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Surveillance Focus
Small-scale pig producers and disease surveillance: key threats
  1. Susanna Williamson,
  2. Cornelia Bidewell,
  3. Livio Pittalis,
  4. Camilla Brena,
  5. Moyna Richey,
  6. Laura Florea,
  7. Alan Wight,
  8. Laura Wilson and
  9. Benedetta Amato
  1. Animal and Plant Health Agency
  2. University of Surrey

Abstract

A series of meetings for small-scale pig producers raised awareness of surveillance for pig diseases in Great Britain and highlighted different types of disease threat. This focus article summarises some key messages from those meetings and two of the threats discussed.

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In October 2019, AHDB Pork, the pig industry levy board, held five meetings for small-scale pig producers in different regions of England. Led by APHA veterinarians, and supported by the British Pig Association, the meetings focussed on how government surveillance for pig disease is undertaken in Great Britain (GB), illustrated by examples of different types of disease threat.

Scanning surveillance for pig diseases in Great Britain

Government funds scanning surveillance (also known as early warning, or passive surveillance) for each of the main livestock species and wildlife in GB. A key reason for this funding is to enable prompt detection and characterisation of new and (re)emerging disease threats, particularly those which could adversely affect animal health and welfare, trade and public health.

Different types of potential disease threats and examples for pigs are shown in Table 1. Factors that affect the likelihood of these threats occurring are also monitored, for example, changes in the countries of origin of imported live pigs or changes in farming practices.

Table 1: Types of threats – pig disease*

Information about scanning surveillance for pigs is available through the following APHA webpages:

Diagnostic submissions to the APHA and its partner postmortem providers in England and Wales, and Scotland’s Rural College in Scotland, especially pigs for postmortem examination, are particularly encouraged where disease is severe, unusual, or unresponsive and where unexpected deaths of previously healthy pigs occur.

Veterinary advice

Good pig health planning and veterinary advice help prevent disease and avoid adverse situations affecting pig health and welfare

When they have concerns about their pigs’ health, pig keepers need to contact their veterinarian promptly. The importance of establishing a relationship with a veterinary practice in advance of any disease concern was emphasised to the small-scale pig keepers. Good pig health planning and veterinary advice (vaccination, worm control, hygiene, suitable diet, constant fresh water supply, etc) help prevent disease and avoid adverse situations affecting pig health and welfare.

Discussion with the veterinary practitioner also allows customised advice to reduce the risk of disease introduction by improving biosecurity measures and sourcing pigs and semen safely. Keeping visitors to a minimum; providing outer clothing and waterproof footwear dedicated to the unit for people contacting the pigs; and preventing pigs having access to kitchen waste or other sources of meat or meat products, are among priority biosecurity measures for all pig keepers to implement.

A guide for pig keepers has been published recently and contains links to other useful sources of information; it can be downloaded from https://ahdb.org.uk/knowledge-library/new-pig-keepers-guide

The requirement to register holdings and pigs and keep this up to date applies to all pig keepers including small-scale herds and pigs kept as pets (see www.gov.uk/guidance/pig-keepers-register-your-holding-and-animals).

Examples of pig disease threats

Exotic notifiable disease: African swine fever

African swine fever (ASF) is a notifiable contagious haemorrhagic virus disease of suids only and is currently of major concern to the pig industry.

ASF entered eastern EU member states in 2014 and has spread principally in wild boar with spillover into domestic pigs. Since entering China in August 2018, it has spread widely and into neighbouring countries in south-east Asia.

An important feature of the virus is that it is present at very high titres in dying pigs and wild boar and is relatively stable, especially at low temperatures and in protein-rich conditions. Thus the virus persists for months in infected pork/wild boar meat or meat products even when cured, smoked, salted or dried and likely for years when frozen. Importing and then feeding such products to pigs or wild boar (which is illegal in the UK) is the most likely route for introduction of ASF to the UK. A Defra border campaign is ongoing to prevent travellers bringing meat or related products into the UK from affected countries.

It is vital that pig keepers take responsibility for ensuring that nothing enters their premises which risks introducing ASF virus in infected food products or on contaminated items, such as footwear, clothing, vehicles or equipment. ASF and biosecurity advice posters for pig keepers are available at https://ahdb.org.uk/african-swine-fever-resources-and-posters

It is also vital that vets attending pigs are familiar with the clinical signs and pathology of ASF which are summarised in Box 1. Further ASF images are available at http://apha.defra.gov.uk/documents/surveillance/diseases/african-swine-fever-images.pdf

Box 1:

African swine fever – summary of clinical signs and pathology

Clinical signs

The African swine fever virus circulating in Asia and Europe is highly virulent and disease is likely to be peracute/acute and cause mortality in all ages of pig and wild boar. Non-specific signs include:

  • Pyrexia (can be >41°C), dullness and loss of appetite

  • Red-purple skin discolouration and, sometimes, haemorrhages

  • Huddling and reluctance to move

  • Death.

The following signs are variable and not all will be present in every pig or in all groups of pigs:

  • Diarrhoea/dysentery

  • Ataxia, incoordination

  • Oculonasal discharges, sometimes epistaxis

  • Dyspnoea and coughing

  • Abortion in breeding herds.

