Molecular Variability of House Finch Mycoplasma gallisepticum Isolates as Revealed by Sequencing and Restriction Fragment Length Polymorphism Analysis of the pvpA Gene

Cloning of cytadhesin protein gene (pvpA) and expression analysis of recombinant fusion protein of Mycoplasma gallisepticum

Chronic respiratory disease (CRD) caused by Mycoplasma gallisepticum (MG) is one of the major respiratory tract infections of the poultry, resulting in significant economic loss to the poultry farmers. Diagnosis of such ailment is highly necessary for effective control measures. In addition, promising molecular tools are warranted for efficient epidemiological tracing of the outbreaks. The study was focused on the elucidation of phase variable cytadhesin protein gene (pvpA) of MG through cloning and expression analysis. A set of primers targeting the pvpA gene of MG was designed. The complete pvpA gene was amplified and cloned into pUC-derived expression vector pRSETA. Finally, the recombinant clones were examined through colony PCR and restriction endonuclease (RE) analysis with EcoR1 and BamH1 enzymes followed by sequencing. The expression of the recombinant pvpA gene was optimized at 1.4mM/μl concentration of Isopropyl-β-D-thiogalactoside induction at 30°C. The recombinant fusion protein was purified by immobilized metal affinity chromatography and characterized by SDS-PAGE followed by confirmation of recombinant cytadhesin fusion protein through western blot analysis. The pvpA gene was successfully cloned and expressed. The deduced amino acid sequence analysis had shown the presence of two direct repeats (DR1 and DR2) along with predicted PRP motifs repeatedly with high proline encoding regions at the carboxy-terminal of pvpA gene indicating its scope for epidemiological studies.

Clinical expression, epidemiology and monitoring of Mycoplasma gallisepticum and Mycoplasma synoviae: an update

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are of clinical and economic importance for the global poultry industry. Many countries and integrations are involved in monitoring programs to control both mycoplasma species. This review provides an extensive historic overview of the last seven decades on the development of the knowledge regarding the factors that influence the clinical expression of the disease, the epidemiology and monitoring of both MG and MS. This includes the detection of new virulent strains, studies unravelling the transmission routes, survival characteristics and the role of other avian hosts. Also the role of molecular typing tests in unravelling epidemiology, and factors that complicate the interpretation of test results such as heterologous mycoplasma infections, use of heterologous oil-emulsion vaccines, use of antibiotic treatments, occurrence of MG and MS strains with low virulence, and last but not least the use of live and/or inactivated MG and MS vaccines are discussed.

Differential house finch leukocyte profiles during experimental infection with Mycoplasma gallisepticum isolates of varying virulence

Leukocyte differentials are a useful tool for assessing systemic immunological changes during pathogen infections, particularly for non-model species. To date, no study has explored how experimental infection with a common bacterial pathogen, Mycoplasma gallisepticum (MG), influences the course and strength of haematological changes in the natural songbird host, house finches. Here we experimentally inoculated house finches with MG isolates known to vary in virulence, and quantified the proportions of circulating leukocytes over the entirety of infection. First, we found significant temporal effects of MG infection on the proportions of most cell types, with strong increases in heterophil and monocyte proportions during infection. Marked decreases in lymphocyte proportions also occurred during infection, though these proportional changes may simply be driven by correlated increases in other leukocytes. Second, we found significant effects of isolate virulence, with the strongest changes in cell proportions occurring in birds inoculated with the higher virulence isolates, and almost no detectable changes relative to sham treatment groups in birds inoculated with the lowest virulence isolate. Finally, we found that variation in infection severity positively predicted the proportion of circulating heterophils and lymphocytes, but the strength of these correlations was dependent on isolate. Taken together, these results indicate strong haematological changes in house finches during MG infection, with markedly different responses to MG isolates of varying virulence. These results are consistent with the possibility that evolved virulence in house finch MG results in higher degrees of immune stimulation and associated immunopathology, with potential direct benefits for MG transmission. RESEARCH HIGHLIGHTS House finches show a marked pro-inflammatory response to M. gallisepticum infection. Virulent pathogen isolates produce stronger finch white blood cell responses. Among birds, stronger white blood cell responses are associated with higher infection severity.

