Development of superficial lung lesions monitored on farm by serial ultrasonographic examination in sheep with lesions confirmed as ovine pulmonary adenocarcinoma at necropsy.

BACKGROUND: This ultrasonographic study monitored lesions involving the lung surface suspected to be the early stages of ovine pulmonary adenocarcinoma (OPA) tumours over 4 months in commercially farmed sheep. The enlargement of these lesions defined ultrasonographically, which likely represent the development of OPA tumours, have important implications for ultrasound screening schedules in veterinary management plans attempting to eliminate OPA by test-and-cull. RESULTS: The lungs of 58 adult Scottish Blackface sheep with ultrasonographic changes at the lung surface consistent with early OPA tumours were examined two to six times over 40 to 290 days. Lesion development, represented in early video recordings by 2-3 mm lesions involving the visceral pleural and comet tails, then a decreasing length of the hyperechoic line representing the normal visceral pleura and increasing depth of the sharply-demarcated and largely uniform hypoechoic areas into the lung parenchyma, was found in 26 of the 58 sheep. The rate at which the sonographic lesions progressed varied considerably and in 10 of 17 Group 1 sheep developed quickly from an estimated depth of 2-30 mm up to 70 mm between 60 and 120 days later. These sonographic lesions were confirmed as OPA at necropsy; histological changes of concurrent bacterial infection were detected in one of these 10 Group 1 sheep. Thirty-one sheep had sonographic changes ≤30 mm consistent with very early OPA at the first examination which had reduced or were not observed at subsequent examination. Five of these 31 sheep were necropsied, 3 had small OPA lesions while 2 had no significant pathology. CONCLUSION: Lesions involving the visceral pleura, with sonographic changes consistent with previous published findings of early OPA, developed over 40-120 days to large masses in 10 of 17 Group 1 sheep with the provisional sonographic diagnosis confirmed histologically at necropsy. While it is possible that atalectic lung could have caused some of the minor sonographic changes there was no microscopic evidence of pathologies other than OPA in nine of 10 Group 1 sheep. We conclude that some small tumours progress to large tumours within 3 months questioning the assumption that OPA is a slow growing tumour in adult sheep taking several years to cause clinical disease. The findings that a proportion of small ultrasonographic lesions are not found again at subsequent scanning illustrates the challenges of interpreting small (< 1-2 cm) lesions during rapid whole flock ultrasonographic examination and we continue to recommend re-scanning suspicious sonographic changes 2 months later.

Investigations into an outbreak of corvid respiratory disease associated with Pasteurella multocida.

The possible cause of disease and mortality in corvids on an outdoor pig unit in the north of England between August 2007 and March 2008 was investigated. Nine carrion crows (Corvus corone corone) and nine rooks (Corvus frugilegus), comprising five live-caught birds with clinical signs of respiratory disease, one live-caught bird without respiratory disease, and 12 birds submitted dead were examined. Clinical signs, gross and histopathological examination, microbiology and toxicology indicated that Pasteurella multocida infection was the cause of disease. Molecular and serotyping analyses showed that P. multocida isolates (obtained from live-caught birds with clinical respiratory disease) were all capsular type F with a mix of somatic serotypes 3, 4 and 7. Immunohistochemistry increased the diagnostic sensitivity of the analysis and detected P. multocida within the pulmonary lesions of all affected live-caught birds and 10 of 12 birds found dead. These findings suggest that wild corvids in the UK can suffer from lung pathology associated with P. multocida and, as potential vectors of P. multocida, may pose a risk to domestic poultry.

Targeting the Main Anatomopathological Features in Animal Models of Myocardial Infarction.

Cardiovascular disease is the leading cause of human mortality and disability worldwide, primarily due to myocardial infarction (MI) and the resultant heart failure. To address this, animal models of MI have been developed to better understand the pathophysiological process and to enable the discovery and development of new therapies. The most commonly used small and large mammal models of MI accurately reproduce histopathologically the four characteristic post-MI phases: cardiac cell death, inflammation, myocardial repair and remodelling. However, differences between the time of onset of each characteristic phase and the kinetics of various cellular reactions between human MI and animal models, and between animal models, require careful consideration when defining the variables to be analysed and the timepoints of assessment in experimental studies. Typically, the progression of the different phases post-MI occur more rapidly in rodent models compared with large-animal models and man, suggesting the use of large-animal models is more translational for studying human MI. This review provides an overview of the main anatomopathological features of small and large animal models of MI and discusses the key species-specific histopathological similarities and differences.

