Avian pasteurellosis: Taxonomy of the organisms involved and aspects of pathogenesis

Retrospective Study of Pasteurella multocida Diagnosed in Commercial Turkeys Submitted to California Animal Health and Food Safety Laboratory System; 1991-2017

Fowl cholera is caused by the bacterium Pasteurella multocida and is known to cause significant economic losses in the commercial turkey industry. Four hundred and thirty cases of P. multocida in commercial turkeys, submitted to the California Animal Health and Food Safety Laboratory System (CAHFS) from January 1, 1991, to December 31, 2017, were analyzed. Records examined included CAHFS branch location, date of submission, clinical signs, company and premise of origin, age and sex of submitted turkeys, macroscopic findings, organs in which P. multocida was isolated, and serotype and fingerprint information. Increased mortality as high as 1200 birds per day was the most common complaint at submission, with acute septicemic lesions observed in the majority of cases. The mean age of turkeys diagnosed with fowl cholera was 14 wk, with a median age of 17 wk. Cases most frequently occurred from September to November, with 36% of cases occurring during this time period. Serotyping was performed in 350 cases, while fingerprinting was performed in 171 cases. Serotypes 3 and 3,4 were frequently identified in the 26-yr time period, while the fingerprints identified varied over time. Despite the decreasing population of commercial turkeys in California since the 1990s, fowl cholera continues to be an economically significant disease in this sector.

Haematology, blood biochemistry, parasites and pathology of common eider (Somateria mollisima) males during a mortality event in the Baltic

A mortality event at the Christiansø colony in the Baltic proper killed 115 common eiders (Somateria mollissima) in mid-May 2016. To complement previous studies of incubating females, 39 males were necropsied and from a subsample of these a biochemical and haematological profile was obtained. The birds were emaciated and cachexic having a 50% reduction in body mass. Twenty-nine eiders were diagnosed with hydropericardium, 15 had hunger edema, three birds had enteritis and a single air sac infection. All birds were infested with intestinal Polymorphus minutus and 32 of these with the intestinal Trematoda spp. Microscopic parasitic investigations identified endoparasitic trematodes of the families Bucephhalidae, Echinostomidae, Notocotyluridae and Levinsiniella. White blood cell count showed slight heterophilia and lymphopenia while the albumin:globulin ratio (0.28) indicated stress, immune supression and inflammatory reactions supported by a high heterophil:lymphocyte index (13). Declined plasma concentration of glucose, fructosamine, amylase, albumin and protein likewise indicated long-term starvation prior to mortality indicating phase III starvation (catabolism of protein). The dramatic increase in aspartate transaminase, glutamate-dehydrogenase, lactate-dehydrogenase and bile acids indicate liver disorders while dehydration, renal, heart and bone disorders was reflected in the increased uric acid, urea, phosphor and potassium values. These findings show that male eiders undergo long-term starvation and multi organ failure similar to that of incubating females previously reported from the same colony. It increases our knowledge of the physiology of starving eiders and add to our understanding of the recurrent mortality events in the colony that seems to be linked to changes in food availability being an important factor together with a warmer climate in a declining Baltic eider population. We recommend future studies to focus on food composition, migration patterns and environmental changes including parasitic infections and global warming.

No selection on immunological markers in response to a highly virulent pathogen in an Arctic breeding bird

In natural populations, epidemics provide opportunities to look for intense natural selection on genes coding for life history and immune or other physiological traits. If the populations being considered are of management or conservation concern, then identifying the traits under selection (or 'markers') might provide insights into possible intervention strategies during epidemics. We assessed potential for selection on multiple immune and life history traits of Arctic breeding common eiders (Somateria mollissima) during annual avian cholera outbreaks (summers of 2006, 2007 & 2008). We measured prelaying body condition, immune traits, and subsequent reproductive investment (i.e., clutch size) and survival of female common eiders and whether they were infected with Pasteurella multocida, the causative agent of avian cholera. We found no clear and consistent evidence of directional selection on immune traits; however, infected birds had higher levels of haptoglobin than uninfected birds. Also, females that laid larger clutches had slightly lower immune responses during the prelaying period reflecting possible downregulation of the immune system to support higher costs of reproduction. This supports a recent study indicating that birds investing in larger clutches were more likely to die from avian cholera and points to a possible management option to maximize female survival during outbreaks.