Comparison of multiple genes and 16S-23S rRNA intergenic space region for their capacity in high resolution melt curve analysis to differentiate Mycoplasma gallisepticum vaccine strain ts-11 from field strains

Mycoplasma gallisepticum (MG) is an important avian pathogen causing significant economic losses in the global poultry industry. In an attempt to compare and evaluate existing genotyping methods for differentiation of MG strains/isolates, high resolution melt (HRM) curve analysis was applied to 5 different PCR methods targeting vlhA, pvpA, gapA, mgc2 genes and 16S-23S rRNA intergenic space region (IGSR). To assess the discriminatory power of PCR-HRM of examined genes and IGSR, MG strains ts-11, F, 6/85 and S6, and, initially, 8 field isolates were tested. All MG strains/isolates were differentiated using PCR-HRM curve analysis and genotype confidence percentage (GCP) values of vlhA and pvpA genes, while only 0, 3 and 4 out of 12 MG strains/isolates were differentiated using gapA, mgc2 genes and IGSR, respectively. The HRM curve analysis of vlhA and pvpA genes was found to be highly correlated with the genetic diversity of the targeted genes confirmed by sequence analysis of amplicons generated from MG strains. The potential of the vlhA and pvpA genes was also demonstrated for genotyping of 12 additional MG strains from Europe and the USA. Results from this study provide a direct comparison between genes previously used in sequencing-based genotyping methods for MG strain identification and highlight the usefulness of vlhA and pvpA HRM curve analyses as rapid and reliable tools specially for diagnosis and differentiation of MG strains used here.

The development and application of a Mycoplasma gallisepticum sequence database

Molecular analysis was conducted on 36 Mycoplasma gallisepticum DNA extracts from tracheal swab samples of commercial poultry in seven South African provinces between 2009 and 2012. Twelve unique M. gallisepticum genotypes were identified by polymerase chain reaction and sequence analysis of the 16S-23S rRNA intergenic spacer region (IGSR), M. gallisepticum cytadhesin 2 (mgc2), MGA_0319 and gapA genetic regions. The DNA sequences of these genotypes were distinct from those of M. gallisepticum isolates in a database composed of sequences from other countries, vaccine and reference strains. The most prevalent genotype (SA-WT#7) was detected in samples from commercial broilers, broiler breeders and layers in five provinces. South African M. gallisepticum sequences were more similar to those of the live vaccines commercially available in South Africa, but were distinct from that of F strain vaccine, which is not registered for use in South Africa. The IGSR, mgc2 or MGA_0319 sequences of three South African genotypes were identical to those of the ts-11 vaccine strain, necessitating a combination of mgc2 and IGSR targeted sequencing to differentiate South African wild-type genotypes from ts-11 vaccine. To identify and differentiate all 12 wild-types, mgc2, IGSR and MGA_0319 sequencing was required. Sequencing of gapA was least effective at strain differentiation. This research serves as a model for the development of an M. gallisepticum sequence database, and illustrates its application to characterize M. gallisepticum genotypes, select diagnostic tests and better understand the epidemiology of M. gallisepticum.

Parallel patterns of increased virulence in a recently emerged wildlife pathogen

A bacterial pathogen of wild songbirds evolved higher virulence following its emergence in two separate regions of the host range.

The evolution of higher virulence during disease emergence has been predicted by theoretical models, but empirical studies of short-term virulence evolution following pathogen emergence remain rare. Here we examine patterns of short-term virulence evolution using archived isolates of the bacterium Mycoplasma gallisepticum collected during sequential emergence events in two geographically distinct populations of the host, the North American house finch (Haemorhous [formerly Carpodacus] mexicanus). We present results from two complementary experiments, one that examines the trend in pathogen virulence in eastern North American isolates over the course of the eastern epidemic (1994–2008), and the other a parallel experiment on Pacific coast isolates of the pathogen collected after M. gallisepticum established itself in western North American house finch populations (2006–2010). Consistent with theoretical expectations regarding short-term or dynamic evolution of virulence, we show rapid increases in pathogen virulence on both coasts following the pathogen's establishment in each host population. We also find evidence for positive genetic covariation between virulence and pathogen load, a proxy for transmission potential, among isolates of M. gallisepticum. As predicted by theory, indirect selection for increased transmission likely drove the evolutionary increase in virulence in both geographic locations. Our results provide one of the first empirical examples of rapid changes in virulence following pathogen emergence, and both the detected pattern and mechanism of positive genetic covariation between virulence and pathogen load are consistent with theoretical expectations. Our study provides unique empirical insight into the dynamics of short-term virulence evolution that are likely to operate in other emerging pathogens of wildlife and humans.

