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September 2010 RVL Monthly Report

Bovine

Salmonellosis was notably prevalent in September. Athlone diagnosed salmonellosis in a two-month-old calf which had died suddenly. Multifocal lobular haemorrhages in the lungs and a fibrinous pericarditis (changes suggestive of septicaemia) were found on post mortem examination and Salmonella dublin was isolated from a range of tissues. Kilkenny necropsied a cow with a history of inco-ordination ante mortem, Salmonella dublin was isolated from several organs. Kilkenny also diagnosed salmonellosis in a three-month-old calf, while Dublin isolated Salmonella dublin from a three-week-old calf with peritonitis.

Clostridial disease was also evident in bovine carcasses examined in the RVLs in September. Kilkenny investigated the sudden death of a thirteen-month-old heifer which had large pale well-demarcated lesions in the liver, which histology confirmed to be coagulative necrosis, while evidence of liver fluke infestation was also found. A diagnosis of black disease (infectious necrotis hepatitis) was made in this case. The occurrence of black disease, like salmonellosis, is associated with fasciolosis. Limerick necropsied an 18-month-old heifer with a swelling around the hip joint. Changes consistent with clostridial myositis were found on examination of muscle around the joint (Figure 1); detection of Clostridium chauvoei in muscle using the fluorescent antibody test (FAT) confirmed blackleg. Sligo reported several cases of blackleg in cattle in the month of September; none of the affected animals had been vaccinated. Cork diagnosed malignant oedema in a six-month-old calf with subcutaneous crepitation and emphysematous reddish-black friable changes in the gluteal muscles, Clostridium septicum was isolated from the affected muscle. 

Muscle with blackleg

Figure 1: Dark, dry emphysematous muscle from an 18-month-old bovine with blackleg. Photo: Alan Johnson.

Parasitism was another regular diagnosis in September. Kilkenny diagnosed ostertagiosis in a nine-month-old bovine with severe diffuse fibrinous abomasitis (Figure 2). Larvae within the abomasal mucosa were detected on histology (Figure 3). In another case of ostertagiosis from a separate premises, Kilkenny observed similar histological changes in the abomasal wall of a three-month-old calf. Athlone diagnosed ostertagiosis in a nine-month-old weanling with a history of diarrhoea and ill thrift, one of a number from the same group with similar clinical signs. A faecal sample from this animal had a very high strongyle egg count, while eosinophilic abomasitis associated with intra-mural parasitic larvae was evident on histology. Cork also reported ostertagiosis from a number of bovine carcass submissions. Limerick tentatively diagnosed larval paramphistomosis in an 18-month-old bullock with a history of depression, poor thrive and diarrhoea. On necropsy, anaemia, hydrothorax and hydroperitoneum were found while a severe rumen fluke infestation and enteritis affecting the proximal small intestine were also in evidence. Limerick also diagnosed severe coccidiosis in a yearling heifer with a history of diarrhoea and nervous signs. Sligo investigated two separate outbreaks of patent hoose pneumonia in weanlings which caused multiple mortalities in each outbreak, while Cork reported several cases of lungworm infestation.

Abomasal mucosa

Figure 2: Congested abomasal mucosa covered in small pitted nodules in a nine-month-old bovine with ostertagiosis. Photo: Donal Toolan.

Larvae in gastric gland

Figure 3: Ostertagia ostertagi larvae inside an abomasal gastric gland in a nine-month-old bovine with ostertagiosis. Photo: Donal Toolan.

Pasteurellosis was diagnosed in a three-month-old calf submitted to Kilkenny. Extensive pneumonia was grossly evident and Pasteurella multocida was isolated from cultured samples. Athlone necropsied a two-month-old calf with a history of sudden death. Fibrinous pericarditis, pulmonary congestion and oedema were among the changes detected that were suggestive of septicaemia. Mannheima haemolytica was isolated from a range of tissues in this case. Athlone detected lesions in the lower digestive tract of a cow submitted for post mortem which were consistent with Johne¿s disease. These lesions included gross corrugation of intestinal mucosa and histology revealed a granulomatous enteritis. The submitting herd had a history of clinical Johne¿s disease. Kilkenny also diagnosed Johne¿s disease in a cow which suffered from chronic ill-thrift and diarrhoea, Mycobacterium avium subspecies paratuberculosis was isolated from faeces  submitted from this cow. Athlone diagnosed Mucosal Disease in a 16-month-old heifer with a history of lethargy, salivation and nasal discharges. Multiple linear ulcerations were found in the oesophageal mucosa (Figure 4), while the detection of BVD antigen in the affected tissues confirmed the diagnosis. Sligo also detected BVD virus infection in a weanling with a severe bronchopneumonia. Athlone investigated the death of a four-month-old calf which suffered from acute respiratory distress ante mortem. On gross examination of the lungs, there was diffuse hepatisation, while the histological changes observed were consistent with BRSV infection.

Mucosal disease

Figure 4: Short linear diphtheritic ulcers in the oesophageal mucosa of a 16-month-old bovine with mucosal disease. Photo: Ger Murray.

