**3. Swine viruses that can be present in boar semen**

#### **3.1 Porcine Reproductive and Respiratory Syndrome Virus**

Porcine reproductive and respiratory syndrome virus (PRRSV) is a single-stranded, positive-sense, enveloped RNA virus that belongs to the family *Arteriviridae*, genus *Arterivirus* (Cavanagh, 1997). PRRSV was first recognized in the late 1980's (Cavanagh, 1997; Meulenberg et al., 1993) and today is found globally in swine producing countries. As the name of the virus implies, PRRSV infection is associated with reproductive failure in pregnant sows and respiratory disease in pigs of all ages. It is less commonly associated with neonatal diarrhea (Albina et al., 1994; Bierk et al., 2001; Neumann et al., 2005; Rossow, 1998; Wensvoort et al., 1991). Although clinical disease associated with PRRSV in growing pigs can be quite severe, no or mild symptoms are typically seen in boars (Wensvoort et al., 1991). One of the main characteristics of PRRSV is its high transmissibility, making it difficult to maintain pig populations free of PRRSV (Prieto & Castro, 2005). The 50% tissue culture infective dose (TCID50) for exposure via oral, intranasal and AI routes was determined to be 105.3, 104.0 and 104.5, respectively (Benfield et al., 2000). Experimental infection in boars has demonstrated seminal shedding of PRRSV (Prieto et al., 1996b; Swenson et al., 1994a), and epidemiological evidence confirms that transmission of PRRSV from fresh semen of acutely infected boars into breeding herds is possible (Robertson, 1992; Yaeger et al., 1993). However, successful transmission is not always achieved (Swenson et al., 1994b; Yaeger et al., 1993) and appears to depend largely on the amount of PRRSV present in the semen (Benfield et al., 2000). In semen of adult boars, PRRSV can persist for variable periods (Christopher-Hennings et al., 1995a; Swenson et al., 1994) suggesting that the virus continues to replicates in the one or more tissues of the reproductive tract. Several

Artificial Insemination and Its Role in Transmission of Swine Viruses 259

been suggested (Cartwright et al., 1971). Semen may also become contaminated with PPV from feces or from the male reproductive organs (Biront & Bonte, 1983; Lucas et al., 1974). Changes in sperm output, ejaculate volume, motility, or morphologic defects have not been observed when the semen quality was evaluated after experimental inoculation of boars with PPV (Thacker et al., 1987a). Acute infection of breeding females with PPV is usually subclinical (Johnson et al., 1976). During initial infection, PPV replicates extensively and can be found in many tissues including lymphoid tissues (Cutlip & Mengeling, 1975a). The major and often only clinical response to PPV infection is reproductive failure. Return to estrus, fewer pigs per litter, and increased numbers of mummified fetuses are often observed (Cartwright & Huck, 1967; Joo et al., 1976). The consequence of PPV infection depends on timing of infection of the fetus: Death and reabsportion are usually observed in 10-30 gestation day embryos, death and mummification are seen when 30 to 70 day gestation fetuses are infected, and an active immune response and survival *in utero* is seen in fetuses when infected after 70 days of gestation (Bachmann et al., 1975; Cutlip & Mengeling, 1975b). The role of semen contamination with PPV leading to clinical reproductive problems has not been clearly established (Lucas et al., 1974; Mengeling & Paul, 1986; Thacker et al.,

Pseudorabies virus (PRV) is a double-stranded DNA virus that belongs to the subfamily *Alphaherpesvirinae* of the family *Herpesvirus* (Mettenleiter, 2000). PRV is distributed worldwide; however, in recent years eradication efforts have been successful to eliminate PRV from the domestic pig population in parts of Europe, Canada, New Zealand and the United States. PRV replication typically occurs in the nasal and pharyngeal mucosa and primary transmission occurs via the nasal route. Viral replication has also been reported to take place in the genital tract and transmission by copulation is therefore possible (Hall, Jr. et al., 1984a; Vannier & Gueguen, 1979). Differences in pathogenicity and duration of virus shedding exist among PRV strains (Maes et al., 1983). Clinically affected boars are often unable to mount a dummy (Guerin & Pozzi, 2005) and can additionally develop respiratory disease (Hall, Jr. et al., 1984b). PRV can be isolated infrequently from urine, preputial membranes, and semen after either natural (Medveczky & Szabo, 1981) or experimental infection (Vannier & Gueguen, 1979). Very high viral concentrations have been reported in semen ranging from 108 to 109 TCID50 per ml (Medveczky & Szabo, 1981) to 103.7 to 104.9 TCID50 per ml (Vannier & Gueguen, 1979). Transient viral excretion for up to 12 days usually occurs during the acute phase of the disease (Ressang, 1973) but viral excretion has been observed for long periods of time after natural infection (Wittmann, 1985). After experimental PRV infection by the intratesticular route, testicular degeneration and transient elevation in sperm abnormalities have been reported (Hall, Jr. et al., 1984a; Larsen et al., 1980). Sows inseminated with contaminated semen may develop vaginitis or endometritis resulting in embryonic death (Maes et al., 2008). Sows infected in the first trimester of pregnancy often reabsorb their fetuses and return to estrus. If sows get infected in the later stages of pregnancy they may abort or have larger numbers of stillborn and weakborn piglets. If susceptible females are infected with PRV close to parturition, there are increased numbers of weakborn pigs with signs of nervous