A long-standing paradox in the study of infectious diseases is why pathogens evolve to cause harm to the very hosts they depend on to survive and reproduce. Research over several decades suggests that this harm, or virulence, is an inevitable by-product of the pathogen replication needed to maximize the chance that a given pathogen will be transmitted to another host. Here we demonstrate that a recently emerged bacterial pathogen of a North American songbird species has gradually become more virulent during each of two emergence events in different regions of the host range. This evolution of higher virulence appears to have been driven by selection for high rates of pathogen replication, because bacterial isolates that are more virulent in finches also attain the highest loads in infected host tissues. Overall, our results indicate that emerging pathogens can evolve to become more virulent in their hosts, at least in the short term, when an increase in the pathogen's ability to replicate is linked with higher virulence. Our findings have important implications for understanding and predicting the severity of disease caused by emerging pathogens in wildlife, domestic animals, and humans.

Extensive variation in surface lipoprotein gene content and genomic changes associated with virulence during evolution of a novel North American house finch epizootic strain of Mycoplasma gallisepticum

Mycoplasma gallisepticum, a significant respiratory and reproductive pathogen of domestic poultry, has since 1994 been recognized as an emergent pathogen of the American house finch (Carpodacus mexicanus). Epizootic spread and pathognomonic characteristics of house finch-associated Mycoplasma gallisepticum (HFMG) have been studied as a model of an emergent to endemic pathogen in a novel host. Here we present comparative analysis of eight HFMG genomes, including one from an index isolate and seven isolates separated spatially and temporally (1994-2008) across the epizootic, and notably having differences in virulence. HFMG represented a monophyletic clade relative to sequenced poultry isolates, with genomic changes indicating a novel M. gallisepticum lineage and including unique deletions of coding sequence. Though most of the HFMG genome was highly conserved among isolates, genetic distances correlated with temporal-spatial distance from the index. The most dramatic genomic differences among HFMG involved phase-variable and immunodominant VlhA lipoprotein genes, including those variable in presence and genomic location. Other genomic differences included tandem copy number variation of a 5 kbp repeat, changes in and adjacent to the clustered regularly interspaced short palindromic repeats, and small-scale changes affecting coding potential and association of genes with virulence. Divergence of monophyletic isolates from similar time/space in the epizootic indicated local diversification of distinct HFMG sublineages. Overall, these data identify candidate virulence genes and reveal the importance of phase-variable lipoproteins during the evolution of M. gallisepticum during its emergence and dissemination in a novel host in nature, likely mediating an important role at the interface between pathogen virulence and host immunity.

Common garden experiment reveals pathogen isolate but no host genetic diversity effect on the dynamics of an emerging wildlife disease

Host genetic diversity can mediate pathogen resistance within and among populations. Here we test whether the lower prevalence of Mycoplasmal conjunctivitis in native North American house finch populations results from greater resistance to the causative agent, Mycoplasma gallisepticum (MG), than introduced, recently-bottlenecked populations that lack genetic diversity. In a common garden experiment, we challenged wild-caught western (native) and eastern (introduced) North American finches with a representative eastern or western MG isolate. Although introduced finches in our study had lower neutral genetic diversity than native finches, we found no support for a population-level genetic diversity effect on host resistance. Instead we detected strong support for isolate differences: the MG isolate circulating in western house finch populations produced lower virulence, but higher pathogen loads, in both native and introduced hosts. Our results indicate that contemporary differences in host genetic diversity likely do not explain the lower conjunctivitis prevalence in native house finches, but isolate-level differences in virulence may play an important role.

