Practical Experience with Swine Fever and

Foot and Mouth Disease: Impact on Selection Programs

 

Jan W.M. Merks

 IPG, Institute for Pig Genetics B.V. (a TOPIGS company), The Netherlands

 

Introduction

The Netherlands is one of the fifteen member states of the European Union (EU), surrounded by Germany (east), Belgium (south) and the North Sea.  The EU policy with regard to list A infectious diseases in farm animals is non-vaccination. This enables countries within the EU to export their animals to countries like the United States or Japan, who allow only import of non-vaccinated farm animals. However, the risk of an outbreak is always there. The Netherlands was exposed to an outbreak of Classical Swine Fever (CSF, Hog Cholera) in 1997 and 1998, and to an outbreak of Foot and Mouth Disease (FMD) in 2001. The outbreaks had serious implications for agriculture, but also for other sectors e.g. tourism and nature parks. This paper describes how CSF and FMD were handled in the Netherlands, what measures were taken after the outbreaks, and what their impacts on the TOPIGS breeding program are.

The contents of this paper are based on information from the web site of the Ministry of Agriculture, Nature Management and  Fisheries in the Netherlands: www.minlnv.nl/mkz (for Foot and Mouth Disease) and www.minlnv.nl/varkenspest (for Classical Swine Fever), and the present situation in the Netherlands with regard to transport regulations for pigs.

 


Figure 1. The Netherlands within the European Union and Dissemination of Classical    Swine Fever in the Netherlands (1997 – 1998)

 

Classical Swine Fever Outbreak 1997 - 1998

Classical Swine Fever (CSF) is caused by an RNA-virus, infecting pigs only. Infection can take place through direct and indirect contact, and by means of swill. In case of acute infection, CSF pigs are feverish (42 o C), slow and have little appetite. The disease disseminates very quickly throughout the farm. In most cases it takes three weeks before most animals are infected. Some pigs, mainly piglets, will die. Chronic CSF is more difficult to detect as pigs do not develop a fever.

The outbreak in the Netherlands started with the first herd officially infected with CSF at February 4, 1997, and the last herd was officially reported on January 15, 1998. During this phase, a total of 429 herds were infected. The disease was probably ‘imported’ by a truck coming from Eastern Europe.

Start phase. The infection started in the province of Noord Brabant. This part of the Netherlands is one of the most densely pig-populated areas in the Netherlands. Although the disease spreads easily, infection was limited to an isolated area in the first phase and 91 herds were infected from February 4, 1997 to April 10, 1997). Unexpectedly, a major AI station got infected. All the boars were killed and the delivery of semen to 1,675 herds was hampered. The government took the following measurements: 1) in a circle of 3 km around an infected herd, all pigs were controlled regularly, and 2) in a circle of 10 km around an infected herd, no transport of any animals was allowed. This was called the ‘surgical’ approach.


Figure 2: Number of Infected and Depopulated Farms per Week (Source: Crisis Centre Swine Fever Automation Department)

Middle phase. In the second phase of the CSF outbreak (April 10, 1997 – September 9, 1997), the infection was apparent in several areas in the South, but still regional. There was a single outbreak in the North of the Netherlands, but the disease did not spread in this area. Three-hundred nine herds were infected in this period, and the capacity for destruction of the animals soon was not sufficient. The government tried to contain the infection by not allowing transport of pigs between all herds in the South of the Netherlands. Newborn piglets, young pigs and heavy slaughter pigs were killed to avoid welfare problems and large economic problems.

Final phase. In this phase, it was possible to restrict new infections to an isolated area. In the last phase of the outbreak, the number of herds infected decreased drastically. Twenty-nine herds were infected between September 10, 1997 and March 1998. The government took more severe measurements in the third phase of the outbreak. It continued its ‘containment’ strategy, including tests on carrier sows. The transport of pigs was limited within compartments (small regions), and all infected and evacuated pigs were killed at the farms.

When the CSF outbreak was over, in total 8,111,118 pigs were killed on infected farms, and herds were depopulated and blocked. One thousand two-hundred eighty-six herds were depopulated. The total costs of the CSF outbreak were a little more than 1 billion US dollars.

