Congenital abnormalities detected in bovine fetal submissions
Nematodirus infection diagnosed with varying clinical presentations in lambs by several centres
Lungworm diagnosed as contributing to mixed respiratory disease in outdoor pigs
Avibacterium paragallinarum (infectious coryza) infection detected in two flocks
Haemonchosis diagnosed in adult alpacas from several farms
These are among matters discussed in the Animal Health and Veterinary Laboratories Agency's (AHVLA's) disease surveillance report for April and May
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Most centres reported findings as part of the AHVLA's surveillance for Schmallenberg virus (SBV)-associated fetal deformity. It became clear that the sensitivity of detection of the virus by PCR in affected bovine fetuses was relatively low; many cases required neurohistopathological diagnosis. One such case, which was outside the currently affected area of southern and eastern England, was diagnosed by Shrewsbury, but the dam of the affected fetus had been imported from mainland Europe where it had become infected. Three other calves submitted to Shrewsbury with congenital defects had been born to cows that had not been imported. They were all negative for SBV by PCR.
At the Royal Veterinary College (RVC), two calves from two farms with marked arthrogryposis, scoliosis and brachygnathia inferior were examined. Both were slightly premature and had been delivered manually with veterinary assistance. Additional findings included expansion of the ventricles in the brain of one and cerebellar hypoplasia in the other. PCR on both was negative, but histopathology showed dysplasia in the cervical spinal cord and a diminished ventral horn area typical of in utero exposure to SBV.
Winchester commented that macroscopic brain lesions in SBV-affected bovine fetuses were less commonly detected than in ovine cases. Arthrogryposis and skeletal deformity appear to be more consistent gross lesions in cattle.
This summary is produced by the AHVLA and is drawn from reports provided by the AHVLA laboratories at Aberystwyth, Bury St Edmunds, Carmarthen, Langford, Lasswade, Leahurst, Luddington, Newcastle, Penrith, Preston, Royal Veterinary College, Shrewsbury, Starcross, Sutton Bonington, Thirsk, Truro, Weybridge and Winchester. AHVLA monthly reports are available online at http://vla.defra.gov.uk/reports/rep_surv.htm
As a result of enhanced surveillance for SBV, several other types of fetal deformity were encountered.
Congenital contraction of forelimb tendons by the RVC.
Perosomus elumbus, a rare partial agenesis of the spinal cord, was diagnosed by Preston. The calf had been delivered by caesarean and had severe arthrogryposis and muscle atrophy of the hindlimbs. The lumbar, sacral and coccygeal vertebrae were absent and the spinal cord ended at the 13th thoracic vertebra. The hindlimbs were attached to the body by soft tissue only.
Congenital articular rigidity syndrome was diagnosed by Starcross in a live three-day-old north Devon calf that had been unable to stand since birth and appeared blind. The forelimbs were bilaterally affected with rigidity, which made it impossible to fully extend the joints. Both hindlegs had similar restrictions of the hock and stifle joints. On postmortem examination, abnormalities in the articular surfaces of the joints were not detected and the brain was grossly normal. PCR examination of the brain proved negative for SBV. A presumptive diagnosis of congenital articular rigidity syndrome was made.
Arnold-Chiari malformation was suspected in a calf submitted to Truro that had kyphoscoliosis and arthrogryposis of both hindlimbs. A meningomyelocoele lesion was present in the sacral region; the cerebellum and a large portion of the cerebrum had herniated through the foramen magnum into the anterior spinal canal. The pathogenesis of Arnold-Chiari malformation is unclear, but the defect is observed occasionally in calves and rarely in other species.
Rotavirus infection and cryptosporidiosis were again the most commonly diagnosed causes of neonatal diarrhoea. Many centres reported increased numbers of diagnoses of diarrhoea due to K99 (F5)-positive E coli. Some cases were associated with a low serum zinc sulphate test concentration. Carmarthen diagnosed E coli infection in a 36-hour-old dairy calf that was one of four to have died out of approximately 40 pre-weaned calves on a dairy farm.