Comparative genome analysis of an avirulent and two virulent strains of avian Pasteurella multocida reveals candidate genes involved in fitness and pathogenicity

BACKGROUND

Pasteurella multocida is the etiologic agent of fowl cholera, a highly contagious and severe disease of poultry causing significant mortality and morbidity throughout the world. All types of poultry are susceptible to fowl cholera. Turkeys are most susceptible to the peracute/acute forms of the disease while chickens are most susceptible to the acute and chronic forms of the disease. The whole genome of the Pm70 strain of P. multocida was sequenced and annotated in 2001. The Pm70 strain is not virulent to chickens and turkeys. In contrast, strains X73 and P1059 are highly virulent to turkeys, chickens, and other poultry species. In this study, we sequenced the genomes of P. multocida strains X73 and P1059 and undertook a detailed comparative genome analysis with the avirulent Pm70 strain. The goal of this study was to identify candidate genes in the virulent strains that may be involved in pathogenicity of fowl cholera disease.

RESULTS

Comparison of virulent versus avirulent avian P. multocida genomes revealed 336 unique genes among the P1059 and/or X73 genomes compared to strain Pm70. Genes of interest within this subset included those encoding an L-fucose transport and utilization system, several novel sugar transport systems, and several novel hemagglutinins including one designated PfhB4. Additionally, substantial amino acid variation was observed in many core outer membrane proteins and single nucleotide polymorphism analysis confirmed a higher dN/dS ratio within proteins localized to the outer membrane.

CONCLUSIONS

Comparative analyses of highly virulent versus avirulent avian P. multocida identified a number of genomic differences that may shed light on the ability of highly virulent strains to cause disease in the avian host, including those that could be associated with enhanced virulence or fitness.

Phenotypic and genotypic characters of isolates of Pasteurella multocida obtained from back-yard poultry and from two outbreaks of avian cholera in avifauna in Denmark

Two outbreaks of fowl cholera in the avifauna in Denmark, affecting primarily eiders but also cormorants, gulls and oyster-catchers were shown to be caused by the same clone of Pasteurella multocida ssp. multocida by restriction enzyme analysis (REA) and ribotyping, using the enzymes HpaII and HhaI and phenotypic characterization. This observation indicated spread by migratory birds. It was shown that the outbreak clone was closely related to isolates of Pasteurella multocida ssp. multocida obtained from back-yard poultry in Denmark, including chickens, pheasants, turkeys and ducks. The only detectable difference between the outbreak clone and some of these strains concerned the size of one fragment. These results indicate a possible exchange of P. multocida ssp. multocida between populations of wild birds and back-yard poultry. Among the DNA fingerprinting methods used, restriction enzyme analysis offered the highest discrimination among thirty strains obtained from back-yard poultry. The restriction enzymes HpaII and HhaI generated almost the same number of profile types, 17 and 15 respectively, but only HpaII differentiated the outbreak clone from the group of closely related strains isolated from back-yard poultry. Ribotyping, using the same enzymes, resulted in 12 and 10 different profile types, respectively. The outbreak isolates did not harbour any plasmids, while six out of the 30 strains originating from back-yard poultry (20%) carried a cryptic plasmid of approximately 3.4 kb.

Molecular characterization of Avian strains of Pasteurella multocida serogroup-A:1 based on amplification of repetitive regions by PCR

Repetitive extragenic palindromic (REP)-PCR (polymerase chain reaction), enterobacterial repetitive intergenic consensus (ERIC)-PCR, and single primer PCR assays were employed to characterize 66 strains of Pasteurella multocida serogroup A:1 isolated from avian species belonging to different regions of India. REP-PCR resulted in amplification of REP sequences from the genome which were in the range of approximately 200 to approximately 3000 bp and accounted for a total of 54 distinguishing profiles (D=0.99). ERIC-PCR analysis also generated amplified products in the range of approximately 200 to approximately 3200 bp categorizing strains into a total of 50 different profiles (D=0.98). Amplification of repetitive regions using a microsatellite primer (GTG)(5), resulted in clear distinctive bands ranging from approximately 200 to approximately 2400 bp. Strains were assigned to 43 profiles (D=0.96). No correlation could be drawn between genotypic profiles and avian hosts with their geographical area of origin. Avian strains of P. multocida serogroup A:1 were found to be highly heterogeneous with diverse profiles. REP-PCR was found to be highly discriminatory and simple method for differentiation of phenotypically similar strains. The present study also indicated that PCR based amplification of repetitive regions of P. multocida is a rapid technique with good discrimination and could be employed directly for routine typing of field isolates from fowl cholera outbreaks.

