Porcine Circovirus Causing Problems: Part 1

CANADA - 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.
calendar icon 27 March 2006
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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.

Next week, we will review treatment, control and prevention measures, as recommended by Swine Services as well as other veterinarians who have worked with cases of PCV2.

For more information, visit our PMWS Technical Zone

Source: JoAnn Alumbaugh - 27th April 2006

Reproduced courtesy Farms.com

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