**2. Impact of viral contamination of semen**

Microbial contamination of boar semen not only reduces semen quality but can also reduce conception rate resulting in considerable economic loss. It is not uncommon that a single boar stud serves multiple breeding herds with an average of 200 to 10,000 sows on each site. The risk for breeding herds becoming infected via AI increases with the number of pathogens present in the semen, the dose of the pathogen(s) in the semen, the number of sows inseminated with the contaminated semen, and the level of protective immunity in the breeding herd. From a practical point of view, most economically important viral diseases are associated with clinical signs, so semen collection from sick boars will not always take place, and consequently the risk of pathogen transmission into susceptible breeding herds by this route may be lower than expected. However, when clinical signs are mild or absent the risk of viral transmission via contaminated semen is a concern.

Artificial insemination is now widely recognized as a route for spread of swine diseases (Thacker et al., 1984) and continues to be a major concern to pig breeders and regulatory authorities in countries where AI is practiced. Many viruses known to contaminate semen have been shown to be highly infectious via the uterine route, and wide dissemination of porcine pathogens by semen could occur when semen is shipped globally. Transmission of viruses via the semen route to breeding females has been experimentally proven for CSFV (de Smit et al., 1999), PRRSV (Yaeger et al., 1993), and PPV (Lucas et al., 1974). It is of importance to note that, although virus-contaminated semen indeed constitutes a serious risk for transmission, it does not guarantee tthat transmission to the sow or gilt by AI will consistently occur (Swenson et al., 1994b; Yaeger et al., 1993). The conditions required for establishment of infection in the breeding female are complex, and lack of transmission might be explained by sow immunity or failure to reach the minimum infectious dose. In this regard, much research has been conducted concerning the risk of transmission of PRRSV by semen, and the minimum dose necessary to establish infection in the sow (Benfield et al., 2000; Prieto et al., 1996b).

Contamination of semen with virus can occur through three possible routes: 1) fecal contamination of semen during collection, 2) systemic viral infection, or 3) local viral infection (testes, accessory gland, etc.). Once virus-contaminated semen is utilized to inseminate a breeding female, the outcome can vary depending on the time of fetal

risk of virus transmission. Monitoring for the presence of other ubiquitous viruses that can be found in semen, such as porcine circovirus type 2 (PCV2), torque teno sus virus (TTSuV), porcine parvovirus (PPV) and porcine adenovirus (PAV) is commonly not a high priority in most countries despite the fact that some of these viruses have been associated with

Due to differences in pathogenicity, economic consequences, geographic localization, and epidemiological parameters, different viruses are commonly assigned different levels of importance. The aims of this review are to summarize the information on swine viruses that can be transmitted via AI, their shedding characteristics in boars, effects of these viruses on naïve breeding animals, testing that is currently done to reduce or prevent the risk of transmission, and current best practices being used to reduce or eliminate virus shedding in

Microbial contamination of boar semen not only reduces semen quality but can also reduce conception rate resulting in considerable economic loss. It is not uncommon that a single boar stud serves multiple breeding herds with an average of 200 to 10,000 sows on each site. The risk for breeding herds becoming infected via AI increases with the number of pathogens present in the semen, the dose of the pathogen(s) in the semen, the number of sows inseminated with the contaminated semen, and the level of protective immunity in the breeding herd. From a practical point of view, most economically important viral diseases are associated with clinical signs, so semen collection from sick boars will not always take place, and consequently the risk of pathogen transmission into susceptible breeding herds by this route may be lower than expected. However, when clinical signs are mild or absent

Artificial insemination is now widely recognized as a route for spread of swine diseases (Thacker et al., 1984) and continues to be a major concern to pig breeders and regulatory authorities in countries where AI is practiced. Many viruses known to contaminate semen have been shown to be highly infectious via the uterine route, and wide dissemination of porcine pathogens by semen could occur when semen is shipped globally. Transmission of viruses via the semen route to breeding females has been experimentally proven for CSFV (de Smit et al., 1999), PRRSV (Yaeger et al., 1993), and PPV (Lucas et al., 1974). It is of importance to note that, although virus-contaminated semen indeed constitutes a serious risk for transmission, it does not guarantee tthat transmission to the sow or gilt by AI will consistently occur (Swenson et al., 1994b; Yaeger et al., 1993). The conditions required for establishment of infection in the breeding female are complex, and lack of transmission might be explained by sow immunity or failure to reach the minimum infectious dose. In this regard, much research has been conducted concerning the risk of transmission of PRRSV by semen, and the minimum dose necessary to establish infection in the sow

Contamination of semen with virus can occur through three possible routes: 1) fecal contamination of semen during collection, 2) systemic viral infection, or 3) local viral infection (testes, accessory gland, etc.). Once virus-contaminated semen is utilized to inseminate a breeding female, the outcome can vary depending on the time of fetal

sporadic reproductive failure in breeding animals.

**2. Impact of viral contamination of semen** 

(Benfield et al., 2000; Prieto et al., 1996b).

the risk of viral transmission via contaminated semen is a concern.

semen.

infection. Early embryonic death may result from direct invasion of the embryo by the pathogen or by uterine epithelial alterations in response to the pathogen (Wrathall & Mengeling, 1979). Until six to seven days after conception, an embryo is surrounded and protected by an impervious barrier called the zona pellucida, which helps the embryo avoid pathogen invasion (Mateusen et al., 2004). However, after entering the blastocyst stage, embryos may become susceptible to viral infections. Fetuses that are infected prior to 70 days of gestation usually die (mummies) and contribute to smaller litter sizes or early termination of pregnancy. Fetuses that are infected around or after 70 days of gestation are able to mount an active immune response against the pathogen and survive intrauterine infection.

As the risk of rapid virus spread via semen is well known, sanitation protocols in AI centers are constantly being reviewed to assure customers that current best practices are in place. A new categorization of viruses has been proposed to further address different risk levels (Guerin & Pozzi, 2005): Category 1 includes viruses for which there is scientific proof of transmission by semen, but without any risks for AI due to official national eradication programs such as FMDV, PRV, CSFV, and ASFV. Category 2 includes viruses for which there is scientific proof of transmission by semen and which can be commonly encountered such as PRRSV. Category 3 includes viruses for which additional scientific proof is needed to better assess the risk of transmission by semen (PCV2, porcine rubulavirus). In addition, some viruses have not been shown to be present in semen and thus are considered nonhazardous to AI.