SPATIAL SPREAD OF AN EMERGING INFECTIOUS DISEASE: CONJUNCTIVITIS IN HOUSE FINCHES

In this paper we quantify the rate of spread of the newly emerged pathogen Mycoplasma gallisepticum of the House Finch, Carpodacus mexicanus, in its introduced range. We compare and contrast the rapid, yet decelerating, rate of spread of the pathogen with the slower, yet accelerating rate of spread of the introduced host. Comparing the rate of spread of this pathogen to pathogens in terrestrial mammalian hosts, we see that elevation and factors relating to host abundance restrict disease spread, rather than finding any major effects of discrete barriers or anthropogenic movement. We examine the role of seasonality in the rate of spread, finding that the rate and direction of disease spread relates more to seasonality in host movement than to seasonality in disease prevalence. We conclude that asymptomatic carriers are major transmitters of Mycoplasma gallisepticum into novel locations, a finding which may also be true for many other diseases, such as West Nile Virus and avian influenza.

Assessing the risks of introduced chickens and their pathogens to native birds in the Galápagos Archipelago

Poultry production is an important economic activity on inhabited islands of the Galápagos archipelago. There has been a recent surge in both small-scale backyard chickens and larger scale broiler production associated with growth in the human population and the tourist industry. With increased poultry production, concerns have been expressed about the increasing risk of transfer of disease from chickens to native Galápagos bird species that may have little resistance to introduced pathogens [Wikelski, M., Foufopoulos, J., Vargas, H., Snell, H., 2004. Galápagos birds and diseases: invasive pathogens as threats for island species. Ecology and Society 9(5). Available from: URL:http://www.ecologyandsociety.org/vol9/iss1/art5]. This study evaluates risks posed by chicken disease to endemic and native Galápagos bird species, based on empirical evidence of pathogens present in chickens on the islands and a literature review of effects of these pathogens in wild species. Pathogens identified in domestic chicken populations of immediate avian conservation concern are Newcastle disease, Mycoplasma gallisepticum, and the proventricular parasite Dispharynx sp. Newcastle disease (avian paramyxovirus-1) poses an imminent threat to Galápagos penguins (Spheniscus mendiculus), flightless cormorants (Phalacrocorax harrisi), and lava gulls (Larus fuliginosus), species with very small population sizes (less than 1500 animals each). Additionally, litter from broiler farms could affect ecological processes in local ecosystems. Improved poultry biosecurity measures are urgently needed on the Galápagos Islands for avian disease management, yet developing these strategies presents political, social, and economic challenges.

A cDNA macroarray approach to parasite-induced gene expression changes in a songbird host: genetic response of house finches to experimental infection by Mycoplasma gallisepticum

In 1994, the bacterial parasite Mycoplasma gallisepticum expanded its host range and swept through populations of a novel host--eastern US populations of the house finch (Carpodacus mexicanus). This epizootic caused a dramatic decline in finch population numbers, has been shown to have caused strong selection on house finch morphology, and presumably caused evolutionary change at the molecular level as finches evolved enhanced resistance. As a first step toward identifying finch genes that respond to infection by Mycoplasma and which may have experienced natural selection by this parasite, we used suppression subtractive hybridization (SSH) and cDNA macroarray approaches to identify differentially expressed genes regulated by the Mycoplasma parasite. Two subtractive cDNA libraries consisting of 16,512 clones were developed from spleen using an experimentally uninfected bird as the 'tester' and an infected bird as 'driver', and vice versa. Two hundred and twenty cDNA clones corresponding 34 genes with known vertebrate homologues and a large number of novel transcripts were found to be qualitatively up- or down-regulated genes by high-density filter hybridization. These gene expression changes were further confirmed by a high throughout reverse Northern blot approach and in specific cases by targeted Northern analysis. blast searches show that heat shock protein (HSP) 90, MHC II-associated invariant chain (CD74), T-cell immunoglobulin mucin 1 (TIM1), as well as numerous novel expressed genes not found in the databases were up- or down-regulated by the host in response to this parasite. Our results and macroarray resources provide a foundation for molecular co-evolutionary studies of the Mycoplasma parasite and its recently colonized avian host.

