Questions and Answers on Pig Virus
Questions and Answers on Pig Virus
What is Post-Weaning Multisystemic Wasting Syndrome (PMWS) PMWS is an emerging viral disease of pigs that is being diagnosed with increasing frequency in Canada, the United States, Europe and Asia. Pig practitioners and diagnosticians in several countries began to recognise it in the early 1990's, and Canadian scientists confirmed the disease in a Saskatchewan pig herd in 1996.
What causes PMWS? PMWS is a multi-factorial disease associated with porcine circovirus type 2 (PCV2), porcine parvovirus (PPV), and porcine reproductive and respiratory syndrome virus (PRRSV). Two of these agents – PPV and PCV2 – are endemic to New Zealand.
How is PMWS diagnosed? Diagnosis is dependent upon three criteria. Presence of compatible clinical signs Presence of characteristic microscopic lesions Demonstration of PCV2 within these lesions
A definite diagnosis is
confirmed by post-mortem examination of samples from pigs
showing the characteristic clinical signs, by finding
histopathological lesions in various internal organs and
confirming the presence of viral material using
immunohistochemistry (IHC) staining.
Has PCV2 been linked with any other diseases? PCV2 is an important part of the cause of Porcine Dermatitis Nephropathy Syndrome. While PMWS remains the most important syndrome associated with PCV2, this virus has been linked with a number of other syndromes in various parts of the world, including certain types of Congenital Tremor in piglets, nervous disease possibly leading to sudden death in weaners, Proliferative and Necrotising Pneumonia (PNP), perinatal myocarditis, low-grade reproductive problems and possibly Sow Abortion and Mortality Syndrome (SAMS).
How does PMWS affect pigs? The disease affects eight to16 week old piglets, often peaking at nine to 10 weeks. Clinical signs include loss of condition, failure to thrive, pallor and possible diarrhoea. Some pigs may exhibit breathing difficulties and jaundice.
How is PMWS spread? It is thought that the disease might be spread through the movement of pigs or possible semen.
Is PMWS very infectious? PMWS is a syndrome caused by a combination of infectious, pig, and environmental factors. Hence clinical disease is often absent despite the presence of infectious agents.
Is there any treatment for PMWS? Currently, there is no vaccine to prevent PMWS and there is no treatment. Mortality rates vary between 4 to 10% but farms with post-weaning mortality up to 60% have been reported. Another feature is the persistent nature of the syndrome – some farms are still affected for two or more years and still experience similar levels of mortality.
How widely spread is PMWS PMWS is recognised as a world wide problem. Australia is free of the disease and although an investigation is underway in New Zealand it has not yet be confirmed.
What can pig farmers do to manage PMWS?
There are numerous important management practices useful for
mitigating the spread of PMWS. Veterinarians, producers,
industry and government representatives from the European
Commission met in September 2001 and put forth "three golden
rules" to control PMWS. These were?:
1. limiting litter to litter contact, both directly, through fostering and multi-suckling, and indirectly from shared needles, equipment, mud, etc., 2. reducing animal stress and susceptibility to disease by limiting exposure to micro organisms, and 3. practising good management, hygiene and biosecurity on the farm. These practices are common sense activities, which can minimise the spread of not only PMWS, but many other diseases, as well.