The place: Prague, capital city of the Czech Republic. The occasion: the 2nd Boehringer Ingelheim European PRRSspective, attended by veterinary practitioners and researchers from across Europe to hear the latest information on controlling the porcine reproductive and respiratory syndrome (PRRS). The theme: 5 Steps to Success, with the day’s programme built around the 5 Step Process developed by Boehringer Ingelheim Animal Health to assist pig farmers and veterinarians in deciding and implementing a strategy to control PRRS in a pork production system.
Summarising the meeting in numbers, swine technical team leader Dr. Oliver Duran said it had comprised 10 hours of content and six excellent speakers as well as those 5 Steps and the 200 people attending. It had also been a valuable opportunity to learn and to exchange ideas about controlling PRRS, which remains probably the most important swine disease economically in the world today.
The programme presentations highlighted that PRRS control is likely to be challenging for years to come and there is still plenty of work to be done, said Dr. Duran, but they also gave real hope of success. New tools are offering a better understanding of the immunology behind PRRS, so valuable in formulating vaccines against it. Structured monitoring programmes allow the development of a good prevention-chain approach to control. Methods that have been shown to work in large production systems in the United States would also be applicable in swine herds in Europe.
A novel way of depicting the results of trials offers another advance by demonstrating how events happen with the passage of time. Genetic sequencing of viral samples is no longer just a theoretical tool for use by academics, with the right planning it can answer where a virus has come from and whether the herd is winning the battle to reduce the number of viral strains present by its operation of better biosecurity.
But one of the main messages from this European PRRSspective, according to Dr. Duran, was the cloud of variability that surrounds PRRS. The virus itself varies, but so too does the pigs’ response to it. The economic outcome of infection is equally variable. Understanding this variability and how to manage it in practice is the key to good control.
He had opened the meeting with remarks about Step 1 of the 5 Step Process, which is to set a goal for the strategy and then make sure that it is understood by everyone involved. Manage your expectations, he said, because a strong dose of reality is needed. The goal must be achievable as well as desirable --- although as your confidence grows with experience, you may become more ambitious in your objectives.
The first action in any control strategy for the breeding herd should be to stabilise its PRRS status. However, the focus in Europe has been way too much on protecting the sow when producers should be thinking in terms of a dedicated whole-herd solution. The prevalence of the virus is about the same in piglets as in sows, at 68% and 71% respectively. Yet current assessments of European vaccination rates are above 55% for sows against less than 20% for piglets.
But progress is being made in protecting piglets. An estimate made in August 2015 had said that there were 180 million unprotected piglets in Europe at that time. A new assessment in August 2016 indicated an improvement to a lower total of 167 million piglets that have not received protection through vaccination.
Professor Michael Murtaugh of the University of Minnesota, USA, insisted that the control of PRRS is indeed achievable. One practice that really works is the mass vaccination of the breeding herd followed by its closure to new pigs for at least 200 days so that the PRRSV status of its animals can stabilise.
Understand that the PRRSV from a pig is not a single virus but a collection of genetic variants, Professor Murtaugh commented. Its gene sequences change constantly. PRRS therefore is always a population of mutants, displaying genetic variation distributed across the whole genome.
Dr. Erin Lowe of Boehringer Ingelheim Vetmedica, USA, discussed the critical control points where sampling and diagnosis might be applied to inform about the PRRS situation in a production flow. The diagnostic tools used most frequently in the United States for this purpose are ELISA to understand exposure of a herd and PCR to check the shedding of the virus.
There are several possible check-points with the breeding-feeding enterprise for taking samples to determine the PRRS status before deciding on control options, said Dr. Lowe. The selection of which ones to use must be tailored to be appropriate to the individual farm and its circumstances. In making the choice, an important question to ask every time is what would be the cost of being wrong regarding the sampling undertaken and the conclusions reached from it.
In the United States, a nationally agreed form of classification of herd status based on diagnostics has supported the development of regional control projects and led to a voluntary US-wide study of the incidence of PRRS in which veterinary practitioners report on breeding herd statuses over time. Currently these weekly reports are being submitted for a total of 442 herds.
According to Dr. PH Rathkjen, senior global technical manager PRRS, the tools available for controlling the disease come in the three main categories of prevention, immunity and exposure. Prevention refers to biosecurity and pig flow management, both aimed at reducing the transmission of the PRRS virus within and between herds.
Dr. Rathkjen highlighted building design as a key point of better biosecurity. Even today, he said, new farms are being built that are not well designed for health control purposes. Equally it makes little sense to simply place incoming gilts in the middle of the sow farm. Unless good in-house quarantine facilities can be arranged for them it may be necessary to rent a barn nearby in order to keep them isolated. The length of time needed to acclimatise gilts properly is a further question --- Dr. Rathkjen’s advice was to aim for 12 weeks.
Maximising immunity brings the case for whole-herd vaccination to provide effective protection and ensure safe, predictable production. From the unpublished results of new studies, re-vaccinating gilts before their introduction to the herd may be worth considering to reduce the viral load as well as protecting them.
To visual an example of the results of vaccination over time, Dr. Rathkjen’s presentation employed a graph that moved to follow changes in the serum viral load and the animal’s clinical score, where pigs were either vaccinated or received no vaccine at two weeks old before being challenged with PRRSV four weeks later and tracked into growing-finishing. In reverse, the animation also could extrapolate lung lesions at day of slaughter back to events in the growing period.
See the face of your enemy, advised Dr. Ivan Hernandez Caravaca of Boehringer Ingelheim Spain. The genetic sequences identifying which variants of the virus are present on the farm can give multiple answers regarding PRRS. The sequencing process has real practical applications at farm level. One is to monitor isolates in a farm or geographic area. Another is to establish the herd’s current status, while a third possibility is to reveal the constraints that could potentially interfere with effective control.
Sequencing to track changes with time is useful also to keep an eye on biosecurity. In one example, finding the same sequence on two separate farms led to the discovery that the same manager visited both of them to do pregnancy testing of sows --- and used the same ultrasound scanner on both sites on the same day.
How often to sequence? Doing it just once per year may address whether something found is a new virus on the farm or an evolution of the resident virus. How to manage the data obtained? Dr. Hernandez referred to the Disease BioPortal internet concept developed originally to provide information on foot-and-mouth disease, but since extended to PRRS with the backing of a US$ 2 million investment by Boehringer Ingelheim. It depicts the real-time evolution of sequences on a farm, in an area and even worldwide.
Are the ways used in Europe for costing PRRS really correct? US swine economist Dr. Dennis diPietre of KnowledgeVentures Inc suggested that this was doubtful. Most probably, he commented, the economic impact of the disease on European pig herds has been under-estimated by being too low on cost effects and too high on expected sales.
He added, most estimates of costs are based on a performance difference measured between healthy and infected pigs, converted into economic impact per pig and multiplied by the number of pigs involved. But extrapolating individual results or averages to the whole herd is unlikely to be an accurate way of costing the disease in the case of PRRS, not least because of the presence of sub-populations affected to different degrees by the infection.
When a dataset from a real operation was made available to him, Dr. diPietre used it to calculate detailed costings in a model taking performance figures from herds in Northern Europe and pig prices from European Union records. This exercise concluded that while total costs in herds without PRRS over a period of three years worked out on average at 36.63 Euros per pig weaned, with the disease these costs increased to 42.14 Euros per pig. Both categories contained a wide and uneven distribution around the mean and this was true also for the calculation of net income, but the principle remained firm that when PRRS strikes it beings a fall in profitability and a greater expectation of operating at a loss.