Evaluation of amplified fragment length polymorphism for differentiation of avian mycoplasma species

Amplified fragment length polymorphism (AFLP) was used for typing avian mycoplasma species. Forty-four avian mycoplasma strains were successfully typed into eight distinct groups, with each representing a different species. Homology of AFLP patterns of 35% or less was used as a cutoff value to differentiate avian mycoplasma strains into different species.

Use of molecular diversity of Mycoplasma gallisepticum by gene-targeted sequencing (GTS) and random amplified polymorphic DNA (RAPD) analysis for epidemiological studies

A total of 67 Mycoplasma gallisepticum field isolates from the USA, Israel and Australia, and 10 reference strains, were characterized by gene-targeted sequencing (GTS) analysis of portions of the putative cytadhesin pvpA gene, the cytadhesin gapA gene, the cytadhesin mgc2 gene, and an uncharacterized hypothetical surface lipoprotein-encoding gene designated genome coding DNA sequence (CDS) MGA_0319. The regions of the surface-protein-encoding genes targeted in this analysis were found to be stable within a strain, after sequencing different in vitro passages of M. gallisepticum reference strains. Gene sequences were first analysed on the basis of gene size polymorphism. The pvpA and mgc2 genes are characterized by the presence of different nucleotide insertions/deletions. However, differentiation of isolates based solely on pvpA/mgc2 PCR size polymorphism was not found to be a reliable method to differentiate among M. gallisepticum isolates. On the other hand, GTS analysis based on the nucleotide sequence identities of individual and multiple genes correlated with epidemiologically linked isolates and with random amplified polymorphic DNA (RAPD) analysis. GTS analysis of individual genes, gapA, MGA_0319, mgc2 and pvpA, identified 17, 16, 20 and 22 sequence types, respectively. GTS analysis using multiple gene sequences mgc2/pvpa and gapA/MGA_0319/mgc2/pvpA identified 38 and 40 sequence types, respectively. GTS of multiple surface-protein-encoding genes showed better discriminatory power than RAPD analysis, which identified 36 pattern types from the same panel of M. gallisepticum strains. These results are believed to provide the first evidence that typing of M. gallisepticum isolates by GTS analysis of surface-protein genes is a sensitive and reproducible typing method and will allow rapid global comparisons between laboratories.

Dynamics of a novel pathogen in an avian host: Mycoplasmal conjunctivitis in house finches

In early 1994, a novel strain of Mycoplasma gallisepticum (MG)--a poultry pathogen with a world-wide distribution--emerged in wild house finches and within 3 years had reached epidemic proportions across their eastern North American range. The ensuing epizootic resulted in a rapid decline of the host population coupled with considerable seasonal fluctuations in prevalence. To understand the dynamics of this disease system, a multi-disciplinary team composed of biologists, veterinarians, microbiologists and mathematical modelers set forth to determine factors driving and influenced by this host-pathogen system. On a broad geographic scale, volunteer observers ("citizen scientists") collected and reported data used for calculating both host abundance and disease prevalence. The scale at which this monitoring initiative was conducted is unprecedented and it has been an invaluable source of data for researchers at the Cornell Laboratory of Ornithology to track the spread and magnitude of disease both spatially and temporally. At a finer scale, localized and intensive field studies provided data used to quantify the effects of disease on host demographic parameters via capture-mark-recapture modeling, effects of host behavior on disease and vice-versa, and the biological and genetic profiles of birds with known phenotypic characteristics. To balance the field-based component of the study, experiments were conducted with finches held in captivity to describe and quantify the effects of experimental infections on hosts in both individual and social settings. The confluence of these various elements of the investigation provided the foundation for construction of a general compartmentalized epidemiological model of the dynamics of the house finch-MG system. This paper serves several purposes including (i) a basic review of the pathogen, host, and epidemic cycle; (ii) an explanation of our research strategy; (iii) a basic review of results from the diverse multi-disciplinary approaches employed; and (iv) pertinent questions relevant to this and other wildlife disease studies that require further investigation.