Interesting cases in December

Cattle
Abortions/mastitis

• There were five cases of bovine abortion attributed to Salmonella Dublin in December and Salmonella Mbandaka was isolated in one case.
• Paired serology demonstrated seroconversion to Salmonella Dublin in two aborted Holstein dairy cows from a herd affected with an increased incidence of abortion and early embryo losses.
• Trueperella pyogenes was isolated in cultures of foetal stomach contents of one of two calves aborted at approximately five months gestation. Both animals had previously had successful calvings in the herd. T.pyogenes is classed as an opportunistic pathogen which is a recognised cause of sporadic abortion in cattle. It can arrive haematogenously from a septic focus elsewhere in the body such as a liver or foot abscess. In a second submission T.pyogenes was isolated from foetal stomach contents and Coxiella burnetii (Q fever) was detected by PCR in foetal tissues. It was unclear if the positive PCR result was significant or an incidental finding. Histopathology is required for further investigation of suspected Q fever abortion cases.
• Two cases of bovine abortion due to Bacillus licheniformis were diagnosed this month.
• There was one case of bovine abortion due to Listeria monocytogenes. L.monocytogenes was isolated in a further abortion submission but in that case L.ivanovii was also isolated along with several other bacteria (Proteus sp, Aeromonas sp.) raising the suspicion of sample contamination in that case. To reduce contamination when collecting foetal stomach contents, it is advisable sample the contents using a sterile needle and vacutainer.
• There were five cases in which foetal fluid tested positive for BVD virus in the antigen ELISA. In four of these cases a bacterial cause of abortion was identified in cultures Salmonella Dublin (2 cases), Bacillus licheniformis (one case) and Listeria monocytogenes (one case). The connection between the foetal BVD results and the bacterial cultures is not completely clear, though it was considered that a transient BVD viraemia could cause immunosuppression and potentially increase the risk of bacteria gaining entry to the uterine environment.
• Antibodies to Neospora caninum were detected in foetal fluid in two cases indicating in-utero exposure of the foetus to this pathogen. Neospora caninum was detected by PCR in foetal tissues in at least one submission this month. Confirmation of Neospora abortion can be achieved through histopathology on fixed tissue.
• There was a significant rise in antibodies to IBR on paired serology in the IBRgE test in an aborted dairy cow which went from a moderate positive to a high positive result indicating likely recent exposure to wild type IBR. IBR virus can cause placentitis and infect the foetus leading to abortions. IBR can also cause abortions secondary to pyrexia/illness without IBR infection of the foetus. In the case of foetal infection with IBR this can be confirmed by histopathological examination, immunohistochemistry of placenta and/or foetal tissues and PCR testing.
• Pasteurella multocida was isolated in cultures of mastitic milk. Pasteurella multocida is a rare cause of mastitis in cows. As it can arise from teat injuries, prevention of teat damage is the most effective method of control of this pathogen. Cow-to-cow spread can occur, and so affected animals should be milked last or with a separate unit. Severe cases can result in endotoxaemia and can be fatal.
• Klebsiella pneumoniae was isolated from two out of four milk samples from dairy cows in a herd which was experiencing a severe outbreak of mastitis. Klebsiella pneumoniae is considered a major pathogen in bovine mastitis and can cause severe clinical disease. It can cause long-term drop in milk production through chronic disease. Udder hygiene and maintaining a clean, dry environment are important measures for control of Klebsiella mastitis.

Respiratory disease

• A postmortem tracheal swab was received from a British blue store calf which had been treated for signs of pneumonia but later died. A necrotic tracheitis identified at gross postmortem was suggestive of a diagnosis of IBR and this was confirmed by PCR testing of a tracheal swab. IBR was detected in fourteen further submissions in December.
• RSV was detected by PCR in over fifty submissions this month. Tissues were received from an approximately six-month-old, pre-weaned, Limousin suckler calf, which was the first death to occur in the group which were showing signs of respiratory disease. The calves had been housed two weeks earlier and had received an intranasal vaccine at that time. Postmortem examination of the case showed marked cranioventral consolidation and hyperinflation and emphysematous bullae in the caudal lungs. PCR testing of lung tissue detected RSV along with Mycoplasma bovis, Histophilus somni and Pasteurella multocida. Histophilus somniwas isolated in cultures of lung tissue. Histopathology of lung identified changes typical of severe bacterial bronchopneumonia consistent with that caused by Histophilus somni and Pasteurella multocida identified on culture /PCR testing. There was mild airway necrosis which could be due to RSV infection, but it was noted that the changes could also be caused by bacterial pathogens. Immunohistochemistry was suggested to further investigate of the role of RSV in this death.
• PI3 was detected in over twenty submissions this month either as the sole viral pathogen or in some cases in combination with Coronavirus or RSV.
• Severe bacterial bronchopneumonia was identified as the likely cause of death of a three-day-old calf. Abundant gram-negative coccobacilli were present and possible pathogens included E.coli, a member of the pasteurellaceae, or salmonellosis. Bacteriology of fresh tissue was suggested to further investigate. There was evidence of meconium in the airways suggestive of distress at calving. Inhalation of meconium, lack of aeration of the lungs and associated inflammation can lead to weakened lung function and increased susceptibility to bacterial infection.
• Postmortem tissues were received from a fifteen-month-old Holstein dairy heifer. Severe consolidation of the lungs and a fibrinous exudate were observed at postmortem examination. Mannheimia haemoltytica was detected by PCR testing. Histopathology of lung tissue identified a severe fulminating bacterial pneumonia consistent with the Mannheimia haemolytica detected on PCR (Figure 1).

