Piglet wasting disease

Present in most pig-producing countries today, piglet wasting disease (PWD) emerged in North America and Europe at the same time in 1996.
PWD affects piglets aged 7 to 15 weeks old. It presents as a fever and loss of appetite. These signs are accompanied by breathing difficulties and sometimes diarrhoea, the whole leading, in severe cases, to the animal wasting away (weight loss) and in certain cases dying. The triggering of severe forms of the disease varies considerably depending on holding and the animals within the same holding.
In sick animals, lesions are observed on different organs (lungs, liver, kidney, lymph nodes, etc.). Viral research conducted on injured organ tissue has revealed the presence of a widespread virus within pigs worldwide: type 2 circovirus (PCV 2).

All circoviruses are associated with diseases that affect the immune system by provoking a reduction in the number of lymphocytes (varieties of white blood cells playing a role in the immune response) in their hosts. Numerous animals may be infected without presenting any clinical signs, however.
While this virus is currently considered to be one of the major causes of PWD, its presence in a holding is not enough by itself to lead to the disease. Other environmental factors also contribute to the expression of PWD in holdings.
The impact of PWD has considerably reduced in France over recent years thanks to the implementation of measures mainly associated with farming techniques (improved hygiene conditions, fewer stressful situations for animals).

Circoviruses

Circoviruses have single-stranded circular DNA genomes and infect vertebrates. They present similarities with the viruses which infect plants (Geminivirus and Nanovirus).
Type 2 circovirus (PCV2) has been isolated in pigs and boars in Europe, North, South and Central America and Asia.
Porcine circoviruses have only been found in pigs, indicating major host specificity. Serological research carried out in exposed human populations and animals (cows, sheep, chickens, rabbits) have always given negative results. PCV2 inoculation tests on diverse cow and sheep breeds have shown that the viruses could infect these cells without viral particles being produced. The infection of different human and ape cell lines by PCV2 does not lead to the production of viral particles.
After more than ten years of research, only pigs, boars and birds have been identified as circovirus hosts to date. These viruses have never been found in humans.

Afssa's activities on piglet wasting disease

Research activities conducted by the Laboratory for studies and research on poultry, pig and fish farming (Afssa-Ploufragan).
The "pig welfare and epidemiology" unit studies the role of sow vaccination (parvovirus/Erysipelothrix rhusiopathiae) on the development of PWD in progeny, in controlled test conditions. It also studies the dynamics of PCV2 circulation in farms.
The "viral genetics and biosafety" unit conducts work on type 2 circovirus (PCV2)
· development of a method for quantifying the genome of the virus in real time
in vitro and in vivo characterisation of PCV2 in an infectious clone
· establishment of tests to identify the non-infectious cofactors which may promote infectious by circovirus (immunostimulation of piglets infected with PCV2)
· study of the role of PCV2 in PWD by a method using DNA microarrays

October 2007