Circovirus type 2 is associated with the swine disease known as Postweaning Multisystemic Wasting Syndrome (PMWS). This disease causes serious health problems in piglets, and its clinical signs include physical deterioration, visible enlargement of the lymph nodes, difficulty breathing (dyspnea) and sometimes diarrhea, pale skin (anemia) and jaundice (more rare). As well as PMWS, circovirus type 2 is associated with a pulmonary disease, an enteritis, reproductive disorders, porcine dermatitis and nephropathy syndrome (PDNS), and a subclinical infection demonstrated by lower-than-average daily weight gain and minor or absent histological lesions. Other clinical symptoms, such as cough, fever, gastric ulceration, meningitis, and sudden death, have also been reported.

Though circovirus is present on all pig farms, not all farms are infected with PMWS. In all pork-producing countries, the PCV2 virus spares very few herds.

Circovirus type 2 can be detected in various secretions: nasal mucus, saliva, tracheal mucus, ocular secretions, and milk. It is also present in urine, feces, and semen. This suggests that PCV2 can be excreted by all of the body's excretion routes.

Many publications show that PCV2's most probable entry route into the body is oronasal, which means that horizontal transmission (between a sow and a piglet or between pigs in a same crate) is a frequent occurrence. 

It was initially shown that all animals on a farm contract the infection between the ages of two and four months. More recent studies show that piglets may be exposed very early on, at birth, or even in utero for some members of a litter. Together, these findings suggest that PCV2 is a highly contagious virus, even though the infection remains unapparent in most cases.

Studies have likewise shown that PCV2 is also transmissible intramuscularly, intraperitoneously or during inoculation in the liver or lymph nodes. In other words, inoculation against the disease during pig fights (bites, skin breakages, etc.) is also possible.

PCV2 has also been detected in fetuses and runts. It is often frequently associated with reproductive disorders, particularly in recently populated farms. The transplacental route may also be considered as a transmission route, even though, in practice, it has mainly led to episodes of abortion. Results from experimentation aimed at demonstrating this type of contamination are clear: PCV2 can be transmitted from a fetus to its neighbour in utero, but not to all fetuses in the same horn. However, it has not been clearly demonstrated that intra-uterine infection is associated with post-natal development of PMWS, for which transmission of maternal immunity is fundamental.^5,6,7

Because the virus is so widespread, confirming its presence in an animal does not constitute a diagnosis of PMWS. The following three criteria must be met:

1. Growth retardation and wasting, often accompanied by dyspnea, larger-than-normal lymph nodes and possibly jaundice;
2. Presence of characteristic histological lesions in the lymph tissues;
3. Moderate to high quantities of PCV2 in the lymph tissues and other affected tissues.

An infection is termed subclinical when the virus is present in the animal without it presenting clinical signs.

Once the animal shows signs of PMWS, there is little or no effective treatment.

From a clinical point of view, vaccination has made it possible to control PMWS by lowering mortality and reducing the number of infected animals on infected farms. It has improved weight gain and feed efficiency in infected farms subclinically.

Proper herd management and biosafety measures can likewise help reduce the disease's harmful effects. To this end, movement and access to visitors should be reduced to a minimum. Control measures against rodents, insects and birds should be implemented.

In addition, buildings should be disinfected and washed regularly before new groups of pigs are introduced.

Quarantine periods should be observed before introducing a new pig into a herd.

Ensure that the farm has a controlled environment (ventilation, temperature, humidity), so that pigs are as unstressed as possible.

And finally, take all measures necessary to control other pathogens on the farm.²

Your veterinarian is the best person to talk to for recommendations that are right for your farm. 

REFERENCES: 

¹ Bulletin Technique Zoetis, April 2014.

² Réseau d’alerte et d’information zoosanitaire, No. 36, 19 May 2005, MAPAQ.

³ Diseases of swine, 8th Edition, Chapter 8: Porcine Circovirus, P. D. Lukert and G. M. Allan.

⁴ Évolution clinique du syndrome de dépérissement post-sevrage- Expo-congrès du porc du Québec.

⁵ Cariolet, R., Blanchard, P., Le Dimna, M., Truong, C., Keranflec'h, A., Beaurepaire, B., Jolly, J. P., Julou, P., de Boisseson, C., Mahe, D., Madec, F., Jestin, A., 2002. A study of different routes of inoculation of porcine circovirus type 2 (PCV2) to specific pathogen free (SPF) sows. Journées Rech. Porcine, 34, 317-323.

⁶ Chae, C., 2005, A review of porcine circovirus 2-associated syndromes and diseases. Vet. J., 169, 326-336.

⁷ McIntosh, K.A., Harding, J.C., Parker, S., Ellis, J.A., Appleyard, G.D., 2006, Nested polymerase chain reaction detection and duration of porcine circovirus type 2 in semen with sperm morphological analysis from naturally infected boars. J. Vet. Diagn. Invest., 18, 380-384.

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