The following material is taken from the GB Emerging Threats Quarterly Report. Vol 22: Q1, January to March 2018. The full report can be found on the Animal & Plant Health Agency (APHA) web pages:
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Total GB diagnostic submissions to APHA and SAC CVS from pigs in January to March 2018 were reduced by 7% compared to the average of the four previous years although higher than in Q1, 2016. There were regional differences in submission levels with those from England mainly affected by these reductions. As noted in the previous two quarters months, there were fewer non-carcase (postal) submissions to APHA in Q1, 2018 although this was partially compensated for by increased submissions of this type to SAC CVS.
No suspect incidents of porcine epidemic diarrhoea (PED) were reported since the one which tested PED PCR negative in January 2018. Diagnostic submissions from non-suspect cases of diarrhoea in pigs submitted to APHA continue to be routinely tested for PEDV on a weekly basis. None have been positive for PEDV in over 700 diagnostic submissions tested under AHDB Pork funding since June 2013.
The first report of African Swine Fever (ASF) in Hungary was made in April 2018 in wild boar. This is another significant development in the continued westward spread of ASF in eastern and central European Union Member States since first detected in the eastern EU in January 2014. This resulted in a further update on ASF in central and eastern Europe from the International Disease Monitoring team which is available on this link: https://www.gov.uk/government/publications/african-swine-fever-in-pigs-in-poland-lithuania-and-latvia
The continued westward spread of ASF emphasises the need to raise awareness amongst all pig keepers across Europe of the need to take stringent external biosecurity precautions to reduce the risk of introduction. These messages, and the importance of not feeding kitchen and catering waste have been highlighted in recent public communications; passing these on to UK pig farmers and keepers is vital: https://www.gov.uk/government/news/pig-keepers-warned-not-to-feed-kitchen-scraps-to-pigs-due-to-african-swine-fever-risk.
The main message to prevent introduction of ASF to UK pigs is to prevent feeding of pigs with pork or wild boar meat or products. Providing dedicated clothing and boots for workers and visitors, limiting visitors to a minimum, and preventing outside vehicles which may be contaminated from coming on to the farm, are all valuable additional procedures to reinforce. An ASF poster for pig keepers has been produced as part of this campaign. This can be downloaded from this link: http://apha.defra.gov.uk/documents/surveillance/diseases/african-swine-fever-poster.pdf.
Resistance to ivermectin was confirmed in the roundworm Oesophagostomum dentatumobtained from a pig farm in England. The initial investigation into suspected reduced ivermectin efficacy was undertaken by the veterinary practitioner in conjunction with APHA and was described in the Q1-2017 report (APHA 2017c). The results from the on-farm study led to a controlled efficacy trial being undertaken at the Moredun Research Institute in collaboration with APHA and AHDB Pork using worms from the farm on which the initial investigation took place. This trial confirmed the finding of the first reported case of resistance to ivermectin in adult O. dentatum worms in the UK. Factors that might have played a role in ivermectin resistance development include long-term use of ivermectin for parasite control in pigs on the farm and continued use of outdoor paddocks without land rotation for decades. Fortunately, FECR testing suggest that benzimidazole treatment remains effective. Wider testing is recommended to determine whether this detection is an isolated incident or is of wider significance.
Faecal egg count reduction (FECR) testing is a well-recognised preliminary test to assess suspected reduced anthelmintic efficacy. It has been used widely in sheep flocks in which anthelmintic resistance in parasitic intestinal worms is an increasing issue. FECR involves collecting faeces for worm egg counts just prior to treatment and again at a specified time interval after treatment (according to which anthelmintic is involved; 14 days for ivermectin), sampling the same sows on each occasion. The mean % reduction in egg counts after treatment is then calculated as a proxy measure of efficacy. There is no laboratory marker for ivermectin (a macrocyclic lactone) resistance and therefore confirmation of this finding depended on performing in vivo infections with worms from the farm in a controlled efficacy trial. A presentation was made to the Pig Veterinary Society at the May 2018 meeting by Michele Macrelli from APHA to raise awareness of the finding and the use of FECRT. The investigation is described in a summary report at this link: https://pork.ahdb.org.uk/health-welfare/health/emerging-diseases/
The diagnostic rate for PRRS in GB in the first quarter of 2018 was the highest recorded quarterly diagnostic rate (16.6%) with the previous highest being in Q4 2016 (12.7%) as shown in Figure 2. The seasonality pattern with a peak in diagnoses in winter months and dip in summer months is familiar. This data supports anecdotal reports from pig practitioners of continued clinical problems associated with PRRS. The rise may well reflect better survival and transmission of the virus in cooler, darker and less dry weather conditions, as well as colder wetter weather making effective cleaning and disinfection harder to achieve. Temperature fluctuations and ventilation issues that can occur over the winter months may also contribute to PRRS as for other respiratory diseases. The majority of diagnoses were made in submissions from pigs in England.
The increasing diversity over time of PRRS virus (PRRSV) strains detected in samples in which PRRS is diagnosed continues as reported previously (APHA, 2016). No PRRSV-2 has been detected to date in GB pigs and the PRRSV-1 strains sequenced to date from 2018 remain within GB clusters, suggesting no new incursions of "foreign" virus strains. When funding allows, APHA sequences PRRSV from diagnostic submissions on a batch basis for surveillance purposes to monitor PRRS strains associated with disease. Veterinarians may also request sequencing on a chargeable basis to assist with epidemiological investigations.