Most centres diagnosed disease due to Salmonella Dublin in older calves, which most commonly presented with diarrhoea. Truro diagnosed infection in a four-month-old dairy calf with severe pneumonia and enlargement of the spleen. S Dublin was isolated in systemic distribution. Eight of 28 calves that had been grazing outside died over a short period of time and losses started approximately one week after a temporary disruption of the water supply. Whether this stress and ‘salt poisoning’ precipitated the severe clinical salmonellosis is not known, but it may have been a contributory factor.
Langford diagnosed fatal abomasitis associated with Sarcina-like organisms (visible in clumps in a Gram-stained smear) in a one-week-old dairy calf that was found dead. At postmortem examination, there was a khaki-coloured mucoid covering over a reddened abomasal mucosa and widespread submucosal emphysema.
Aberystwyth diagnosed hypomagnesaemia in a three-month-old suckler calf that was found convulsing and had died despite treatment with intravenous calcium and magnesium and subcutaneous magnesium. The aqueous humour magnesium concentration was marginal, probably due to treatment and autolysis. Bone ash contained only 0.2 per cent magnesium, with a calcium:magnesium ratio of 188:1 (a ratio of ≤70:1 is usually seen in normal animals and >90:1 is consistent with hypomagnesaemia). The calf was one of a group of 12 calves housed with their dams that had been fed silage and barley. Analysis of ash from rib or tail bones may be useful in the diagnosis of hypomagnesaemia in animals up to about six months old.
Submissions of suspect cases of SBV infection decreased as the lambing season neared its end. Starcross diagnosed SBV infection on four premises. One of the affected lambs had an overshot jaw and a spinal deformity. A lamb from another premises had brachygnathia, a small head, torticollis and ankylosis of the neck. Dissection confirmed a very small brain, absence of the cerebellum and a brain stem and spinal cord that were narrow and ribbon like. The final submission was two lambs with similar abnormalities – in one, all the joints of the hindleg were fixed in extension, while in the other the front legs were fixed in flexion. In one, the lower jaw was undershot and the skull asymmetrical. Also, the spine was twisted, the cervical vertebrae were fused and the spinal cord was noted to be very narrow. In the other lamb, there was spina bifida at the level of the pelvis and the neck was twisted and ankylosed. In this lamb the spinal cord was grossly normal, but the brain was elongated and the cerebellum misshapen. Histological examination of the first lamb showed ventral myelodysplasia, which is typical of SBV-induced pathology. In the lamb with spina bifida, histopathological findings were consistent with Arnold-Chiari malformation. However, the pathologist was of the opinion that the arthrogryposis and spina bifida may have been an effect of less severe changes associated with SBV infection.
Nematodirus infection, with varying clinical presentations, was diagnosed by several centres. Carmarthen diagnosed infection in a 10-week-old Charollais lamb, which was one of two to die in a group of 150 ewes and lambs. The lamb was in very good condition and had been found dead without any prior signs. The flock had been lambed indoors and had been turned out to grass for eight weeks. Large numbers of Nematodirus battus worms were found in the small intestine.
Leahurst diagnosed nematodirosis in an eight-week-old Texel-cross ram lamb. Lambs had been treated with a coccidiostat when they were seen scouring 10 days after turnout and a variable response had been reported. The lamb submitted had passed fresh blood in its faeces for three days before it died. Postmortem examination revealed a focal 1 cm diameter ulcer in the caecal mucosa and histopathology confirmed multiple smaller ulcers, associated with colonisation by clostridial organisms. The small intestinal burden of N battus worms was approximately 10,200, which could potentially have been fatal. Coccidial oocysts of the pathogenic species Eimeria ovinoidalis were identified in the contents of the large intestine and it was likely that coccidiosis had contributed to the disease seen.
