Classical swine fever in The Netherlands 1997-1998: a description of organisation and measures to eradicate the disease.

The central and regional organisation of the campaign to eradicate the CSF epidemic in The Netherlands in 1997/1998 is described. The main instruments used in the campaign were based on stamping-out and movement restrictions specified by the European Union. Additional instruments were used for the first time, namely, pre-emptive culling of contact and neighbouring farms, compartmentalisation of transport, monthly serological screening in established surveillance areas and supervised repopulation of all farms in the former surveillance zone. Two other measures, the killing of very young piglets and a breeding ban were introduced to reduce production in established surveillance zones. Several factors complicated the eradication campaign, for instance, the late detection of the first infection; artificial insemination as a source of infection; the organisation of pig farming in The Netherlands, with its highly concentrated production and dependence on the transport of stock from one unit to another; insufficient rendering capacity; decreasing sensitivity of clinical inspection; and extremely high costs.

The classical swine fever epidemic 1997-1998 in The Netherlands: descriptive epidemiology.

The objective of this paper is to describe the severe epidemic of classical swine fever (CSF) in The Netherlands in 1997-1998 under a policy of non-vaccination, intensive surveillance, pre-emptive slaughter and stamping out in an area which has one of the highest pig and herd densities in Europe. The primary outbreak was detected on 4 February 1997 on a mixed sow and finishing pig herd. A total of 429 outbreaks was observed during the epidemic, and approximately 700,000 pigs from these herds were slaughtered. Among these outbreaks were two artificial insemination centres, which resulted in a CSF-suspect declaration of 1680 pig herds (mainly located in the southern part of The Netherlands). The time between introduction of CSF virus (CSFV) into the country and diagnosis of CSF in the primary outbreak was estimated to be approximately 6 weeks. It is presumed that CSFV was spread from The Netherlands to Italy and Spain via shipment of infected piglets in the beginning of February 1997, before the establishment of a total stand-still of transportation. In June 1997, CSFV is presumed to be introduced into Belgium from The Netherlands. Pre-emptive slaughter of herds that had been in contact with infected herds or were located in close vicinity of infected herds, was carried out around the first two outbreaks. However, this policy was not further exercised till mid-April 1997, when pre-emptive slaughter became a standard operational procedure for the rest of the epidemic. In total, 1286 pig herds were pre-emptively slaughtered. (approximately 1.1 million pigs). A total of 44 outbreaks (10%) was detected via pre-emptive slaughter. When there were clinical signs, the observed symptoms in infected herds were mainly atypical: fever, apathy, ataxia or a combination of these signs. In 322 out of 429 outbreaks (75%), detection was bases on clinical signs observed: 32% was detected by the farmer, 25% by the veterinary practitioner, 10% of the outbreaks by tracing teams and 8% by screening teams of the veterinary authorities. In 76% of the outbreaks detected by clinical signs, the farmer reported to have seen clinical symptoms for less than 1 week before diagnosis, in 22% for 1-4 weeks before diagnosis, and in 4 herds (1%) the farmer reported to have seen clinical symptoms for more than 4 weeks before diagnosis. Transportation lorries played a major role in the transmission of CSFV before the primary outbreak was diagnosed. It is estimated that approximately 39 herds were already infected before the first measures of the eradication campaign came into force. After the first measures to stop the spread of CSFV had been implemented, the distribution of the most likely routes of transmission markedly changed. In most outbreaks, a neighbourhood infection was indicated. Basically, there were two reasons for this catastrophe. Firstly, there was the extent of the period between introduction of the virus in the region and detection of the first outbreak. As a result, CSFV had opportunities to spread from one herd to another during this period. Secondly, the measures initially taken did not prove sufficient in the swine- and herd-dense region involved.

The foot-and-mouth disease epidemic in The Netherlands in 2001.

An outbreak of foot-and-mouth disease (FMD) in Great Britain was reported on 21 February 2001, followed by an outbreak of FMD in The Netherlands a month later. This Dutch index outbreak occurred on a mixed, veal-calf/dairy-goat farm in Oene, in the central part of The Netherlands. The most-likely route of infection was the import of Irish veal-calves to this Dutch herd via an FMD-contaminated staging point in France. With hindsight, more herds seemed to be infected by the time the index outbreak was confirmed. The regular EU control measures were implemented, in combination with pre-emptive culling of herds within 1km of each outbreak. Nevertheless, more outbreaks of FMD occurred. Most of the virus infections on those farms were "neighborhood infections". Because the situation seemed out of control locally and the destruction capacity became insufficient, it was decided to implement an emergency vaccination strategy for all biungulates in a large area around Oene to stop further spread of the virus. All susceptible animals on approximately 1800 farms in this area were vaccinated. All farms subsequently were depopulated, starting from 2 weeks after vaccination. In total, 26 outbreaks were detected (the last outbreak on 22 April 2001). In total, approximately 260,000 animals were killed.