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: I. Soil ingestion, soil-metal partitioning and potential availability to pasture herbage and livestock.

This paper first evaluates the relative importance of the soil-plant-animal and soil-animal pathways of Zn, Cu and (especially) Pb investigated over a 15-month study period at 12 floodplain sites located within and downstream of the mineralised and historic mining area of mid-Wales, and secondly considers the implications of a sequential extraction procedure (SEP) undertaken on soils of varying particle size sampled from the study locations. Generally, very good agreement was found between the chemical partitioning of the three metals for each of the physical soil fractions subjected to the SEP. The availability of Pb to pasture vegetation, especially at the contaminated sites, is indicated with its associations with the more soluble (i.e. exchangeable and Fe/Mn oxide) soil phases, yet soil and/or plant barriers effectively restrict above-ground herbage concentrations of this metal. Consequently, with sheep ingesting soil at rates varying according to season from 0.1% to 44% or more of dry matter intake, the soil-animal pathway accounts for the majority of Pb consumption through most of the year, and at moderately and highly contaminated sites significant quantities of relatively soluble soil-Pb can be ingested at rates exceeding safety threshold limits.

First cases of squirrelpox in red squirrels (Sciurus vulgaris) in Scotland.

Squirrelpox, caused by a poxvirus, is a major threat to the remaining UK red squirrel population. The spread of antibody-positive grey squirrels has been monitored in the UK for the past decade. In 2005 grey squirrels that had been exposed to the virus appeared in the south of Scotland for the first time, followed approximately two years later by the appearance of squirrelpox disease in the local red squirrels. Four squirrels were examined. They all had gross external lesions and histological lesions typical of squirrelpox disease, but no significant internal lesions. The diagnosis was confirmed by PCR, electron microscopy and serology.

Causes of Mortality and Lesions Observed Post mortem in European Moles (Talpa europaea) in Cornwall, South-west England.

European moles (Talpa europaea) are a common species in the UK, but there are few published data on the causes of mortality in these animals. An opportunistic post-mortem study was carried out on 44 moles found dead or dying in Cornwall, UK. Assessment of muscle condition and fat reserves, where possible, indicated that most (27 of 37, 73%) were in good nutritive condition. The majority had died of trauma (n = 40, 91%), the principal cause of which was predation (n = 36, 81.8%) by foxes and domestic cats and dogs. The carcases were in a variable state of preservation, but 28 cases were suitable for histopathological examination. This revealed lesions in the lungs of 92.8 % (26 of 28) of the animals. The commonest lesions comprised localized infiltration of the parenchyma by macrophages and eosinophils and in most cases the lesions were unlikely to have been of clinical significance; in two cases they were associated with infection by a parasitic nematode. One mole showed severe pneumonitis and hepatitis caused by infection with Toxoplasma gondii. Adiaspiromycosis was diagnosed in two moles, one by direct microscopical examination of the lung and one by histopathology; the lesions were not considered to be of clinical significance. Severe pleurisy and pericarditis caused by infection with Streptobacillus moniliformis was seen in a mole that had suffered bite wounds to a foot previously. Cholangitis due to infection by a protozoal parasite, provisionally identified as Cyclospora talpae, was a common histopathological finding (11 of 28, 39.3%); infection by the parasite did not appear to affect body condition adversely. Miscellaneous conditions identified were ulcerative dermatitis associated with gram-positive cocci (n = 1), extra medullary haemopoiesis in spleens (six of 12, 50%) and mineralized foci in pulmonary blood vessels (three of 28, 10.7%). No significant pathology was seen in the kidneys. This study suggests that the health status of moles in Cornwall is generally good and predation is a common cause of mortality. Pulmonary disease, associated in some cases with nematode infections, is also prevalent, but probably of little clinical significance. There is a high prevalence of cholangitis due to infection with a protozoan parasite believed to be C. talpae. Other diseases identified include adiaspiromycosis, streptobacillosis and toxoplasmosis.

Brucella ceti associated pathology in the testicle of a harbour porpoise (Phocoena phocoena).

