Interesting cases in January

Cattle
Abortions/mastitis

• Salmonella Dublin, Campylobacter fetus, Listeria monocytogenes, Bacillus licheniformis and Trueperella pyogenes were isolated from foetal stomach contents in cases of bovine abortion this month.
• A heavy and pure growth of the yeast Candida galbrata was isolated in fungal cultures of foetal stomach contents in a case of bovine abortion. Candida galbrata is a recognised pathogen in humans and cattle and as it was isolated as heavy and pure growth in cultures it was of likely significance. Abortions due to Candida species are uncommon in cattle. It was suggested that if further cases occur on this farm to consider submitting placental samples for histopathology as placental lesions may be present in mycotic abortions.
• Foetal fluids were positive for BVD antigen in at least five cases of bovine abortion this month. In two of these cases a significant bacterial cause of abortion was also identified in cultures.
• Evidence of Neospora caninum infection was detected by PCR of foetal tissues in several cases and in at least one case by detection of antibodies in foetal fluid. One of the PCR positive cases underwent histopathology on brain tissue which confirmed Neospora infection in the central nervous system and confirmed Neospora as the likely cause of abortion.
• Streptococcus canis was isolated from milk submitted for mastitis cultures. Streptococcus canis is a rare cause of bovine mastitis. Typically, it is associated with sporadic cases but occasionally it may cause outbreaks of mastitis due to cow-to-cow spread.

Respiratory disease

• IBR was detected in nasal swabs from a two- year-old fattening heifer with signs of respiratory distress, increased upper airway noise and halitosis. Other cattle in the group had been showing similar signs and two had died. Necrotising tracheitis was observed at postmortem of one animal. In another IBR case a recently calved cow showed signs of pyrexia, increased upper respiratory tract noise and increased respiratory rate. IBR was detected in nasal swabs by PCR and a bulk tank IBRgE serology was strongly positive for antibody to wild type IBR. On a third farm convalescent blood samples were received from animals which had shown signs of clinical IBR several weeks before. Of three animals tested two had seroconverted from negative to strong positive in the IBR antibody test and the third had gone from a low positive result to a high antibody level, confirming recent exposure to IBR in all three animals. At least 19 further cases of IBR were detected by PCR in January.
• A group of calves underwent thoracic ultrasound on arrival at a rearing unit, and scans were deemed to be clear of lung lesions and the calves appeared in good health. Three weeks later re-scanning identified significant lung pathology as present indicating that the disease had occurred post arrival. Pooled PCR testing of four nasal swabs from affected calves detected Coronavirus as well as Histophilus somni, Pasteurella multocida and Mannheimia haemolytica. The significance of these findings on nasal swabs can be difficult to interpret. Bovine coronavirus has been suggested in some studies to be involved in BRD, but it can also be found in healthy cattle. The findings of Histophilus somni, Pasteurella multocida and Mannheimia haemolytica from nasopharyngeal swabs are of uncertain significance as they can be carried in the upper respiratory tract of healthy cattle. However, a study by Doyle (2017) found there was very good correlation between nasal or NP swabs or BAL samples and trans-tracheal washes with regards to Mannheimia haemolytica, Pasteurella multocida and Mycoplasma bovis. Reference : D Doyle, B Credille, T W Lehenbauer, R Berghaus, S S Aly, J Champagne, P Blanchard, B Crossley, L Berghaus, S Cochran, A Woolums. Agreement Among 4 Sampling Methods to Identify Respiratory Pathogens in Dairy Calves with Acute Bovine Respiratory Disease. J Vet Intern Med. 2017 May; 31(3):954-959.
• There were significant rising antibody levels to RSV on paired serology of all five tested beef bulls from a group in which there had been a significant respiratory disease outbreak the previous month. RSV was detected by PCR of nasal swabs or lung tissue in at least 43 other cases of respiratory disease in cattle in January.
• On one farm multiple calves aged around two months were affected with respiratory disease, drooping ears and some had swollen joints. Mycoplasma bovis, Pasteurella multocida and Mannheimia haemolytica were detected by PCR of lung tissue. Histopathology identified chronic fibrous bronchointerstitial pneumonia. As with many cases of bovine respiratory disease findings were complex indicating multiple underlying components. There were changes consistent with Mycoplasma bovis infection but also a fibrinous pneumonia and pleurisy component more typical of pasteurellosis.
• Klebsiella pneumoniae was isolated in profuse growths from the lung tissue of a Holstein cow which showed signs of respiratory distress three days after calving. At postmortem the lungs appeared discoloured and congested and there was a large amount of serosanguineous fluid present in the thorax. Histopathology of lung revealed moderate-marked, acute, multifocal, necrotising pneumonia with extensive fibrinosuppurative pleuritis and abundant intralesional bacteria. The changes in the lung were most suggestive of septicaemia in this case. K.pneumoniae is a known cause of pneumonia, septicemia and mastitis in cattle.
• Post-mortem tissues were received from a yearling Holstein-Friesian dairy heifer. The animal showed clinical signs of respiratory disease but failed to improve even with several treatments and died one week later. At this time several others in the group also showed signs of respiratory disease. At postmortem examination diffuse lung pathology was observed. No lungworms were seen in the airways. Respiratory PCR testing of lung tissue detected none of the eight common respiratory pathogens. Histopathology identified extensive, severe, subacute, fibrinonecrotising interstitial pneumonia with fibrinous pleuritis as well as extensive, severe, subacute fibrinous pericarditis. A septicaemia was suggested as a possible cause of the interstitial pneumonia and ruling out salmonellosis with culture or PCR testing was suggested. In addition to the disease processes identified in the lungs, A dense population of round cells was found attached to one section of the pericardium. assisted in identifying. Scattered mast cells and few structures resembling Hassal’s corpuscle were seen throughout suggesting this may have been part of a thymoma. Thymomas are not uncommon in cattle, but most will go unrecognized due to the lack of clinical signs associated with them.