1987b; Wrathall & Mengeling, 1979).

**3.3 Pseudorabies Virus** 

system disease.

studies have since been carried out to determine the temporal localization of the virus in different organs and tissues (Prieto et al., 2003; Sur et al., 1997) and vascular dissemination and replication of PRRSV in tissues of the reproductive tract was confirmed (Sur et al., 1997). In addition, migration of infected monocytes and macrophages directly from blood and lymph of the reproductive tract into the semen has also been suggested as a mechanism for PRRSV contamination of semen (Christopher-Hennings et al., 1998; Prieto et al., 2003). PRRSV has been detected in semen samples of experimentally infected boars ranging from 4 to 92 days post infection (Christopher-Hennings et al., 1995a, 1998). This marked variability may be due to individual host factors (Christopher-Hennings et al., 1995a, 2001; Swenson et al., 1994a), the breed of the boars (Christopher-Hennings et al., 2001), and the strain of virus used in the experimental inoculation. European and North American PRRSV strains differ genetically and antigenically (Bautista et al., 1993; Meng et al., 1995). A bioassay has been used to determine the presence of infectious PRRSV in semen samples for a period of time lasting from 4 to 42 days post infection (Swenson et al., 1994a). In semen, PRRSV is sometimes associated with drastic changes in quality (reduced motility, abnormal acrosomes, morphological alterations, etc.) and volume of the semen (Teuffert et al., 1998). Conversely, some researchers have found that the quality of semen remains within normal limits after infection with PRRSV (Swenson et al., 1994a; Yaeger et al., 1993). The etiological role of PRRSV in reproductive failure of swine is firmly established (Christianson et al., 1993; Lager & Mengeling, 1995; Mengeling et al., 1994; Prieto et al., 1996a; Terpstra et al., 1991). The effect of PRRSV on reproductive parameters was found to be highly related to strain pathogenicity (Prieto et al., 1997). Sows and gilts bred by infected boars (Gradil et al., 1996; Yaeger et al., 1993) or with experimentally contaminated semen (Prieto et al., 1997; Swenson et al., 1994b) typically show seroconversion to PRRSV, even in the absence of detectable viremia (Christopher-Hennings et al., 1995a, 2001). It has been reported that insemination of seronegative or pre-immunized gilts with boar semen containing PRRSV often has little to no effect on conception rates, but may result in early embryonic infection and death (Prieto et al., 1997). In addition, PRRSV can be a major cause of prenatal death in commercial swine herds and often preweaning mortality is also increased.

#### **3.2 Porcine Parvovirus**

Porcine parvovirus (PPV) is a small, single-stranded, non-enveloped DNA virus (Molitor et al., 1984) that belongs to the family *Parvoviridae*, genus *Parvovirus*. PPV is considered ubiquitous in the pig population. The main routes of transmission of PPV are oronasal and transplacental. In general, infection of growing pigs and mature boars with PPV alone is not associated with clinical disease (Allan et al., 2000; Brown, Jr. et al., 1980; Kennedy et al., 2000; Krakowka et al., 2000). There is evidence that PPV-isolates vary in pathogenicity (Mengeling & Cutlip, 1976; Oraveerakul et al., 1993). PPV-isolates have been classified as nonpathogenic (Mengeling & Cutlip, 1976; Paul et al., 1979), pathogenic to nonimmunocompetent fetuses leading to death (Mengeling, 1979), pathogenic to immunocompetent fetuses and inducing dermatitis (Choi et al., 1987; Kresse et al., 1985; Lager et al., 1992; Lager & Mengeling, 1994), and enteric PPV-strains (Dea et al., 1985; Duhamel et al., 1991). PPV has previously been isolated from semen of naturally infected boars (Cartwright & Huck, 1967). Boars can shed the virus in semen during the acute phase of infection (Gradil et al., 1990); shedding beyond this phase has not been demonstrated, but the possibility of immunotolerant carriers of PPV as a result of early *in utero* infection has been suggested (Cartwright et al., 1971). Semen may also become contaminated with PPV from feces or from the male reproductive organs (Biront & Bonte, 1983; Lucas et al., 1974). Changes in sperm output, ejaculate volume, motility, or morphologic defects have not been observed when the semen quality was evaluated after experimental inoculation of boars with PPV (Thacker et al., 1987a). Acute infection of breeding females with PPV is usually subclinical (Johnson et al., 1976). During initial infection, PPV replicates extensively and can be found in many tissues including lymphoid tissues (Cutlip & Mengeling, 1975a). The major and often only clinical response to PPV infection is reproductive failure. Return to estrus, fewer pigs per litter, and increased numbers of mummified fetuses are often observed (Cartwright & Huck, 1967; Joo et al., 1976). The consequence of PPV infection depends on timing of infection of the fetus: Death and reabsportion are usually observed in 10-30 gestation day embryos, death and mummification are seen when 30 to 70 day gestation fetuses are infected, and an active immune response and survival *in utero* is seen in fetuses when infected after 70 days of gestation (Bachmann et al., 1975; Cutlip & Mengeling, 1975b). The role of semen contamination with PPV leading to clinical reproductive problems has not been clearly established (Lucas et al., 1974; Mengeling & Paul, 1986; Thacker et al., 1987b; Wrathall & Mengeling, 1979).