Brucellosis is reported increasingly in marine mammals and the marine species of Brucella are capable of causing community acquired zoonotic infections in humans as well as abortion in cattle as a result of experimental infection. This case report describes pathology associated with an isolate of Brucella ceti that was successfully cultured from, and immunolabelled in, the testis and epididymis of an adult sexually mature free-living harbour porpoise (Phocoena phocoena). This is the first report of such pathology in any species of cetacean, and suggests the potential for sexual transmission and/or sterility as sequelae to infection similar to those reported in terrestrial animals.

Diagnosis of preclinical scrapie in live sheep by the immunohistochemical examination of rectal biopsies.

In most sheep infected with a transmissible spongiform encephalopathy (tse) the disease-associated prion protein (PrP(d)) accumulates in tissues of the lymphoreticular system, suggesting that it might be detected in biopsy specimens. A procedure has been developed to obtain biopsy specimens of rectal mucosa in which PrP(d) has been detected by immunohistochemistry in preclinically infected sheep of all susceptible PrP genotypes. It is probable that PrP(d) increases with the age of sheep or period of incubation. PrP(d) was detectable approximately halfway through the incubation period, with sheep of some PrP genotypes showing positive results earlier than others. For a preclinical diagnosis, the risk of a false negative result was approximately 9 per cent for samples containing 10 follicles, a figure that was reached in 87 per cent of the biopsies. The rectal biopsies had the same sensitivity and time of onset of PrP(d) accumulation as biopsies of the palatine tonsil, but provided larger numbers of follicles. The procedure is simple and quick, does not require dedicated specific instruments, sedation or general anaesthesia, and can be performed repeatedly on the same sheep without detrimental effects to either the animal or the number of follicles obtained.

Complex Gill Disease: an Emerging Syndrome in Farmed Atlantic Salmon (Salmo salar L.).

Gill disorders have become a significant problem during the marine phase of farming Atlantic salmon (Salmo salar L.). The term complex gill disease (CGD) includes a wide range of clinical gill disease presentations generally occurring from the end of summer to early winter on marine Atlantic salmon farms. The gross and histological lesions observed are the resultant culmination of exposure to a mixture of environmental insults, pathogenic organisms and farm management practices. None of the three principal agents purportedly associated with CGD (Desmozoon lepeophtherii, salmon gill poxvirus or Candidatus Branchiomonas cysticola) have been cultured successfully in-vitro, so individual in-vivo challenge studies to identify their pathogenesis have not been possible. Studies of cohabitation of single pathogen-infected fish with naïve fish, and epidemiological investigations are required urgently to elucidate the roles of these pathogens and other factors in CGD.

A Fatal Case of Louping-ill in a Dog: Immunolocalization and Full Genome Sequencing of the Virus.

Louping-ill (LI), caused by louping-ill virus (LIV), results in a frequently fatal encephalitis primarily affecting sheep and red grouse (Lagopus lagopus scotica), but it does occur in other species. An adult male Border collie dog was definitively diagnosed with fatal LI and the lesion profile, LIV antigen distribution and full genome sequence of the LIV responsible were investigated to determine if this differed significantly from sheep-derived LIV. No gross lesions were present. The histological lesions were confined to the central nervous system and comprised of lymphocytic perivascular cuffs, glial foci, neuronal necrosis and neuronophagia. Immunolocalization of viral antigen showed small amounts present in neurons only. These histological and immunohistochemical findings were similar to those reported in affected sheep. Compared with published full genome sequences of sheep-derived LIV, only very minor differences were present and phylogenetically the virus clustered individually between a subclade containing Scottish strains, LIV 369/T2 and G and another subclade containing an English isolate LIV A. The LIV isolated from the dog shares a common progenitor with LIV A. These findings suggest there is no canine-specific LIV strain, dogs are susceptible to sheep-associated strains of LI and with the increase in tick prevalence, and therefore exposure to LIV, a safe, effective vaccine for dogs may be required.

Fatal Sarcoptes scabiei infection of blue sheep (Pseudois nayaur) in Pakistan.

Sarcoptes scabiei was detected for the first time in skin scrapings, hair pluckings, and histologic sections from a blue sheep (Pseudois nayaur) from the Shimshali Pamir in the Karakorum range of the western Himalaya in Pakistan (36 degrees 28'N, 75 degrees 36'E). Local reports suggest many hundred animals have been affected by a severe skin disease over a 10-yr period, but the shy nature of this species and the extreme climate that they inhabit meant only a single affected animal was available for detailed evaluation. The severe skin lesions were confined to the forelegs and brisket, and many Sarcoptes scabiei mites were present in all the samples examined. Histologic preparations of the skin showed hyperkeratotic and parakeratotic hyperkeratosis of the epidermis with a severe exudative dermatosis with many polymorphonuclear neutrophils and gram-positive cocci, yet no eosinophils. These findings might suggest the lack of an appropriate immune response to the parasite or other coping strategies because there has been no abatement of the clinical signs in affected animals over several years. Treatment options are limited due to the behavior of the species and its habitat. The blue sheep is a primary source of prey for the endangered snow leopard (Panthera uncia) and continued depletion could have serious consequences for the survival of the latter.

