(80% of the initial population size) the disease may fade out.” This, Prof Kolbasov concluded on the basis of the situation in Russia – where wild boar population densities are not as large as in Central and Eastern EU. He showed a slide showing a decreasing trend in both the wild boar density as well as the number of ASF cases in the Saratov region in Russia.


2. The PRRS situation in China is complex The complexity of the situation around Porcine Reproductive and Respiratory Syndrome (PRRS) in China, became very clear at the IPVS Congress. The event was held in conjunction with the 2018 International PRRS Symposium, which led to plenty of attention being paid to the PRRS problem in China. The congress’ president, Prof Yang Hanchun, gave a clear outline of the situation and explained what is happening. Globally, PRRS has been around for over 20 years now and the virus has proven to be complex, as strains continue to vary and evolve, meaning that control of the virus through vaccina- tion remains difficult. Especially in China, where biosecurity on farms can be quite low and where swine farm density on the other hand is high, the disease can spread quickly.


Prof Yang Hanchun, president of the Chongqing IPVS Congress.


Chinese attempts to control HP-PRRS One of the most remarkable elements of Prof Yang’s keynote speech was that he explained how local Chinese attempts to control highly pathogenic PRRS (HP-PRRS) had led to new vi- rus strains. The HP-PRRS was discovered in 2006 and ‘devas- tated the pig industry’, leading to ‘inestimable economic losses’, Prof Yang said, reminding his audience. Various (locally developed) modified live vaccines to target the HP-PRRS appeared in the Chinese market as from 2011, he described. He continued to say, “However, reproductive failures in sows, such as sporadic abortion, stillbirth and weak piglets, and respiratory diseases in growing pigs are very common on pig farms practising vaccination.” He noticed that there had been ‘massive, multiple vaccina- tions and unlimited use of the modified live vaccines’ – and that unlimited use of these locally produced vaccines some- times made things worse instead of better. He said, “Indeed, several emerged or isolated strains of PRRSv with enhanced virulence have been recognised to be likely revertants of one HP-PRRSv modified live vaccine.” He continued to say, “In recent years, almost real HP-PRRSv could not be monitored from clinical samples of pigs with PRRS manifestations; on the contrary, various PRRSv-like viruses and/or viruses evolved from HP-PRRSv modified live vaccines were detected or isolated easily, proposing that HP-PRRSv has been extinct almost in China at present.” Prof Yang also touched on various other problems related to PRRS in China. Most notably, he stated that since 2014, a new strain has surfaced, called ‘NADC30-like’ virus, suggesting that the strain may have entered from North America.


Recombinant PRRS virus All of this has also come together, Prof Yang said: “Our un- published data show that, of the four isolates from a single pig farm practicing HP-PRRSv modified live vaccines, one strain is a recombinant virus generated from the recombina- tion event between two HP-PRRSv modified live vaccine- evolved viruses, and another one is a recombinant virus be- tween two HP-PRRSv modified live vaccine-evolved viruses from one modified live vaccine, and another two strains are recombinant viruses from NADC30-like and a HP-PRRSv modified live vaccine-evolved virus.” He concluded, “Obviously, HP-PRRSv modified live vaccines also contribute to the recombination of PRRSv besides the entry of NADC30-like.” Prof Yang closed off giving various recommendations on how to structurally improve the PRRS situation.


3. Genetics offer promising health solutions A genetic approach may well hold the key to make pigs bet- ter prepared for disease challenges. At the congress, results were presented around both Porcine Reproductive and Respiratory Syndrome (PRRS) virus, as well as Actinobacillus


▶ PIG PROGRESS | Volume 34, No. 6, 2018 7


PHOTO: VINCENT TER BEEK


PHOTO: SHUTTERSTOCK


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