Aortic aneurysm was diagnosed in a two-month-old calf submitted to Kilkenny for post mortem examination. There was oedema of the ventral neck and brisket, pulmonary oedema and nutmeg liver were in evidence, while the heart was impinged by a large thoracic mass which was comprised of a dilated segment of aorta, 15 cm in length and containing a thrombus. Kilkenny also investigated the case of a three-month-old calf with a history of abdominal distension which persisted for a week ante mortem. A perforating abomasal ulcer and an associated severe fibrino-suppurative peritonitis were noted on post mortem examination. Dublin necropsied a seven-year-old dairy cow which was found dead in a field of lush silage aftergrass, which the cow had been moved onto five days earlier. Subcutaneous emphysema of the ventral thorax and abdomen, and interlobular emphysema of the lungs were the main necropsy findings. A presumptive diagnosis of peracute fog fever was made on the basis of pathological findings and history provided. Animals with peracute fog fever can be found dead without premonitory signs.  Fog fever occurs in cattle grazing on pasture (typically aftergrass) with a high content of the amino acid L-tryptophan. This is converted in the rumen by bacterial action to 3-methyl indole, a potent pnemotoxin. Dublin diagnosed ragwort poisoning in a two-year-old suckler cow suffering from ill thrift. She had been grazed on poor grassland containing ragwort. The cow¿s liver was severely fibrosed,  and hepatic encephalopathy was also found. Dublin necropsied a post-parturient cow which became lethargic and depressed after a difficult calving. A transmural uterine tear and an associated diffuse fibrino-suppurative peritonitis were readily detected at post mortem.

Cork examined a two-week-old calf with widespread petechial and ecchymotic haemorrhage on mucosal and serosal surfaces (Figure 5), and severe intra-luminal intestinal haemorrhage. BVD virus testing proved negative, while hypoplasia of haemopoietic cells, evident upon microscopic examination of bone marrow, was consistent with a diagnosis of Bovine Neonatal Pancytopaenia (BNP). Sternum samples from a two-week-old calf which had a history of excessive bleeding, were submitted to Dublin. A lack of haemopoietic cells in bone marrow and a negative PCR result for BVD virus in tissues also indicated a diagnosis of BNP in this case.

Conjunctival haemorrhage

Figure 5: Conjunctival haemorrhage in a two-week-old calf with bovine neonatal pancytopenia. Photo: Cosme Sanchez.

A  seasonal increase in abortion cases was reported in September. Kilkenny and Limerick recorded an increase in Salmonella dublin abortion cases while  Athlone isolated Salmonella dublin from two third-trimester aborted foetuses submitted from the same dairy herd. Both foetuses were malodorous and slightly swollen by gas, as is common for foetuses infected with Salmonella dublin. Athlone diagnosed congenital hepatic fibrosis in an eight-month-old foetus. This foetus had a swollen abdomen, ascites and an enlarged firm liver which was found to be fibrotic on histological examination. This condition is likely to arise from a heritable or spontaneous genetic mutation. In a separate case, Athlone suspected Ureaplasma diversum as the cause of abortion of a near full term foetus. This suspicion was based on histological examination of tissues, and was not confirmed. The condition is sporadic and rare.

Ovine

Kilkenny diagnosed parasitic gastroenteritis in a ewe with a faecal egg count of almost 20,000 eggs per gram of faeces, while Athlone investigated the death of a lamb with a history of pining for several weeks antemortem  which showed evidence of diarrhoea and a faecal sample had a very high strongyle egg count, findings consistent with parasitic gastroenteritis. Athlone necropsied two ewes with a history of sudden death. Both ewes had friable livers heavily infected with immature liver flukes, confirming a diagnosis of acute fasciolosis. Athlone necropsied a seven-month-old ram lamb which was recently purchased and died suddenly. The rumen contained a lot of grain which had a characteristic odour of fermentation. A rumen pH of 5.2 was consistent with acute rumenal acidosis (commonly known as grain engorgement or barley poisoning).

Porcine

Kilkenny diagnosed bacterial meningitis in a seven-week-old piglet with a history of nervous signs.  Streptococcus suis type 2  was isolated from the piglet¿s brain. Dublin detected novel pandemic H1N1 influenza virus in four weanling piglets with a history of ill thrift, and which presented with pneumonia on post mortem examination. Dublin also investigated mortalities in late-gestation sows in a large pig unit. A diffuse suppurative meningitis was found in necropsied sows and Streptococcus equi subspecies zooepidemicus was isolated from several tissues including the brain.

Equine

Limerick necropsied a six-month-old foal with a short history of colic ante mortem.  Intestinal obstruction associated with a large number of Parascaris equorum worms was evident. P. equorum is a large ascarid worm which is common in foals, and rarely causes clinical signs unless it occurs in sufficient numbers to cause a physical obstruction, as in this case.

Avian

Dublin examined a hen from a small back-yard layer flock with a history of lameness and depression. Detection of amyloid aggregations in liver samples on histology confirmed a diagnosis of amyloidosis. Avian amyloidosis is caused by chronic infection or stress.  Liver and articular surfaces are recognised sites for amyloid deposition. Dublin also diagnosed egg peritonitis in four young breeder hens that presented with fibrino-suppurative peritonitis on post mortem examination. Escherichia coli was isolated from tissues, and the remaining flock responded well to antibiotic therapy.