During several stages of the outbreak, the main carriers of the disease were different. An epidemical analysis of the infection routes shows that in the start phase >60 % of the infection was caused by the transport of pigs, especially live pigs before the first official case. In the middle phase, the neighbourhood was the main source of infection (>60 %). Farms within a circle of an infected farm were in severe danger, persons visiting farms (veterinarians and officers) and probably also birds and mice carried the disease from one farm to another. In the final phase, again transport was the main cause of spreading the disease: live and dead pigs had to be evacuated from ‘closed’ areas and live pigs on their way to the slaughterhouse. From the overall epidemical analysis it appeared that the main infection routes of CSF are from neighbouring herds, transport and persons (Figure 3).

 

Figure 3. Overview infection routes Classical Swine Fever (Source: Crisis Centre Swine Fever Epidemiology Department Uden)

 

Foot and Mouth Disease 2001

Foot and Mouth Disease is a very infectious and severe disease that can infect cloven-hoofedanimals: cattle, pigs, sheep, goat, but also wild swine, deer and a number of zoo animals. Humans are not infected. FMD infected animals are feverish and looking sick, have less appetite and show blisters on the tongue between skin and claw. About 5 % of the infected animals will die, but for young animals this is higher.

 


Figure 4. Foot and Mouth Disease in Europe and in the Netherlands (2001)

 

The FMD outbreak in 2001 in Europe started in the UK with the first official case was reported on February 20, 2001 in Essex (Figure 4). Immediately, the Netherlands stopped import for all animals from the UK, and depopulated 11 herds that had imported animals from the UK in the previous weeks. France followed the UK on March 12, 2001 with its first FMD case. The Netherlands stopped imports of animals from France as well and depopulated 3 herds that had animal imports from France in the previous weeks. Nevertheless, on March 178, 2001, the Netherlands had their first official case of FMD, later traced back to Irish calves that had contact in France with UK sheep. The Dutch government ordered a full transport stop for all animals, feed, milk and manure for 3 days. On March 21, 2001, the government started preventive vaccination in the contained area. This proved to be effective. In total, only 26 herds in the Netherlands were infected (only cattle/sheep herds). If compared to the CSF outbreak of 1997/1998, the disease was under control very quickly. However, a price had to be paid by all farmers and owners of cloven-hoofed animals in an area surrounding outbreaks. Their vaccinated animals had to be killed when the infection was over. In April and May 2001, 200,000 animals on 2,600 farms were killed from the centre to the outer circle. On May 23, 2001, two months after the first official case, all cloven-hoofed animals in the marked areas had been killed and destroyed at destruction plants.

 

Governmental measures taken after the 1997/1998 CSF outbreak

The impact of CSF and FMD on Dutch (pig) farms was huge – their world changed. Next to the fact that the Dutch government ordered that in the future, 25% fewer pigs would be produced, a number of rules with regard to transport and hygiene were worked out and implemented between 1998 and 2001 for pigs only. After the FMD outbreak a similar set of rules was and still are being worked out for the other farm animal species.

The regulation with regard to transport of pigs in the Netherlands is known as ‘Regeling Varkensleveringen’, effective since April 1, 2000. It replaces the (temporary) regulation that became effective during the CSF outbreak in 1997. ‘Regeling Varkensleveringen’ is a strict regulation of transport of pigs and hygienic protocol for pig farms in the Netherlands, distinguishing four categories of farms: A, B, C and D (Figure 5). Transport of pigs is only allowed with an official permit. Pigs must be transported directly from one farm to another or to the slaughterhouse (no pig collection is allowed).  All transport trucks must be cleaned and disinfected on the place of delivery.

 


Figure 5. Farm Categories according to ‘Regeling Varkensleveringen’ (April 2000)

 

The four categories are as follows:

-          A – farms are closed farms producing piglets. No new pigs may enter the farm, except for pigs from A – or C – farms, after a quarantine period. The following set of rules applies:

o        import of pigs with > 6 weeks interval,

o        hygiene protocol for farm and visitors (incl. shower for all visitors),

o        each 4 weeks testing (blood samples) for CSF and other diseases,

o        recording of all medical treatments and each 4 months external audit, and

o        address of supplier can be changed once / 12 months.

-          B – farms produce piglets. Only pigs (> 25 kg) from 1 A – or C – farm may enter a B – farm with > 6 weeks interval. The address of the supplier can be changed once per 12 months.

