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How is PRRS transmitted in pigs?

How is PRRS transmitted in pigs?

Transmission of PRRS in pigs within herds can be classified as direct, when it is transmitted by direct contact from infected animals to others, and indirect transmission when it is transmitted through fomites or vectors. Regarding direct transmission, we can differentiate between vertical transmission, from sows to their offspring, and horizontal transmission, from infected pigs to their mates.

PRRS in pigs can be transmitted from infected to susceptible pigs through different routes:

The main route is direct transmission when infected pigs are in contact with others on the same farm, or in the same barn or pen. To evaluate direct transmission between pigs on the farm we should consider the different routes of virus shedding and its duration. So, PRRS virus can be shed for a long time through multiple routes: nasal secretions, saliva or semen and also, although less frequently, through milk, colostrum, urine or feces. Taking into account all these routes of shedding, we can establish different routes of exposure for the susceptible pigs: oronasal, sexual or percutaneous.

Besides this direct horizontal transmission, vertical transmission can also occur when the PRRS virus crosses the placental barrier during the last trimester of gestation and it can replicate in the endometrial and placental tissues. So, vertical transmission from pregnant sows to their piglets is a very important factor for the circulation of PRRS in pigs.

Indirect transmission is also possible. As we explained in the previous post, Transmission between herds, different vectors and contaminated fomites can spread the PRRS virus on the farm and to other farms as well. In addition, airborne transmission is possible between different pens or barns, or through slurry. It should be borne in mind that the PRRS virus can survive for days in favorable conditions such as organic material, high humidity and low temperatures.

In order to control the transmission not just of PRRS in pigs, but also other secondary bacterial pathogens, different standardized management protocols have been established amongst which Mc Rebel procedures(Management Changes to Reduce Exposure to Bacteria to Eliminate Losses) are the most popular. Basically, rules applied are focused on decreasing contact between potentially susceptible pigs and potentially infected pigs (i.e: all-in-all-out, isolation of sick animals, avoiding or minimizing cross fostering…..)

Finally vaccination cannot develop complete protection against PRRS infection, but the vaccination of breeders and piglets can confer a higher immunity status to the herd, decreasing the shedding of PRRS virus from infected animals and increasing the potential infective dose of susceptible pigs. So, UNISTRAIN® PRRS, a live-attenuated PRRS vaccine, VP-046 BIS strain, can be a useful tool for the control and stabilization of PRRS in pigs. UNISTRAIN® PRRS can be used both in breeders and piglets and has demonstrated heterologous protection against different highly pathogenic strains of both genotype I and genotype II.