#### **3.3 Pseudorabies Virus**

258 A Bird's-Eye View of Veterinary Medicine

studies have since been carried out to determine the temporal localization of the virus in different organs and tissues (Prieto et al., 2003; Sur et al., 1997) and vascular dissemination and replication of PRRSV in tissues of the reproductive tract was confirmed (Sur et al., 1997). In addition, migration of infected monocytes and macrophages directly from blood and lymph of the reproductive tract into the semen has also been suggested as a mechanism for PRRSV contamination of semen (Christopher-Hennings et al., 1998; Prieto et al., 2003). PRRSV has been detected in semen samples of experimentally infected boars ranging from 4 to 92 days post infection (Christopher-Hennings et al., 1995a, 1998). This marked variability may be due to individual host factors (Christopher-Hennings et al., 1995a, 2001; Swenson et al., 1994a), the breed of the boars (Christopher-Hennings et al., 2001), and the strain of virus used in the experimental inoculation. European and North American PRRSV strains differ genetically and antigenically (Bautista et al., 1993; Meng et al., 1995). A bioassay has been used to determine the presence of infectious PRRSV in semen samples for a period of time lasting from 4 to 42 days post infection (Swenson et al., 1994a). In semen, PRRSV is sometimes associated with drastic changes in quality (reduced motility, abnormal acrosomes, morphological alterations, etc.) and volume of the semen (Teuffert et al., 1998). Conversely, some researchers have found that the quality of semen remains within normal limits after infection with PRRSV (Swenson et al., 1994a; Yaeger et al., 1993). The etiological role of PRRSV in reproductive failure of swine is firmly established (Christianson et al., 1993; Lager & Mengeling, 1995; Mengeling et al., 1994; Prieto et al., 1996a; Terpstra et al., 1991). The effect of PRRSV on reproductive parameters was found to be highly related to strain pathogenicity (Prieto et al., 1997). Sows and gilts bred by infected boars (Gradil et al., 1996; Yaeger et al., 1993) or with experimentally contaminated semen (Prieto et al., 1997; Swenson et al., 1994b) typically show seroconversion to PRRSV, even in the absence of detectable viremia (Christopher-Hennings et al., 1995a, 2001). It has been reported that insemination of seronegative or pre-immunized gilts with boar semen containing PRRSV often has little to no effect on conception rates, but may result in early embryonic infection and death (Prieto et al., 1997). In addition, PRRSV can be a major cause of prenatal death in

commercial swine herds and often preweaning mortality is also increased.

Porcine parvovirus (PPV) is a small, single-stranded, non-enveloped DNA virus (Molitor et al., 1984) that belongs to the family *Parvoviridae*, genus *Parvovirus*. PPV is considered ubiquitous in the pig population. The main routes of transmission of PPV are oronasal and transplacental. In general, infection of growing pigs and mature boars with PPV alone is not associated with clinical disease (Allan et al., 2000; Brown, Jr. et al., 1980; Kennedy et al., 2000; Krakowka et al., 2000). There is evidence that PPV-isolates vary in pathogenicity (Mengeling & Cutlip, 1976; Oraveerakul et al., 1993). PPV-isolates have been classified as nonpathogenic (Mengeling & Cutlip, 1976; Paul et al., 1979), pathogenic to nonimmunocompetent fetuses leading to death (Mengeling, 1979), pathogenic to immunocompetent fetuses and inducing dermatitis (Choi et al., 1987; Kresse et al., 1985; Lager et al., 1992; Lager & Mengeling, 1994), and enteric PPV-strains (Dea et al., 1985; Duhamel et al., 1991). PPV has previously been isolated from semen of naturally infected boars (Cartwright & Huck, 1967). Boars can shed the virus in semen during the acute phase of infection (Gradil et al., 1990); shedding beyond this phase has not been demonstrated, but the possibility of immunotolerant carriers of PPV as a result of early *in utero* infection has

