Can be verified with laboratory methods if the purchased piglets were vaccinated against PRRSV?

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Can be verified with laboratory methods if the purchased piglets were vaccinated against PRRSV?


Answered by: Tomasz Stadejek   I   Published on: August 23, 2017

An outsourced fattening farm receives piglets claimed to be vaccinated with a MLV PRRSV vaccine. Several weeks after arrival pigs start to exhibit respiratory symptoms compatible with PRRS. Can be verified with laboratory methods if the purchased piglets were vaccinated against PRRSV? Does it make sense to vaccinate them upon arrival?

Serological response of animals vaccinated against PRRSV can differ between individuals. Some pigs may not show any response, or very low level of ELISA antibodies. Positive results of ELISA prove contact of a population with PRRSV (wild type or modified live vaccine).

The larger the number of pigs tested, the more accurate is the diagnosis. PRRS ELISA can detect antibodies starting from 10-14 days after the contact with the virus. Some pigs can seroconvert later than others. ELISA results are very difficult to interpret in individual pigs. The antibodies detected in ELISA are usually targeted against nucleocapsid protein. These antibodies play no role in immunity against PRRSV. There are no commercially available ELISA kits (or experimental ones) to verify the level of immunity.

Pigs negative in ELISA can still be immune. Vaccines against PRRS usually don’t protect pigs against infection for entire life. They are intended to limit virus shedding and clinical signs after infection. Vaccines may differ in efficacy in different farms. This is due to the antigenic diversity of PRRSV and other factors compromising pig immunity. It has to be remembered that PRRSV immunity is slow to develop and needs several weeks to be protective.

The best way to assess PRRSV dynamics in a vaccinated population is PCR surveillance, including nucleotide sequencing, to make sure that the virus detected is not a vaccine. PCR detection of wild type PRRSV in a population soon after vaccination may indicate limited efficacy of vaccination protocol (vaccination routine, timing, health status of pigs).

If high amounts of PRRSV are detected in sick animals, the virus can be considered an important factor of the disease condition. Vaccination of piglets upon arrival on the farm can be considered but the best is if piglets are transported at least 4 weeks after vaccination on the source farm. ELISA can still be immune.

Vaccines against PRRS usually don’t protect pigs against infection for entire life. They are intended to limit virus shedding and clinical signs after infection. Vaccines may differ in efficacy in different farms. This is due to the antigenic diversity of PRRSV and other factors compromising pig immunity.

It has to be remembered that PRRSV immunity is slow to develop and needs several weeks to be protective. The best way to assess PRRSV dynamics in a vaccinated population is PCR surveillance, including nucleotide sequencing, to make sure that the virus detected is not a vaccine. PCR detection of wild type PRRSV in a population soon after vaccination may indicate limited efficacy of vaccination protocol (vaccination routine, timing, health status of pigs). If high amounts of PRRSV are detected in sick animals, the virus can be considered an important factor of the disease condition.

Vaccination of piglets upon arrival on the farm can be considered but the best is if piglets are transported at least 4 weeks after vaccination on the source farm.


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