Background and history

Although the virus which causes swine vesicular disease (SVD) virus is different from that causing foot-and-mouth disease (FMD) it produces a disease in pigs that is clinically indistinguishable from FMD. So if you are concerned about SVD in your pigs read also the FMD section.

Importance of SVD

Although clinically SVD is similar to FMD it causes little impact on productivity. Often it can be so mild that the pigs do not appear lame particularly if they are on straw bedding. What is more, it is strictly a disease of pigs and does not infect cattle, goats, sheep or other species. Why then is it regarded as so important that governments, such as those in the EU, bring in costly slaughter and eradication policies? It is for the very reason first stated, namely, that it is clinically indistinguishable from FMD. They are afraid that if SVD became widespread in the pig populations of FMD free and fringe areas that pig farmers and pig veterinarians may become accustomed to seeing vesicles on pigs noses and feet and not report them or even consider FMD.

One could argue that an expensive slaughter policy is unnecessary, that SVD could be made notifiable (i.e. any pigs with vesicles would have to be reported to the authorities) and that accurate rapid tests (e.g. ELISAs and PCRs) could be available in all diagnostic laboratories, but such an argument would be academic. The fact is that most governments in free and fringe areas would adopt a slaughter and eradication policy if there were a risk of contamination. If you farm in such an area you have to live with such a policy.

Clinical signs

SVD does not infect or affect cattle, sheep, goats or any species other than the pigs. So, unlike FMD, if you keep other livestock they will not be affected.

Clinical signs of SVD are much the same as FMD so read that section.

If there is no slaughter policy and pigs are not killed some may lose the claws off some of their toes. SVD does not usually cause abortion and boars are not sufficiently lame to stop serving sows. Mortality among all age groups is low.

The pigs recover completely in 2-3 weeks but you may see bruises under the claws which gradually move down under the horn as it grows (about 2mm per week).

In fringe areas (e.g. in the EU) it is a serious problem because the herd will almost certainly be compulsorily slaughtered and although compensation is likely to be paid, the farm cannot be restocked for at least three months. This is twice as long as for FMD because the SVD virus is much tougher and survives longer. Furthermore, after that time small numbers of susceptible pigs may have to be introduced onto the farm to act as sentinels. If there is still residual virus in the premises these sentinels are likely to come down with disease and the farm will have to be emptied and disinfected again.

The pig farm is a long time out of production even if the sentinels do not develop disease but if they do it is even longer with all the financial hardship that this will cause. So-called recrudescences on farms which had been slaughtered out, disinfected and later restocked, were a major problem in the early days of the SVD eradication programmes in Europe.

Diagnosis

This is the same as for suspected FMD. Read the FMD section. SVD cannot be distinguished from FMD on clinical grounds so to confirm the presumptive diagnosis, samples have to be sent without delay to an appropriate laboratory.

Treatment and prevention

• Vaccination - There is only one main serotype of SVD and theoretically it should be possible to produce an effective vaccine but in endemic areas the disease is too mild to warrant it. Vaccination is not allowed in fringe areas because it might mask the disease and go undiagnosed.

Other precautions

• Countries in free and fringe areas apply strictly-enforced national preventative measures against the introduction of SVD. The main features of these measures are control over the importation of pigs and of pig meat products from counties in which SVD occurs. Pig meat products are particularly dangerous because, unlike the FMD virus, SVD virus is tough and survives rigor mortis. If infected pig meat gets into the food chain there is a risk of uncooked waste being eaten by pigs which could trigger off an outbreak. To prevent this many countries have brought in cooked waste feed policies which forbid the feeding of animal products to pigs unless they have been processed through a licensed processing plant.
• If the disease does enter a free or fringe area, a slaughter policy is implemented similar to that described for FMD. All diseased and in-contact pigs are slaughtered. A standstill on animal movement is usually imposed and tracings are carried out to check possible spread of the disease through previous contacts.
• If you farm in the EU which is an SVD-risk region you should keep in mind the possibility (small though it may be) of contamination of your herd and you should take simple appropriate precautions.
• The greatest risk is from contaminated pig lorries returning from Italy where the disease is still present. The virus survives well in lorries and pigs can become infected by mouth or via skin abrasions. The lorry collecting your pigs for slaughter is the obvious danger.
• You should not feed pig meat products.
• Windborne spread does not occur in SVD so the simple precautions outlined later in this chapter should be effective.