European and American Subgroup C Isolates of Avian Metapneumovirus belong to Different Genetic Lineages

Avian metapneumovirus subtype B in a Northern shoveler (Spatula clypeata) wintering in Italy: implications for the domestic-wild bird interface?

Avian metapneumovirus (aMPV) is an important pathogen in poultry, primarily affecting chickens and turkeys, and it causes acute respiratory disease or reproductive disorders. Considering previous molecular or serological evidence of aMPV in different wild bird species, the role of non-domestic hosts in the virus epidemiology has been called into question. A molecular survey was therefore performed on wild aquatic bird species sampled during the Italian Avian Influenza Surveillance plan from 2021-2023 in the Bologna province. A total of 250 oropharyngeal swabs were collected and screened for all circulating aMPV subtypes through multiplex real-time RT-PCR. An aMPV-B strain, named aMPV/B/Italy/Northern_shoveler/80/21, was detected in an adult Northern shoveler (Spatula clypeata) wintering in Italy in 2021, and it was characterized by partial amplification and sequencing of the attachment glycoprotein gene. Phylogenetic analysis showed close relationships between this strain and those circulating in Italian poultry from 2014-2019. Given the high aMPV-B burden on the Italian poultry sector and the similarity of aMPV/B/Italy/Northern_shoveler/80/21 strain to those circulating in chickens and turkeys, potential virus spillover from domestic to wild birds could have occurred at the livestock-wildlife interface. Considering that aMPV-B is well adapted to gallinaceans, this represents one of the rare molecular detections of this subtype in waterfowl species. Expanding aMPV monitoring and conducting further biological studies on wild hosts are essential for a better understanding of their role in maintaining aMPV circulation.RESEARCH HIGHLIGHTSWild birds sampled in Italy tested for aMPV detection and characterization.aMPV-B found for the first time in a wintering Northern shoveler.Close phylogenetic relationship with aMPV-B strains circulating in Italian poultry.

Isolation and identification of a subtype C avian metapneumovirus in chickens in Jiangsu, China

Avian metapneumovirus (aMPV) is a viral pathogen that mainly causes respiratory signs and drops in egg production in turkeys, chickens, and ducks. Here, an aMPV subgroup C (aMPV/C) strain, designated GX22-01, was isolated and identified from severe respiratory disease in broiler breeder chickens in 2022 in Jiangsu, China, as evidenced by indirect immunofluorescence and western blotting using specific anti-viral protein antibodies and by sequence analysis of viral nucleoprotein (N) gene. N gene sequencing indicated that the GX22-01 strain shares a high identity (94.3%-99.8 %) with aMPV/C isolates, especially with Chinese aMPV/C isolates from ducks and chickens, which are divided into aMPV/C cluster through N gene-based phylogenetic analysis. The aMPV/C GX22-01 strain was continuously passaged in Vero cells and the viral titers approximately reached 106.0 TCID50/0.1 mL. Pathogenic analysis showed that aMPV/C GX22-01 strain inoculation caused respiratory signs in 2-week-old specific-pathogen-free (SPF) chickens and resulted in pathogenic damage in tracheae and lung tissues, accompanied by positive viral signals using indirect immunohistochemistry. These results provide epidemiological and pathogenic data for developing effective measures against aMPV/C infection in China.

Isolation and characterization of an avian metapneumovirus subtype C circulating in Cherry Valley ducks

Since 2023, an infectious upper respiratory tract disease has been persisted in outbreaks among in a flock of Cherry Valley ducks in Shandong Province, China. This outbreak was traced to avian metapneumovirus subtype C (aMPV-C), a significant pathogen associated with egg-drop and acute respiratory diseases in poultry. It is noteworthy that prior to this, aMPV-C infection had not been previously documented in Cherry Valley ducks within China. In this study, we successfully isolated and characterized the aMPV-C LY0913 strain from the affected Cherry Valley duck flock. Sequence analysis showed that the fusion (F) protein of LY0913 exhibited a 97.8-98.7 % amino acid similarity with seven other aMPV-C strains, displaying the closest relationship to the strains isolated from Muscovy ducks in southern China in 2010. Furthermore, five concurrent amino acid mutations were identified in the F protein, providing valuable insights into the outbreak of aMPV-C in Cherry Valley ducks. The LY0913 strain demonstrated typical cytopathic effects on Vero cells and caused mortality in Cherry Valley duck embryos. In vivo infection of Cherry Valley ducklings with LY0913 reproduced the typical clinical signs and pathological lesions observed in the original infected cases. This study is the first to identify aMPV-C as a causative agent of respiratory disease in Cherry Valley ducks in China, highlighting its emergence and potential risk to previously unaffected avian populations. Urgent enhanced surveillance and biosecurity measures are strongly recommended to prevent further spread within duck flocks.

Molecular characterization of avian metapneumovirus subtype C associated with hydrosalpinx fluid and egg drop syndrome in Jinding ducks

A disease called "hydrosalpinx fluid and egg drop syndrome" (HFEDS) was observed in four flocks of Jinding ducks (Anas platyrhynchos domesticus) in Northeast China during the years 2022 to 2023. Here, we investigated the possible involvement of avian metapneumovirus (AMPV) infection. Full-length genome sequencing and sequence analysis of two AMPV strains showed that they belong to Eurasian lineage of AMPV subtype C. Based on surface glycoprotein (G) sequence comparisons, the Eurasian lineage can be divided into two sublineages (E1 and E2), and sublineage E2 is circulating in Jinding duck populations in Northeast China.

Introduction of Avian metapneumovirus subtype A to the United States: molecular insights and implications

Avian metapneumovirus (aMPV) poses a significant threat to the poultry industry worldwide, primarily affecting turkeys and chickens. The recent detection of aMPV-A and -B subtypes in the United States marks a significant shift after a prolonged period free of aMPV following the eradication of the previously circulating subtype C. Hence, the demand for molecular diagnostic tests for aMPV has arisen due to their limited availability in the US market. In this study, we present the molecular characterization based on the complete genome sequence of aMPV subtype A, which was detected in the US for the first time. Four RT-qPCR positive samples were subjected to next-generation sequencing analysis, resulting in the assembly of one complete and one near-complete genome sequences. Phylogenetic analysis revealed that the isolated strains clustered within the aMPV-A subtype and were most closely related to recent Mexican strains. A detailed amino acid analysis identified unique mutations in the G gene of the US isolates compared to Mexican strains. Additionally, we compared the performance, cross-reactivity, and limit of detection of our revised aMPV subtype-specific RT-qPCR test with two commercial kits, demonstrating similar detection and subtyping capabilities. These findings highlight the importance of accurate diagnostic methods for disease management in the poultry industry, provide valuable insights into the epidemiology of aMPV, and underscore the need for continued vigilance and surveillance to mitigate its impact on poultry production.

