Progress in eradication and control programmes against Aujeszky's disease (pseudorabies) in France

Abstract - Since July 1990, a national programme to eradicate Aujeszky's disease (AD) has been imposed in all regions of France, mainly with official funding. The Ministry of Agriculture and regional pig producer organisations have based their national programme on a strict identification of pigs, a precise census of pig herds and pigs, on the control of animal movement, on the establishment of financial compensation, and on the appropriate rules adapted to the epidemiological situation. Different eradication strategies have been adopted according to the different regions of France. In the major part of the territory, a programme based on strict sanitary measures has been implemented. In these regions, vaccination is forbidden (except derogation) and a certain percentage of the breeding animals in each herd is serologically examined every year. If infected pigs are detected, an official committee decides, on a case-by-case basis, which of the three courses of action to take: (1) total slaughter, (2) partial slaughter, or (3) a special vaccination programme, with backup serological examinations of fattening pigs and breeders performed by veterinary services long enough to ensure that the herd does not pose an epidemiological risk to the neighbourhood. In these cases, serial measures are also carried out associated with vaccination to progressively clean up these infected herds: improvement of hygienic conditions, all-in/all-out policy in certain parts of the herd... In three main regions: Brittany, Nord-Pas de Calais, Corsica, with higher prevalence of AD infection and/or higher density of pig herds, a compulsory vaccination of breeding and fattening pigs has been decided. In some cases, fattening pigs from farrow-to-finish herds can remain unvaccinated under the condition that they be submitted to a systematic serological screening, four times per year. Since 1983, in the whole territory only breeders coming from free nucleus herds can be commercialised. Progressively, the same measures are being applied to piglets, as the farrowing herds are systematically submitted to serological screening. In regions with strict sanitary measures, as a result of measures implemented, fifty-five departments have been recognised as officially free of AD by a European decision; in these departments, vaccination is not used at all and if an outbreak occurs, the herd is totally slaughtered. In the regions of the Pays de Loire (except Loire Atlantique and Mayenne), Poitou-Charentes, Aquitaine and Midi-Pyrénées, herd prevalence has remained null from 1995 to 1997 and up to now (even if the results of the campaigns are known, the data from 1997 to now are not yet official). In the regions in which medical measures have been implemented, the results are variable according to the regions. In the Nord-Pas-de-Calais, the herd prevalences of Aujeszky's disease in 1995, 1996 and 1997 were 8%, 14% and 13%, respectively. But, test and removal started during 1996, which could explain an increase of prevalence for 1996. In Brittany, considerable progress has been made during these 3 years as the herd prevalence was 25% in 1995, 12% in 1996 and 7% in 1997 (official data not yet available for 1997). A programme of prophylaxis against AD can be successful if a set of measures is carried out. This was the case in France and it clearly appears the only efficient way. Indeed, a control or eradication programme cannot be based only on one type of measure such as slaughter or vaccination. Therefore, in France, we are convinced that the success of measures depends on a programme based both on general and specific measures. After 7 to 16 years of implementation of the measures described, experience based on failures and successes can be given. Sanitary measures have always successfully controlled AD in France and, at midterm, the cost of these measures was relatively low. Even if the level of prevalence is different for regions within the same country, it remains possible to obtain an officially free status in some of them. It is much more difficult to obtain eradication or control of the disease when medical measures are applied. But, it has to be said that, in the regions with medical prophylaxy, the initial level of herd prevalence of AD infection was higher with a high density pig population. Such conditions create a situation which is difficult to manage.