Notifiable and exotic diseases threatening UK pigs

In response to the need to raise awareness and disseminate up-to-date information about current international disease threats to the UK pig herd, the Pig Veterinary Society hosted a meeting at Stoneleigh on October 14 to provide veterinary surgeons and allied industries with key information on the recognition of African and classical swine fevers, foot and mouth disease and porcine epidemic diarrhoea, and to provide information on the reporting of notifiable diseases. Here, vet Alex Thomsett of the George Veterinary Group summarises the meeting

Making The Call: Notifiable and Exotic diseases threatening UK pigs was a meeting that attracted speakers from the Animal and Plant Health Agency (APHA, formerly AHVLA), The Pirbright Institute, BPEX and the Friedrich Loefler Institute (the German national reference laboratory for both African and classical swine fevers). They comprehensively covered the clinical signs, diagnosis and transmission of these significant disease threats.

The speakers also went on to discuss prevention and control strategies, as well as what to do if an outbreak of notifiable disease is suspected. They finished with an update on the proximity of these notifiable and exotic diseases to the UK.

A notable point made was that incursion and spread of all of the diseases discussed could be prevented if there was strict and stringent application of, and adherence to, biosecurity measures at international, national and farm level.

African and classical swine fevers (ASF/CSF)
Although different at the microscopic level, these two diseases are virtually indistinguishable in their clinical presentation and laboratory testing is essential to make a diagnosis and differentiate them. The main clinical signs in infected pigs are summarised in Table 1.

Dr Sandra Blome from the Friedrich Loefler Institute said it was vital for pig producers to be vigilant to changes in disease patterns on their unit, for example, spikes in mortality, increased numbers of abortions, “shaking” piglets or any of the clinical signs noted in the table.

She highlighted that some of the clinical signs of the swine fevers were non-specific and could resemble diseases that are endemic in UK pigs, especially early in the course of a swine fever outbreak. These endemic diseases are summarised in Table 2.

It was important to understand the epidemiology and presentation of these diseases as this could help differentiate them from the swine fevers and assist in recognising when the clinical presentation could be swine fever, making it necessary to “make the call”.

Where there’s suspicion of swine fever or any other notifiable disease, it was essential that this was reported to the local APHA field office immediately.

One of the key take-home messages of the meeting was “if in doubt, make the call”, as the earlier a swine fever outbreak is detected, the better the chances of rapid control and elimination.

Another main message was the importance of biosecurity in preventing the entry of ASF/CSF to a country and onto pig farms. The “ham sandwich” theory as a source of swine fever virus, which was suspected to be how infection was introduced into East Anglia in 2000, has been reproduced experimentally and resulted in infection of a group of pigs that then spread infection to in-contact pigs.

This emphasises the need to prevent any pork products being taken into pig units to reduce the risk of disease introduction. It’s illegal to feed such products to pigs. There’s no cure for either CSF or ASF, no effective vaccine available for ASF, and CSF vaccination is not permitted in the UK.

Foot and mouth disease virus (FMDv)
Many will remember the dark days of 2001, the last major FMDv outbreak in the UK. This is a disease affecting not only pigs, but any cloven hooved animal (cattle, sheep and goats). Pigs are important in the cycle of this disease as, although they don’t become carriers, once infected they rapidly amplify and excrete the virus in large amounts increasing the ease of transmission to other livestock units.

Infected pigs have a high temperature, reduced appetite, may be reluctant to move and lie down suddenly due to painful foot lesions causing lameness. Mouth and snout lesions also occur, but are less obvious and heal faster than the foot lesions in pigs.

In the early stages, fluid blisters (vesicles) are visible as raised clear fluid-filled whitened

skin at the junction between the foot and the hoof. These blisters rupture leaving reddened erosions, and in serious cases the hooves can even be shed. Even though large numbers of pigs in a group become lame, mortality is only seen in young piglets.

Other vesicular diseases causing foot and mouth lesions can resemble the clinical signs of FMDv (Table 3). These are indistinguishable clinically, and should be reported as suspect FMDV with laboratory testing determining which disease is present.

Pigs can become infected with FMDV by contact with infected animals, airborne spread from a neighbouring infected holding, or by contact with infected items such as farm equipment (including lorries), food (including pork and pork products), clothing and footwear. In fact, anything that’s come into contact with infected animals can transmit disease. Once again strict biosecurity was highlighted as essential in preventing entry of FMDV to a pig unit.

Like ASF/CSF no treatment is available, and again vaccination is not permitted in the UK.

Porcine epidemic diarrhoea virus (PEDv)
Derek Armstrong – now at DairyCo, but still with strong links to BPEX – reminded the audience that PEDv wasn’t a notifiable disease, didn’t raise food safety concerns, didn’t affect humans or other animals and wasn’t a new disease to the UK. However, the form of the disease that has been rife in the US since April 2013 is much more severe than that seen in the UK in the past.

It causes high mortality (up to 100%) in young piglets and spreads very easily. Since its identification in the US, PEDv had been responsible for the death of millions of piglets, causing a large gap in the production of affected units, and resulting in significant economic losses.

This “new” virulent form of PED had now been reported in the US, Canada, Asia and South America. It was yet to be reported in Europe or the UK, but this wasn’t a reason for complacency.

The typical clinical signs of PED are summarised in Table 4. They resemble those of transmissible gastroenteritis (TGE) and a diagnosis can only be achieved by laboratory testing of faeces or intestinal contents from affected pigs.

Infection is acquired by eating infected faeces, therefore any method by which pigs are exposed to contaminated faecal material will result in disease. PED is extremely easy to spread and pigs can be infected by ingesting only a tiny amount of infectious material. So far, the original route of entry of the virus into the US has not been established, emphasising the need to ensure that biosecurity protocols on all UK pig units are reviewed and strengthened to cover all possible means of entry.

The powerful and alarming presentations given by Derek Armstrong and BPEX’s Martin Smith reinforced the need to keep this disease out of the UK. If it did enter UK pigs, preventing its onward spread would be very difficult, although Canada’s co-ordinated government and industry efforts in improving biosecurity across the whole industry chain have significantly limited the number of units that have been infected.

International monitoring
Andrew Gresham of the APHA explained how the UK authorities continually monitor new and on-going notifiable disease outbreaks across the world (this information is published at: https://www.gov.uk/government/collections/animal-diseases-international-monitoring).

The mapping and assessment of these outbreaks informs us which regions are posing new or changing disease threats, enabling preventative measures to be put in place or strengthened as necessary (see Table 5).

The challenge was then thrown open to the audience to take on their responsibility in the front line of protection of the UK from the next notifiable or exotic disease outbreak. Understanding the main risks of disease introduction, identifying weaknesses in biosecurity and encouraging these to be rectified where possible, and recognising and reporting outbreaks early are activities in which veterinary surgeons attending pigs play a key role.

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