Interesting cases in November

Cattle
Abortions

• Trueperella pyogenes was isolated from the stomach contents of an aborted foetus. The dam aborted the foetus at around five months gestation following signs of illness and a drop in milk yield in the preceding days.
• Listeria monocytogenes was isolated from a bovine foetus aborted at 4-5months gestation.
• Salmonella Dublin was identified as the cause of abortion in six cases in November and Salmonella Montevideo in two abortion cases.
• Seroconversion to Salmonella Dublin was demonstrated by paired S.Dublin antibody ELISA testing in a Holstein-Friesian cow from a herd with higher-than-expected abortions and early embryonic losses. Of three other cows from the herd which were tested on the same submission (single serology) two were positive for antibodies to Salmonella Dublin.
• Q fever (Coxiella burnetii) was detected by PCR in one abortion case in November. Detection of this agent in PCR could be an incidental finding as histopathology is required to reach a diagnosis.

Respiratory disease

• Haemothorax, lung abscessation and consolidation of lung tissue were observed at postmortem examination of an adult dairy cow. Microscopically, pulmonary vascular abscess formation with accompanying fibrinous pneumonia were observed (Figure 1). The findings supported the practitioners’ suspicion of pulmonary thromboembolism as the cause of death in this case. Pulmonary thromboembolism in cattle often arises secondary to rumenitis and liver abscessation leading to thrombus formation in the caudal vena cava.

Figure 1: Cow pulmonary thromboembolism. Caption ‘A large vessel occluded by fibrin, inflammatory cells and bacteria in a cow with a septic pulmonary thromboembolism’.

• A dairy farm reported issues with heifers joining the milking herd which then developed nasal discharge, followed by chronic mucoid discharge. Paired blood samples were taken from acute cases to check for seroconversion to respiratory pathogens. Of five animals sampled one had clear evidence of seroconversion to BVD between first and second samples. Of the others two had high antibody levels which remained high on the second sample, one went from a low positive to a high positive result and the remaining animal appeared to be in the process of seroconversion to BVD having gone from a negative to a suspicious result for antibody to BVD. One of the five animals also seroconverted to PI3 virus.
• Salmonella Dublin was isolated from pooled nasal swabs of neonatal (48hrs old) dairy calves showing signs of pyrexia and respiratory disease. Freshly calved cows were also showing signs of pyrexia. One recently calved cow which died following a short illness and was sent to a postmortem facility was diagnosed as having salmonellosis caused by Salmonella Dublin. Salmonellosis can occasionally present as neonatal calf illnesses or deaths/ illness in adult cattle with out obvious signs of enteritis. We can also test nasal swabs in the Salmonella PCR test if there are concerns over its involvement in respiratory disease.
• Postmortem tissues were received from a neonatal beef calf (six hours old). It was the third calf to die of a similar age in the herd. Histopathology identified a moderate to marked, necrotising interstitial pneumonia with lymphocytic bronchiolitis. The lymphoplasmacytic infiltrate suggested an insult of longer duration than the age of the calf, suggesting a likely in-utero insult (e.g. a chronic bacterial infection). The necrosis of terminal airways and interstitium was indicative of a more acute change. Possible pathogens which could be responsible for such changes include BHV-1 IIBR) , RSV, PI3, Mycoplasma bovis, Ureaplasma diversum, and BVD. It was considered possible that a placentitis could have been present and if there were further cases histopathology of the placenta was recommended.

Gastrointestinal disease

• An adult Longhorn cow died after showing signs suspicious of hepatic encephalopathy. There was a history of liver fluke infestation in the herd. Histopathology identified severe and widespread hepatic fibrosis which would likely be associated with hepatic failure. Hepatic encephalopathy in cattle often presents as reduced appetite and depression and may progress to head pressing, visual impairment, circling, seizure and coma or can even present as sudden death. It is thought that the neurological signs may be related to accumulation of ammonia and by-products of amino acids in the brain secondary to liver dysfunction. Cirrhosis due to long term damage by liver fluke was thought to be the possible underlying cause in this case though toxins from plants, particularly those containing pyrrolizidine alkaloids (e.g ragwort), endotoxaemia (eg due to mastitis, metritis) and fatty liver disease are all possible causes.
• E.coli F5 (K99) antigen was detected in faecal samples from a neonatal calf. The presence of F5 antigen in neonates is consistent with enterotoxigenic E.coli infection. Colonisation of the intestinal tract by the bacteria causes excessive secretion of fluid into the intestinal lumen and rapid dehydration. After five days of age the F5 antigen can no longer bind to the intestinal mucosa and calves are no longer susceptible to this infection.
• Salmonella enteritica subsp. enterica serotype Stanleyville was isolated from faecal samples from a ten-week-old dairy calf with scour. Salmonella Stanleyville is a rare serotype in the UK having been isolated only once from horses and once from poultry since 2021.
• A recently calved heifer became ill and recumbent with profuse scour. PCR testing for MAP was positive with a Ct value of 22 indicating heavy shedding of MAP bacteria consistent with diagnosis of Johne’s disease. Liver and rumen fluke eggs were seen by microscopy confirming patent fascioliasis and patent rumen fluke infection.

Skin and eye disease

• A Rothia sp. was isolated from eye swabs from a Limousin cross cow which was one of numerous cattle in the herd with signs of recurrent Infectious Keratoconjunctivitis. The problem had started during the summer, but more new cases had occurred since housing. Mixed bacterial growths of mainly commensals and contaminants were cultured from two eye swabs but in one of these a Rothia sp. was identified. Rothia sp. have been found with higher frequency in diseased eyes than in healthy eyes in one study, though the significance of the finding was uncertain.

Systemic and miscellaneous disease

• A group of spring born dairy cross calves presented with lameness, inflammation of the interdigital space and pyrexia of >400C. Large numbers of ticks were seen on the animals at clinical examination. EDTA blood samples were taken and tested for the presence of Anaplasma phagocytophilum by PCR. Two of three animals tested were positive confirming Tick-borne Fever. Although Foul-in-the-foot or interdigital necrobacillosis, caused by Fusobacterium necrophorum was the suspected cause of the foot lesions in this case, this condition is not specifically associated with Tick-borne-fever. TBF is however known to cause immunosuppression which can predispose to bacterial infections.
• Blood samples were received from a cow in county Somerset which was reported to be pale and lethargic. Haematology revealed significant anaemia with a PCV of 11% (RI 24-40%) and an absolute reticulocyte count of 34x 10^9/L indicative of a regenerative response. Reactive lymphocytes were observed consistent with antigenic stimulation. PCR testing for Babesia sp. was positive confirming a diagnosis of Babesiosis. Magnesium was 0.5mmol/l (RI 0.7-1.3mmol/l) indicating there was also hypomagnesaemia.
• A ten-year-old Belted Galloway cow which had recently dramatically lost condition and had a dry cough tested positive for BVD virus in the antigen ELISA with a result indicative of a high level of virus (3.9OD). Optical Density (OD) is a measure of how much light is absorbed by a sample in a spectrophotometer. In the context of ELISA, it reflects the amount of colour developed in the wells of the assay plate, which is proportional to the concentration of the target analyte (e.g proteins antibodies) present in the sample.