Tracing the Flight: Investigating the Introduction of Avian Metapneumovirus (aMPV) A and B

Avian metapneumovirus (aMPV) has been identified as an important cause of respiratory and reproductive disease, leading to significant productive losses worldwide. Different subtypes have been found to circulate in different regions, with aMPV-A and B posing a significant burden especially in the Old World, and aMPV-C in North America, albeit with limited exceptions of marginal economic relevance. Recently, both aMPV-A and aMPV-B have been reported in the U.S.; however, the route of introduction has not been investigated. In the present study, the potential importation pathways have been studied through phylogenetic and phylodynamic analyses based on a broad collection of partial attachment (G) protein sequences collected worldwide. aMPV-B circulating in the U.S. seems the descendant of Eastern Asian strains, which, in turn, are related to European ones. A likely introduction pathway mediated by wild bird migration through the Beringian crucible, where the East Asian and Pacific American flight paths intersect, appears likely and was previously reported for avian influenza. aMPV-A, on the other hand, showed a Mexican origin, involving strains related to Asian ones. Given the low likelihood of trade or illegal importation, the role of wild birds appears probable also in this case, since the region is covered by different flight paths directed in a North-South direction through America. Since the information on the role of wild birds in aMPV epidemiology is still scarce and scattered, considering the significant practical implications for the poultry industry demonstrated by recent U.S. outbreaks, further surveys on wild birds are encouraged.

A Receptor Integrin β1 Promotes Infection of Avian Metapneumovirus Subgroup C by Recognizing a Viral Fusion Protein RSD Motif

Avian metapneumovirus subgroup C (aMPV/C) causes respiratory diseases and egg dropping in chickens and turkeys, resulting in severe economic losses to the poultry industry worldwide. Integrin β1 (ITGB1), a transmembrane cell adhesion molecule, is present in various cells and mediates numerous viral infections. Herein, we demonstrate that ITGB1 is essential for aMPV/C infection in cultured DF-1 cells, as evidenced by the inhibition of viral binding by EDTA blockade, Arg-Ser-Asp (RSD) peptide, monoclonal antibody against ITGB1, and ITGB1 short interfering (si) RNA knockdown in cultured DF-1 cells. Simulation of the binding process between the aMPV/C fusion (F) protein and avian-derived ITGB1 using molecular dynamics showed that ITGB1 may be a host factor benefiting aMPV/C attachment or internalization. The transient expression of avian ITGB1-rendered porcine and feline non-permissive cells (DQ cells and CRFK cells, respectively) is susceptible to aMPV/C infection. Kinetic replication of aMPV/C in siRNA-knockdown cells revealed that ITGB1 plays an important role in aMPV/C infection at the early stage (attachment and internalization). aMPV/C was also able to efficiently infect human non-small cell lung cancer (A549) cells. This may be a consequence of the similar structures of both metapneumovirus F protein-specific motifs (RSD for aMPV/C and RGD for human metapneumovirus) recognized by ITGB1. Overexpression of avian-derived ITGB1 and human-derived ITGB1 in A549 cells enhanced aMPV/C infectivity. Taken together, this study demonstrated that ITGB1 acts as an essential receptor for aMPV/C attachment and internalization into host cells, facilitating aMPV/C infection.

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.

Longitudinal Survey on aMPV Circulation in French Broiler Flocks following Different Vaccination Strategies

In recent years, the impact of respiratory disease resulting from Avian Metapneumovirus (aMPV) infection has been generally rising in the broiler industry in Europe. In this context, in order to investigate aMPV contribution to the clinical picture and the potential benefits of diversified vaccination strategies compared to nonvaccination policies, a longitudinal monitoring was performed, also evaluating Infectious Bronchitis Virus (IBV) presence. Broiler flocks located in Western France, where aMPV has already proven to be a health and productivity issue, were screened by RT-PCR on rhino-pharyngeal swabs, and the viruses were genetically characterized by sequence analysis. For a more comprehensive picture of aMPV molecular epidemiology and evolution in France, aMPV subtype B strains detected from 1985 to 1998 were sequenced and included in the analysis. The survey confirmed the detection of aMPV subtype B in commercial broiler flocks in France, together with a certain heterogeneity demonstrated by the circulation of more recent and historical French field strains. No IBV field strains were detected. The implementation and evaluation of different management choices and vaccine strategies suggests once again that immunization does not prevent infection but contributes greatly to the containment of the clinical manifestations.

Avian metapneumovirus: A five-plex digital droplet RT-PCR method for identification of subgroups A, B, C, and D

End-point and real-time avian metapneumovirus (AMPV) RT-PCRs have been developed to detect one or two of the four recognized subgroups (A,B,C, and D) simultaneously or for broad range AMPV detection. Current subgroup specific tests target variable areas of the genome which makes these PCRs sensitive to specificity defects as recently documented. In the current study, a single five-plex digital droplet RT-PCR targeting the conserved viral polymerase gene of AMPV, which is less prone to genetic drift, has been designed. This digital droplet RT-PCR was capable of identifying each of the four AMPV subgroups. Each subgroup was identified according to a specifically assigned fluorescent amplitude. Specificity, which was tested including 31 AMPV strains, non-AMPV avian viruses and closely related human respiratory viruses, was 100%. The specific limit of detection for extracted viral RNA was estimated between 1 and 3 copies/μl. This tool simplifies the number of tests required for AMPV genotype diagnostics and should be theoretically less effected by viral genome evolution due to its target region. Ultimately, application of this test will contribute to an improved understanding of the global geographic distribution and subgroup host range of field strains.