**3.2 Porcine Parvovirus** 

Pseudorabies virus (PRV) is a double-stranded DNA virus that belongs to the subfamily *Alphaherpesvirinae* of the family *Herpesvirus* (Mettenleiter, 2000). PRV is distributed worldwide; however, in recent years eradication efforts have been successful to eliminate PRV from the domestic pig population in parts of Europe, Canada, New Zealand and the United States. PRV replication typically occurs in the nasal and pharyngeal mucosa and primary transmission occurs via the nasal route. Viral replication has also been reported to take place in the genital tract and transmission by copulation is therefore possible (Hall, Jr. et al., 1984a; Vannier & Gueguen, 1979). Differences in pathogenicity and duration of virus shedding exist among PRV strains (Maes et al., 1983). Clinically affected boars are often unable to mount a dummy (Guerin & Pozzi, 2005) and can additionally develop respiratory disease (Hall, Jr. et al., 1984b). PRV can be isolated infrequently from urine, preputial membranes, and semen after either natural (Medveczky & Szabo, 1981) or experimental infection (Vannier & Gueguen, 1979). Very high viral concentrations have been reported in semen ranging from 108 to 109 TCID50 per ml (Medveczky & Szabo, 1981) to 103.7 to 104.9 TCID50 per ml (Vannier & Gueguen, 1979). Transient viral excretion for up to 12 days usually occurs during the acute phase of the disease (Ressang, 1973) but viral excretion has been observed for long periods of time after natural infection (Wittmann, 1985). After experimental PRV infection by the intratesticular route, testicular degeneration and transient elevation in sperm abnormalities have been reported (Hall, Jr. et al., 1984a; Larsen et al., 1980). Sows inseminated with contaminated semen may develop vaginitis or endometritis resulting in embryonic death (Maes et al., 2008). Sows infected in the first trimester of pregnancy often reabsorb their fetuses and return to estrus. If sows get infected in the later stages of pregnancy they may abort or have larger numbers of stillborn and weakborn piglets. If susceptible females are infected with PRV close to parturition, there are increased numbers of weakborn pigs with signs of nervous system disease.

Artificial Insemination and Its Role in Transmission of Swine Viruses 261

Classical swine fever virus (CSFV) is a small, enveloped, positive-sense, single-stranded RNA virus in the genus *Pestivirus* of the family *Flaviviridae* (Becher et al., 1999). CSFV has been eradicated from many countries including Australia, New Zealand, North America, and Western Europe; however, it has been periodically reintroduced into domestic pigs that are in contact with wild boars. During the CSFV epizootic of 1997-1998 in the Netherlands (de Smit et al., 1999), two AI centers became infected and more than 100,000 sows from approximately 1,700 farms were affected (Hennecken et al., 2000) highlighting the economic importance of disease spread though AI centers. The main transmission route of CSFV is oronasally with primary virus replication in tonsils.Data from natural infection(Hennecken et al., 2000) and experimental inoculations (Choi & Chae, 2003; Floegel et al., 2000) have demonstrated that CSFV can be excreted in semen from infected boars. Boars experimentally infected with CSFV shed the virus in semen for up to 53 days post-infection (Choi & Chae, 2003). The virus does not affect the semen quality and motility and concentration are within normal range. Sows that were inseminated with contaminated semen seroconverted; however, the virus was shown to cross the placental barrier and infected the fetuses causing embryonic mortality (de Smit et al., 1999). CSFV continues to be important, especially in areas where CSFV is endemic, because the virus is highly contagious and infection of pregnant sows, in contrast to acute infections in piglets, may not be apparent (Hare et al., 1985; Ressang, 1973). If clinically normal CSFV immunotolerant piglets are born, they can spread virus for months without showing signs of disease or developing an antibody

