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August 2009 RVL Monthly Report

Cattle

Athlone found histopathological and serological evidence of neosporosis in a bovine foetus in the seventh month of gestation. There was also serological evidence of Leptospira hardjo infection in the foetus. This foetus was the fourth abortion in a group of fifty autumn calvers.  Two of five blood samples from comrade cows showed serological evidence of Neospora infection, and all five had positive L. hardjo titres. There was no history of vaccination against leptospirosis on the farm.  

All centres reported on cases of patent hoose in calves. In one case of hoose investigated by Sligo, Bovine Herpes Virus type 1 (BHV1) virus was also detected in the lungs. The BHV virus was linked to an outbreak of respiratory disease among beef bulls on the same farm a few weeks earlier. A five-month old weanling was presented to Athlone. There were diffuse lesions of pneumonia, pulmonary congestion and haemorrhagic tracheitis. Consolidation of the apical and cardiac lobes was also noted. Arcanobacterium pyogenes was isolated on routine culture. Tests for BHV1, parainfluenza virus type 3 (PI3) and respiratory syncytial virus (RSV) were negative. However, histology revealed the presence of signet ring cells and hyaline membrane formation, changes which are frequently associated with RSV infection.  

Bovine viral diarrhoea (BVD) virus associated disease was diagnosed in cattle of various ages during the month. An aborted foetus presented to Sligo was found to be positive for BVD virus. A one-week old calf which wouldn¿t suck or stand after birth was presented to Athlone. On gross examination severe pneumonia with consolidation of the apical and cardiac lobes was noted. Multifocal white lesions were present throughout the consolidated lung lobes. Mild pericarditis was also noted. On histopathology, severe fibrinopurulent bronchopneumonia was present. BVD virus was identified. Testing of the dam to determine her status was advised. BVD virus was detected in two heavy store bullocks by Sligo. Both animals were severely dehydrated and had enteritis. In another case Sligo diagnosed Mucosal Diseases in a two-year old bullock that developed an intractable scour, progressing to death within a week. There were severe oesophageal lesions with classical multifocal linearly arranged boat-shaped ulcers (figure 1).

Ulceration of oesophagus

Figure 1: Ulceration of the oesophagus associated with BVD virus infection in a two-year old bullock (photo: Colm O'Muireagain).

Two suspected incidents of acute bracken fern poisoning were investigated by Kilkenny. In the first incident a two-year old heifer was presented for post mortem examination with a history of epistaxis. The animal exhibited multifocal haemorrhage and generalised lymphadenopathy. Six apparently normal cattle randomly selected from the same group grazing rough hill pasture and with access to bracken fern were subsequently blood-sampled. Two of the six had thrombocytopaenia and three had leucopaenia. In a separate incident, blood samples were submitted from two adult cattle out of a group of 40 in which five were febrile, with rectal temperatures in excess of 107°C. Two cattle from the group had already died. Both animals sampled had profound leucopaenia and thrombocytopaenia. Subsequently, a six-year old cow from this group which presented clinically with bilateral hyphaema (accumulation of blood in the anterior chamber of the eye) and vulval haemorrhage (figure 2), died and was found to have multifocal haemorrhage when examined post mortem (figure 3).

Vulval haemorrhage

Figure 2: Vulval haemorrhage in a six-year old cow with suspected bracken fern poisoning (photo: Donal Sammin).

Haemorrhages in mesentery

Figure 3: Haemorrhages in the mesentery of a six-year old cow with suspected bracken fern poisoning (photo: Donal Sammin).

A blood sample submitted to Athlone from a cow with profuse diarrhoea, pneumonia, ocular opacity, severe weight loss and milk drop. A test for Malignant Catarrhal Fever (MCF) was positive i.e. Ovine Herpesvirus 2 specific DNA was detected in the sample. Limerick examined a young cow that died suddenly. Post-mortem examination showed that the immediate cause of death was haemorrhage into the peritoneal cavity from blood vessels at the root of the mesentery.  Histopathology of mesentery and blood vessels in the region showed evidence of infection. It was considered likely that there was an earlier intestinal rupture and leakage of gastro-intestinal contents, as Ciliates (non pathogenic protozoan inhabitants of the gastro-intestinal tract) were seen in the area where the haemorrhage occurred (Figure 4).

