29 Mar 2019
In his latest report from Axiom laboratories, veterinary clinical pathologist James Barnett focuses on respiratory disease in the months of December, January and February.
James Barnett
Job Title
Image © hakat / Adobe Stock
Presented are selected cases from the ruminant diagnostic caseload of Axiom Veterinary Laboratories.
Axiom provides a farm animal diagnostics service to more than 300 farm and mixed practices across the UK, and receives both clinical and pathological specimens as part of its caseload. The company is grateful to clients for the cases presented in this article.
The focus for this newsletter is respiratory disease in the months of December, January and February.
Infectious bovine rhinotracheitis (IBR) was confirmed in several herds on PCR testing of nasal and nasopharyngeal swabs, and on paired serology.
In one case, a 14-week-old beef finisher died after a one-day history of pyrexia and increased upper respiratory tract noise. Postmortem examination (PME) revealed necrotising tracheitis and cranially distributed pneumonia.
Histopathology was strongly suggestive of IBR, but no inclusion bodies were seen. IBR was detected by PCR testing on pooled trachea and lung. The animal had received an IBR marker vaccine one month earlier.
Clinical signs in other confirmed cases included malaise, dyspnoea, sloughing nasal mucosa, ocular and nasal discharge, excessive drooling and increased lung sounds.
Respiratory syncytial virus (RSV) infection has been confirmed on at least 10 occasions – on PCR testing of swabs from clinical cases, or in lung tissue or tracheobronchial swabs taken at PME.
Findings on histopathology included severe bronchointerstitial pneumonia, with necrotising bronchiolitis with syncytium formation. Where gross findings were reported, these included pulmonary consolidation, and emphysema and bullae formation. RSV infection also was demonstrated by active seroconversion.
In one six-month-old Aberdeen Angus cross – 1 of 20 calves in a rearing unit where widespread pneumonia had occurred – bullae and pulmonary consolidation were seen on PME. RSV was detected by PCR testing on lung tissue and histopathology of the lung was consistent with RSV infection.
Parainfluenza-3 (PI3) infection was confirmed on paired serology in a two-month-old calf. It is rare for active seroconversion to be demonstrated in calves of this age, due to the presence of maternal antibody.
Mycoplasma bovis infection was confirmed by PCR testing on lung tissue in five cases. Where gross postmortem findings were reported, multifocal pulmonary abscessation and/or consolidation were seen.
Mixed infections were suspected in a number of cases:
M bovis was also suspected on histopathology of fixed lung from one casualty in an outbreak of pneumonia in dairy calves – characteristic caseonecrotic bronchopneumonia was detected.
Active seroconversion to IBR, RSV and M bovis was seen in 15-month-old beef finishers; to both RSV and PI3 in one group of preweaned suckler calves; and to RSV and M bovis in a group of pyrexic, coughing cows with increased lung sounds and purulent nasal discharge.
P multocida was isolated in pure, heavy growth from lung of a post-weaned Aberdeen Angus-cross beef finisher, with active suppurative bronchopneumonia on histopathology. This was likely to be secondary to pre-existing airway damage associated with chronic bronchointerstitial pneumonia – potentially due to historic pneumotropic viral infection, bacterial bronchitis or mycoplasmal infection.
Fusobacterium infection was diagnosed on histopathology of lung from a five-year-old dairy cow that died after a five-day period of lethargy. Multifocal caseous pulmonary abscesses and abomasitis were present on PME and Gram-negative filamentous bacteria consistent with Fusobacterium were present within abscesses. This raised the possibility of haematogenous spread from the alimentary tract.
Lungworm was diagnosed by the Baermann technique in post-weaned Aberdeen Angus calves in two different herds.
Atypical pneumonia associated with Mycoplasma ovipneumoniae infection was diagnosed on histopathology in a thin Welsh mountain ewe, with pale infiltrative lesions on gross PME. It was originally thought to be ovine pulmonary adenocarcinoma (OPA). In a second flock, it was diagnosed in thin four to six-week-old lambs.
Infection is often acquired during housing – particularly in overcrowded conditions, typically in the perinatal period before lambs are turned out. The infection predisposes to secondary bacterial infection and results in illthrift in affected lambs.
Atypical pneumonia also was diagnosed on histopathology in one of two one-month-old lambs to die acutely with respiratory signs – an unusual outcome for this generally mild pneumonia, particularly as no secondary fulminating bacterial pneumonia was present.
Histopathology of lung in a second lamb examined in this flock to die acutely was consistent with a fulminating bacterial bronchopneumonia, and organisms such as Mannheimia haemolytica and Bibersteinia trehalosi were likely to be implicated. It was advised routine bacterial culture of the affected lung would have helped provide a more definitive diagnosis.
Adverse environmental conditions, stress, management change and concurrent disease would predispose to such infection, and it was advised that consideration be given to vaccination to reduce overall morbidity and mortality.
Five cases of OPA were diagnosed on postmortem lung histopathology. Most cases present as with chronic illthrift and exercise intolerance from two years or older. However, in two cases, evidence existed of a secondary bacterial pneumonia, which is a common complication in cases of OPA; such cases present with severe pneumonia or sudden death.
Seroconversion to maedi visna was detected in five sheep from different flocks. Where history was provided, the presenting sign was illthrift.
Steptococcus ovis was isolated from the thoracic cavity in a five-year-old ram with pyothorax, pulmonary consolidation and microabscesses.
S ovis has been isolated previously from cases of pneumonia and other pyogenic infections in sheep.
Swine influenza was diagnosed in 1 of 2 pigs examined postmortem, from a herd in which 11 weaned pigs had died over a three-day period, when Influenza A virus was detected by PCR testing in lung.
This was likely to explain the reported coughing among all ages of pigs, but did not explain the reported high mortality.
The presence of microabscesses in the lungs of one of the pigs suggested secondary bacterial involvement and Pasteurella multocida was subsequently isolated from the lung. This was likely to have caused the death of the pig.
