but not a subgroup C, virus. Infected turkeys were assessed for antibody production and the presence of viral genomic RNA in tracheal swabs. The virus with a deleted SH gene also showed the greatest impairment of replication both in cell culture and in infected turkeys. This contrasts with the situation with other pneumoviruses in culture and in model animals, where deletion of the SH gene results in little effect upon viral yield and a good antibody response. Replication of the G- and M2-2-deleted viruses was impaired more severely in turkeys than in cell culture, with only some animals showing evidence of virus growth and antibody production. There was no correlation between virus replication and antibody response, suggesting that replication sites other than the trachea may be important for induction of antibody responses.

Laboratory evaluation of a quantitative real-time reverse transcription PCR assay for the detection and identification of the four subgroups of avian metapneumovirus

Avian metapneumovirus (AMPV) is an important pathogen causing respiratory diseases and egg drops in several avian species. Four AMPV subgroups have been identified. The laboratory diagnosis of AMPV infections relies on serological methods, on labour-intensive virus isolation procedures, and on recently developed subgroup specific reverse transcription PCR (RT-PCR) protocols. In the present study, both the specificity and sensitivity of a commercial real-time reverse transcription PCR (RRT-PCR) for the detection and identification of the four AMPV subgroups were evaluated. Fifteen non-AMPV avian viruses belonging to 7 genera and 32 AMPV belonging to the 4 subgroups were tested. No non-AMPV virus was detected, whereas all AMPV viruses were identified in agreement with their previous molecular and antigenic subgroup assignment. The sensitivity and quantitating ability of the RRT-PCR assay were determined using serial dilutions of RNA derived either from AMPV virus stocks or from runoff transcripts. In all cases, linear dose/responses were observed. The detection limits of the different subgroups ranged from 500 to 5000 RNA copies and from 0.03 to 3.16TCID50/ml. The results were reproducible under laboratory conditions, thus showing that quantitative RRT-PCR is a new and powerful tool for the rapid and sensitive detection, identification and quantitation of AMPVs.

Subgroup C avian metapneumovirus (MPV) and the recently isolated human MPV exhibit a common organization but have extensive sequence divergence in their putative SH and G genes

The genes encoding the putative small hydrophobic (SH), attachment (G) and polymerase (L) proteins of the Colorado isolate of subgroup C avian pneumovirus (APV) were entirely or partially sequenced. They all included metapneumovirus (MPV)-like gene start and gene end sequences. The deduced Colorado SH protein shared 26.9 and 21.7 % aa identity with its counterpart in human MPV (hMPV) and APV subgroup A, respectively, but its only significant aa similarities were to hMPV. Conserved features included a common hydrophobicity profile with an unique transmembrane domain and the conservation of most extracellular cysteine residues. The Colorado putative G gene encoded several ORFs, the longer of which encoded a 252 aa long type II glycoprotein with aa similarities to hMPV G only (20.6 % overall aa identity with seven conserved N-terminal residues). The putative Colorado G protein shared, at best, 21.0 % aa identity with its counterparts in the other APV subgroups and did not contain the extracellular cysteine residues and short aa stretch highly conserved in other APVs. The N-terminal end of the Colorado L protein exhibited 73.6 and 54.9 % aa identity with hMPV and APV subgroup A, respectively, with four aa blocks highly conserved among Pneumovirus: Phylogenetic analysis performed on the nt sequences confirmed that the L sequences from MPVs were genetically related, whereas analysis of the G sequences revealed that among MPVs, only APV subgroups A, B and D clustered together, independently of both the Colorado isolate and hMPV, which shared weak genetic relatedness at the G gene level.

Detection and differentiation of avian pneumoviruses (metapneumoviruses)

The available detection methods for avian pneumoviruses (turkey rhinotracheitis virus; genus Metapneumovirus) in turkeys, domestic fowl and other species are reviewed. The advantages and disadvantages of virus isolation techniques, virus or genome (polymerase chain reaction) detection and serology are discussed. Some of the problems likely to be encountered are considered, including the detection of yet to be discovered subtypes, as are the factors that are likely to influence the outcome of the work.

Nucleotide sequences of the F, L and G protein genes of two non-A/non-B avian pneumoviruses (APV) reveal a novel APV subgroup

Sequence analysis was performed of all or part of the genes encoding the fusion (F), polymerase (L) and attachment (G) proteins of two French non-A/non-B avian pneumovirus (APV) isolates (Fr/85/1 and Fr/85/2). The two isolates shared at least 99.7% nt and 99.0% aa sequence identity. Comparison with the F genes from subgroup A, subgroup B or Colorado APVs revealed nt and aa identities of 70.0-80. 5% and 77.6-97.2%, respectively, with the L gene sharing 76.1% nt and 85.3% aa identity with that of a subgroup A isolate. The Fr/85/1 and Fr/85/2 G genes comprised 1185 nt, encoding a protein of 389 aa. Common features with subgroup A and subgroup B G proteins included an amino-terminal membrane anchor, a high serine and threonine content, conservation of cysteine residues and a single extracellular region of highly conserved sequence proposed to be the functional domain involved in virus attachment to cellular receptors. However, the Fr/85/1 and Fr/85/2 G sequences shared at best 56.6% nt and 31.2% aa identity with subgroup A and B APVs, whereas these isolates share 38% aa identity. Phylogenetic analysis of the F, G and L genes of pneumoviruses suggested that isolates Fr/85/1 and Fr/85/2 belong to a previously unrecognized APV subgroup, tentatively named D. G-based oligonucleotide primers were defined for the specific molecular identification of subgroup D. These are the first G protein sequences of non-A/non-B APVs to be determined.

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.