Clinical Pathology of the Critically Endangered Gough Bunting (Rowettia goughensis).

The Gough bunting (Rowettia goughensis) is indigenous to Gough Island and critically endangered due to predation by invasive house mice (Mus musculus). A planned ecosystem restoration by eradication of house mice via aerially delivered rodenticide requires a reproductively balanced population of Gough buntings being held in captivity to avoid primary and secondary poisoning. To aid disease detection during the period of captivity, Gough buntings (n = 25; five adult females, 15 adult males and five juveniles) were captured, measured and sampled to determine reference ranges for routine haematological and biochemical parameters and to identify any faecal bacterial species and intestinal and haemoparasites. Adult females had significantly higher blood glucose (P = 0.02 and 0.05 for different analyzers) and globulins (P = 0.02) than adult males or juveniles, and juveniles had consistently higher, although not significant, concentrations of creatine kinase. Juveniles had significantly (P = 0.007) more heterophils than adults; eosinophils were rare in adults and absent in juveniles and azurophils were absent from all individuals sampled. No parasite eggs were found in the faeces and no haemoparasites were found in blood smears. Several faecal bacterial species were recorded including Enterococcus spp. (n = 12), Klebsiella spp. (n = 7), Staphylococcus aureus (n = 6), Staphylococcus intermedius (n = 1), Escherichia coli (n = 1) and Pseudomonas spp. (n = 1). No overt clinical or subclinical disease was found in any of the birds examined, which suggests they are suitable for short-term captivity during ecosystem restoration and the data will provide key haematological and biochemical reference ranges for monitoring their health. However, the capture of a reproductively balanced population may require significant effort due to the relative difficulty with which females were caught.

Role of Schmallenberg virus infection in congenital malformations in ruminants in Scotland in 2017.

Scotland's Rural College (SRUC), together with the Moredun Research Institute, carries out surveillance for Schmallenberg virus (SBV) infection in cattle and sheep. This article reports findings relating to diagnoses of fetopathy associated with SBV infection and other congenital malformations in these species made between January 1 and May 5, 2017.

Clinical Pathology of the Vulnerable Gough Moorhen (Gallinula comeri).

The Gough moorhen (Gallinula comeri) is native to Gough Island, Tristan da Cunha, and listed as Vulnerable by the International Union for Conservation of Nature due to its restricted range and susceptibility to introduced predators. A planned ecosystem restoration by eradication of introduced house mice (Mus musculus) via aerially delivered rodenticide requires a reproductively balanced population of Gough moorhens to be held in captivity to avoid primary and secondary poisoning. To aid disease detection during the period of captivity, Gough moorhens (n = 43; 25 adult females and 18 adult males) were captured, measured and sampled to determine ease of sexing by morphometrics, to establish reference ranges for routine haematological and biochemical parameters and to identify any intestinal and haemoparasites as well as determine which faecal bacteria were present. Male Gough moorhens had significantly greater mean body mass (P = 0.019) and head and bill length (P = 0.001) compared with females, but the overlapping ranges showed genetic identification of sex was required for accurate determination. Plasma globulin and total protein concentrations were significantly greater in female compared with male birds (P = 0.032 and P = 0.012, respectively) and probably related to egg yolk production. No haemoparasites or gastrointestinal parasites were found in any bird and there were no sex-related differences in the haematology. Multiple bacterial taxa were isolated from the faeces of all birds including Enterococcus spp. (n = 42), Klebsiella spp. (n = 40), Staphylococcus aureus (n = 33), Staphylococcus intermedius (n = 16), Escherichia coli (n = 41) and Pseudomonas spp. (n = 7). No clinical or subclinical disease was found in any of the birds examined, suggesting they are suitable for short-term captivity but rapid on-island genetic-based sex determination will be essential to ensure a reproductively balanced population.

