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PEV-8 Link to Polioencephalomyelitis Suspected

by 5m Editor
21 January 2009, at 8:39am

UK - The Monthly Surveillance Report from the Veterinary Laboratories Agency (VLA) for November 2008 highlights disease caused by nematode worms in sows and three outbreaks of salmonellosis. Pneumonia caused by the PRRS virus was found to be the cause of increased mortality in weaned pigs. Further work carried out into an outbreak of porcine neurological disease first reported in 8- to 10-week-old pigs in June 2008 has raised the possibility of the involvement of the PEV-8 virus.

Alimentary Tract Diseases

Oesophagostomum

Three adult pigs were submitted from a 140-animal herd comprising of rare breeds where six adult pigs had died in the last month. It was reported that the animals had lost weight but remained bright although they demonstrated ataxia before death. All were emaciated and some had mild pneumonia and peritonitis, however the consistent finding in all three pigs were very large numbers of Oesophagostomum spp. nematode worms in the colon.

Oesophagostomiasis is usually considered as a cause of ill thrift and reduced productivity and heavy infestations in the UK are infrequent, at least in housed pigs. However in this case the findings suggested that parasitism was an underlying cause of death, and indicated that a worming programme was required on the farm.

Salmonellosis

Bury diagnosed two outbreaks of salmonellosis due to Salmonella Typhimurium infection. In the first incident, a sample of colon was submitted from six-week-old pigs with diarrhoea, wasting and some deaths. Necrotising colitis had been identified in an on-farm necropsy. Salmonella Typhimurium phage type 193 was isolated. Forty of 150 pigs on an indoor nursery unit were affected, with 20 deaths.

In the second incident, eight-week-old pigs were affected. Wasting, malaise and inappetence were reported in a group of 1,200 Hampshire pigs being reared outdoors from which 20 had died. Sows were vaccinated for PCV2. A chronic necrotising typhlocolitis was identified in two pigs submitted, one of which had a mild polyarthritis and the second had a chronic mild pneumonia. Salmonella Typhimurium phage type 208 was isolated from internal viscera as well as the intestines pointing to salmonella septicaemias and PRRS virus was detected in both spleens by PCR. As PRRS virus is immunosuppressive, its presence in these growing pigs was considered significant.

Sutton Bonnington also diagnosed the condition affecting a group of 85 pigs in which 20 had died.

Respiratory Diseases

Swine influenza

Swine influenza was suspected on clinical grounds when about 35 of a group of 70 farrowing sows became affected with inappetence, pyrexia and dyspnoea on an indoor breeding unit of 570 sows. The problem later spread to other dry sows and weaners. Approximately 60 per cent of a batch of 700 weaners were reported to be coughing. Sows were vaccinated with live PRRSV, weaners were vaccinated for PCV2 and Mycoplasma hyopneumoniae.

Two sow plucks submitted to Bury had gross lesions consistent with acute to subacute bronchointerstitial pneumonias with multifocal patchy consolidation suggestive of possible swine influenza virus infection. Two growing pigs were also submitted; one with a severe bronchopneumonia and the other, which was pre-weaned, with a mild multifocal pneumonia, pericarditis and polyarthritis. No swine influenza virus was isolated from these, however, a subacute bronchiolitis was present and immunohistochemistry confirmed active swine influenza infection in the pre-weaned pig and one sow pluck. Paired serology from sows and convalescent sera from growing pigs failed to demonstrate seroconversion or seropositivity possibly due to antigenic differences between field and laboratory strains of the virus. This is being investigated further and attempts to isolate and identify the virus are continuing.

PRRS

Six, six-week-old growing pigs were sacrificed to investigate an increased incidence of respiratory disease and mortality in post-weaning piglets. The pigs originated from a 450-sow farrow-to-finish indoor high health status intensive herd. Post mortem examination revealed accumulations of haemorrhagic frothy mucous in the trachea, bronchi and bronchioles. Areas of coalescing petechial haemorrhage were present over the caudal parts of the diaphragmatic lobes of the lungs of all the pigs but with varying severity. The demonstration of PRRSV by PCR in lung tissue together with positive serology indicated a primary pneumonia caused by the virus.

Other Diseases

Iron deficiency anaemia

A live moribund piglet aged 7 weeks was submitted to Preston with clinical signs of lethargy and poor condition. Three out of a litter of 10 had been affected with two previous deaths. The affected piglets had lost condition from 3-4 weeks of age. Post mortem examination revealed a slightly rounded heart but no other gross abnormalities. Tests on blood revealed a microcytic hypochromic anaemia and low serum iron (1.8µmol/litre compared to the reference range of 11-32).

Nervous Diseases

Polioencephalomyelitis

Further work carried out into an outbreak of porcine neurological disease first reported in the June 2008 monthly report resulted in the demonstration of a virus closely related to porcine enterovirus -8 (PEV-8) as the cause of hind limb ataxia in 8- to 10-week-old pigs. Histopathology had demonstrated a non-suppurative polioencephalomyelitis and use of a virus micro-array and subsequent nucleic acid sequencing identified the likely causative virus. Work to further characterise the agent is ongoing. PEV-8 has been associated with reproductive disorders (SMEDI syndrome) and possibly enteritis but not previously with polioencephalomyelitis.

Further Reading

- You can view the full report by clicking here.
- Find out more information on the diseases mentioned in this article by clicking here.

5m Editor