Characterization of avain metapneumovirus subgroup C isolated from chickens in Beijing, China

Avian metapneumovirus (aMPV) is an important causative agent that causes acute respiratory disease and egg-dropping in chickens and turkeys. Here, we characterized an aMPV subgroup C (aMPV/C) from 320-day-old broiler breeder chickens with severe respiratory diseases in Beijing, China, as evidenced by RT-PCR typing and confirmation of the nucleoprotein (N) gene sequence. The N gene sequence of the aMPV/C strain (designated BJ17) exhibited no deletions or insertions and possessed 94.6% to 99.6% identity to those of published aMPV/C isolates. The phylogenetic tree of the nucleotide sequences constructed using the neighbor-joining clustering method showed that the BJ17 strain formed one cluster with other aMPV/C viruses and formed one subcluster with published Chinese aMPV/C isolates regardless of Muscovy duck or chicken origins. Comparative analysis of the N proteins showed that a unique amino acid residue D at position 110 might be associated with regional distribution due to its occurrence in all the Chinese aMPV/C isolates only. Strain BJ17 was successfully isolated by cultured Vero cell passage and further inoculated in 3-wk-old specific-pathogen-free chickens for the examination of pathogenicity. Animal experimental results showed that BJ17-inoculated chickens had severe respiratory diseases and inflammatory lesions, as demonstrated by pathological changes and aMPV antigen in the nasal turbinate, tracheae, and lung tissues. These results enrich the available information regarding the epidemiology and pathogenicity of aMPV/C in chickens, which may facilitate the development of effective measures against aMPV/C infection in China.

Detection and Genome Sequence Analysis of Avian Metapneumovirus Subtype A Viruses Circulating in Commercial Chicken Flocks in Mexico

Avian metapneumoviruses (aMPV subtypes A-D) are respiratory and reproductive pathogens of poultry. Since aMPV-A was initially reported in Mexico in 2014, there have been no additional reports of its detection in the country. Using nontargeted next-generation sequencing (NGS) of FTA card-spotted respiratory samples from commercial chickens in Mexico, seven full genome sequences of aMPV-A (lengths of 13,288-13,381 nucleotides) were de novo assembled. Additionally, complete coding sequences of genes N (n = 2), P and M (n = 7 each), F and L (n = 1 each), M2 (n = 6), SH (n = 5) and G (n = 2) were reference-based assembled from another seven samples. The Mexican isolates phylogenetically group with, but in a distinct clade separate from, other aMPV-A strains. The genome and G-gene nt sequences of the Mexican aMPVs are closest to strain UK/8544/06 (97.22-97.47% and 95.07-95.83%, respectively). Various amino acid variations distinguish the Mexican isolates from each other, and other aMPV-A strains, most of which are in the G (n = 38), F (n = 12), and L (n = 19) proteins. Using our sequence data and publicly available aMPV-A data, we revised a previously published rRT-PCR test, which resulted in different cycling and amplification conditions for aMPV-A to make it more compatible with other commonly used rRT-PCR diagnostic cycling conditions. This is the first comprehensive sequence analysis of aMPVs in Mexico and demonstrates the value of nontargeted NGS to identify pathogens where targeted virus surveillance is likely not routinely performed.

Molecular Survey on A, B, C and New Avian Metapneumovirus (aMPV) Subtypes in Wild Birds of Northern-Central Italy

Simple Summary

Avian metapneumovirus (aMPV) is a common pathogen in poultry and has been detected in wild birds, suggesting the possible role in viral dissemination. A feature of aMPV is its genetic and antigenic variability, which has allowed the identification of various subtypes of the virus with different characteristics in terms of host tropism. Two new subtypes of aMPV were recently identified in gulls and parakeets. We aimed to explore the epidemiology of old and new aMPV subtypes in wild birds. Samples were collected in Italy during the surveillance of avian influenza in wild species and were tested with two multiplex real time RT-PCRs that were able to detect and distinguish the aMPV subtypes (A, B, C, gull, and parakeet subtypes). All of the individuals were negative, except for one mallard that was positive for aMPV subtype C. The M and G genes of this strain were molecularly characterized and revealed similarities with Chinese and European strains, including an Italian sequence that was previously detected in a widgeon. These findings confirm the susceptibility of mallards, which are closely related to domestic species, highlighting the importance of the epidemiological monitoring of aMPV circulation.

Abstract

Recent insights into the genetic and antigenic variability of avian metapneumovirus (aMPV), including the discovery of two new subtypes, have renewed interest in this virus. aMPV causes a well-known respiratory disease in poultry. Domestic species show different susceptibility to aMPV subtypes, whereas sporadic detections in wild birds have revealed links between epidemiology and migration routes. To explore the epidemiology of aMPV in wild species, a molecular survey was conducted on samples that were collected from wild birds during avian influenza surveillance activity in Italy. The samples were screened in pools by multiplex real time RT-PCR assays in order to detect and differentiate subtypes A, B, C, and those that have been newly identified. All the birds were negative, except for a mallard (Anas platyrhynchos) that was positive for aMPV subtype C (sampled in Padua, in the Veneto region, in 2018). The sequencing of partial M and full G genes placed the strain in an intermediate position between European and Chinese clusters. The absence of subtypes A and B supports the negligible role of wild birds, whereas subtype C detection follows previous serological and molecular identifications in Italy. Subtype C circulation in domestic and wild populations emphasizes the importance of molecular test development and adoption to allow the prompt detection of this likely emerging subtype.

First detection of Avian metapneumovirus subtype C Eurasian Lineage in a Eurasian wigeon (Mareca penelope) wintering in Northeastern Italy: an additional hint on the role of migrating birds in the viral epidemiology

Avian metapneumovirus (aMPV) economically affects the global poultry industry causing respiratory and reproductive disorders. Considering the paucity of data on the aMPV occurrence in European free-ranging avifauna, a molecular survey was conducted on wild birds of 23 species belonging to the orders Anseriformes, Charadriiformes or Passeriformes, captured alive and sampled in Northeast Italy as part of the national Avian influenza virus (AIV) surveillance activities. A total of 492 oropharyngeal swabs, collected from 2007 to 2010, all AIV negative, were screened from aMPV by subtype-specific qRT-PCR. An aMPV-C strain, named aMPV/C/IT/Wigeon/758/07, was found in a wintering young Eurasian wigeon (Mareca penelope) sampled in November 2007. The matrix, fusion, and attachment glycoprotein genes of the detected strain were subsequently amplified by specific independent RT-PCRs, then sequenced, and compared in a phylogenetic framework with known aMPV homologous sequences retrieved from GenBank. Close genetic relationships were found between the aMPV/C/IT/Wigeon/758/07 strain and subtype C Eurasian lineage strains isolated in the late 1990s in French domestic ducks, suggesting epidemiological links. Eurasian wigeons are indeed medium to long-range migrant dabbling ducks that move along the Black Sea/Mediterranean flyway, our finding might therefore be related to migratory bridges between countries. To our knowledge, this is the first molecular evidence of the occurrence of a subtype C in Italy and backdates the aMPV-C circulation to 2007. Moreover, results suggest the susceptibility of Eurasian wigeons to aMPV. Broader investigations are needed to assess the role of wild ducks and the significance of the wildfowl/poultry interface in the aMPV-C epidemiology.