Lambs are Susceptible to Experimental Challenge with Spanish Goat Encephalitis Virus.

Spanish goat encephalitis virus (SGEV) is a member of the genus Flavivirus, family Flaviviridae, and causes encephalomyelitis in goats. The aim of this study was to determine whether sheep are susceptible to experimental challenge with SGEV by two different routes. The results show that SGEV can infect sheep by both the subcutaneous and intravenous routes, resulting in neurological clinical disease with extensive and severe histological lesions in the central nervous system. Lambs challenged subcutaneously developed more severe lesions on the ipsilateral side of the brain, but the lesion morphology was similar irrespective of the route of challenge. The clinical presentation, pathogenesis, lesion morphology and distribution shows that SGEV is very similar to louping ill virus (LIV) and therefore any disease control plan must take into account any host species and SGEV vectors as potential reservoirs. Furthermore, discriminatory diagnostics need to be applied to any sheep or goat suspected of disease due to any flavivirus in areas where SGEV and LIV co-exist.

Vaccination against Louping Ill Virus Protects Goats from Experimental Challenge with Spanish Goat Encephalitis Virus.

Spanish goat encephalitis virus (SGEV) is a recently described member of the genus Flavivirus belonging to the tick-borne encephalitis group of viruses, and is closely related to louping ill virus (LIV). Naturally acquired disease in goats results in severe, acute encephalitis and 100% mortality. Eighteen goats were challenged subcutaneously with SGEV; nine were vaccinated previously against LIV and nine were not. None of the vaccinated goats showed any clinical signs of disease or histological lesions, but all of the non-vaccinated goats developed pyrexia and 5/9 developed neurological clinical signs, primarily tremors in the neck and ataxia. All non-vaccinated animals developed histological lesions restricted to the central nervous system and consistent with a lymphocytic meningomyeloencephalitis. Vaccinated goats had significantly (P <0.003) greater concentrations of serum IgG and lower levels of IgM (P <0.0001) compared with unvaccinated animals. SGEV RNA levels were below detectable limits in the vaccinated goats throughout the experiment, but increased rapidly and were significantly (P <0.0001) greater 2-10 days post challenge in the non-vaccinated group. In conclusion, vaccination of goats against LIV confers highly effective protection against SGEV; this is probably mediated by IgG and prevents an increase in viral RNA load in serum such that vaccinated animals would not be an effective reservoir of the virus.

Detection of Louping ill virus in clinical specimens from mammals and birds using TaqMan RT-PCR.

The identification of Louping ill virus (LIV) in clinical specimens has been routinely achieved by virus isolation using susceptible pig kidney cells and subsequent serological analysis. While this method is sensitive and detects infectious virus, it is relatively labour intensive and time-consuming. In view of the veterinary and potential medical importance of LIV, a rapid and precise detection method for routine use that employs the TaqMan reverse transcription polymerase chain reaction (RT-PCR) has been developed to detect LIV RNA extracted from field samples. The TaqMan assay was evaluated against virus isolation using 22 cell culture grown LIV isolates, which had previously been partially characterised by sequencing, and material from 63 suspect field cases. Histopathological and/or serological reports were available for 39 of the suspect cases, providing additional diagnostic information to evaluate the results obtained from the TaqMan RT-PCR assay. The TaqMan assay was as sensitive as the cell culture infectious virus assay currently used and had the advantage that it was able to detect LIV in clinical specimens from which infectious virus could not be isolated possibly due to the presence of high levels of LIV antibody.

Postmortem diagnosis of preclinical and clinical scrapie in sheep by the detection of disease-associated PrP in their rectal mucosa.

Samples of tissue from the central nervous system (cns), the lymphoreticular system (lrs) and the rectal mucosa of a large number of scrapie-exposed sheep, with and without signs of clinical disease, were examined immunohistochemically for evidence of disease-associated prion protein (PrP(d)). The rectal mucosa has received almost no attention so far in scrapie diagnosis, despite its abundant rectoanal mucosa-associated lymphoid tissue, and its accessibility. The scrapie-confirmed cases included 244 with clinical disease, of which 237 (97.1 per cent) were positive in the rectal mucosa, and 121 apparently healthy sheep, of which 104 (86 per cent) were positive in the rectal mucosa. PrP(d) was detected in 86.4 to 91.5 per cent of the other lrs tissues of the healthy sheep examined and in 77.7 per cent of their cns tissues. The stage of infection, therefore, affected the probability of a positive result in the rectal mucosa, whereas the breed, PrP genotype, age and sex had little or no independent effect. Accumulations of PrP(d) were observed in the rectal mucosa and other lrs tissues of vrq/arr sheep with preclinical and clinical scrapie, albeit with a lower frequency and magnitude than in sheep of other PrP genotypes. Western immunoblotting analyses of samples of rectal mucosa gave the characteristic PrP glycoprofile, with a sensitivity similar to that of immunohistochemistry.

