Post weaning multisystem wasting syndrome (PMWS) was first diagnosed in Canada in 1991. It is caused Circovirus of Type 2 (PCV-2). France was the first European country that faced the problems associated with the infection. Nowadays scientists have showed that PCV causes significant economic losses worldwide. Let’s try and understand what Circovirus is, what the risks to pigs are and how we can protect our livestock from the infection.
What Circovirus is and what are its related factors?
Circovirus disease is an contagious disease of weaned piglets caused by Circovirus. It is featured by delay in growth and development, by skin and respiratory affections. Causative agent is small and it belongs to the family of Circoviridae according to the classification of the International Taxonomy Committee. The virus’ diameter is 17 nm and it contains single-strain circular DNA genome. They distinguish between nonpathogenic (PCV-1) and pathogenic Circovirus. The latter is extremely resistant to environmental changes and it multiplies in the immune system cells. The virus mainly concentrates in the spleen and lymph nodes in a pig organism.
Hardness of the course of the disease depends on the environment pigs live in. So when scientists tried to infect the pigs with PCV-2 deliberately under sterile conditions of the laboratory the disease didn’t occur. As it turned out later the reason was a lack of stress factor (drafts, excessive crowding of piglets in the nest, bad air, mixing pig of different pig groups etc.) and also absence of other associated infections that stimulate manifestation of diseases as follows: respiratory reproductive syndrome, parvoviral infection etc.
Under the conditions of industrial production of pigs animals occasionally experience stress. When pigs are transferred to growing unit they face some mutual misunderstandings that cause conflicts and start to fight and bite each other’s vulnerabilities. The microclimate plays an important role for growers. As a matter of fact when newly weaned piglets are moved to a room where the temperature is below 18 degrees they immediately feel cold and their organisms increase concentration of steroid hormones (e.g. cortisol) and their immune status changes. All these become a trigger for development of Circovirus infection. Besides it should be noted the disease affects not only weak but also quite healthy piglets.
The disease is common in many countries with developed pig production industry as it is evidenced by numerous serological surveys of livestock. Currently PCV-2 antibodies have been found in almost every pig farm and a share of seropositive animals may reach 100%.
Usually the infection is spread by ill animals or by latently infected pigs of different age groups by means of urine, feces, saliva, sperm, secretion of nose and eyes. But it takes place a vertical transmission (from a sow to a piglet) quite often too. Immunization of piglets by any adjuvants in early period of life can activate an infection process too.
After contamination the virus multiplies in a number of places and first of all in endothelial cells, epithelial cells, macrophages and lymphocytes. Scientists are still unable to determine which cells the early replication takes place in.
What symptoms can be a sign of the emergence of Circovirus infection in a herd?
What does one have to pay special focus when diagnosing pigs?
Why do they advise to conduct pathology study of pigs that died because of Circovirus infection?
What forms of treatment and prevention are the most common in pig production industry?
Answers on these and others questions will be found in a full version of the article in «Profitable pig production» magazine of № 2 (8), 2012.