Many factors have been associated with PRRS transmission between herds. Amongst these factors, the introduction of infected animals and the use of contaminated semen are considered to be the most important since PRRS in pigs is mainly transmitted through direct contact with infected pigs and their secretions such as saliva, nasal discharges, semen or feces. However, airborne transmission and contaminated transport can be also considered to be an important source of PRRS infection between herds.
Biosecurity is the key to prevention of the inter-herd transmission of PRRS in pigs. Sometimes, the list of biosecurity rules and measures to avoid the entry of new pathogens into the farm can be endless and almost impossible to implement fully. For this reason, evaluation of the different risk factors and their importance in terms of the transmission of PRRS between herds is crucial. Once we identify the most dangerous factors for the introduction of PRRS into the farm we will be able to establish and focus on limited biosecurity rules but with the highest level of effectiveness for the protection of your herd. At the same time monitoring the PRRS status on the farm farm can also help us to determine the PRRS control program.
PRRS in pigs is transmitted mainly through direct contact with infected pigs and their physiological fluids, such as saliva, nasal secretions, semen or feces. So, we can consider the entry of infected pigs to be the most important cause of the spread of PRRS between farms and herds. Other main causes for the introduction of PRRS into a farm are contaminated semen and vehicles.
Nowadays, most boar stations in Western Europe and North America are PRRS-free and strict controls are applied in order to ensure that semen is completely PRRS-free. Unfortunately, in most countries we pay less attention to the control and disinfection of vehicles, so currently, we could consider this to be the second main risk for the transmission of PRRS in pigs from one farm to another.
In addition, airborne transmission can also play a very significant role in PRRS infection between farms, especially in high-density pig production areas. At this point, air filtration should be considered as the best biosecurity barrier to avoid PRRS infection from neighboring farms. Different air filtration systems have shown good results in several studies and field trials, but up to now no one can be considered 100% effective for the prevention of farm infection.
Indeed, different fomites, birds or insects or even humans, can be also considered a risk for the transmission of PRRS in pigs, but with a lower epidemiological importance than those mentioned above: animals and semen, vehicles and air.
Finally, regional PRRS control or eradication plans and programs can also play a very important role in the reduction of transmission of PRRS from farm to farm and even from region to region. So far these have only been introduced in some regions of the USA and Canada, but they have provided the first results on the reduction of the number of PRRS outbreaks and they will probably be extended to other areas of Europe and Asia in the near future.