Structural Development, Cellular Differentiation and Proliferation of the Respiratory Epithelium in the Bovine Fetal Lung.

Fetal bovine lung samples of 11 different gestational ages were assigned to a classical developmental stage based on histological morphology. Immunohistochemistry was used to characterize the morphology of forming airways, proliferation rate of airway epithelium and the presence of epithelial cell types (i.e. ciliated cells, club cells, neuroepithelial cells (NECs) and type II pneumocytes). Typical structural organization of pseudoglandular (84-98 days gestational age [DGA]), canalicular (154-168 DGA) and alveolar (224-266 DGA) stages was recognized. In addition, transitional pseudoglandular-canalicular (112-126 DGA) and canalicular-saccular (182 DGA) morphologies were present. The embryonic stage was not observed. A significantly (P <0.05) higher proliferation rate of pulmonary epithelium, on average 5.5% and 4.4% in bronchi and bronchioles, respectively, was present in the transitional pseudoglandular-canalicular phase (112-126 DGA) compared with all other phases, while from 8 weeks before term (224-266 DGA) proliferation had almost ceased. The first epithelial cells identified by specific marker proteins in the earliest samples available for study (84 DGA) were ciliated cells and NECs. Club cells were present initially at 112 DGA and type II pneumocytes at 224 DGA. At the latest time points (224-226 DGA) these latter cell types were still present at a much lower percentage compared with adult cattle. This study characterized bovine fetal lung development by histological morphology and cellular composition of the respiratory epithelium and suggests that the apparent structural anatomical maturity of the bovine lung at term is not matched by functional maturity of the respiratory epithelium.

Differences in Virulence Between Bovine-Derived Clinical Isolates of Pasteurella multocida Serotype A from the UK and the USA in a Model of Bovine Pneumonic Pasteurellosis.

The time of onset and subsequent degree and progression of clinical signs, bacterial colonization and tissue pathology during experimental disease induced by intratracheal inoculation of either a UK or USA isolate of Pasteurella multocida serotype A recovered from clinical cases of bovine pneumonia were determined. Calves aged 8 weeks were challenged with 300 ml phosphate buffered saline (PBS) alone (group 1, n = 3, negative control) or containing 7.1 × 10(8) colony forming units (cfu) of UK isolate (group 2, n = 8) or 5.8 × 10(8) cfu of USA isolate (group 3, n = 8). Bronchoalveolar lavage (BAL) at 0, 1 and 4 days post challenge (dpc) and at the time of necropsy examination (7-8 dpc) showed no significant differences between groups 2 and 3 in bacterial numbers recovered. No P. multocida were recovered from group 1 animals. No clinical disease was present in group 1 calves and in group 3 was limited to scour in 1 calf at 1 dpc. All calves in group 2 had reduced food intake at 4-5 dpc, five had periods of dullness, three a mild nasal discharge at 1 dpc, four had mild to substantial respiratory stridor and one was killed at 6 dpc for humane reasons. Rectal temperatures remained about 39°C in group 1 calves, but increased in P. multocida-challenged calves to 40-41°C within 8-12 h of challenge. Significantly (P = 0.01) greater percentages of lung surface area were consolidated in group 2 (mean ± SD, 21 ± 10.1) compared with group 3 (7 ± 8.6) calves. Significantly more extensive and severe histological lesions were present in the lung lobes (P = 0.006) and lymph nodes (P = 0.02) of group 2 compared with group 3 calves. Pleurisy was present in group 2 calves only and no pathology was present in group 1. Pulsed-field gel electrophoresis (PFGE) produced 11 (group 2, UK isolate) or 10 (group 3, USA isolate) bands with differences in banding patterns. Results overall showed that two isolates, distinct geographically and genetically (by PFGE), caused pneumonic pasteurellosis in a single host with significantly different severity of pathology. This information is relevant to the development of novel vaccine control and interpretation of diagnostic results.