Foot and mouth disease virus (FMDV) is a small single-stranded positive-sense RNA virus which belongs to the genus *Apthovirus* in the family *Picornaviridae* (Carrillo et al., 1990)*.*  FMDV is endemic in Asia, some areas in South America and in Africa. FMDV can be isolated from all excretions and secretions including urine, feces, milk and semen (Lubroth & Brown, 1995). Infected pigs develop fever, lethargy and lameness which is associated with vesicular lesions in the hoof area (Mebus, 1978). Infection with FMDV leads to viremia, with subsequent systemic dissemination of the virus, including the genital tract and the skin around the preputial orifice (Alexandersen et al., 2001). FMDV has been detected in boar semen before and during manifestation of clinical signs of the disease. The viral concentration in semen has been found to be low (Guerin & Pozzi, 2005). After natural infection, FMDV has been isolated from infected boar semen for up to 9 days, but AI with contaminated semen failed to transmit the disease to sows (McVicar et al., 1977). To the authors' knowledge, an effect on semen quality has not been described. Abortion storms can

be observed and are mainly due to the high fever and clinical illness of the dams

Japanese B encephalitis virus (JBEV) is a member of the *Flavivirus* genus of the family *Flaviviridae* (Solomon et al., 2003)*.* JBEV is a mosquito-borne pathogen affecting humans and animals. This virus represents an economically important reproductive pathogen of breeding pigs, especially in Asia and Northern Australia, and is a common cause of

**3.7 Classical Swine Fever Virus** 

response (de Smit et al., 1999).

**3.8 Foot and Mouth Disease Virus** 

**3.9 Japanese B Encephalitis Virus** 

#### **3.4 Porcine Rubulavirus**

Porcine rubulavirus (PoRV), also known as La-Piedad-Michoacan paramyxovirus (LPMV), is associated with blue eye disease in pigs. This virus was first isolated in Mexico in the early 1980's. PoRV belongs to the genus *Rubulavirus* and family *Paramyxoviridae.* Only one serotype has been recognized to date. Subclinically infected pigs are the primary source for PoRV transmission which occurs primarily via oronasal route. Boars, like other adult animals infected with PoRV, generally do not show clinical signs except for epididymitis and orchitis and in some cases loss of libido (Maes et al., 2008). Transmission of the virus through semen has not been proven experimentally; however, PoRV has been recovered from semen, testes, and other tissues of the reproductive tract for up to 49 days after inoculation (Solis et al., 2007). Based on semen evaluation in herds naturally infected with PoRV, approximately 30% of boars develop temporary or permanent infertility. Semen abnormalities include a decrease in concentration, increased morphologically abnormal sperm, decreased sperm motility and viability, and azoospermia (Maes et al., 2008). Most sows are clinically normal with a few animals developing corneal opacity. Infected breeding herds may experience increased returns to estrus and a reduction in farrowing rates.

#### **3.5 Porcine Enteric Picornaviruses**

Porcine enterovirus (PEV) and porcine teschovirus (PTV) are single-stranded positive-sense RNA viruses in the family *Picornaviridae*. PEV and PTV infections are commonly transmitted between pigs by oral exposure to contaminated feces; however, contamination of semen via aerosol during semen collection cannot be excluded (Guerin & Pozzi, 2005). PTV has been isolated from the male genital tract (Phillips et al., 1972); however, insemination of gilts with PTV contaminated semen had no effect on their fertility (De Meurichy & Pensaert, 1977). PEV can cause seminal vesiculitis, sperm abnormalities, and decrease libido (Phillips et al., 1972). Usually, there are no clinical signs in the sows. Although evidence is limited, there are reports that suggest that semen contaminated with PEV and PTV could cause embryonic and neonatal death (Dunne et al., 1969).

#### **3.6 African Swine Fever Virus**

African swine fever virus (ASFV) is a double-stranded, linear DNA virus in the genus *Asfivirus* of the family *Asfarviridae* (Tabares et al., 1980). ASFV replicates in monocytes and macrophages of the lymph nodes near the site of viral entry and subsequently spreads through the blood system, the lymphatic system, or both (Maes et al., 2008). ASFV transmission is generally vector-borne via tick bites (Parker et al., 1969); however, infections can also occur through direct interaction of sick and naïve animals (Plowright et al., 1970). Clinical signs range from subclinical to severe acute systemic disease that can resemble other hemorrhagic diseases in pigs. In naïve pigs, acute disease is characterized by high fever, loss of appetite, and hemorrhages in the skin (Moulton & Coggins, 1968). ASFV has been experimentally isolated from semen (Schlafer & Mebus, 1987; Thacker et al., 1984). Effect on semen quality and volume has to the authors knowledge not been reported. Under experimental conditions, ASFV has been shown to induce abortion when sows were infected between 38 and 92 days of gestation (Schlafer & Mebus, 1987). It was determined that abortion resulted from the effect of the virus on the dam (clinical illness) rather than direct effect on the fetuses (Schlafer & Mebus, 1987).