Avian Metapneumovirus Subgroup C Induces Mitochondrial Antiviral Signaling Protein Degradation through the Ubiquitin-Proteasome Pathway

The mitochondrial antiviral signaling (MAVS) protein, a critical adapter, links the upstream recognition of viral RNA to downstream antiviral signal transduction. However, the interaction mechanism between avian metapneumovirus subgroup C (aMPV/C) infection and MAVS remains unclear. Here, we confirmed that aMPV/C infection induced a reduction in MAVS expression in Vero cells in a dose-dependent manner, and active aMPV/C replication was required for MAVS decrease. We also found that the reduction in MAVS occurred at the post-translational level rather than at the transcriptional level. Different inhibitors were used to examine the effect of proteasome or autophagy on the regulation of MAVS. Treatment with a proteasome inhibitor MG132 effectively blocked MAVS degradation. Moreover, we demonstrated that MAVS mainly underwent K48-linked ubiquitination in the presence of MG132 in aMPV/C-infected cells, with amino acids 363, 462, and 501 of MAVS being pivotal sites in the formation of polyubiquitin chains. Finally, E3 ubiquitin ligases for MAVS degradation were screened and identified and RNF5 targeting MAVS at Lysine 363 and 462 was shown to involve in MAVS degradation in aMPV/C-infected Vero cells. Overall, these results reveal the molecular mechanism underlying aMPV/C infection-induced MAVS degradation by the ubiquitin-proteasome pathway.

Serological and Molecular Characterization of Avian Metapneumovirus in Chickens in Northern Vietnam

Avian Metapneumovirus (aMPV) is a causative agent of respiratory disease complex in turkeys and chickens that has recently been detected in Vietnam. Due to its novelty, this study was conducted to elucidate the distribution of aMPV in several provinces in northern Vietnam. By the application of Enzyme-Linked Immunosorbent Assay (ELISA) and nested Reverse Transcription-Polymerase Chain Reaction (RT-PCR), this study demonstrated the circulation of aMPV in 12 out of 14 cities/provinces with positive rates of 37.6% and 17.2%, respectively. All nested RT-PCR positive samples were aMPV subgroup B. By pairing the detection results with age groups, it was observed that aMPV infections occurred in chickens of all ages. Additionally, by genetic characterization, aMPV strains were demonstrated to not be attenuated vaccine viruses and to belong to at least two genetic clades. Overall, the obtained results provided insights into the prevalence of aMPV and indicated a greater complexity of respiratory diseases in chickens in Vietnam.

Development of A recombinant nucleocapsid based indirect ELISA for the detection of antibodies to avian metapneumovirus subtypes, A, B, and C

Nucleocapsid (N) protein is the most highly expressed of all avian metapneumovirus (aMPV) viral proteins and stimulates a substantial immune response in infected animals. Codon optimized recombinant N (rec-N) protein from aMPV subtypes A, B, and C were expressed using the baculoviral expression system in Trichoplusia ni (Tni) insect cells. A mixture of purified rec-N antigens from each subtype was used as a coating antigen and was evaluated in indirect ELISA (iELISA) to assess antibody response in serum samples collected from experimentally infected chickens and turkeys with different aMPV subtypes. Also, archived field serum samples that were collected from different poultry submissions were used. Receiver operating characteristic (ROC) analysis was performed using chicken and turkey serum samples that were confirmed by indirect fluorescent antibody (IFA) test for serostatus (positive n = 270, negative n = 610). The ROC analysis showed sensitivity and specificity of 97 % at a cut-off value of 0.25. The rec-N iELISA was compared with a commercial whole virus-based APV kit. The rec-N iELISA showed comparable results in detecting antibody response in aMPV infected chicken sera but was more sensitive in detecting early antibody response in aMPV infected turkey serum samples. Our results further confirm the presence of aMPV antibodies in Canadian domestic poultry populations. The developed aMPV-rec N iELISA offers a safe and valuable alternative to whole virus-based iELISA for serodiagnosis and seroepidemiological surveillance of the disease in domestic poultry.

What is new on molecular characteristics of Avian metapneumovirus strains circulating in Europe?

In the present study, one hundred and sixteen partial G gene sequences of Avian metapneumovirus (aMPV) subtype B, obtained during routine diagnostics in different European Countries in the last few years (2014-2019), were analysed by sequence and phylogenetic analyses in order to draw an updated picture of the molecular characteristics of circulating strains. Nucleotide sequences were compared with other sequences of European and non-European aMPV-Bs collected prior to that period or retrieved from GenBank. Phylogenetic relationships among the aMPV-B strains, reconstructed using the maximum likelihood method implemented in MEGA X, demonstrated that aMPV-B has evolved in Europe from its first appearance, frequently displaying a clear relation with the geographic area of detection. The 40% of aMPV-B viruses analysed were classified as vaccine-derived strains, being phylogenetically related, and showing high nucleotide identity with live commercial vaccine strains licensed in Europe. The remaining 60% were classified as field strains since they clustered separately and showed a low nucleotide identity with vaccines and vaccine-derived strains. The phylogenetic tree showed that the virus has continued to evolve from its first appearance in the '80s since more recently detected strains belonged to clades phylogenetically distant from the older strains. Unlike vaccine-derived strains, field strains tended to cluster according to their geographic origin and irrespective of the host species where the viruses had been detected. In conclusion, the molecular characterization of aMPV-B and the differentiation between vaccines and field strains through G gene sequence analysis can be a useful tool towards correct diagnosis and should be routinely applied in order to better address the control strategies.