Preston received an 11-month-old Icelandic ewe lamb in poor body condition. It had been euthanased after failing to respond to treatment. Two animals in a flock of 30 had shown similar vague clinical signs of malaise and recumbency. Biochemistry antemortem demonstrated moderate hypoalbuminaemia, hypoglobulinaemia, markedly raised creatinine kinase (consistent with recumbency), and markedly raised gamma-glutamyl transpeptidase and glutamate dehydrogenase levels. Trace element and vitamin E levels were considered to be adequate and there was marginal hypocalcaemia. On postmortem examination, moderate hydroperitoneum and hydrothorax were noted, consistent with hypoproteinaemia. There was marked osteopenia/osteoporosis with very thin cortices of long bones that could easily be broken. Faeces were soft and there was a very high trichostrongyle worm egg count. Histopathology of the liver demonstrated periportal vacuolar hepatopathy consistent with a negative energy balance. Osteoporosis was evident on histopathology of the bone. There was marked bone marrow hypoplasia, consistent with chronic debility. Marked narrowing of the growth plates suggested a protein calorie deficiency. Advice to monitor for worm burdens was given. Marked osteopenia after weaning has been demonstrated in lambs suffering from moderate to heavy degrees of naturally acquired gastrointestinal nematode infection (Thamsborg and Hauge 2001).
Red foot disease was diagnosed on gross examination of a one-day-old Welsh mountain lamb, which was one of three affected in a small flock of 90 ewes. All three lambs had patchy alopecia and sloughing of the hoof horn. In the lamb presented for examination, there was no hoof horn on the hindlimbs and the underlying corium was exposed (Fig 1). There was also ulceration of the dorsal tongue. Red foot disease is seen in both Scottish blackface and Welsh mountain sheep. The exact cause of the condition is not known, but it is likely to be inherited.
Pneumonia due to lungworm (Metastrongylus species) was detected in two submissions from outdoor units. The intermediate host for this species of lungworm is the earthworm, to which outdoor pigs have greater access. Earthworms, and the lungworm larvae within them, can survive for more than five years, which makes it likely that there is carry-over of lungworm infection on land that is re-used for pigs.
In the first submission, respiratory disease due to Glässer's disease and porcine circovirus type 2-associated disease (PCVAD) was diagnosed in 13-week-old pigs. In the four days before submission, 20 deaths had occurred in various tents with 40 of 2500 pigs showing respiratory disease mainly presenting as laboured breathing and a small amount of coughing with mortality. The pigs had been vaccinated for Mycoplasma hyopneumoniae and porcine respiratory and reproductive syndrome virus (PRRSV), but not porcine circovirus type 2 (PCV-2). Fibrinous polyserositis was present, from which Haemophilus parasuis was isolated. Histopathology with immunohistochemistry on the lungs and lymph nodes confirmed PCVAD. One pig had numerous lungworm present in smaller bronchi. It had been thought that these pigs were the progeny of sows vaccinated for PCV-2; however, further investigation indicated that this was not the case and PCV-2 vaccination of weaners was initiated together with anthelmintic treatment for the lungworm infestation.
In the second submission, respiratory disease and wasting in successive batches of outdoor weaners, from about two weeks after arrival from outdoor breeding units, was investigated in three pigs of different ages. Pigs were described as being bright but mortality had increased from 3 to 5 per cent. Pigs had been vaccinated for PRRSV and M hyopneumoniae at weaning. Findings differed in each of the pigs; the five-week-old pig was in poor body condition with necrotising pneumonia and abscesses from which Streptococcus suis type 1 was isolated. This pig also had candidiasis of the oesophagus, which was probably due to a combination of debility and gastric reflux due to concurrent gastric ulceration. In the seven-week-old pig, Glässer's disease was confirmed by isolation of H parasuis from fibrinous polyserositis lesions. In the third pig, which was 13 weeks old, many lungworm were visible in the smaller airways and histopathology confirmed severe verminous pneumonia. Interestingly, the pigs had been on the land for a maximum of 18 months. Before the unit had been established, the land had been a gravel pit and it had never been used for pigs. Pigs were wormed on entry, with successive batches going onto the same land. Investigations are ongoing to determine whether lungworm infection was seeded onto the unit in pigs from one of the breeding units.
