August 2005

Current Findings in the Regional Veterinary Laboratories
August 2005
Kilkenny examined a one-month old calf with a history of inappetance, abdominal pain and
jaundice. A fluorescent antibody test (FAT) was positive for Leptospira icterohaemorrhagiae.
Limerick also suspected that leptospirosis caused the death of a five-month old calf. The calf died
within twenty-four hours of being found in a recumbent state by the herd owner. Post-mortem
examination showed pronounced jaundice, widespread petechiation and oedema.
A 15-month old bullock which suffered intermittent scour and ill thrift for two weeks and which
presented with neurological symptoms terminally was presented to Dublin. Histolopathology of the
liver revealed extensive fibrosis, megalocytosis and bile duct proliferation, pathological changes
highly suggestive of ragwort toxicity. Histological examination of the brain revealed extensive
vacuolation of tissues indicative of hepatic encephalopathy. Ragwort poisoning was also diagnosed
in an eight-month old weanling submitted to Limerick. This was the second animal to die within a
couple of days. Twelve animals from the same herd died in March from the same condition.
Athlone reported clostridial myocarditis in a six-month old calf. Clostridium chauvoei
involvement was confirmed using an FAT. Blackleg was also diagnosed by Sligo in a four-month
old suckler calf from an unvaccinated herd. Two of the best calves in the herd had died on the two
hottest days of the year (29ºC). Dublin found that the sudden death of a six-month old pedigree
Limousin heifer was linked to Clostridium novyi infection. There was an extensive pleuritis and
pericarditis with large volume of pleural fluid.
Athlone investigated an outbreak of fog fever in a herd of suckler cows. Initial signs were
observed six days after the animals had been moved to lush after-grass. Four deaths occurred in the
group of forty cows. Sligo reported several outbreaks of a syndrome of coughing and milk drop in
adult dairy cows, where the epidemiology was suggestive of hoose re-infection. This is seen where
animals with an acquired resistance to Dictyocaulus viviparus are grazed on heavily infected
pastures. Although this immunity is sufficient to prevent the establishment of patent infections, the
resulting hypersensitive immune reaction to the migrating larvae in the lungs is sufficient to cause
respiratory disease and production losses.
Sligo reported that acute bracken poisoning was diagnosed on four separate holdings during July.
The main presenting signs were severe haematuria, petechial and ecchymotic haemorrhages on
serosal surfaces and frank haemorrhage into the GIT. One carcass submitted showed significant
haemorrhage from injection sites where therapy had been administered. (Figure 1).
High bulk milk somatic cell counts are typically a problem in dairy herds at this time of year. 331
individual milk samples were examined by the RVLs during the month (Figure 2). Staphylococcus
aureus remained the most commonly isolated pathogen, being cultured from 145 (44 per cent) of the
samples tested. The antibiotic sensitivity patterns remain pretty consistent, with penicillin resistant strains
acounting for over 50 per cent of the Staph. aureus isolates (Figure 3).
Dublin examined a three-month old ram lamb that had died suddenly. The ram was on a grass diet
with barley supplementation. Post-mortem findings were consistent with a diagnosis of rumen
acidosis. Rumen pH was 4.4 and protozoan motility was absent.
A pedigree Suffolk ram was submitted to Sligo with a history of chronic weight loss and diarrhoea.
There had been no response to treatment with anthelmintics and minerals/trace elements. Acid-fast
organisms were observed in a faecal smear and Johne’s disease was suspected. The post mortem
findings tended to support this tentative clinical diagnosis, with extensive thickening and severe
corrugation of the wall of the large and lower small intestine (Figure 4). However, a faecal sample
contained 2,000 strongyle eggs per gram and histological examination revealed lesions suggestive
of severe and chronic parasite challenge, including villous atrophy, granulomatous eosinophilic
enteritis and the presence of numerous nematode larvae in the bowel wall. The failure to respond to
repeated anthelmintic therapy might reflect the level of challenge and the fact that the ram was
returned to the same heavily contaminated paddock after each treatment.
A drop in egg production and egg quality in a large free range layer flock investigated by Cork was
ascribed to egg drop syndrome (EDS) based on increased titres to EDS virus from the first to the
second monitoring of flock blood samples.
Cork identified necrotic enteritis disease (Clostridium perfringens was isolated) in broiler
breeders aged 21 weeks. The flock was divided between three houses and the disease was
confirmed in birds from two of the houses. Strict hygienic precautions were introduced and the
disease did not occur in birds in the third house while treatment of the birds in the other two houses
suppressed the disease.
Limerick reported Rhodococcus equi infection in a six-week old foal. The foal was ill for five
days and was being treated for pneumonia. Brocho-pneumonia was the principal lesion seen on
post-mortem examination. Sligo gave advice to a practitioner who wished to carry out a field postmortem on a mare that had died following an acute colic. There had been no response to treatment
and a severe diarrhoea was seen just before death. The post-mortem had revealed lesions consistent
with a necrotic colitis. This scenario was a recognised complication of treating foals with
erythromycin for Rhodococcus equi-pneumonia , where coprophagia of the foal's faeces by the dam
can lead to Clostridium difficile overgrowth and fatal acute colitis in the mare. In this case,
although the mare’s faol was on treatment for Rhodococcus equi-pneumonia with erythromycin, the
condition was not confirmed, nor was Clostridium difficile isolated, but it seems a likely possibility.
Other Species
Limerick diagnosed heavy coccidial infection in pigeons with a history of diarrhoea and ill thrift.
Pigeons from a loft where a large number of deaths had occurred were examined by Athlone and
were found to have succumbed to aflatoxin poisoning.
Cork examined a juvenile hen harrier (Circus cyaneus) that had been found dead. No gross lesions
were seen but Erysipelothrix rhusiopathiae was isolated from organs cultured.
Twelve pheasants, six-weeks old, from a group of one thousand, were submitted to Cork for
examination following the deaths of up to ten per cent of the group. The birds had been moved to a
new pen two days before the deaths started. The gizzards of all twelve birds were impacted,
principally with seeds of the common cleaver (Galium aparine) (Figure 5).
In another group of pheasants, Syngamus trachea infection was confirmed at post-mortem in sixweek old pheasants. Fifty per cent losses had occurred in a group of 1,400 birds brought in 10 days
Figure 1 “Carcass and urine sample of an animal with bracken poisoning – photo Michéal Casey”
Figure 2 “Bacterial isolates from milk samples submitted to the RVLs”
Figure 3 “Staphylococcus aureus antibiotic sensitivity patterns seen during August”
Figure 4 “Intestinal wall of a ram with parasitic enteritis – photo Michéal Casey”
Figure 5 <insert 0508Cork2> “Galium aparine- The common cleaver – photo Sorcha Spillane”