Complete Genome Sequence of an Avian Metapneumovirus Subtype B Strain from Hungary

Avian metapneumoviruses (aMPVs), which have been reported in many countries, cause acute upper respiratory tract disease in chickens and turkeys. Using next-generation sequencing, we report here the complete genome sequence of an aMPV subtype B strain that was isolated from a turkey in Hungary in 1989.

Avian metapneumoviruses (aMPVs), which have been reported in many countries, cause acute upper respiratory tract disease in chickens and turkeys. Using next-generation sequencing, we report here the complete genome sequence of an aMPV subtype B strain that was isolated from a turkey in Hungary in 1989.

Proteome Analysis in a Mammalian Cell line Reveals that PLK2 is Involved in Avian Metapneumovirus Type C (aMPV/C)-Induced Apoptosis

Avian metapneumovirus subtype C (aMPV/C) causes an acute respiratory disease that has caused serious economic losses in the Chinese poultry industry. In the present study, we first explored the protein profile in aMPV/C-infected Vero cells using iTRAQ quantitative proteomics. A total of 921 of 7034 proteins were identified as significantly altered by aMPV/C infection. Three selected proteins were confirmed by Western blot analysis. Bioinformatics GO analysis revealed multiple signaling pathways involving cell cycle, endocytosis, and PI3K-Akt, mTOR, MAPK and p53 signaling pathways, which might participate in viral infection. In this analysis, we found that PLK2 expression was upregulated by aMPV/C infection and investigated whether it contributed to aMPV/C-mediated cellular dysfunction. Suppressing PLK2 attenuated aMPV/C-induced reactive oxygen species (ROS) production and p53-dependent apoptosis and reduced virus release. These results in a mammalian cell line suggest that high PLK2 expression correlates with aMPV/C-induced apoptosis and viral replication, providing new insight into the potential avian host cellular response to aMPV/C infection and antiviral targets.

First Molecular Characterization of Avian Metapneumovirus (aMPV) in Turkish Broiler Flocks

Viral respiratory diseases, including avian metapneumovirus (aMPV), have a significant economic impact on poultry industries. The frequency and genotype diversity of aMPV in Turkish broiler flocks is not known at present. The aim of this study was to report the first molecular identification and phylogeny of aMPV, which is circulating in Turkish broiler flocks. Trachea tissue samples and tracheal swabs were collected from 110 broiler flocks distributed in different geographical regions in Turkey between March 2017 and March 2018. Detection of aMPV was confirmed with the use of universal reverse transcriptase (RT) PCR, and eight (7.2%) broiler farms were positive for aMPV. Sequence analysis of the G gene revealed the exclusive presence of subtype B viruses. Three field isolates clustered closely with a 2002 Israel isolate, indicating a potential transmission route between these two countries and through the Middle East. The remaining five field isolates were closely related to a vaccine strain, even though broiler flocks in Turkey are not routinely vaccinated against aMPV. Therefore, we speculate these five isolates could have originated from nearby vaccinated turkey farms. Additionally, the presence of some nucleotide substitutions compared to the reference vaccine sequence suggests prolonged circulation and evolution of the original vaccine virus or a vaccine subpopulation was selected under field conditions. This evidence emphasizes the need for further detailed and more systemic approaches to evaluate aMPV spread and evolution in order to design effective control strategies.

Single reaction, real time RT-PCR detection of all known avian and human metapneumoviruses

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Detection of all known avian and human MPV subgroups in a single reaction rRT-PCR.

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Highly sensitive and specific method using SYBR Green I technology.

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Complete validation of the method for detection of avian metapneumoviruses.

Current molecular methods for the detection of avian and human metapneumovirus (AMPV, HMPV) are specifically targeted towards each virus species or individual subgroups of these. Here a broad range SYBR Green I real time RT-PCR was developed which amplified a highly conserved fragment of sequence in the N open reading frame. This method was sufficiently efficient and specific in detecting all MPVs. Its validation according to the NF U47-600 norm for the four AMPV subgroups estimated low limits of detection between 1000 and 10 copies/μL, similar with detection levels described previously for real time RT-PCRs targeting specific subgroups. RNA viruses present a challenge for the design of durable molecular diagnostic test due to the rate of change in their genome sequences which can vary substantially in different areas and over time. The fact that the regions of sequence for primer hybridization in the described method have remained sufficiently conserved since the AMPV and HMPV diverged, should give the best chance of continued detection of current subgroups and of potential unknown or future emerging MPV strains.

Avian metapneumovirus subgroup C induces autophagy through the ATF6 UPR pathway

An increasing number of studies have demonstrated that macroautophagy/autophagy plays an important role in the infectious processes of diverse pathogens. However, it remains unknown whether autophagy is induced in avian metapneumovirus (aMPV)-infected host cells, and, if so, how this occurs. Here, we report that aMPV subgroup C (aMPV/C) induces autophagy in cultured cells. We demonstrated this relationship by detecting classical autophagic features, including the formation of autophagsomes, the presence of GFP-LC3 puncta and the conversation of LC3-I into LC3-II. Also, we used pharmacological regulators and siRNAs targeting ATG7 or LC3 to examine the role of autophagy in aMPV/C replication. The results showed that autophagy is required for efficient replication of aMPV/C. Moreover, infection with aMPV/C promotes autophagosome maturation and induces a complete autophagic process. Finally, the ATF6 pathway, of which one component is the unfolded protein response (UPR), becomes activated in aMPV/C-infected cells. Knockdown of ATF6 inhibited aMPV/C-induced autophagy and viral replication. Collectively, these results not only show that autophagy promotes aMPV/C replication in the cultured cells, but also reveal that the molecular mechanisms underlying aMPV/C-induced autophagy depends on regulation of the ER stress-related UPR pathway.