Gastrointestinal disease

• In one herd thirteen calves had died within 24-48 hours of birth, showing signs of salivation and liquid diarrhoea. A faecal sample from a one-day old calf showing these signs tested positive for F5 (K99) E.coli antigen confirming enterotoxigenic Escherichia coli infection.
• A fifteen-month-old Angus cross bullock presented for loss of condition and persistent scour. No nematode or fluke eggs were identified on microscopy and testing for BVD antigen and OvHV2 (MCF) by PCR were both negative. Johne’s PCR testing on faeces was positive, supporting a diagnosis of Johne’s disease in this case.
• Samples were received from a fourteen-month-old bullock which was observed to have scour prior to death. At gross postmortem the gut had a thickened appearance. The strongyle egg count in a faecal sample was 1250epg , confirming a heavy gastrointestinal parasite burden. Salmonella cultures were negative. Histopathology revealed marked chronic ulcerative/necrotising gastroenteritis and colitis with vasculitis, but the underlying cause of the changes was not evident. No viral inclusions were seen to implicate adenovirus and BVD was excluded by PCR testing. It was not clear whether the vasculitis observed was a primary lesion or secondary lesion and it was suggested to also rule out malignant catarrhal fever (MCF) as a cause of vasculopathy. Given the high worm egg count, parasitic gastroenteritis with secondary infection remained a possible cause for the lesions.
• There were at least eight cases of gastrointestinal disease associated with Salmonella Dublin in January, seven with Salmonella Typhimurium, four with Salmonella Mbandaka and one of Salmonella Give. Salmonella Give is a serotype most associated with poultry but can cause scour and abortions in cattle and in this case was the cause of acute and severe dysentery in a heavily pregnant dairy cow.
• Fixed samples of jejunum and caecum were received from an eighteen-month-old Galloway heifer which was one of three which had presented as thin and scouring. Necrotic enteritis had been observed at the gross examination. Unfortunately, due to poor preservation the jejunal sample was not useful for diagnostic interpretation but the sample from the caecum showed evidence of a moderate multifocal necrotising typhilitis with evidence of damage to the crypts/ glands but with no obvious underlying cause. Crypt/gland damage may be mediated by toxins, mucosal ischaemia or viral infections such as BVD, coronavirus (winter dysentery) or coccidiosis. Coccidiosis was thought unlikely in an animal of this age, unless immunologically naive due to lack of exposure and heavily exposed to pathogenic coccidia (or immunosuppressed due to, for example, persistent BVD viraemia). Liver analysis identified evidence of copper, selenium, and cobalt deficiency with levels of all trace elements falling below the expected reference intervals. It was not clear what role if any the trace element deficiency may have had in the gastrointestinal disease.

Skin and eye disease

• Treponema phagedenis, one of the treponeme species associated with digital dermatitis in cattle was detected by PCR testing of a swab from lesions on the medial coronary band of an affected cow.
• Some animals in a group of eight to twelve-month-old dairy heifers showed signs of skin lesions and intense pruritis. No ectoparasites were seen on microscopy but fungal elements were present. Trichosporon sp. were isolated in dermatophyte cultures confirming a diagnosis of ringworm. Five animals in the group were blood sampled, and all had raised pepsinogen levels consistent with significant abomasal damage due to parasitism. Outbreaks of ringworm in cattle may be associated with concurrent disease (such as parasitic gastroenteritis) and poor immunity.

