New PRRS Virus, Possible Vaccine Failures Reported

UK - The Monthly Surveillance Report from the Veterinary Laboratories Agency (VLA) for October 2008 highlights the occurrence of the European strain of PRRS virus and apparent vaccine failures against Mycoplasma and Streptococcus.

2 December 2008

4 minute read

Europe

Porcine Reproductive & Respiratory Syndrome (PRRS)

A litter of aborted foetuses, of varying sizes and some of which had been mummified was submitted to Thirsk from a large breeding unit. These piglets were born from a gilt which had received PRRS vaccine. Post-mortem examination revealed a large range in size of pigs with severe mummification in some. Many foetuses had oedema of the head, and one foetus in particular had marked haemorrhages throughout the subcutaneous tissue and pinpoint haemorrhages in the kidney, which were quite marked. Culture was unrewarding but PCR from this foetus was positive by PCR for the European strain of PRRS virus. In addition, histopathology revealed predominantly mononuclear inflammatory cell infiltrates in heart and liver, which suggested a viral aetiology and possibly iatrogenic.

Swine Dysentery

Bury reported two outbreaks of swine dysentery (SD), both in indoor all-in, all-out finisher units geographically distant from one another. In the first, the disease was confirmed on a unit with no previous history of infection. Five of 25 22-week-old pigs were seen to have blood flecked diarrhoea and two died. A reddened colonic mucosa and bloody intestinal contents were found in an on-farm post-mortem examination. The source of infection was suspected to be a neighbouring SD positive unit which was cleaning out with birds being a possible means of transmission.

In the second, Brachyspira hyodysenteriae was detected by PCR in faeces from 21-week-old pigs with diarrhoea; a group B salmonella was also isolated. Although swine dysentery was previously diagnosed on this unit in 2006, the unit was considered clear of SD and infection was strongly suspected to have entered with the pigs which were supplied from a rearing unit where the stockman also looked after pigs on SD positive units.

Langford also diagnosed the disease as the cause of ill thrift and diarrhoea in a group of 40, 10-12 week-old growing pigs. Salmonella typhimurium U288.

An outbreak of scour in six-week old weaners on a Contract Rearing Unit was investigated by Bury. Four dead animals were examined, the consistent finding being necrotising enteritis and colitis. Salmonella Typhimurium phage type U288 was isolated from these pigs. A Salmonella sampling visit to this farm was carried out.

Mycoplasma

Four 12-14 week old pigs were submitted for necropsy. Many weaned pigs on the unit had shown signs of pneumonia despite vaccination with a single-dose Mycoplasma hyopneumoniae vaccine, but serology from 10 pigs indicated field exposure in 18-week-old pigs. The unit was reportedly PRRS-free. Two pigs submitted for post mortem demonstrated a purulent pneumonia, one pig had classic Glasser's disease and the fourth pig had lesions typical of Enzootic Pneumonia (EP). M. hyorhinis was isolated from three carcasses and M. hyopneumonia was isolated from the fourth pig's lungs. Investigations are ongoing as to why the vaccine did not provide protection; the incident was reported to VMD.

Neurological Diseases

An outbreak of nervous disease in 6 to 8-week-old piglets was investigated by Winchester. Four affected pigs were submitted for post mortem examination which revealed fibrinopurulent meningitis in one carcase and a generalised polyserositis in other carcasses. Septicaemia involving Streptococcus suis type 2 was confirmed despite an on-farm vaccination programme against this organism. This may have been a new strain introduced into the herd, and for which the vaccine did not give adequate protection. A SARS report was sent to VMD.