A Reverse Genetics Approach for the Design of Methyltransferase-Defective Live Attenuated Avian Metapneumovirus Vaccines

Avian metapneumovirus (aMPV), also known as avian pneumovirus or turkey rhinotracheitis virus, is the causative agent of turkey rhinotracheitis and is associated with swollen head syndrome in chickens. aMPV belongs to the family Paramyxoviridae which includes many important human pathogens such as human respiratory syncytial virus (RSV), human metapneumovirus (hMPV), and human parainfluenza virus type 3 (PIV3). The family also includes highly lethal emerging pathogens such as Nipah virus and Hendra virus, as well as agriculturally important viruses such as Newcastle disease virus (NDV). For many of these viruses, there is no effective vaccine. Here, we describe a reverse genetics approach to develop live attenuated aMPV vaccines by inhibiting the viral mRNA cap methyltransferase. The viral mRNA cap methyltransferase is an excellent target for the attenuation of paramyxoviruses because it plays essential roles in mRNA stability, efficient viral protein translation and innate immunity. We have described in detail the materials and methods used to generate recombinant aMPVs that lack viral mRNA cap methyltransferase activity. We have also provided methods to evaluate the genetic stability, pathogenesis, and immunogenicity of live aMPV vaccine candidates in turkeys.

Role of trypsin in the replication of Avian metapneumovirus subtype C (strain MN-2a) and its entry into the Vero cells

To understand the molecular mechanisms of Avian metapneumovirus (aMPV) and the requirements involved in the infection and fusion, trypsin treatment was done in the different stages of virus; before infection, during entry and after virus infection followed by aMPV infection. The growth kinetics of aMPV was compared in time dependent manner. The effect of trypsin was found in the later stage of aMPV infection increasing the numbers of infected cells with the significant higher titer of infectious virions to that of trypsin treated before infection, during entry and aMPV. A serine protease inhibitor reduced aMPV replication in a significant way, whereas cysteine peptidase (E-64), aspartic protease (pepstatin A), and metalloprotease (phosphoramidon) inhibitors had no effect on aMPV replication. Inoculation of aMPV on Vero cells expressing the membrane-associated protease TMPRSS2 resulted in higher virus titers than that inoculated on normal Vero cells and is statistically significant (p < 0.05). Also, an inhibitor of clathrin/caveolae-mediated endocytosis had no effect on virus progeny, indicating that aMPV does not use the endocytic pathway for entry but undergoes direct fusion. The effect of lysosomotropic agents was not significant, suggesting that aMPV does not require low-pH environment in endosomes to fuse its envelope with the plasma membrane.

A sensitive, reproducible, and economic real-time reverse transcription PCR detecting avian metapneumovirus subtypes A and B

Use of real-time PCR is increasing in the diagnosis of infectious disease due to its sensitivity, specificity, and speed of detection. These characteristics make it particularly suited for the diagnosis of viral infections, like avian metapneumovirus (AMPV), for which effective control benefits from continuously updated knowledge of the epidemiological situation. Other real-time reverse transcription (RT)-PCRs have been published based on highly specific fluorescent dye-labeled probes, but they have high initial cost, complex validation, and a marked susceptibility to the genetic variability of their target sequence. With this in mind, we developed and validated a SYBR Green I-based quantitative RT-PCR for the detection of the two most prevalent AMPV subtypes (i.e., subtypes A and B). The assay demonstrated an analytical sensitivity comparable with that of a previously published real-time RT-PCR and the ability to detect RNA equivalent to approximately 0.5 infectious doses for both A and B subtypes. The high efficiency and linearity between viral titer and crossing point displayed for both subtypes make it suited for viral quantification. Optimization of reaction conditions and the implementation of melting curve analysis guaranteed the high specificity of the assay. The stable melting temperature difference between the two subtypes indicated the possibility of subtyping through melting temperature analysis. These characteristics make our assay a sensitive, specific, and rapid tool, enabling contemporaneous detection, quantification, and discrimination of AMPV subtype A and B.

Methyltransferase-defective avian metapneumovirus vaccines provide complete protection against challenge with the homologous Colorado strain and the heterologous Minnesota strain

Avian metapneumovirus (aMPV), also known as avian pneumovirus or turkey rhinotracheitis virus, is the causative agent of turkey rhinotracheitis and is associated with swollen head syndrome in chickens. Since its discovery in the 1970s, aMPV has been recognized as an economically important pathogen in the poultry industry worldwide. The conserved region VI (CR VI) of the large (L) polymerase proteins of paramyxoviruses catalyzes methyltransferase (MTase) activities that typically methylate viral mRNAs at guanine N-7 (G-N-7) and ribose 2'-O positions. In this study, we generated a panel of recombinant aMPV (raMPV) Colorado strains carrying mutations in the S-adenosyl methionine (SAM) binding site in the CR VI of L protein. These recombinant viruses were specifically defective in ribose 2'-O, but not G-N-7 methylation and were genetically stable and highly attenuated in cell culture and viral replication in the upper and lower respiratory tracts of specific-pathogen-free (SPF) young turkeys. Importantly, turkeys vaccinated with these MTase-defective raMPVs triggered a high level of neutralizing antibody and were completely protected from challenge with homologous aMPV Colorado strain and heterologous aMPV Minnesota strain. Collectively, our results indicate (i) that aMPV lacking 2'-O methylation is highly attenuated in vitro and in vivo and (ii) that inhibition of mRNA cap MTase can serve as a novel target to rationally design live attenuated vaccines for aMPV and perhaps other paramyxoviruses.

IMPORTANCE

Paramyxoviruses include many economically and agriculturally important viruses such as avian metapneumovirus (aMPV), and Newcastle disease virus (NDV), human pathogens such as human respiratory syncytial virus, human metapneumovirus, human parainfluenza virus type 3, and measles virus, and highly lethal emerging pathogens such as Nipah virus and Hendra virus. For many of them, there is no effective vaccine or antiviral drug. These viruses share common strategies for viral gene expression and replication. During transcription, paramyxoviruses produce capped, methylated, and polyadenylated mRNAs. Using aMPV as a model, we found that viral ribose 2'-O methyltransferase (MTase) is a novel approach to rationally attenuate the virus for vaccine purpose. Recombinant aMPV (raMPV) lacking 2'-O MTase were not only highly attenuated in turkeys but also provided complete protection against the challenge of homologous and heterologous aMPV strains. This novel approach can be applicable to other animal and human paramyxoviruses for rationally designing live attenuated vaccines.