Ciliated protozoan organism

Figure 4: Ciliated protozoan organism seen in the mesentery at the site where haemorrhage had occurred in a young cow (photo: Dave Kelly).

A four-year old cow was presented to Athlone, one of a number which became recumbent over a one-week period. Consolidation of the apical and cardiac lobes of both lungs with diffuse pneumonia and emphysema was noted. There was putrid fluid present in one quarter of the udder. The kidney selenium level was found to be in the toxic range. Further investigation revealed that the animals had received barium selenate in the preceding weeks. While recumbency is a typical presentation of selenium toxicity, other signs such as hair loss and cracking of hooves were not noted in this case. It was concluded that while the mastitis was the ultimate cause of the cow¿s death, the toxic selenium level compounded the problem.

Sheep

Sligo reported that a Suffolk-cross lamb, which died shortly after being found in acute respiratory distress at pasture, had a large diaphragmatic hernia, with the reticulum and part of the rumen passing through a traumatic tear into the thorax.  This is a very unusual finding in a sheep.  The cause was certainly traumatic, but not identified.

Focal symmetrical encephalomalacia probably associated with clostridial enterotoxaemia was diagnosed by Sligo in a lamb that had a history of neurological signs. The lamb was one of a group of lambs which had exhibited similar clinical signs.  The lambs had received an initial clostridial vaccine but had not received a booster vaccine. 

Chronic fascioliasis was diagnosed in two ewes submitted to Athlone with reported clinical signs of scour and wasting. Both carcases were in very poor body condition and were anaemic.  There was a heavy burden of adult flukes in the gall bladders with very significant chronic liver damage.  Faecal parasitology was positive for liver fluke eggs.  These cases occurred in spite of dosing in December and March.  Following the third wet summer in a row many herd/flock owners will have to review the fluke control programmes on their farms, many of which are inadequate for current conditions.

Other Species

A three-week old foal was submitted to Sligo with a history of weight loss and abdominal pain.  It had also developed a firm cylindrical subcutaneous mass in the crest of its neck. At post mortem all of the abdominal and thoracic adipose tissue was grossly abnormal - firm yellowish and waxy, with a slightly nodular appearance.  It also appeared to be congested - more vascular than normal.  The subcutaneous fat was similarly affected and the fat pad running along the nuchal ligament was dramatically affected - this was the palpable mass reported by the referring veterinary surgeon.  On histological examination generalised steatitis and fat necrosis were the only lesions observed. Generalised steatitis, or yellow fat disease, has been described in foals since the 1950s, usually as a sporadic condition (De Bruijn et al., 2006).  It is characterised by extensive adipose cell degeneration and inflammation of adipose tissue.  During these processes, progressive oxidation of unsaturated fatty acids may occur, resulting in the production of lipofuschin pigment, giving the lesion their characteristic yellow colour.  Because of the role of oxidation in the pathogenesis, low levels of antioxidants such as tocopherol or selenium, failure to absorb these transplacentally in the normal way, or low vitamin E in the dam's colostrum have been suggested in the past as possible underlying causes. 

A liver swab taken from a sea-bass (Dicentrachus labrus) with diffuse haemorrhages yielded a pure culture of Psychrobacter phenylpyruvicus in Limerick. The fish had died in an aquarium that was open to the public. P. phenylpyruvicus is a rare cause of infections in humans.

Reference: De Bruijn CM, Veldhuis Kroeze EJB, Sloet van Oldruitenborgh-Oosterbaan MM. (2006) Yellow fat disease in equids. Equine Veterinary Education, 18: 38-44.