**5.1 Biosecurity**

Strict biosecurity measures should be maintained, involving all of the following: (1) *Location of the boar stud:* To avoid introduction of pathogens via aerosol routes, boar studs are often located in remote areas away from pig dense populations. (2) *Protection from aerosol contamination:* High traffic areas and location next to heavily travelled roads have shown to be a risk factor for exposure to airborne viruses (Otake et al., 2002). Boar stud owners often attempt to protect the boars by implementing filter systems for incoming air in AI centers to safeguard boars against the entry of airborne pathogens (Dee et al., 2005, 2006). (3) *Incoming replacement boars:* Replacement boars are typically isolated for 30 to 60 days and housed in a separate off-site facility. During the isolation time, the health status of the boars is evaluated. Animals that test positive for any disease of concern are typically not allowed to enter. During the isolation time, incoming boars are often vaccinated against diseases present in the resident boars. The annual boar replacement rate in AI centers is typically 60% (Singleton, 2001). (4) *Employees and visitors:* Strict regulations are typically in place for people entering AI centers. Often, there is 24 to 72 hour down-time required during which time people are not allowed to have contact with other live pigs. In addition, there is often a shower in/shower out requirement for all visitors and employees. (5) *Deliveries:* Any deliveries (clothes, mail, supplies, feed, tools, and equipment) are brought to a special entrance with no direct contact with the boar stud and are fumigated prior to entry into the boar studs. (6) *Rodent and insect control:* Rodents and insects have been shown to be capable of carrying several pig viruses (Lorincz et al., 2010; Otake et al., 2003a, 2003b; Plowright et al., 1970) and appropriate prevention measures need to be in place. (7) *Implementation of a regular and appropriate cleaning and disinfectant procedure.* 

#### **5.2 Routine surveillance testing**

266 A Bird's-Eye View of Veterinary Medicine

pathogens in boar semen. Many of these are highly sensitive, specific and rapid (Christopher-Hennings et al., 1995b). In the case of PRRSV, reverse transcriptase-PCR is today considered to be the most sensitive diagnostic technique. It allows for the detection of as little as 100 TCID50 per seminal dose (Christopher-Hennings et al., 1995b; Gradil et al., 1996), 20 times less virus than what has been shown experimentally to result in transmission

Serology is a simple and relatively inexpensive way to survey for pathogens that should not be present in the boar stud. The main disadvantage of serology is the time period between pathogen exposure and detectable levels of antibodies in a boar which may range from a few days to weeks during which time the boar is not identified as being positive and may

The best way to prevent disease transmission via semen is to assure pathogens are not introduced to the boar studs by maintaining very strict biosecurity measures (Madec et al., 1999) and routine surveillance. Due to the high risk of dissemination of disease via AI, the most important goal is to provide pathogen-free semen, which is feasible with adequate

Strict biosecurity measures should be maintained, involving all of the following: (1) *Location of the boar stud:* To avoid introduction of pathogens via aerosol routes, boar studs are often located in remote areas away from pig dense populations. (2) *Protection from aerosol contamination:* High traffic areas and location next to heavily travelled roads have shown to be a risk factor for exposure to airborne viruses (Otake et al., 2002). Boar stud owners often attempt to protect the boars by implementing filter systems for incoming air in AI centers to safeguard boars against the entry of airborne pathogens (Dee et al., 2005, 2006). (3) *Incoming replacement boars:* Replacement boars are typically isolated for 30 to 60 days and housed in a separate off-site facility. During the isolation time, the health status of the boars is evaluated. Animals that test positive for any disease of concern are typically not allowed to enter. During the isolation time, incoming boars are often vaccinated against diseases present in the resident boars. The annual boar replacement rate in AI centers is typically 60% (Singleton, 2001). (4) *Employees and visitors:* Strict regulations are typically in place for people entering AI centers. Often, there is 24 to 72 hour down-time required during which time people are not allowed to have contact with other live pigs. In addition, there is often a shower in/shower out requirement for all visitors and employees. (5) *Deliveries:* Any deliveries (clothes, mail, supplies, feed, tools, and equipment) are brought to a special entrance with no direct contact with the boar stud and are fumigated prior to entry into the boar studs. (6) *Rodent and insect control:* Rodents and insects have been shown to be capable of carrying several pig viruses (Lorincz et al., 2010; Otake et al., 2003a, 2003b; Plowright et al., 1970) and appropriate prevention measures need to be in place. (7) *Implementation of a* 

**5. Prevention of introduction of viruses into boar studs** 

*regular and appropriate cleaning and disinfectant procedure.* 

of PRRSV in gilts (Shin et al., 1997).

**4.3.4 Detection of antibodies** 

shed the virus via semen.

control measures.

**5.1 Biosecurity** 

Commercial AI centers need be regularly checked for conformity with specific criteria, assuring that their products are free of certain pathogens and contain a minimal or acceptable number of microorganisms (Guerin & Pozzi, 2005; Prieto et al., 2004). Many veterinary diagnostic laboratories took this need into account and started to offer daily service for boar studs.