-          C – farms are farms importing pigs from 1 A – farm only. They have to obey the following set of rules (similar to A-farms):

o        import of pigs with > 6 weeks interval,

o        hygiene protocol for farm and visitors (incl. shower for all visitors),

o        each 4 weeks testing (blood samples) for CSF and other diseases,

o        recording of all medical treatments and each 4 months external audit, and

o        address of supplier can be changed once / 12 months.

-          All other pig farms are D – farms.

In general, NO transport of pigs from one farm to another farm is allowed, except:

-          A – farms can deliver to all farms without restrictions.

-          B – farms can deliver pigs of < 35 kg to

o        < 5 D – farms within a period of four weeks, and

o        < 13 D – farms within a period of 12 months.

-          C – farms can deliver pigs to

o        1 A – farm,

o        < 31 B – farms within 12 months, and

o        D – farms without restriction (> 80 kg).

-          D – farms can only transport pigs to the slaughterhouse.

 

Impact on TOPIGS selection program

The measures that have been taken after the CSF outbreak of 1997/1998 had implications on the structure of the breeding program, the exchange of genetics and hygiene measures. The genetic progress was not affected by the outbreak of CSF or FMD or by the ‘Regeling Varkensleveringen’. This was mainly due to the fact that 100 % AI was used in pure and crossbreeding since 1992. The structure of the breeding program had to be changed as soon as the measures had come into place:

-          Breeding herds had to become A – farms,

-          All pure breeding had to be organized within farms,

-          Relationships between breeders and customers for gilts (and boars) had to become fixed,

-          The sales of boars for natural mating was reduced to almost zero, and

-         Commercial producers changed from buying gilts towards breeding of own replacement gilts with use of AI (now about 30 – 40 % of sow replacement in the Netherlands).


Figure 6. Sales of boars per 4 weeks for South and North region

 

On the long term the TOPIGS breeding program is changing further:

-          The number of (closed) breeding herds will have to be reduced, especially in the boar lines,

-          In the future part of the pure breeding in the sow lines will take place on the commercial farms,

-          TOPIGS will further extend the satellite nucleus breeding system around the world, and

-          In the future the exchange of genetics between breeding herds will take place along semen and embryos.

 

Next to the changes in the structure of the breeding organisation, the focus of the organization and those working in it will change. There will be increased attention for hygienic protocol and the health of the boars that enter the AI units. Fast and accurate PCR tests on semen will be applied to check for CSF, FMD (since 2001), Aujeszky disease (Psuedorabies), PRRS and SVD in cases of disease risks. The results are available within 6 hours and are so accurate that they detect < 1 or2 virus parts per dose. Furthermore, the improvement and application of non-surgical embryo transfer (nsET) in order to transport genetics safely between farms will continue.

 

Conclusions

From the experiences with the CSF and FMD outbreaks in the Netherlands it is obvious that the transport of pigs and other animals is the main cause of spreading these diseases. The best way of eradication of both CSF and FMD in countries with a non-vaccination policy seems to be:

-          Immediate ban on all transports of all animals,

-          Containment of the infected area(s),

-          Vaccination of all (farm) animals susceptible to the disease in the closed / contained area(s) to stop further infection, and

-          Depopulation of the whole area.

 

Breeding and AI organisations should be aware that transmission of the FMD and CSF along semen is possible before AI boars are sick.

Breeding and AI can adapt their breeding structure such that their products are safe and disseminated safely, by:

 

-          Arranging closed breeding herds and fixed relationships between breeder and customer to limit the risks of disease transmission,

-          Further extension of the satellite nucleus breeding system to improve the health status and the risks of contamination, and

-          Giving the major role to semen and embryos to pass genetic progress to the commercial level around the world.

 

The CSF outbreak in 1997 / 1998 in the Netherlands provided an enormous experience to tackle FMD in 2001 fast and effectively. It also improved the health awareness and hygienic measurements in Dutch pig breeding programs enormously, which resulted in professional safe and high level pig genetics.

Acknowledgements

Dra. Hanneke Feitsma and ir. Anne-Marie Neeteson are acknowledged for their contributions to this paper.

 

2001 NSIF Proceedings