The threat of African swine fever

The International Disease Monitoring team is an important group within Defra’s APHA. Its function is to keep an eye on exotic new and notifiable animal diseases around the world and make assessments of the risks that they pose to the UK’s livestock industries. It provides advice and recommendations to APHA and wider government on this subject as well as publishing information for the general public.

Intelligence data are gathered from a number of sources, including official reports to the OIE (World Organisation for Animal Health) and the European Union. EU Member States with exotic notifiable disease outbreaks make regular presentations to the Animal Health and Animal Welfare section of the Standing Committee on Plants, Animals, Food and Feed (SCoPAFF). This information is frequently reviewed by the International Disease Monitoring team. The team also uses unofficial sources, such as Pro-Med email alerts, local media reports and personal contacts, which provide the remainder of the information and help to give an accurate picture on the ground.

Monitoring the disease

In the case of African swine fever, the official reporting system provides the basis for regularly updated maps of the westward spread of disease across Europe from the Caucasus area over the past 11 years. The latest map is shown in Figure 1.

These maps show recent confirmed cases of disease in domestic pig herds and feral wild boar, which are also being proactively sampled and tested for African swine fever. Some EU countries pay hunters to shoot and submit wild boar carcasses, while others just rely on finding dead animals to test.

There are more wild boar carcasses submitted in EU Member States because there is an active surveillance programme in place. Some other countries outside of the EU have lower levels of surveillance, and case numbers are reduced as a result. This doesn’t mean that they are free of disease, just that it has not been detected and reported. It is important to bear this in mind when viewing the map in Figure 1.

As can be seen, there have been some long-distance jumps of disease, and in these cases, human involvement is suspected as the most likely transmission route. This may have been through indirect spread by vehicles or equipment or, more likely, by the inadvertent feeding (or scavenging) of infected meat products to wild boar.

The protocol following an outbreak in Great Britain

If an outbreak of disease was detected in Great Britain, pigs on the affected farm would be culled immediately and epidemiological investigations initiated. This situation is covered by the various country Exotic Disease Control Strategies, which state that movement restrictions are to be immediately imposed on suspect premises and if disease is confirmed, Protection and Surveillance Zones will be applied.

One of the first on-farm actions that would be undertaken is the blood sampling of a proportion of the different groups of pigs on the infected premises at slaughter. By looking at the levels of virus and antibodies present in the samples, a picture would emerge of the order in which the groups had been infected and approximately when the virus had entered the pig herd.

Armed with an estimate of when the disease is likely to have entered the herd, disease tracings time windows can be identified. Tracings would be initiated for both the potential source and spread of infection. In other words, we would want to find out where the virus had come from and where it might have gone to.

Tracings deal with many different potential pathways and this is especially important with African swine fever virus, as it can survive in the environment for several days. As a result, we would want to trace vehicles, equipment, manure, carcasses and people, as well as, most importantly, any live pigs that had left the infected premises during the spread tracing window.

In the case of source tracings, we would also be looking at movements of similar items (pigs, vehicles, equipment, visitors) onto the premises during the potential source tracing window. In addition, this would include a check for any feeding of or access to infected meat products, as well as usual sources of feed and bedding and an assessment of wildlife in the area. A final route to consider would be semen for artificial insemination purposes, as this too can contain the virus.

There are a number of ways in which vets and pig producers can assist APHA staff with their investigations; these are listed below.

Accurate, up-to-date records should be kept, including:

1. Movements of live animals on and off the premises (legal requirement)
2. Movements within the premises or pyramid
3. Movements of carcasses
4. Where and when manure or slurry has been spread
5. Movements of lorries (feed, bedding, livestock, deadstock, etc)
6. All visitors and their vehicles (delivery drivers, vets, fieldsmen, electricians, pest controllers, etc)
7. Records of feed and bedding suppliers
8. An updated staff list with contact details
9. Details of porcine semen deliveries or despatches

It is also helpful to look at farm premises with regard to biosecurity and consider the following questions:

• Do people and vehicles clean and disinfect both on and off the premises?
• Can wildlife access buildings? eg rodents, birds, larger mammals
• Can wildlife access grazing in outdoor units?
• Are there specific risk factors in the local area? eg municipal dumps, footpaths, picnic sites, laybys, Eastern European workers or visitors, local populations of feral wild boar
• Do staff have contact with pigs on other premises? Do they keep pigs of their own?
• Do deadstock collection vehicles enter the farm or collect from the boundary?
• Are incoming pigs quarantined before mixing with resident stock?
• Are pigs or semen imported?

Although many of these factors cannot be altered, the knowledge of their existence could help APHA staff in their investigations and will also alert pig producers to the fact that they face a greater risk of acquiring disease. This in turn may lead them to change their business model, if appropriate, to address these concerns.

The current 21-day standstill for pig movements should help curtail the rapid spread of disease between premises; however, it does not apply within registered pig pyramids. Therefore, it is important that disease signs are recognised early and suspicions reported to APHA rapidly. The prompt reporting of movements through the eAML2 electronic system (in England and Wales) and ScotEID (in Scotland) is another key disease control feature that should facilitate the tracings process.

A campaign to highlight the dangers of swill feeding has recently been launched. It is important to remind the public that any feeding of meat products, including the feeding of swill, kitchen scraps and catering waste to any pigs, including pet pigs, wild boar and feral pigs, is illegal.

It is important for everyone to work together when combatting notifiable disease incursions into the national pig herd in order to preserve our current high levels of pig health and welfare and our international trading status.

WEB RESOURCES

The International Disease Monitoring Team’s reports are available at: gov.uk/government/collections/animal-diseases-international-monitoring
A list of African swine fever signs and symptoms can be found at: gov.uk/guidance/african-swine-fever