#### **3.7 Classical Swine Fever Virus**

260 A Bird's-Eye View of Veterinary Medicine

Porcine rubulavirus (PoRV), also known as La-Piedad-Michoacan paramyxovirus (LPMV), is associated with blue eye disease in pigs. This virus was first isolated in Mexico in the early 1980's. PoRV belongs to the genus *Rubulavirus* and family *Paramyxoviridae.* Only one serotype has been recognized to date. Subclinically infected pigs are the primary source for PoRV transmission which occurs primarily via oronasal route. Boars, like other adult animals infected with PoRV, generally do not show clinical signs except for epididymitis and orchitis and in some cases loss of libido (Maes et al., 2008). Transmission of the virus through semen has not been proven experimentally; however, PoRV has been recovered from semen, testes, and other tissues of the reproductive tract for up to 49 days after inoculation (Solis et al., 2007). Based on semen evaluation in herds naturally infected with PoRV, approximately 30% of boars develop temporary or permanent infertility. Semen abnormalities include a decrease in concentration, increased morphologically abnormal sperm, decreased sperm motility and viability, and azoospermia (Maes et al., 2008). Most sows are clinically normal with a few animals developing corneal opacity. Infected breeding

herds may experience increased returns to estrus and a reduction in farrowing rates.

Porcine enterovirus (PEV) and porcine teschovirus (PTV) are single-stranded positive-sense RNA viruses in the family *Picornaviridae*. PEV and PTV infections are commonly transmitted between pigs by oral exposure to contaminated feces; however, contamination of semen via aerosol during semen collection cannot be excluded (Guerin & Pozzi, 2005). PTV has been isolated from the male genital tract (Phillips et al., 1972); however, insemination of gilts with PTV contaminated semen had no effect on their fertility (De Meurichy & Pensaert, 1977). PEV can cause seminal vesiculitis, sperm abnormalities, and decrease libido (Phillips et al., 1972). Usually, there are no clinical signs in the sows. Although evidence is limited, there are reports that suggest that semen contaminated with PEV and PTV could cause embryonic

African swine fever virus (ASFV) is a double-stranded, linear DNA virus in the genus *Asfivirus* of the family *Asfarviridae* (Tabares et al., 1980). ASFV replicates in monocytes and macrophages of the lymph nodes near the site of viral entry and subsequently spreads through the blood system, the lymphatic system, or both (Maes et al., 2008). ASFV transmission is generally vector-borne via tick bites (Parker et al., 1969); however, infections can also occur through direct interaction of sick and naïve animals (Plowright et al., 1970). Clinical signs range from subclinical to severe acute systemic disease that can resemble other hemorrhagic diseases in pigs. In naïve pigs, acute disease is characterized by high fever, loss of appetite, and hemorrhages in the skin (Moulton & Coggins, 1968). ASFV has been experimentally isolated from semen (Schlafer & Mebus, 1987; Thacker et al., 1984). Effect on semen quality and volume has to the authors knowledge not been reported. Under experimental conditions, ASFV has been shown to induce abortion when sows were infected between 38 and 92 days of gestation (Schlafer & Mebus, 1987). It was determined that abortion resulted from the effect of the virus on the dam (clinical illness) rather than direct

**3.4 Porcine Rubulavirus** 

**3.5 Porcine Enteric Picornaviruses** 

and neonatal death (Dunne et al., 1969).

effect on the fetuses (Schlafer & Mebus, 1987).

**3.6 African Swine Fever Virus** 

Classical swine fever virus (CSFV) is a small, enveloped, positive-sense, single-stranded RNA virus in the genus *Pestivirus* of the family *Flaviviridae* (Becher et al., 1999). CSFV has been eradicated from many countries including Australia, New Zealand, North America, and Western Europe; however, it has been periodically reintroduced into domestic pigs that are in contact with wild boars. During the CSFV epizootic of 1997-1998 in the Netherlands (de Smit et al., 1999), two AI centers became infected and more than 100,000 sows from approximately 1,700 farms were affected (Hennecken et al., 2000) highlighting the economic importance of disease spread though AI centers. The main transmission route of CSFV is oronasally with primary virus replication in tonsils.Data from natural infection(Hennecken et al., 2000) and experimental inoculations (Choi & Chae, 2003; Floegel et al., 2000) have demonstrated that CSFV can be excreted in semen from infected boars. Boars experimentally infected with CSFV shed the virus in semen for up to 53 days post-infection (Choi & Chae, 2003). The virus does not affect the semen quality and motility and concentration are within normal range. Sows that were inseminated with contaminated semen seroconverted; however, the virus was shown to cross the placental barrier and infected the fetuses causing embryonic mortality (de Smit et al., 1999). CSFV continues to be important, especially in areas where CSFV is endemic, because the virus is highly contagious and infection of pregnant sows, in contrast to acute infections in piglets, may not be apparent (Hare et al., 1985; Ressang, 1973). If clinically normal CSFV immunotolerant piglets are born, they can spread virus for months without showing signs of disease or developing an antibody response (de Smit et al., 1999).