#### **5.3 General semen handling and storage**

To reduce the unavoidable presence of bacteria in the ejaculate and to prolong *in vitro* longevity of sperm, use of antimicrobials in semen is a common part of most semen extenders. Apart from a possible dilution effect of pathogens, semen processing and addition of antimicrobials does not eliminate viruses. The use of effective antiviral agents to render semen virus-free has so far not been adopted in the swine AI industry. However, several best practices for handling, storage conditions, and use of fresh semen have been described to reduce the potential for transmission of viral pathogens (Guerin & Pozzi, 2005). For boars, the immediate use of fresh semen increases the risk of pathogen transmission (Prieto et al., 2004).

#### **5.4 Vaccination**

The use of modified-live and inactivated-virus vaccines in boars can be highly effective in eliminating or decreasing shedding of viruses and with that decreasing the risk of virus transmission by AI. For example, vaccination against PPV may help to reduce shedding of the virus following infection. This has also been shown for PCV2 under experimental conditions (Opriessnig et al., 2011). In many countries, vaccination is done as part of a PRV eradication program (Siegel & Weigel, 1999). In the case of PRRSV, the use of a modified live virus vaccine shortened or eliminated virus shedding in boars challenged with wild-type virus for 50 days after vaccination (Christopher-Hennings et al., 1997; Nielsen et al., 1997). However, based on other studies it appears that PRRSV vaccination provides only partial protection (Nielsen et al., 1997). Moreover, semen shedding has been demonstrated after vaccination with a modified live vaccine virus (Christopher-Hennings et al., 1997). In addition, the modified live PRRSV vaccine virus has been shown to be shed in the semen in low levels (Christopher-Hennings et al., 1995b). In contrast, an inactivated vaccine, did not clearly reduce subsequent shedding of wild-type virus in semen (Christopher-Hennings et al., 1997; Stevenson et al., 1994). The presence of PRRSV in semen was demonstrated by PCR in most of the vaccinated boars during an interval of 7–21 days post-vaccination, although some boars sporadically shed the virus for longer periods of time (Christopher-Hennings et al., 1997). Similarly, when a swine bioassay was used, the presence of infectious virus in semen samples of vaccinated boars was confirmed 14 days post-vaccination (Nielsen et al., 1997).

#### **6. Summary**

Virus contamination of boar semen poses a great risk for breeding herds worldwide due the possibility of fast introduction of viruses into large naïve and susceptible populations.

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**15** 

V.G. Papatsiros

 *Greece* 

 *University of Thessaly,* 

**Porcine Herd Health Management** 

*Clinic of Medicine, Faculty of Veterinary Medicine,* 

**Practices for the Control of PRRSV Infection** 

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious viral disease that was first recognized almost simultaneously in Western Europe (Wensvoort et al., 1991) and North America in the late 1980s (Keffaber, 1989). The causative agent is PRRS virus (PRRSV), a small single-stranded positive sense RNA virus, classified in the order Nidovirales, family Arteriviridae and genus Arterivirus. Since its appearance, PRRS has devastated the worldwide swine industry with tremendous economic losses (Neumann et al., 2005). PRRSV causes reproductive failure in breeding stock (e.g. premature farrowings, late term abortions, poor farrowing rate, mummified fetuses and stillborn piglets), as well as respiratory disease, elevated mortality and reduction of growth performance in piglets and growing / finishing pigs (Cho & Dee, 2006). Generally, after an acute outbreak of a PRRSV infection, herds may undergo a chronic loss of production in growing / finishing pigs and an endemic infection of breeding stock characterized by several outbreaks throughout the year (Stevenson et al., 1993). The severity of PRRS may result from a number of factors such as differences in virulence among the PRRSV isolates, probable recombination between the different isolates within the same farm, immune status, host susceptibility and concurrent infections (other viruses and bacteria) and hygiene monitoring programme (Goldberg et al., 2000). PRRSV infected pigs are more susceptible to some bacterial (e.g. *Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Bordatella bronchiseptica, Pasteurella multocida, Haemophilus parasuis*, *Streptococcus suis*) and viral diseases (e.g. swine influenza virus, Aujezky's disease virus, porcine respiratory coronavirus, porcine circovirus 2 - PCV2) (Brockmeier et al., 2002). One of the main pathogens involved in the porcine respiratory disease complex (PRDC) is PRRSV, as it has an additive or synergistic effect with the above other bacteria or viruses, that leads to a more severe and chronic respiratory disease in growing / finishing pigs

Before trying to control diseases at the farm level, it is very important to get information about what we really have to control. For instance, it is important to understand the pathogenesis, epidemiology and clinical forms of diseases. Therefore, the more scientific knowledge is known about PRRS, the better are the chances that this disease will be kept under control at relatively low losses. Table 1 shows some basic information of PRRSV

infection at farm level (Cho & Dee 2006; Zimmerman et al., 2006).

**1. Introduction** 

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