Pigs huddling together six days after infection with virulent African swine fever virus: they have very high temperatures (>41°C), are clearly sick and lethargic and have lost their appetite, either not eating or picking at food. One pig on the left shows reddening of the pinnae of the ears

Images courtesy of The Pirbright Institute

Pathology

Lesions are variable and not all will be present in every pig or in all groups of pigs:

  • Haemorrhages – skin, lymph nodes, kidney (cortex – strip off capsule, ‘turkey egg’ kidney), bladder, larynx, heart, lung, liver, serosal and mucosal surfaces

  • Enlarged, reddened (may be almost black) lymph nodes

  • Spleen enlarged, dark and more friable

  • Blood-stained effusions in pericardium, abdomen and thorax.

Kidney: marked multiple haemorrhages over the cortex. Haemorrhages may be more subtle than this. The kidney capsule must be stripped off to look for these
Enlarged haemorrhagic hepatogastric lymph node: multiple lymph nodes are similarly lesioned and they can be almost black in colour

Pyrexia is a non-specific but consistent finding in ASF and assessing rectal temperatures when examining sick pigs is important.

Spread of ASF by pig-to-pig contact can be slower than some other diseases

Spread of ASF by pig-to-pig contact following introduction can be slower than some other diseases and when infection is first introduced into a herd, just one or two pigs in a group may show clinical signs and death. Spread across a wider group may take one to two weeks, after which increasing mortality is seen.

This slower spread is associated with minimal transmission by aerosol, the fact that virus shedding only starts shortly before clinical signs appear, and relatively low amounts of virus in excretions and secretions from pigs in the early stages of infection (although there are very high amounts of virus in blood and tissues of dying pigs).

In small herds, illness and rapid death in one or more previously healthy pigs should prompt the owner to seek veterinary attention. If clinical signs and/or postmortem findings are suggestive of swine fever, this must be reported immediately to the APHA (see ‘Contacting the APHA, p 18). A statutory veterinary investigation then takes place to rule out or confirm the suspected disease.

Change in endemic disease trend: rise in swine dysentery diagnoses

Since 2017 there has been an upward trend in the diagnostic rate for swine dysentery

This threat example illustrates a change detected in a disease already present in GB pigs. Since 2017 there has been an upward trend in the diagnostic rate for swine dysentery (SD) with outbreaks confirmed in small-scale and commercial pig herds in different regions across GB. These show that biosecurity weaknesses exist which need to be addressed. The main features of SD are described in Box 2.

Box 2:

Main features of swine dysentery caused by brachyspira hyodysenteriae

  • Diarrhoea, often but not always with blood and mucus

  • Poor growth or wasting which may go unnoticed in slow-growing or non-commercial pigs

  • Large intestinal pathology with colitis

  • Severity affected by age, immunity, diet, stress, strain of Brachyspira hyodysenteriae

  • Swine dysentery is a priority for pig industry control as infected commercial herds are not profitable

  • Transmission is faeco-oral from infected pigs or anything contaminated with infected faeces

  • Prompt diagnosis is important using PCR and culture

  • Culture is slower, but is essential to obtain isolates for:

    • antimicrobial resistance testing

    • whole genome sequencing and typing

    • identifying novel Brachyspira species

Information and advice on diagnosis are available at:

Whole genome sequencing and antimicrobial susceptibility testing of Brachyspira hyodysenteriae is currently performed under pig disease surveillance funding at no charge and reported to the keeper’s veterinary practice. These assist disease control and help confirm or identify potentially linked outbreaks.

At least eight distinct multilocus sequence type (MLST) groups have been identified from incidents from 2017 to 2019, thus the increase in diagnoses is not due to a single spreading strain of B hyodysenteriae. One of these groups (MLST ST52) is often involved in cases diagnosed in small herds suggesting possible connections.

The development of resistance in B hyodysenteriae to antimicrobials commonly used in the control of SD is a recognised risk, particularly in situations where medication is used long term. Control of SD using additional/alternative interventions (eg, all-in, all-out management systems; cleaning and disinfection; and partial and total depopulation leading to eradication) must aim to minimise, or better eliminate, the need for antimicrobial treatment.

‘Living with’ SD is not desirable as such herds remain a source of infection.

It is also important that anyone importing live pigs, even in small numbers, takes steps to ensure that they are not infected with B hyodysenteriae. There is advice in the National Pig Association import protocol aiming to prevent importation of exotic pathogens, or new pathogen strains, to the UK in live pigs (www.pigvetsoc.org.uk/files/document/1250/2019%20NPA%20Import%20Protocol.pdf).

The pig industry has several initiatives to tackle the rise in SD cases and these are just as relevant to small herds as they are to commercial ones. These include the #MuckFreeTruck campaign (https://twitter.com/hashtag/muckfreetruck?src=hash) to improve lorry cleaning and disinfection, and the Significant Diseases Charter (https://pork.ahdb.org.uk/health-welfare/health/significant-diseases-charter/).

The Charter is open to all pig keepers and, in the event of an outbreak, has an important role in sharing information quickly among those who participate, thus helping to limit spread of infection and assist disease control. The Charter covers SD and porcine epidemic diarrhoea at present.

The small-scale pig evening meetings provided an excellent opportunity to raise awareness about SD and the British Pig Association is in discussion with the Pig Veterinary Society, AHDB Pork and others to create guidance for small-scale herds.

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