#### **3.8 Foot and Mouth Disease Virus**

Foot and mouth disease virus (FMDV) is a small single-stranded positive-sense RNA virus which belongs to the genus *Apthovirus* in the family *Picornaviridae* (Carrillo et al., 1990)*.*  FMDV is endemic in Asia, some areas in South America and in Africa. FMDV can be isolated from all excretions and secretions including urine, feces, milk and semen (Lubroth & Brown, 1995). Infected pigs develop fever, lethargy and lameness which is associated with vesicular lesions in the hoof area (Mebus, 1978). Infection with FMDV leads to viremia, with subsequent systemic dissemination of the virus, including the genital tract and the skin around the preputial orifice (Alexandersen et al., 2001). FMDV has been detected in boar semen before and during manifestation of clinical signs of the disease. The viral concentration in semen has been found to be low (Guerin & Pozzi, 2005). After natural infection, FMDV has been isolated from infected boar semen for up to 9 days, but AI with contaminated semen failed to transmit the disease to sows (McVicar et al., 1977). To the authors' knowledge, an effect on semen quality has not been described. Abortion storms can be observed and are mainly due to the high fever and clinical illness of the dams

#### **3.9 Japanese B Encephalitis Virus**

Japanese B encephalitis virus (JBEV) is a member of the *Flavivirus* genus of the family *Flaviviridae* (Solomon et al., 2003)*.* JBEV is a mosquito-borne pathogen affecting humans and animals. This virus represents an economically important reproductive pathogen of breeding pigs, especially in Asia and Northern Australia, and is a common cause of

Artificial Insemination and Its Role in Transmission of Swine Viruses 263

Pyrexia and anorexia are frequently observed in aborting dams (Park et al., 2005). The virus is also able to replicate in the zona pellucida-free embryos, leading to embryonic death (Mateusen et al., 2004, 2007). Delayed farrowing (>118 days of gestation) (Ladekjær-Mikkelsen et al., 2001) or pseudopregnancy (Josephson & Charbonneau, 2001) is less frequently observed with PCV2-associated reproductive failure. PCV2 affected litters are commonly composed of increased numbers of non-viable fetuses (mummified and stillborn)

Swine vesicular disease virus (SVDV) is a small, non-enveloped single-stranded positivesense RNA virus, in the family *Picornaviridae*, genus *Enterovirus* (Nardelli et al., 1968)*.*  Documented outbreaks of this disease have been limited to selected countries in Asia, Europe and Central America. Clinical signs include appearance of vesicles around the coronary bands, snout, tongue and lip (Kanno et al., 1995) making this disease an important differential for FMDV. After natural infection, SVDV has been isolated from infected boar semen for up to four days, but AI with contaminated semen failed to transmit the disease to

Pigs are also susceptible to non-CSFV pestiviruses, including bovine viral diarrhea virus (BVDV) and border disease virus (BDV), which are associated with disease in cattle and sheep, respectively. Pigs congenitally infected with these viruses may shed large amounts of virus. Previously, BVDV has been isolated from oropharyngeal fluid, urine and semen of a

Retroviruses are RNA viruses that exist in two main groups: endogenous or exogenous retroviruses. Endogenous retroviruses are thought to be present in all vertebrates accounting for approximately 8% of their genomes (Tucker et al., 2006). All pigs carry PERV in their genome (Wilson, 2008) and three porcine endogenous retrovirus (PERV) subtypes have been identified based on their envelope sequence and tropism in cell culture (Le et al., 1997; Wilson et al., 2000): PERV-A, PERV-B and PERV-C (Martin et al., 2000a, 2000b; Patience et al., 1997; Specke et al., 2001; Takeuchi et al., 1998). More recently, the possible existence of exogenous porcine retrovirus in pigs was proposed (Scobie et al., 2004; Wood et al., 2004). It was demonstrated that a human-tropic recombination between PERV-A and PERV-C (designated as PERV-A/C) was not a product of *in vitro* recombination; instead PERV-A/C appeared to exist *in vivo* as an exogenous virus (Wood et al., 2004). Furthermore, a PERV-A/C recombinant was isolated from porcine peripheral blood mononuclear cells and was not present in a proviral form in the miniature swine genome (Scobie et al., 2004a; Wood et al., 2004). The PERV A/C virus is a recombination within the *env* region and is thought to arise from exogenous recombination of mRNA (Martin et al., 2006). Shedding via

at parturition (Madson & Opriessnig, 2011).

