March case highlights

March showed the usual seasonal increase in submissions to both the central laboratory in Edinburgh and to the PM room at Thurso. As lambing and calving continues at pace there are understandably queries about Schmallenberg virus (SBV) presentations, sampling and incidence.

SBV clinical signs in neonates include:

• Arthrogryposis
• Torticollis
• Scoliosis
• Kyphosis
• Brachygnathia inferior
• Mild to marked hypoplasia of the cerebrum, cerebellum and spinal cord
  
  

Any suspect cases should be sampled using the sampling list below:

• Brainstem
• Umbilicus / amniotic fluid scrape (simple samples, see below)
• Foetal fluid
• Spleen
• Dam blood
  
  

These samples should be taken in addition to foetal stomach content, foetal fluid, fresh placenta and fixed tissues (brain, spinal cord if possible, lung, heart, liver, spleen, placenta) for a full abortion investigation. Please note the detection of the virus in brain tissue is dependent on the stage of gestation that the foetus became infected, and therefore a PCR test may be negative despite SBV involvement. It may also be useful to add SBV serology to any barren ewe or cow screens that are being carried out to assess for exposure.

From GB data there have been 219 confirmed cases of abortion due to SBV in sheep since the 1st of January this year. Only 20 of these were from farms in Yorkshire or north of Yorkshire. Below are some cases that came through the PM room at Thurso or were sent from the Highlands and Islands to the central laboratory in Edinburgh that might be of interest.

Trilineage hypoplasia of the bone marrow (also known as bleeding calf syndrome) was diagnosed in an 18-day-old heifer calf. Three days prior to submission the calf was reported to be dull and pyrexic with some fresh blood in the faeces noted and was treated with antibiotic and NSAID injections. The animal was admitted to the vets for intravenous fluid administration on the next day and died overnight. At postmortem examination the external findings of note were pale mucous membranes, petechial haemorrhages in the conjunctiva & gums and black faeces at the anus. On incising into the carcass, the blood was noted to be very watery with no evidence of clotting activity recorded. The overall appearance was of a very pale carcase with multiple petechiae and ecchymotic haemorrhages through muscles and body walls and varying petechial and ecchymotic haemorrhages through the organs. The heart in particular had large ecchymoses and a profuse amount of serosanguinous pericardial fluid. Marked haemorrhage was also noted around injection sites and the location of the IV catheter.

The interim gross diagnosis was one of bovine neonatal pancytopenia (BNP) and further history was sought as this condition has historically been linked to the use of Pregsure® BVD vaccine.

The dam had previously reared two calves, she had been served this year by artificial insemination using semen that had previously been used in the herd although not in this dam. There was no history of Pregure® use in this herd.
Bacteriology of the lung, liver and spleen including selective media for Salmonella did not identify any significant organisms with only the lung having a scant growth and the rest of the organs recording no growth. BVD PCR testing proved negative. Histologic examination noted acute haemorrhages in the lung, epicardium, thymus and splenic capsule. There was also fibrinosuppurative exudate on the splenic capsule and some fibrin on the epicardium suggesting end stage septicaemia. There were scant numbers of haematopoietic cells, mostly myeloid in the sternum with the majority of the tissue being made up of adipose tissue giving a diagnosis of marked trilineage hypoplasia.
A very small number of trilineage hypoplasia cases have been identified over the years that have no association with the use of Pregsure®. It is considered most likely to be acquired, maternal antibody related or possibly related to repeated vaccine use or genetic disorders. Other possible causes of trilineage hypoplasia can be ruled out with a good clinical history such as acute bracken toxicity and trichothecene mycotoxicosis which is associated with feeding of mouldy foodstuffs.

If presented with a pale carcase with unexplained haemorrhage and lack of clotting it is important to rule out bleeding due to thrombocytopenia associated with BVDV infection, and bleeding associated with bacterial septicaemias. Diagnosis of trilineage hypoplasia requires a fixed sample of the sternum.

If you are interested in reading further on this interesting case, there are a couple of useful references below. If you cannot access these please email us and we can send them over to you.

Millar M, Scholes S, Bazeley K, Floyd T, Holmes P, Hateley G. Vet Rec. 2016 Dec 17;179(24):632-633.
Possible preventive strategy for bovine neonatal pancytopenia.
Bell CR, Scott PR, Kerr MG, Willoughby K. Vet Rec. 2010 Nov 6;167(19):758

Hypocuprosis was diagnosed in a five-year-old cross bred ewe. This was the first of two submissions this month from a flock of 200 with ill thrift reported in six. This animal was recumbent two days prior to submission following treatment with calcium and vitamin B1 appeared to improve before being found dead. She was due to lamb in approximately eight weeks and had been scanned as carrying twins. Postmortem examination reported approximately a third of the reticulum wall appeared thickened with a change in pigmentation, but this did not at a gross level seem to involve the mucosa. The fairly advanced autolysis was noted as likely to hinder diagnostic testing especially histology. Parasitology detected a moderate burden with 350 strongyle eggs per gram (epg) and fluke eggs detected suggesting a patent liver fluke burden although no adult fluke were seen in the liver which could reflect a light burden. Analysis of the liver tissue showed both copper and selenium to be low = with a copper value of 94 µmol/kg DM (314-7850 µmol/kg DM) and selenium result of 0.32 mg/kg DM (0.9 – 3.5 mg/kg DM).

Histology was hampered by the autolysis but changes suggestive of energy imbalance were reported in the liver. An intense cellular infiltrate most marked in the sub epithelium but extending throughout the muscle layers was detected in the reticulum wall. Where still apparent the cells have round to oval, occasionally bean-shaped speckled nuclei. Occasional mitoses are present, approximately 1 per high powered field. Occasional small lymphocytes are also present. These unusual findings were suspected to be a round cell tumour and features suggest it could have been a plasma cell tumour which has been previously reported in the mediastinum of sheep. This was considered to be an incidental (if interesting) finding.

A further submission from this cohort revealed evidence of parasitic burdens and a localised severe, acute, necrotising suppurative localised bronchopneumonia associated with Bibersteinia trehalosi.
This case supports the need for fresh samples and submissions from more than one animal to improve the chances of getting a diagnosis that can be used to improve the health and productivity of the remaining animals in the cohort. This also highlights the importance of monitoring trace element status across the herd and or flock.

Ovine Pulmonary Adenocarcinoma was diagnosed in a three-year-old Scottish blackface ewe from a group of 240 ewes that moved to winter grazing in October 2023. The batch was vaccinated with Heptavac P and treated with a product containing levamisole and triclabendazole in September 2023. At the time of submission ten deaths across the age groups had been reported with no clinical signs noted prior to death, a range of body condition scores was noted. Previous submissions and testing had not detected any trace element deficiencies or patent parasitic burdens. A postmortem examination on farm was carried out with the following gross changes noted: watery red fluid in the thoracic cavity; fibrinous adhesions in pleura; left cranial and middle lobes and all of right lung firm with multiple abscesses; free fluid and gelatinous clots in the pericardial sac. Histological examination of the lung indicated extensive ovine pulmonary adenocarcinoma (OPA) with abscess formation and acute bacterial, suppurative pneumonia. There was also histological evidence of a parasitic burden in the abomasum and small intestine.

The findings of OPA associated with bacterial pneumonia and parasitism may explain the range of ages in ewes that died and the variety of BCS seen in this group. Continued representative parasite monitoring and control as well as regular scanning for OPA should be considered.

Posted by SRUC Veterinary Services on 25/04/2024