Figure 1: Section of lung from a heifer showing extensive inflammation and necrosis typical of Mannheimia haemolytica fulminating pneumonia.

• Lungworm larvae with appearance consistent with Dictyocaulus viviparus were observed by microscopy in faecal samples from suckler cows which had a previous history of clinical disease due to lungworm and were noted to be coughing again at housing. D.viviparus larvae were detected by PCR in further two cases and a further three submissions identified animals that were seropositive for antibody to D.viviparus , consistent with lungworm exposure.

Gastrointestinal disease

• Parasitic gastroenteritis was thought to be the cause of low body condition score and ill-thrift in a single animal in a group of 18-24-month-old cattle on an organic unit. The Strongyle egg count in a faecal sample was 1800epg, consistent with a heavy gastrointestinal parasite burden. There was evidence of hypoalbuminaemia on biochemistry which was likely to be linked to the gastrointestinal parasitism. In addition to the parasitism, the animal had evidence of low copper and selenium status and a pooled sample for inorganic iodine from the cohorts indicated that there was a low iodine intake in the group.
• Salmonella 61:k:1,5,7 was isolated from a faecal sample from a yearling Limousin cross steer with a three-week history of weight loss and scour. A potentially significant Strongyle egg count of 250epg had been recorded at the practice. This serotype of Salmonella is considered host adapted to sheep and is very uncommonly reported in cattle. It was queried whether the animal was co-grazing or had any other contact with sheep.
• In one submission Salmonella Typhimurium was isolated from faecal samples. Six cows on the farm had presented with acute onset scour and profound milk drop within two days.
• A pooled faecal sample from three calves tested positive for Cryptosporidium parvum, Rotavirus and Coronavirus antigens.
• Bovine coronavirus was detected by PCR in faecal samples from scouring freshly calved heifers, confirming a suspected diagnosis of Winter dysentery.

Skin and eye disease

• Cutaneous lymphoma was diagnosed in a mature dairy cow with skin lumps. Sporadic lymphoma/leukosis usually affects animals younger than 4 years of age, with multicentric, thymic and cutaneous forms less commonly seen. The practitioner was advised to contact their local APHA office in case further investigation regarding the (very unlikely) possibility of the notifiable disease enzootic bone leukosis (EBL) was required.
• Tissues were received from a ten-year-old Highland cow with a friable, necrotic mass cranial to the right horn base. The mass had previously been excised but had regrown to about four time its previous size to approximately 10cm diameter. It was noted that the mass had a hard overlying scab but the underlying tissue was soft and haemorrhagic. Histopathology of a section of the tissue identified the mass as a likely squamous cell carcinoma, though the small sample prevented definitive diagnosis in this case. SCC in cattle are usually locally invasive but don’t tend to metastasise until later in the course of disease. Spread in the first instance is usually to local lymph nodes.
• Dermatophyte sp. was detected by PCR of hair plucks/skin scabs from a twenty-month-old bull with round, raised scaly skin lesions suspicious of ringworm infection. Mild pruritis was also observed in this case.

Systemic and miscellaneous disease

• Mannheimia haemolytica was isolated in cultures of lung tissue from a weaned calf which was noted to have been a poor doer for some time prior to death. The isolate was thought to be a significant finding as a possible cause of pericarditis (and possibly peritonitis) which were seen at gross postmortem examination.
• Salmonella Dublin was isolated from a liver swab from an eight-week-old dairy cross calf. The liver had appeared grossly enlarged and the gall bladder distended at postmortem examination.
• Blackleg caused by Clostridium chauvoei was diagnosed by FAT (Fluorescent antibody testing) of muscle tissue sampled from a cow which was one of four from the same holding to have ‘dropped dead’ with no premonitory signs within twenty-four hours.
• A yearling Limousin cross animal showed signs of bilateral blindness with corneal opacity, pyrexia (>40.50C), crusting of the muzzle, drooling and condition loss over a period of more than ten days. Testing confirmed that the animal had seroconverted to OvHV-2, making Malignant Catarrhal Fever (MCF) highly likely to be the cause of these clinical sings. MCF was diagnosed by PCR testing in four cases this month.
• A round cell tumour most likely to be lymphoma was identified on histopathology testing of tissues from a five-year-old dairy cow. There was a history of rapid condition loss, pyrexia and lymph node enlargement of the prescapular, cervical and mandibular lymph nodes. Cardiomegaly and endocarditis were seen on postmortem examination and the lung tissue appeared pale. As with the cutaneous lymphoma case above, reporting to APHA was recommended in case further investigation was required to rule out enzootic bovine leukosis.