Surveillance findings related to PRRS have recently been provided in an interactive dashboard format.: https://public.tableau.com/profile/siu.apha#!/vizhome/Porcinereproductiveandrespiratorysyndrome/PRRS. Respiratory signs, wasting or found dead remain the main clinical signs reported for GB PRRS diagnoses. The three most common concurrent diagnoses with PRRS are streptococcal disease (mainly Streptococcus suis), pasteurellosis and salmonellosis, as illustrated in Figure 3 below, which is extracted from the PRRS dashboard. Although not one of the commonest concurrent diagnoses, gastric ulceration has been a significant feature of several 2018 PRRS outbreaks as described in the February and March 2018 APHA surveillance reports in the Veterinary Record (APHA, 2018a and 2018b).
In the first quarter of 2018, the trend in the diagnostic rate for swine influenza increased as illustrated in Figure 7. There is a less consistent seasonality pattern for swine influenza diagnoses through the GB surveillance network than for PRRS and swine influenza detected by testing outside the network, including through saliva (oral fluid) testing, is not captured in the GB surveillance data.
There were nine diagnoses of swine influenza in Q1-2018 and, for the first time since the November 2009 when pH1N1/09 was first detected in pigs in GB, no pH1N109 was detected in this quarter: this will be monitored in the coming months. Of the swine influenza A virus strains which were typed, H1N2 was predominant and it is worth noting that almost all H1N2 strains now identified in GB pigs are the reassortant H1N2 swine influenza A virus strain.
There have been four further diagnoses of swine dysentery in Q1 of 2018, all in South or North Yorkshire. With the submitting veterinary practitioner's permission, SAC CVS provided the Brachyspira hyodysenteriae isolates to APHA for tiamulin minimum inhibitory concentration (MIC) testing at no charge. None of the isolates tested to date from 2017 and 2018 have had an MIC above the clinical break point, and the tested isolates were thus considered sensitive to tiamulin.
AHDB Pork have been promoting awareness of the Significant Diseases Charter amongst producers and encouraging them to sign up and declare diseases such as swine dysentery, should they be diagnosed.
Eight outbreaks of pneumonia and pleurisy caused by Actinobacillus pleuropneumoniaewere diagnosed in different regions of England in the first quarter of 2018 compared to 14 during the whole of 2017, resulting in a small rise in the diagnostic rate for disease due to A. pleuropneumoniae in pig submissions to the GB surveillance network.
A letter in Nature describes a novel enteric coronavirus, distinct from PED and TGE, causing diarrhoea and high mortality in neonatal piglets in China in 2017 (Zhou and others, 2018). Evidence indicates the virus recently moved from horseshoe bats into pigs and the index case herd is in a region fairly close to where severe acute respiratory syndrome (SARS) emerged in humans from bats via an intermediate host
A publication from the US on survival of pathogens in shipped animal feed ingredients contains findings relevant to risk pathways for introduction to UK from Asia and elsewhere of a variety of viral pathogens affecting livestock (Dee and others, 2018). The work was undertaken in part in response to the report on the possible origin of PED in the US (USDA, 2015). That report comprehensively reviewed the potential risk pathways for PED introduction into the US which are relevant to other enteric coronaviruses and to the UK and included introduction through contamination of animal feed ingredients, feed supplements, their packaging, pet treats, or people. Contamination of reused feed ingredient bags (tote bags), transported out of China was identified as the most likely route by which PED could have been introduced to the US. Research described in the new publication demonstrated survival of several notifiable disease viruses or their proxys (e.g. PEDV, ASFV, Senecavirus A as proxy for FMDV) and non-notifiable viruses (e.g. PRRSV, PCV2) in conditions simulating their transport from China to USA. Awareness of this research is being raised by communications to veterinarians, the pig industry and feed companies including highlighting again the need to avoid reusing tote bags for transport of feed.
Brachyspira suanatina has previously only been described in pigs in Scandinavia in 2007. A publication from Germany (Rohde and others, 2018) with an accompanying editorial (Hampson, 2018) reports the first description of B. suanatina infection in pigs outside Scandinavia and confirms the ability of this Brachyspira species to cause severe swine dysentery.
The last two quarterly GB pig disease surveillance reports described publications about a novel porcine circovirus, porcine circovirus type 3 (PCV3) in samples from both healthy pigs and pigs with a variety of disease presentations from several countries including the US, China, Italy, Poland and the UK. Evidence suggests that PCV3 is widespread in pigs globally but until there has been more systematic evaluation of the virus in diseased and healthy pigs, and experimental infections, there is still uncertainty regarding how significant a role PCV3 plays in porcine disease. Two recent publications on PCV3 indicate that this virus, although newly discovered in pigs, has been in the pig population for a number of years. A retrospective study of sera submitted for diagnostic reasons confirm PCV-3 circulation at least since 1996 in the Spanish pig population with a low/moderate frequency and PCV-3 did not appear to be linked to any specific pathological condition or age group (Klaumann and others, 2018). Work by Saraiva and others (2018) suggests that its evolution is not a recent event and that PCV3 has likely been circulating in pig-producing countries for some time before its first detection. No experimental infections with PCV3 have yet been reported and no zoonotic concern is reported. Archived sample sets in GB pigs which are available for possible PCV3 testing, funding allowing, are being identified.
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