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Porcine Circovirus In Canada

by 5m Editor
10 April 2006, at 12:00am

By JoAnn Alumbaugh and published by Farms.com - If you are a pork producer, chances are you’ve encountered problems with Circovirus Type 2 (PCV2), a newly recognized virus that has been associated with a number of disorders. The virus itself has been around a long time, and most herds test positive, even if they’ve never seen clinical signs.

However, more and more herds are having problems with the virus, and the economic losses are significant. Dr. George Charbonneau and Dr. Steve Wolfgram with Swine Services are veterinary practitioners whose practice services the Ontario pork production industry. The emphasis at Swine Services is on preventive herd health management programs. These two, along with associates Ann Coyle, Jean Smith and Ken Marenger, put together a discussion paper on PCV2, excerpts of which are included in this commentary. Swine Services gathered this information from a number of sources, and the volume of research on PCV2 continues to grow. While there are a number of syndromes associated with PCV2, the most common and recognized problem is postweaning multisytemic wasting syndrome (PMWS).

Circovirus Type 2 (PCV2) is a single-strand, non-enveloped, circular DNA virus that is resistant to many disinfectants. It is also resistant to drying and survives well in the environment. One of its forms, PMWS, must meet three criteria, according to research at Seoul National University: The presence of compatible clinical signs; the presence of characteristic microscopic lesions; and the presence of PCV2 within these lesions. In order to establish the diagnosis, techniques are required that link virus and tissue lesions. The etiology of PMWS is not well understood, but increased knowledge of the causal factors will allow producers to apply preventive interventions.

Circovirus Type 2 was first reported in Saskatchewan in the mid-1990s. By the end of that decade, PCVD had been identified in many countries around the world. Besides postweaning multisystemic wasting syndrome (PMWS), which is associated with dysfunction of numerous body systems in the growing pig, other disorders include:

Porcine Dermatitis and Nephropathy Syndrome (PDNS) – a disease of older growing pigs that involves the development of abnormal immune complexes and is expressed primarily by skin and kidney lesions. This syndrome can occur in both acute and chronic forms. Signs usually include skin lesions that start as red, blotchy areas. These red areas may spread in size and join up with each other. The red areas may then become scabbed over. Skin lesions usually affect the lower part of the body and the backs of the legs but can occur on other parts of the body, and signs can look similar to Classical Swine Fever or African Swine Fever.

PCV2 and Swine Respiratory Disease (SRD) – associated with respiratory disease and more specifically, Proliferative and Necrotizing Pneumonia (PNP). Signs of this disease include fever, difficult breathing, cough, unthriftiness and enlarged lymph nodes followed by death.

PCV2 Abortion and Reproductive Failure – associated with reproductive failure including increased abortions, stillbirths and mummified pigs as well as increased preweaning mortality. Neonatal mortality has been reported in Canada and Denmark.

These disorders can cause increased morbidity, mortality and treatment costs. In addition, average daily gain, feed efficiency and reproductive performance are also adversely affected. The disease can occur in the absence of other significant pathogens but PCVD is more severe in combination with other agents. The virus is spread horizontally from pig to pig via manure and body fluids. There is also some suspicion that subclinical vertical transmission from sow to piglets may lead to PMWS.

While PMWS is not a new disease, there has been a widespread epidemic since the mid-1990s. Symptoms include wasting, difficult breathing, unthriftiness, enlarged lymph nodes, paleness, jaundice, emaciation, diarrhea and death (up to 40%). PCV2 is endemic in most pig populations around the world, and a laboratory diagnosis is always required for confirmation. Initially, a tentative diagnosis is based on herd history and clinical signs.

Veterinary practitioners Dr. George Charbonneau and Dr. Steve Wolfgram of Swine Services in Ontario, Canada, put together a discussion paper on PCV2 with associates Ann Coyle, Jean Smith and Ken Marenger. We referred to this paper last week, which was formulated from a number of sources, and we again use this informative piece as our primary source. We will continue to follow this disease, as research is ongoing.

When it comes to identifying PCV2, a laboratory diagnosis is always required. Dr. John Kolb, Senior Manager Swine Biologicals for Boehringer Ingelheim says, “The key issue is to make an accurate diagnosis. Initially, a tentative diagnosis is based on herd history or clinical signs. Gross post mortems may show evidence of skin lesions, hepatitis, enteritis and interstitial pneumonia, among other signs. According to Swine Services’ discussion paper, typically the lungs fail to collapse when the chest is opened if the problem is PCV2.