Isolation and characterization of a subtype C avian metapneumovirus circulating in Muscovy ducks in China

Subtype C avian metapneumovirus (aMPV-C), is an important pathogen that can cause egg-drop and acute respiratory diseases in poultry. To date, aMPV-C infection has not been documented in Muscovy ducks in China. Here, we isolated and characterized an aMPV-C, designated S-01, which has caused severe respiratory disease and noticeable egg drop in Muscovy duck flocks in south China since 2010. Electron microscopy showed that the isolate was an enveloped virus exhibiting multiple morphologies with a diameter of 20-500 nm. The S-01 strain was able to produce a typical cytopathic effect (CPE) on Vero cells and cause death in 10- to 11-day-old Muscovy duck embryos. In vivo infection of layer Muscovy ducks with the isolate resulted in typical clinical signs and pathological lesions similar to those seen in the original infected cases. We report the first complete genomic sequence of aMPV-C from Muscovy ducks. A phylogenetic analysis strongly suggested that the S-01 virus belongs to the aMPV-C family, sharing 92.3%-94.3% of nucleotide identity with that of aMPV-C, and was most closely related to the aMPV-C strains isolated from Muscovy ducks in France. The deduced eight main proteins (N, P, M, F, M2, SH, G and L) of the novel isolate shared higher identity with hMPV than with other aMPV (subtypes A, B and D). S-01 could bind a monoclonal antibody against the F protein of hMPV. Together, our results indicate that subtype-C aMPV has been circulating in Muscovy duck flocks in South China, and it is urgent for companies to develop new vaccines to control the spread of the virus in China.

Molecular comparisons of full length metapneumovirus (MPV) genomes, including newly determined French AMPV-C and -D isolates, further supports possible subclassification within the MPV Genus

Four avian metapneumovirus (AMPV) subgroups (A-D) have been reported previously based on genetic and antigenic differences. However, until now full length sequences of the only known isolates of European subgroup C and subgroup D viruses (duck and turkey origin, respectively) have been unavailable. These full length sequences were determined and compared with other full length AMPV and human metapneumoviruses (HMPV) sequences reported previously, using phylogenetics, comparisons of nucleic and amino acid sequences and study of codon usage bias. Results confirmed that subgroup C viruses were more closely related to HMPV than they were to the other AMPV subgroups in the study. This was consistent with previous findings using partial genome sequences. Closer relationships between AMPV-A, B and D were also evident throughout the majority of results. Three metapneumovirus "clusters" HMPV, AMPV-C and AMPV-A, B and D were further supported by codon bias and phylogenetics. The data presented here together with those of previous studies describing antigenic relationships also between AMPV-A, B and D and between AMPV-C and HMPV may call for a subclassification of metapneumoviruses similar to that used for avian paramyxoviruses, grouping AMPV-A, B and D as type I metapneumoviruses and AMPV-C and HMPV as type II.

Viral replication and lung lesions in BALB/c mice experimentally inoculated with avian metapneumovirus subgroup C isolated from chickens

Avian metapneumovirus (aMPV) emerged as an important respiratory pathogen causing acute respiratory tract infection in avian species. Here we used a chicken aMPV subgroup C (aMPV/C) isolate to inoculate experimentally BALB/c mice and found that the aMPV/C can efficiently replicate and persist in the lungs of mice for at least 21 days with a peak viral load at day 6 postinoculation. Lung pathological changes were characterized by increased inflammatory cells. Immunochemical assay showed the presence of viral antigens in the lungs and significant upregulation of pulmonary inflammatory cytokines and chemokines including MCP-1, MIP-1α, RANTES, IL-1β, IFN-γ, and TNF-α were detected following inoculation. These results indicate for the first time that chicken aMPV/C may replicate in the lung of mice. Whether aMPV/C has potential as zoonotic pathogen, further investigation will be required.

Avian metapneumovirus subgroup C infection in chickens, China

Avian metapneumovirus causes acute respiratory tract infection and reductions in egg production in various avian species. We isolated and characterized an increasingly prevalent avian metapneumovirus subgroup C strain from meat-type commercial chickens with severe respiratory signs in China. Culling of infected flocks could lead to economic consequences.

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.

The pathogenicity of avian metapneumovirus subtype C wild bird isolates in domestic turkeys

Background

Avian metapneumovirus subtype C (aMPV/C) causes severe upper respiratory disease in turkeys. Previous report revealed the presence of aMPV/C in wild birds in the southeast regions of the U.S.

Methods

In this study, aMPV/C positive oral swabs from American coots (AC) and Canada geese (CG) were passaged three times in the respiratory tract of specific pathogen free (SPF) turkeys and used as aMPV/C P3 virus isolates in subsequent studies.

Results

Wild bird P3 isolates showed similar growth characteristics when compared to virulent aMPV/C in chicken embryo fibroblast ( CEF) cell cultures and their glycoprotein G gene sequence was closely related to the G gene of aMPV/C Colorado reference virus. Three-day-old commercial or SPF turkeys were inoculated oculonasally with wild bird aMPV/C P3 isolates. At 5 and 7 days post-inoculation (DPI), severe clinical signs were observed in both of the AC and CG virus-exposed groups. Viral RNA was detected in tracheal swabs by reverse transcriptase polymerase chain reaction (RT-PCR). In addition, immunohistochemistry showed virus replication in the nasal turbinate and trachea. All virus-exposed turkeys developed positive antibody response by 14 DPI.

Conclusions

Our data demonstrate that aMPV/C wild bird isolates induced typical aMPV/C disease in the domestic turkeys.

Biochemical characterization of the small hydrophobic protein of avian metapneumovirus

Avian metapneumovirus (AMPV) is a paramyxovirus that has three membrane proteins (G, F, and SH). Among them, the SH protein is a small type II integral membrane protein that is incorporated into virions and is only present in certain paramyxoviruses. In the present study, we show that the AMPV SH protein is modified by N-linked glycans and can be released into the extracellular environment. Furthermore, we demonstrate that glycosylated AMPV SH proteins form homodimers through cysteine-mediated disulfide bonds, which has not been reported previously for SH proteins of paramyxoviruses.