Characterization of sucrose-negative Pasteurella multocida variants, including isolates from large-cat bite wounds

To validate the identification of Pasteurella multocida-like bacteria negative for acid formation from sucrose, including isolates from bite wounds caused by large cats, 17 strains were phenotypically and genotypically characterized. Phylogenetic analysis of partially sequenced rpoB and infB genes showed the monophyly of the strains characterized and the reference strains of P. multocida. The sucrose-negative strains formed two groups, one related to reference strains of P. multocida and the other related to a separate species-like group (taxon 45 of Bisgaard). DNA-DNA hybridization further documented the species-like nature of this group. Ribotyping showed the heterogeneity of all strains except four strains that shared the same ribotype and that were isolated from bovine lungs. Phylogenetic analysis by 16S rRNA sequence comparison showed the monophyly of the strains characterized and the reference strains of P. multocida. Two strains isolated from leopard bite wounds were related to the type strain of P. dagmatis; however, they represented a new taxon (taxon 46 of Bisgaard), in accordance with their distinct phenotypic and genotypic identifications. The present study documents that sucrose-negative strains of P. multocida-like bacteria belong to two genotypically distinct groups. The study further confirms the phenotypic heterogeneity of P. multocida strains and documents two new species-like taxa of Pasteurella related to P. multocida. Until diagnostic tools have been further elaborated, special care should be taken in the identification of Pasteurella-like bacteria isolated from bite wounds caused by large cats. The evidence of phenotypic and genotypic divergence calls for the further development of PCR tests and DNA sequencing to document doubtful isolates.

Genomic-scale analysis of Pasteurella multocida gene expression during growth within liver tissue of chickens with fowl cholera

We have recently reported the gene expression profile of Pasteurella multocida during growth in the blood of chickens with fowl cholera. Here we report the gene expression profile of P. multocida during growth in the livers of similarly infected chickens. We compared expression profiles of bacteria harvested from the livers of infected chickens with late-stage fowl cholera with those of bacteria grown in rich medium. Independent analysis of bacterial expression profiles from three individual chickens indicated that 93 P. multocida genes were always differentially expressed during growth in liver tissue. Of these 93 genes, 49 were upregulated and 44 downregulated in the host. Many of the upregulated genes were involved in energy production and conversion (9/49) and carbohydrate transport and metabolism (8/49), and a number of these have been shown to be induced under anaerobic conditions in other species. The downregulated genes were generally of unknown or poorly characterised functions (14/44). Comparison of the differentially regulated gene sets identified for growth in liver with those identified previously for growth in blood allowed the identification of a core set of 13 upregulated and 16 downregulated genes that were differentially regulated in at least five of the six infections studied.

Acapsular Pasteurella multocida B:2 can stimulate protective immunity against pasteurellosis

We have previously shown that a Pasteurella multocida cexA mutant (PBA875) was impaired in capsule export and highly attenuated in virulence for mice (J. D. Boyce and B. Adler, Infect. Immun. 68:3463-3468, 2000). In this study we show that immunization with high, but not low, doses of PBA875 can confer significant protection against wild-type challenge. We have also constructed a genetically defined acapsular P. multocida strain (AL18) by inactivation of bcbH, a gene predicted to be involved in polysaccharide biosynthesis. AL18 failed to produce immunoreactive polysaccharide as determined by immunofluorescence and Western immunoblot. Immunization of mice with live AL18 conferred significant protection against wild-type challenge, while immunization with similar doses of either killed wild-type or killed AL18 failed to confer protection.