Current Findings in the Regional Veterinary Laboratories
September 2007
Cattle
Salmonella dublin was the most frequent bacterial pathogen cultured from bovine
foetal material submitted to all centres during the month. Kilkenny found that a
considerable number of blood samples from recently aborted cows were serologically
positive for Neospora caninum antibody. One positive sample was from an aborted
cow in the sixth month of gestation, the sixth case on that farm over a short period.
Lesions of tuberculosis (TB) were seen in the bronchial (figure 1) and mediastinal
lymph glands of two four-month old calves submitted to Limerick from a herd that
had a large number of TB reactors in a recent herd test. Mycobacterium bovis was
isolated following culture of the glands in the Central Veterinary Research Laboratory
in Backweston.
Hoose pneumonia was recorded in all centres during the month. Dublin examined a
six-month old heifer calf, the third to die in a group where all animals were coughing.
Before opening the carcass, long thin white worms were seen around the nostrils, and
large numbers then were found on examination of the trachea and the bronchi. Gross
pulmonary lesions included consolidation and interlobular oedema, with exudative
bronchointerstitial pneumonia evident on histopathological examination. Kilkenny
diagnosed pre-patent hoose in a 22-month old cow that was grazing with cattle of
mixed ages. The clinical signs were most severe in the 18 to 24 month age group, but
older cows and calves were also coughing. The continual use of long acting
anthelminthic preparations in calves during the first season at grass can prevent the
development of immunity resulting in clinical disease in subsequent grazing seasons.
Kilkenny confirmed the presence of Bovine Viral Diarrhoea (BVD) virus in poorly
growing animals from different farms. Histories included a poorly growing threemonth old calf and a bullock with dribbling and ill thrift. Sligo diagnosed mucosal
disease in a 16-month old bullock that was found dead, having been only recently
purchased by an exporter. At post mortem there was evidence of melena and scour. A
weanling was presented to Athlone following a short episode of green scour. A
polymerase chain reaction (PCR) test carried out on lymphoid tissue proved positive
for BVD viral antigen. An enzyme-linked immunosorbent assay (ELISA) test carried
out on blood samples taken from the rest of the group of 50 weanlings was positive
for BVD antigen in 11 cases.
A weanling heifer, the second loss from a group of 15, was submitted to Cork
following rapid death subsequent to signs of panting and collapse. The animal was
found to have lesions consistent with blackleg in the left Longus colli muscle. A
fluorescent antibody test (FAT) carried out on an impression smear taken from the
area was positive for Clostridium chauvoei. The deep location of this muscle in the
thorax was considered to be the reason why subcutaneous emphysema was not a
feature in the clinical signs or immediately following death. Athlone also reported on
a case of blackleg involving a six-month old weanling.
Dublin investigated a suspect outbreak of bovine botulism during the month. In this
case a two-year old bullock was presented, from a group of 30 bullocks grazing
adjacent to a heap of poultry litter. Before euthanasia at the laboratory, the bullock
was in lateral recumbency and had hind limb, tail and anal paralysis. It was still able
to retract the tongue and move its front legs. Samples were taken for Clostridium
botulinum toxin testing and results are pending. The animal had a leucocytosis,
neutrophilia and raised levels of the muscle enzyme, creatine kinase. The bullock also
had evidence of ostertagiasis.
Sheep
Athlone visited an organic sheep farm which was experiencing large losses of lambs.
It was the fourth year of a wasting and scour problem among the lambs. Adult sheep
were largely unaffected. The results of tests suggested that parasitism played a major
role in the problem, with high faecal egg counts recorded in all cases. The
combination of a lack of dosing, the damp environmental conditions of the past
summer, and the use of the same ground on a continual basis appears to have lead to
the large losses.
Pigs
Cork examined a 13-week old pig that showed dermatitis with caudal/perineal
distribution, enlarged lymph nodes (lymphadenosis), pulmonary hyperaemia,
cranioventral pulmonary consolidation and enlarged kidneys with multifocal petechial
haemorrhages (figure 2). Porcine dermatitis and nephropathy syndrome (PDNS) was
diagnosed on the basis of gross lesions, vasculitis in different organs, multinucleated
giant cells in lymph nodes and spleen and positive immunohistochemistry staining to
porcine circovirus 2 (PCV2) in macrophages within some of the germinal centres of a
lymph node and the spleen.
Non-suppurative meningoencephalitis was diagnosed by Dublin in a sow, which
presented in lateral recumbency approximately one week before farrowing. The unit
had already lost the sows with a similar presentation. The inflammatory infiltrate in
the brain was mainly lymphoid in nature but also contained small numbers of
multinucleate giant cells, which were ZN negative. The cause of the condition was not
elucidated. The sow also had severe neutrophilic and histiocytic lymphadenitis
affecting lymph nodes of the head, from which Streptococcus canis was cultured.
Poultry
Avian vibrionic hepatitis (associated with Campylobacter jejuni) was suspected in a
hen submitted to Cork that presented with an enlarged liver with randomly distributed
grey pinpoint foci of necrosis that were surrounded microscopically by lymphocytic
and granulocytic infiltration.
Other Species
Caecal impaction was found by Limerick in a four-month old foal that was found in a
collapsed state, and died shortly afterwards. A very heavy parasite burden is thought
to have contributed to the problem by interrupting or slowing motility. Sligo
diagnosed rupture of a mediastinal abscess into the thoracic cavity as the cause of
death in a Shetland pony with metastatic Streptococcus equi subspecies equi infection
(Bastard Strangles). The horse had arrived in this country from the Netherlands. Two
weeks later it became dull and pyrexic before dying after a short course of therapy.
The most obvious lesion at post mortem was bilateral diffuse fibrino-purulent
pleuropneumonia with mediastinal and bronchial lymphatic abscessation. Limerick
diagnosed gastric rupture in a five-year old pregnant Irish Draught mare that was
found dead.
Paraquat poisoning was suspected by Sligo in a six-year old dog. The lungs were
haemorrhagic and lung histopathology revealed lesions strongly suggestive of
paraquat poisoning. No trace of paraquat was found on toxicology. This may be
accounted for by the fact the poison had been metabolised by the time the sample was
taken.
Kilkenny found gross lesions of TB in a wild deer that was culled because of a high
incidence of bovine tuberculosis in local cattle herds. Wild deer were frequent visitors
to the farm. Gross lesions were found in the retropharyngeal and mesenteric lymph
nodes. Histological findings were consistent with TB and Mycobacterium bovis was
isolated. Dublin also found lesions of TB in two wild deer culled for similar reasons.
CAPTIONS FOR PHOTOS
Figure1
“"Lesions of TB in the bronchial lymph node of a four-month old calf – photo Alan
Johnson”
Figure 2
“Porcine dermatitis and nephropathy syndrome (PDNS) in a 13-week old pig- photo
Pat Sheehan”