First full-length sequences of the S gene of European isolates reveal further diversity among turkey coronaviruses

An increasing incidence of enteric disorders clinically suggestive of the poult enteritis complex has been observed in turkeys in France since 2003. Using a newly designed real-time reverse transcriptase-polymerase chain reaction assay specific for the nucleocapsid (N) gene of infectious bronchitis virus (IBV) and turkey coronaviruses (TCoV), coronaviruses were identified in 37% of the intestinal samples collected from diseased turkey flocks. The full-length spike (S) gene of these viruses was amplified, cloned and sequenced from three samples. The French S sequences shared 98% identity at both the nucleotide and amino acid levels, whereas they were at most 65% and 60% identical with North American (NA) TCoV and at most 50% and 37% identical with IBV at the nucleotide and amino acid levels, respectively. Higher divergence with NA TCoV was observed in the S1-encoding domain. Phylogenetic analysis based on the S gene revealed that the newly detected viruses form a sublineage genetically related with, but significantly different from, NA TCoV. Additionally, the RNA-dependent RNA polymerase gene and the N gene, located on the 5' and 3' sides of the S gene in the coronavirus genome, were partially sequenced. Phylogenetic analysis revealed that both the NA TCoV and French TCoV (Fr TCoV) lineages included some IBV relatives, which were however different in the two lineages. This suggested that different recombination events could have played a role in the evolution of the NA and Fr TCoV. The present results provide the first S sequence for a European TCoV. They reveal extensive genetic variation in TCoV and suggest different evolutionary pathways in North America and Europe.

Topology and cellular localization of the small hydrophobic protein of avian metapneumovirus

The small hydrophobic protein (SH) is a type II integral membrane protein that is packaged into virions and is only present in certain paramyxoviruses including metapneumovirus. In addition to a highly divergent primary sequence, SH proteins vary significantly in size amongst the different viruses. Human respiratory syncytial virus (HRSV) encodes the smallest SH protein consisting of only 64 amino acids, while metapneumoviruses have the longest SH protein ranging from 174 to 179 amino acids in length. Little is currently known about the cellular localization and topology of the metapneumovirus SH protein. Here we characterize for the first time metapneumovirus SH protein with respect to topology, subcellular localization, and transport using avian metapneumovirus subgroup C (AMPV-C) as a model system. We show that AMPV-C SH is an integral membrane protein with N(in)C(out) orientation located in both the plasma membrane as well as within intracellular compartments, which is similar to what has been described previously for SH proteins of other paramyxoviruses. Furthermore, we demonstrate that AMPV-C SH protein localizes in the endoplasmic reticulum (ER), Golgi, and cell surface, and is transported through ER-Golgi secretory pathway.

The cellular endosomal sorting complex required for transport pathway is not involved in avian metapneumovirus budding in a virus-like-particle expression system

Avian metapneumovirus (AMPV) is a paramyxovirus that principally causes respiratory disease and egg production drops in turkeys and chickens. Together with its closely related human metapneumovirus (HMPV), they comprise the genus Metapneumovirus in the family Paramyxoviridae. Little is currently known about the mechanisms involved in the budding of metapneumovirus. By using AMPV as a model system, we showed that the matrix (M) protein by itself was insufficient to form virus-like-particles (VLPs). The incorporation of M into VLPs was shown to occur only when both the viral nucleoprotein (N) and the fusion (F) proteins were co-expressed. Furthermore, we provided evidence indicating that two YSKL and YAGL segments encoded within the M protein were not a functional late domain, and the endosomal sorting complex required for transport (ESCRT) machinery was not involved in metapneumovirus budding, consistent with a recent observation that human respiratory syncytial virus, closely related to HMPV, uses an ESCRT-independent budding mechanism. Taken together, these results suggest that metapneumovirus budding is independent of the ESCRT pathway and the minimal budding machinery described here will aid our future understanding of metapneumovirus assembly and egress.

Detection by reverse transcriptase-polymerase chain reaction and molecular characterization of subtype B avian metapneumovirus isolated in Brazil

Subtype B avian metapneumovirus (aMPV) was isolated and detected by reverse transcriptase-polymerase chain reaction (RT-PCR) in Brazilian commercial laying chicken flocks with no history of vaccination against aMPV and presenting respiratory signs and decreased egg production. RT-PCR results from samples from three affected flocks revealed that the three isolates were subtype B. Partial sequence analysis of the G glycoprotein gene confirmed that the samples belonged to subtype B and were not of the vaccine type. Comparison of nucleotide and amino acid sequences of the G gene of the three Brazilian aMPV samples with subtype B isolates from other countries revealed 95.1% to 96.1% identity. Nucleotide sequences showed 100% identity among the Brazilian subtype B samples and 95.6% identity with the subtype B vaccine strain used in Brazil. This work describes the circulation of subtype B aMPV in Brazil and discusses its importance in terms of disease epidemiology.

Viral respiratory diseases (ILT, aMPV infections, IB): are they ever under control?

1.

The use of vaccines is the main approach to control of the economically important poultry viral respiratory diseases infectious laryngotracheitis (ILT), avian metapneumovirus (aMPV) infections and infectious bronchitis (IB). This paper appraises the current methods of vaccine control in the light of the nature of each virus and epidemiological factors associated with each disease.

2.

Infectious laryngotracheitis virus (ILTV) exists as a single type with a wide range of disease severity. It is a serious disease in certain regions of the world. Recent work has distinguished molecular differences between vaccine and field strains and vaccine virus can be a cause of disease. Vaccines have remained unaltered for many years but new ones are being developed to counter vaccine side effects and reversion and reactivation of latent virus.

3.

Avian metapneumoviruses, the cause of turkey rhinotracheitis and respiratory disease in chickens exists as 4 subtypes, A, B, C and D. A and B are widespread and vaccines work well provided that accurate doses are given. Newer vaccine developments are designed to eliminate reversion and possibly counter the appearance of newer field strains which may break through established vaccine coverage.

4.

IB presents the biggest problem of the three. Being an unstable RNA virus, part of the viral genome that codes for the S1 spike gene can undergo mutation and recombination so that important antigenic variants can appear irregularly which may evade existing vaccine protection. While conventional vaccines work well against homologous types, new strategies are needed to counter this instability. Molecular approaches involving tailoring viruses to suit field challenges are in progress. However, the simple use of two genetically different vaccines to protect against a wide range of heterologous types is now a widespread practice that is very effective.

5.

None of the three diseases described can claim to be satisfactorily controlled and it remains to be seen whether the newer generations of vaccines will be more efficacious and cost effective. The importance of constant surveillance is emphasised and the testing of novel vaccines cannot be achieved without the use of vaccine-challenge experiments in poultry.