Page 53 of 201
Three of the 10 30 had a gross necropsy diagnosis of metabolic disease with a note of suspected hypomagnesaemia;
Two of the 10 20 had a gross necropsy diagnosis of enteric disease; Two of the 10 20 had a gross necropsy diagnosis of no significant lesion; and,
Three animals had a gross necropsy diagnosis of encephalitis n=1, misadventure trauma n=1 and respiratory disease n=1.
There were eight animals that had a clinical syndrome of misadventure recorded. The diagnoses recorded for these animals at gross necropsy included:
Six of the 8 75 had a gross necropsy diagnosis of misadventure including animals that had been trapped in a rail or gate, trampled in a race and miscellaneous trauma
leading to severe preputial bruising; One animal 12.5 had a gross necropsy diagnosis of respiratory disease; and.
One animal 12.5 had a gross necropsy diagnosis of no lesion.
7.7 Histology
Histology findings were not available until collected samples had been imported back into Australia, processed and examined by pathologists working as part of the project team. For
those voyages where a ship returned to Fremantle directly after completing one voyage to begin another voyage, samples were collected within weeks of the end of one voyage. There
were occasions where a ship completed a voyage as part of this project and then sailed to another port either in Australia or elsewhere in the world. In a small number of cases there
was a delay of some months from the end of a voyage until the ship docked in Fremantle again and samples from the participating voyage could be unloaded and processed for
examination.
Between 1 and 16 tissues were collected from animals at necropsy, with an average of 6 ± 3 tissues per animal. The most commonly collected tissues were lung collected from 99 of
necropsies, heart 80, kidney 74, liver 73, trachea 67.5, and rumen 46.2.
Collected tissue samples were labelled and stored in formalin on the ship for the return journey and were collected when the ship docked at Fremantle. Samples were transported
to the DAFWA laboratory and processed for routine microscopic examination to describe presence or absence of pathologic changes in tissues.
Abnormal or pathologic changes were detected in about 40 of tissue samples. Approximately 50 of tissues were histologically normal and the remaining samples were
unsuitable for examination mainly because the tissues were too autolysed to allow effective examination and in some cases, because the tissues were not relevant to the clinical
category or gross necropsy changes for that animal.
Rapid onset of autolysis of internal organs is a common issue during the voyage because of environmental conditions. In addition there was usually a time delay between death and
necropsy and in some cases this delay was exacerbated because necropsies were being performed by a single AAV in conjunction with other routine tasks.
Page 54 of 201
The lung was collected for histological examination from 195 out of 197 99 necropsies. Histologic examination of the 195 lung tissue samples resulted in the following findings:
A total of 127 of the 195 animals 65 had histologic evidence of respiratory disease based on examination of lung tissue.
Of the 127 animals with histologic evidence of lung disease, the most common pathology observed was bronchopneumonia, which was present in 82 of cases. In some cases
bronchopneumonia was observed in combination with pleuritis. Interstitial pneumonia was observed far less commonly 6 in animals with histologic evidence of respiratory disease.
There were occasional cases of pleuritis without lung tissue involvement and tracheitis
.
Pneumonia means inflammation of the functional tissues of the lungs; bronchopneumonia means inflammation of the lungs and of the larger airways
bronchioles; pleuritis or pleuropneumonia means the inflammation has extended to the outer pleural surface of the lung; interstitial pneumonia means inflammation
of the functional tissue of the lungs without inflammation of the bronchioles; tracheitis means inflammation of the trachea.
Descriptions of histologic lesions in lung tissue – including morphology of intralesional
bacteria where present – were used to identify the viral and bacterial pathogens considered
most likely to be causing the infection. This approach was based in part on extensive scientific descriptions of the most common pathogens viruses and bacteria that cause
respiratory disease in cattle and the typical histologic changes in lung tissue in animals with respiratory disease known to be caused by infection with specific pathogens.
The common and most important bacterial pathogens associated with respiratory disease in cattle include: Histophilus somni, Mannheimia haemolytica, Pasteurella multocida and
Mycoplasma bovis.
The common and most important viral pathogens and their abbreviated names include: BCoV : Bovine corona virus;
BoHV-1 : Bovine herpes virus 1; BRSV : Bovine respiratory syncytial virus;
BVDV : Bovine viral diarrhoea virus; and BPIV-3 : Bovine parainfluenza virus 3.
Histologic evidence of bacterial infection in association with pneumonia lesions was present in 92 of 102 lung tissue samples from animals with pneumonia 90. Five samples had
histologic changes that were consistent with primary viral infection 5 of 102. Five samples had equivocal histologic changes that did not allow characterisation of the likely
infectious agents.
Of the 92 pneumonia cases with histologic evidence suggestive of bacterial infection: 46 of 92 50 had changes that were suggestive of bacterial infection without
specifically suggesting any one of the four bacteria of interest; 26 of 92 28 had changes that were suggestive of Mycoplasma bovis infection in
combination with one or more of the other three bacterial agents;
Page 55 of 201
14 of 92 15 had changes that were suggestive of Mycoplasma bovis infection as a primary cause of pneumonia; and,
6 of the 92 7 had changes that were suggestive of bacterial infection in combination with viral infection.
A large body of descriptive information was generated on histologic changes in tissue samples collected during the project. The information was used in conjunction with all other
available information relevant to disease before death, at necropsy and in pathologic examination of tissues or swabs to determine the most likely cause of death. Further
descriptions of histologic changes are not provided here because the range of changes presented in isolation is likely to be relatively uninformative.
In some cases histologic evidence in other tissues was noteworthy because it identified unusual potential diseases or was suggestive of specific pathogens of interest.
For example, there were 16 cases where examination of heart tissue identified pathology involving the heart. These included 10 animals with myocarditis lesions and in these 10
animals histologic changes were suggestive of specific conditions:
Acute myocarditis lesions were observed in five animals and in three of these there were concurrent lesions in other tissues that were considered consistent with systemic
infection with Histophilus somni, also called Haemophilus septicaemia or Haemophilus somnus disease complex; and
Chronic myocarditis lesions were observed in five animals and three of these had sarcocysts present in the heart muscle, indicating infection with Sarcocystis species of
sporozoan parasite.
7.8 Molecular results