**3.11.1 Swine Vesicular Disease Virus** 

sows (McVicar et al., 1977).

**3.11.3 Porcine retroviruses** 

**3.11 Other viruses that are of minor importance** 

**3.11.2 Non-Classical Swine Fever Virus pestiviruses** 

congenitally infected, infertile boar (Terpstra & Wensvoort, 1997).

the semen route occurs, since PERVs are embedded in the genome.

infertility in Japanese pigs (Habu et al., 1977). Infection of susceptible boars resulted in edematous, congested testes and semen with numerous abnormal spermatozoa and significantly decreased total and motile sperm counts (Habu et al., 1977). These changes are usually temporary and most boars recover completely. JBEV has been isolated from the testicles of boars with orchitis and also can be shed in the semen for 5 weeks (Habu et al., 1977). JBEV infection can easily be transmitted if gilts are inseminated with infected semen (Guerin & Pozzi, 2005; Habu et al., 1977).

#### **3.10 Porcine Circovirus type 2**

Porcine circovirus type 2 (PCV2) is a small, single-stranded, ambi-sense DNA virus that belongs to the family *Circoviriade*, genus *Circovirus* (Tischer et al., 1982)*.* PCV2 is a ubiquitous virus and most herds worldwide are seropositive for PCV2 (Dulac & Afshar, 1989; Edwards & Sands, 1994; Segalés et al., 2008; Tischer et al., 1986). When first described in 1998, PCV2 was linked to disease mainly characterized by wasting and generalized lymphadenopathy in growing pigs (Allan et al., 1998; Morozov et al., 1998). Since that time, PCV2 has been associated with several disease manifestations in pigs commonly referred to as PCV-associated disease (PCVAD) which includes systemic disease, respiratory disease, enteric disease, porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure in dams (late term abortions and stillbirths) (Choi & Chae, 2001; Harms et al., 2002; Kim et al., 2004a; Kim et al., 2004b). PCV2-associated reproductive disease under field conditions is rare. The main route of transmission has been postulated to be the fecal-oral route (Segalés et al., 2005); however, due to the rapid spread and the extensive use of AI, semen transmission has been suggested as a potentially significant route of dissemination of PCV2 (Horlen et al., 2007; Lawton et al., 2004; Rose et al., 2003; Sibila et al., 2004; West et al., 1999). Mature boars infected with PCV2 generally lack clinical signs and lesions (Larochelle et al., 2000; Madson et al., 2008). The virus has been detected in semen of naturally and experimentally infected boars, even after the appearance of antibodies in the serum (Larochelle et al., 2000). In the acute phase of infection, PCV2 DNA was detected in serum and semen at two and five days post inoculation, respectively (Larochelle et al., 2000; Madson et al., 2008). Detection of PCV2 viremia commonly precedes the detection of semenassociated virus (Madson et al., 2008), but semen shedding has been reported in the absence of viremia (Larochelle et al., 2000). Anti-PCV2 antibodies typically develop by two weeks post inoculation (Larochelle et al., 2000; Madson et al., 2008). Following intranasal inoculation, intermittent semen shedding of PCV2 DNA was observed during a 47 day observation period (Larochelle et al., 2000). Intermittent semen shedding was confirmed by a different study (Grasland et al., 2008) after testing semen samples for 56 days in four inoculated boars. In contrast, continuous semen shedding was observed following intranasal and intramuscular inoculation following a 90 day observational period (Madson et al., 2008). In addition, naturally infected boars were found to sporadically shed PCV2 DNA in semen for up to 27.3 weeks in a PCV2 positive boar stud (McIntosh et al., 2006). Peak PCV2 shedding in semen occurs between nine and 20 days post inoculation (Grasland et al., 2008; Madson et al., 2008). Changes in morphology, motility, or quantity are not commonly associated with natural or experimental PCV2 infection (Madson et al., 2008; McIntosh et al., 2006). Clinical signs of PCV2 infection in the dam are typically absent or unapparent; however, a low percentage of females may abort due to systemic illness. Pyrexia and anorexia are frequently observed in aborting dams (Park et al., 2005). The virus is also able to replicate in the zona pellucida-free embryos, leading to embryonic death (Mateusen et al., 2004, 2007). Delayed farrowing (>118 days of gestation) (Ladekjær-Mikkelsen et al., 2001) or pseudopregnancy (Josephson & Charbonneau, 2001) is less frequently observed with PCV2-associated reproductive failure. PCV2 affected litters are commonly composed of increased numbers of non-viable fetuses (mummified and stillborn) at parturition (Madson & Opriessnig, 2011).

#### **3.11 Other viruses that are of minor importance**