Systemic and miscellaneous diseases
One of two seven-month-old kune kune pigs on a smallholding died following clinical signs over the previous 10 days and was submitted to Bury St Edmunds. Clinical signs began with frank blood in the faeces and a few days later blood was noted in the urine. Approximately 10 days later, the pig was lethargic and anorexic and it died. It was reported to have been fed kitchen waste and the surviving pig was reported as pyrexic and dull. Gross findings were suggestive of coagulopathy/haemorrhagic diathesis and included haemorrhages (Fig 2) into the mucosae, skeletal muscle, omentum, intestinal mucosa and serosa, myocardium, lymph nodes and spleen, with blood clots in the renal pelvis and ecchymotic haemorrhages in the bladder. The farm was using difenacoum rodenticide and anticoagulant toxicity was a potential cause of clinical signs. Due to the overall history, the case was reported as suspected swine fever. However, this was negated following a farm visit by a Veterinary Officer that determined that the surviving pig was clinically normal and there may have been greater access to rodenticide than initially reported, in addition to the consumption of poisoned rats. The case was subsequently investigated under the Wildlife Incident Investigation Scheme (WIIS), which confirmed that three weeks before death the pig had accessed a bait box containing difenacoum. Advice was given regarding the correct use of rodenticides and prompt disposal of dead rodents. A liver assay indicated the presence of difenacoum. It is uncertain whether the residue concentration was sufficient to have been the sole cause of death, but it is likely to have been a contributory factor.
Spotty liver syndrome
A reduction in egg production of approximately 5 per cent in 47-week-old, free-range layer hens on a multiage site was investigated. Postmortem examination revealed mild enteritis and multiple, pale focal lesions throughout the liver substance, suggestive of spotty liver syndrome (SLS or avian vibrionic hepatitis). Multifocal necrotic hepatitis was confirmed by histopathology, endorsing the diagnosis. The aetiology of the condition, which can be associated with free-range layers around peak lay in Great Britain, is unconfirmed, but is thought to be caused by Campylobacter species (Crawshaw and Irvine 2012). The AHVLA is currently interested in gathering further information about SLS and would be interested to hear the experiences of veterinarians and producers by way of a 12-month case series study questionnaire that can be completed either on paper or as an online survey. Further information can be found at http://vla.defra.gov.uk/science/sci_spotty_liver.htm.
Broilers and broiler breeders
Baby chick nephropathy
Elevated mortality led to the submission of two-day-old broiler breeder chicks. Postmortem examination revealed carcase dehydration, pallor of the kidneys and urate crystal deposition, often in the pericardial sac (visceral gout), which was consistent with a diagnosis of so-called baby chick nephropathy. Other chick placements on the premises that were housed in different sheds, but with the same brooding conditions, were not affected.
Caecal coccidiosis and Eimeria acervulina infection were diagnosed in a batch of 21-day-old broilers submitted to investigate the cause of blood-stained litter material. Findings at postmortem examination revealed soft, creamy caecal contents in some carcases. Histological examination of the caecum revealed mucosal scarring with large numbers of coccidial forms that were consistent in size and location with E tenella. Examination of the duodenum revealed abundant clusters of coccidial forms that were consistent in size and location with those of E acervulina.
Duck virus enteritis
Several separate submissions were received following acute onset illness and mortality (20 to 50 per cent) from small and ornamental flocks of domestic waterfowl. Affected species comprised Muscovy, Aylesbury and Indian runner ducks. In two of the cases, the presence of a water body and contact of domestic ducks with wild mallards (Anas platyrhynchos) was reported. Postmortem examination findings consistently included multifocal necrotic hepatitis, diphtheritic plaque-like necrotic lesions of the oesophageal and cloacal mucosa, bloody intestinal contents and petechial haemorrhages of the viscera. These gross findings are virtually pathognomonic for the presence of duck virus enteritis (DVE), a herpesvirus infection seen mainly between April and June each year in Great Britain. The source of infection is often attributed to migratory mallards that serve as carriers of the virus. The diagnosis of DVE can be confirmed by histopathology and/or virus isolation.