Systemic and miscellaneous disease

• Postmortem tissues were received from a three-month-calved primiparous Holstein-Friesian dairy cow which showed sudden signs of discomfort, milk drop and recumbency. Multifocal abscessation of lung, heart, kidney and udder tissue as well as an external abscess (location unknown) were observed at postmortem examination. Heavy growths of Trueperella pyogenes were cultured from both lung and heart abscesses. On histopathology severe and ongoing pathology was observed, with chronic abscessation in the heart and lung. There was marked bacterial endocarditis, and extensive infarcts in the kidney with an underlying chronic nephritis. It was not possible to determine the initiating cause, but embolic spread of bacteria from a focus elsewhere, such as mastitis, metritis, foot abscess or injection site lesion was suggested as a possibility.
• Postmortem tissues were received from a White Park cow. At gross examination liver abscessation had been observed, multifocal firm and red areas were seen within the lung tissue and there was extensive ulceration in the rumen. On histopathology the lesions in the lung were identified as intravascular fibrin thrombi with intralesional fungal hyphae (fungal emboli) (Figure 1). Given the extensive lesions seen in the rumen, it was considered possible that the spread had occurred from that site. In the liver there was a locally extensive, severe, chronic-active, necrotising hepatitis with intralesional bacteria. The observed bacteria were demonstrated to be gram-negative and Fusobacterium necrophorum was considered the likely cause of this bacterial abscess. Again, the rumen was the most likely site of origin of the bacteria.

Figure 1 : Fungal hyphae (arrows) seen in a thrombus within a vessel in the lung of a cow

• Significant cardiac fibrosis was seen on histopathology of heart tissue from a dairy cow which had died suddenly. It was not possible to determine the underlying cause of fibrosis, though a historic bacteremia or toxic insult were thought possible. It was also difficult to know whether the fibrosis could have been associated with the death, but it was considered a possibility if it had triggered a sudden dysrhythmic event.
• Endocarditis was thought to be the possible cause of leukocytosis (WBCC = 21.4 x10^{^9}, RI = 4-10 x 10^{^9}) in a first lactation dairy heifer which showed signs of inappetence, milk drop and had a heart murmur on auscultation.
• Formalin fixed brain and spinal cord were received from a six-month-old Aberdeen Angus cross calf which had shown signs of opisthotonus, blindness, nystagmus and paddling movements prior to death. Histopathology of the brain identified severe, subacute, symmetrical, necrotising polioencephalopathy, consistent with a diagnosis of cerebrocortical necrosis (CCN). The lesion distribution and nature were thought to be most suggestive of a thiamine dependent encephalopathy or sulphate toxicity. The former is commonly associated with recent changes in diet resulting in rumen dysbiosis and the production of thiaminase with subsequent vitamin B1 deficiency. Sulphate toxicity is associated with excess intake through concentrate food and/or water.
• Mucosal disease subsequent to persistent infection with BVD virus, was suspected to be the cause of diarrhoea and mouth ulcers in a calf (age and breed unknown). The animal was positive for BVD in the antigen ELISA test confirming BVD viraemia.
• Malignant Catarrhal Fever (MCF) due to infection with Ovine herpes virus -2 was diagnosed by PCR testing in at least two cases this month.
• Lipomatosis (abdominal fat necrosis) was identified as the cause of a mass found adjacent to the large intestine in an eight-year-old dexter cow which had initially presented with signs resembling milk fever. Although initial treatment appeared successful the cow later deteriorated and died. Histopathology identified the mass as necrotic fat, typical of the condition lipomatosis which can occur in any part of the omental, mesenteric or retroperitoneal fat. The aetiology is unclear and although it is most usually an incidental finding, it was noted that it could be the potential cause of gastrointestinal obstruction.
• Fourteen store calves showed signs of polyarthritis shortly following an outbreak of respiratory disease in the same group. The farm had recently started buying in dairy-cross calves for stores/finishing but also had a Galloway suckler herd on farm. Joint fluid was aspirated from the carpal joint of one of the affected animals and this sample tested positive for Mycoplasma bovis by PCR. Nasopharyngeal swabs taken from the animals with signs of respiratory disease had also tested positive for M.bovis. It was suspected that the pathogen had been introduced into the herd with the bought-in animals as M.bovis infection had not been previously identified in the suckler herd.