When Porcine Dermatitis and Nephropathy Syndrome is involved, the kidneys are mottled in appearance and have multiple small red hemorrhages over the surface. In reproductive failure, massive infiltration of virus has been detected around the lesions of myocarditis in the heart of the fetus or stillborn pig. Of primary importance is the involvement of your veterinarian and a laboratory diagnosis for a definitive diagnosis. “Unfortunately, PCV2 has become the ‘new PRRS,’ in that it can get the blame for a lot of problems,” states Kolb. As a result, sometimes producers don’t make the management changes that are necessary because they are hard or unpleasant. Treatment, control and prevention should include a review of the following points:

  • Feed – Although no specific nutritional factors with respect to energy, protein, mineral or vitamins have been associated with the disease, it has been suggested that increased levels of Vitamin E and selenium may enhance immune system function. Vitamin C has also been suggested to be helpful. Review ration expectations by pig weight to ensure sufficient density for optimum immune function and lean gain potential. Also, make sure pigs have adequate access to feeders, so they don’t have to fight for food. Dr. Kolb suggests you reduce crude protein and use synthetic amino acids – this seems to help when liver and kidney function are reduced.

  • Water – Again, no specific nutritional factors with water have been associated with PCV2, but inadequate access to water will increase stress levels. Control excessive water contaminants, stray voltage, restricted water flow at the drinkers and make sure an adequate number of drinkers per pen are available.

  • Environment – Ventilation, temperature and stocking densities are all important for disease control. Try to minimize stress as much as possible Pen partitions should be designed to prevent nose-to-nose contact between pigs to reduce the PCV2 viral challenge. Cross-fostering and mixing – Cross-fostering of pigs after 24 hours of birth may help spread the virus, and this should be avoided whenever possible. If late fostering needs to be used, set up a nurse sow in a separate area specifically for this purpose. Try to keep mixing of pigs at a minimum. Mixing increases pig-to-pig contact and places pigs under stress. Both these factors appear to significantly increase the prevalence of the disease. Implement all in/all out production at all levels, and keep group sizes as small as possible.

  • Sanitation – Rooms should be washed thoroughly to remove all visible signs of manure from floors, walls, feeders and drinkers. Use products that remove fats, minerals and biofilm in order to allow the disinfectant to work. Clean rooms early in the downtime so they have a maximum amount of time to dry. This will greatly reduce the population of pathogens. Make sure the disinfectant selected is appropriate for the potential triggering diseases as well as PCV2.

  • Equipment disinfection – Implement strict hygiene measures on processing equipment and ensure good hygiene standards when processing pigs. Use new needles and sterilize instruments. It has been suggested that needles and instruments be dipped in a 2%solution of Virkon S for 60 seconds between pigs to kill the virus. Aerial disinfection may reduce the spread of the virus, though this hasn’t been proven. Whenever possible, allow pens to dry out before restocking. Leaving a room completely dry with or without supplemental heating is one of the most effective ways of killing viruses and bacteria.

  • Concurrent disease – Parasitic burdens in the breeding herd result in lower immunity, and this leaves the door open for a PCV2 infection. Cofactors or triggers that amplify the PCVD problem need to be controlled as well. PRRS virus, Swine Influenza virus and Mycoploasma hyopneumonia are examples of disease organisms that work synergistically with Porcine Circovirus.

  • Hospital Pen/Recovery Room – If pigs show signs of PCV2 infection, they should be promptly moved to the hospital pen. The longer sick pigs are left with healthy pigs, the greater the likelihood more pigs will become infected. On this same note, Dr. Kolb suggests you humanely euthanize pigs that have lost considerable weight. They will not recover due to significant organ damage, and they are shedding massive amounts of virus into the environment.

  • Medication – Antibiotics do not have a direct affect on PCV2, though they may help prevent bacterial infections that might precede or follow PCV2 disease.

  • Vaccination – The timing of vaccinations should be reviewed. While at the present time there is no vaccine for PCV2 in the United States, researchers are continuing to work on finding answers to this disease.

As with most treatment and control programs, good management is the key. While that might not keep your herd from becoming infected, it can at least minimize the economic impact of the disease. Most importantly, work with your veterinarian to develop a protocol for your herd. We will continue to report on new information surrounding PCV2 as it becomes available.

For more information, visit our PMWS Technical Zone

Source: JoAnn Alumbaugh - April 2006
Reproduced courtesy Farms.com