The Whole Herd Approach for effective PRRS Control

In pig dense areas, with high PRRS (porcine reproductive and respiratory syndrome) prevalence, whole herd protection against the devastating effects of PRRSV are the only sustainable way to control infection, transmission and the negative effects on production. PRRS infection causes poor reproductive performance in breeding herds, as well as respiratory disease, slower growth and increased mortality in growing pigs. PRRS affects all types of herd, irrespective of size or health status. It is widespread geographically in Asia, Europe and the Americas and it is considered to be the most economically important viral disease in the main pig production countries across the globe. Due to difficulties in eradicating PRRS from areas or countries, linked to biosecurity challenges and transmission of the virus within and between farms, successful control of PRRS requires a combination of strict management measures and vaccination of both sows and piglets, also characterized as Whole Herd Vaccination.

The basic elements of PRRS control

The Infection/Prevention Chain concept is a tool for disease management understanding, under a whole herd (systematic) approach, where we are putting together new and existing knowledge in swine diseases management, connecting epidemiological events (infection chain) alongside the herd/production system (production chain), using a logical chain thinking to create this new concept focused in disease prevention in a comprehensive way (prevention chain).

Persistence of infection, shedding patterns, vertical transmission, horizontal transmission and lateral infection should be considered as critical epidemiological pieces participating in the “infection chain” of swine pathogens throughout the complete production process (whole herd) resulting in the clear manifestation of clinical symptoms with the correspondent production and financial losses due to the increase of mortality, cull rate, treatments and lack of performance, also subclinical forms of the diseases. This “chain” starts with gilt development and introduction into the sow herd and ends in growth-finish populations or keeps going with gilt production. This “chain thinking” allows us having a more linked and comprehensive approach to understand the epidemiology and prevention of major infectious agents by matching “production chain” with “infection chain”, resulting in a “prevention chain” extremely focused in the entire production system and stages instead of just the sow or only the piglet.

Therefore, this approach can help to modify or re-adjust the intervention strategies (animal flow, management and prevention protocols), utilized for controlling or preventing the disease, considering the whole “infection chain” of the agent, allowing an appropriate “prevention chain” approach. The goal is to create a way of thinking where the understanding of the root of the problem is considered as the first step of this whole herd approach.

Develop solutions options, the 4th step in the systematic PRRS control approach

In order to develop solutions to control PRRS virus in a herd, there are 3 major requirements; Prevent infection, by prevention introduction of new virus through optimization of biosecurity and pig flow management. Maximise immunity, by establishing a solid immunity in the whole herd trough vaccination of both sows and piglets with a vaccine which is effective across a wide range of PRRS strains. Minimise exposure, by reducing circulation of herd’s PRRS virus (resident) using a PRRS control programme, tailored to the needs of the farm.

It is obvious that vaccines used for this purpose should have some basic features; PRRS vaccines should induce strong heterologous immunity, in order to deliver clinical protection and prevent infection and reduce virus shedding to block the chain of infection within a herd, without any residual pathogenicity. In other words; safe, stable and efficacious vaccines.

The new PRRS EU vaccines from Boehringer Ingelheim Animal health fit perfectly into this whole herd approach proposed for PRRSV control. PRRS MLV vaccines, are supposed to deliver both direct and indirect benefits. The most obvious direct benefit of PRRS vaccination is reduced; mortality, culled pigs, abortions, feed consumption rates and increased; farrowing rates, number of weaned pigs, and ADWG. Some indirect benefits connected to PRRS vaccination and control are reduction of risk of virus exposure, by reduction of wild-type virus load and genetic diversity.

Late 2015 BI-AH registered 2 new PRRS Modified Live Virus (MLV) vaccines, Ingelvac PRRSFLEX® EU for pigs, and ReproCyc® PRRSEU for sows, to fulfill the requirements mentioned above. Both vaccines are recommended for use in whole herd PRRS control programmes, where all animals in a herd are vaccinated. Sows vaccinated with the sow specific vaccine, ReproCyc® PRRS EU have significant shorter viremia and significantly lower numbers of viremic sows after exposure to PRRS virus, compared to unvaccinated controls. This resulted in a significant reduction of the negative reproductive disorders associated with PRRSV. Not only is the vaccine able to reduce the transplacental virus transmission after challenge, it also reduces the negative impact of PRRS virus infection (mortality, clinical signs and weight gain) during the first 20 days of life in piglets born from vaccinated sows. This vaccination approach allows for protection of the sows against PRRS related reproductive disorders and also to protect the offspring until they can be protected by the piglet vaccination for the rest of their life.

The piglet specific vaccine, Ingelvac PRRSFLEX® EU has been shown to reduce lung lesions, virus load in blood and lung tissues as well as negative effects of PRRS infection on daily weight gain. The vaccine is able to reduce the respiratory clinical signs related to PRRS.

Growing pigs represent the majority of infected animals. The number of young animals is more than 10 times as high as the number of breeding animals in a herd. Even though the piglet vaccination rate in Europe over the last year has more than doubled, one of the major contributions from the Ingelvac PRRSFLEX EU vaccination program, more than 80 % of the pig population in Europe are still without any kind of protection against PRRSV. Because of that, growing pigs represent the biggest threat to other herds/barns/animals. Vaccination is an important tool in the reduction of viremic load and shedding.

PH Rathkjen

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