An investigation of two separate small layer flocks located in southern England resulted in the detection of Avibacterium paragallinarum, the causative organism of infectious coryza. In both flocks, upper respiratory tract signs were observed within a few days of the arrival of point-of-lay pullets aged 16 to 17 weeks. Morbidity ranged from 15 to 30 per cent with clinical signs including mouth breathing, sneezing and occasional infraorbital sinus swellings. Postmortem findings included excess mucus in the nasal passages, infraorbital sinuses and trachea, and airsacculitis. In one of the cases, a similar disease episode had occurred on delivery of the previous batch of pullets, indicating a more widespread problem, but the owner had not investigated it at the time. In common with infectious coryza cases investigated and reported previously by the AHVLA (Anon 2011, Welchman and others 2011), there was concurrent infection with other agents, including infectious bronchitis virus, Mycoplasma gallisepticum, E coli, avian Pasteurella-like organisms and Aspergillus fumigatus. Such multifactorial infections can often be a feature of respiratory disease episodes in backyard and hobby flocks.
Further information about infectious coryza can be found at http://vla.defra.gov.uk/science/sci_coryza.htm.
Pheasant coronavirus-associated nephritis
Adult breeding pheasant losses were investigated on several occasions, leading to the diagnosis of pheasant coronavirus-associated nephritis. Characteristic postmortem findings were observed, including white urate deposits over the viscera of affected birds (‘visceral gout’), accompanied in one case by ‘articular gout’, and marked enlargement and pallor of the kidneys. The diagnosis was confirmed by histopathology and detection of infectious bronchitis virus by PCR testing.
Haemonchosis was diagnosed in adult alpacas on three premises and suspected, on the basis of pathological findings and a high faecal worm egg count, on a fourth. Postmortem findings in these animals included emaciation and carcase pallor, indicating anaemia and oedema, which in turn suggested hypoproteinaemia. Terminal streptococcal septicaemia was a complicating factor in one animal and Mycoplasma haemolamae, a potential bloodborne pathogen, was identified in another. Haemonchosis is potentially a serious cause of parasitic gastritis in British camelids; many cases are diagnosed at postmortem examination. A review of AHVLA records indicated that at least 20 cases were diagnosed in England and Wales between 2000 and 2011. The diagnosis can be confirmed by demonstrating worms in the stomach at postmortem examination or by using a differential fluorescent staining test on faecal samples from suspected cases.
An adult roe deer (Capreolus capreolus) from an estate where 20 of an estimated population of 70 had died over the previous two weeks was submitted for postmortem examination. Abnormal rumen contents and a high aqueous humour urea level suggested that the deer had died as a result of uraemia, possibly due to grazing land recently treated with urea fertiliser. There is some interest in roe deer mortality because, on the continent, an enteropathy of unknown aetiology has been recognised. It is not clear if a similar condition affects roe deer in the UK.
A six-month-old muntjac deer (Muntiacus reevesi) was found floppy and falling over and it died rapidly. There had been others affected similarly in previous years. It had been one of a small group in a small paddock with little access to grass or browse, that were fed flaked maize and concentrate as well as some carrots. The postmortem examination found that the rumen was full of liquid content, mainly concentrate, consistent with a diagnosis of ruminal acidosis. Clostridial enterotoxaemia and malignant catarrhal fever were ruled out.
There were two investigations into the possibility of SBV affecting wild deer. Two separate fallow deer (Dama dama) fetuses were submitted and SBV PCR tests gave negative results in both. Alternative diagnoses were not found. On the continent, SBV seropositive deer have been detected and the AHVLA Diseases of Wildlife Scheme will continue passive surveillance for SBV on deer fetuses and neonates found with suspicious lesions.
Three red kites (Milvus milvus) were submitted as part of the WIIS investigating possible poisoning incidents in wildlife. One of them had been found comatose by a member of the public and died soon after submission to a wildlife hospital. The other two had been found dead in a pheasant release pen in the same small wood. Postmortem examinations revealed that the animals were in good body condition, but with empty stomachs. There were subcutaneous and epicardial haemorrhages in two of the birds, which raised the possibility of poisoning with anticoagulants. Results of toxin testing are awaited with interest.
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