Foot-and-Mouth disease control using vaccination: the Dutch experience in 2001.

A first case of foot-and-mouth disease (FMD) was confirmed on a farm in Oene on 21 March 2001. The Dutch eradication strategy for the area which is densely populated with susceptible animals was immediately applied: stamping out the infected herd and pre-emptive culling of all susceptible animals on farms within a radius of 1 km around an infected farm. If the organisation was unable to cull infected herds within 24 hours after detection and the neighbouring farms within four days, emergency ring vaccination would be applied. By 26 March it was clear that capacity problems prevented the required rapid culling and therefore the decision to apply emergency vaccination was taken. On 28 March vaccination of all susceptible animals was started in 2 km zones around infected farms. In the area where the first outbreak occurred, by 1 April 11 farms were found to be infected. Tracing the links between these infections was difficult, the farms being at a greater distance than 4 km from each other and fear increased that the disease could not be contained in this area. It was therefore decided to vaccinate a larger area: "Vaccination area Noord Veluwe". Suppressive vaccination was chosen. This implied that all vaccinated animals should be killed and destroyed. Vaccination rapidly reduced the number of new infections. In total 26 farms became infected with FMD. The last affected farm was confirmed on 22 April 2001. The last vaccinated animal was culled on 25 May 2001. EU rules also gave the option of choosing protective vaccination. The consequence was that only vaccinated cattle could stay alive. The status 'FMD-free without vaccination' however would then be recovered 12 months after the last outbreak. This consequence was too damaging to the export interests of the country. The killing of healthy vaccinated animals became the predominant factor in the discussion of farmers, politicians and the general public. The need for adjustments in the FMD eradication strategy and in the OIE and EU rules concerning FMD was strongly expressed in the International FMD Conference held in Brussels in December 2001. Since then these rules have been changed and as a result of this a more animal-friendly eradication of FMD is now possible.

Lessons from the foot and mouth disease outbreak in The Netherlands in 2001.

The Netherlands had recently developed a new strategy for the eradication of foot and mouth disease (FMD). When FMD was confirmed in Great Britain and France, recent imports of susceptible animals from these countries were traced and preventive measures were taken. On 21 March 2001, FMD was confirmed in The Netherlands. The disease was introduced by calves which became infected at a staging post in Mayenne, France, where infected sheep from Great Britain were present. A total of 26 farms were infected. Emergency vaccination of all susceptible animals was applied. Suppressive vaccination was chosen, implying that all vaccinated animals had to be slaughtered. Ring vaccination of all susceptible animals within 2 km of an infected herd was the standard procedure. However, in the 'Noord Veluwe', vaccination had to be applied to a larger area. The last affected farm was confirmed on 22 April 2001. Emergency vaccination contained the FMD infection rapidly. The last vaccinated animal was slaughtered on 25 May 2001. Many farmers were not convinced that the killing of their healthy, vaccinated animals was justified and tried to prevent the culling, but without success. Politicians and the public at large are now strongly opposed to the large-scale slaughter of vaccinated animals should a future outbreak of FMD occur. The Office International des Epizooties (OIE: World organisation for animal health) should incorporate control of vaccinated animals with non-structural protein (NSP) tests in the chapter on FMD in the International Animal Health Code.

Tracing systems used during the epidemic of classical swine fever in the Netherlands, 1997-1998.

Any outbreak of an animal disease classified as a List A disease by the Office International des Epizooties, such as classical swine fever (CSF), has severe consequences for animal welfare, livestock production, exports of animals and animal products and the environment. Experience shows that early detection and response to a suspected disease outbreak will maximise the effectiveness of the emergency response actions and minimise the social, economic and environmental costs associated with the outbreak. The development and implementation of measures designed to minimise the risk of diseases entering a country or region has been the predominant animal health management strategy in most countries. However, even the strongest preventive management systems do not guarantee that outbreaks of animal diseases will not occur. Tracing, a procedure that begins with a known infected individual, herd or flock, and which traces all possible locational and interactive exposures in both directions, back towards the source and forward to contacts, is the backbone of disease emergency management. The authors provide an introduction to, and general overview of, tracking and tracing systems used during a recent epidemic of CSF in the Netherlands from 1997 to 1998.