Biosecurity management practices for the prevention and control of PRRS

Porcine reproductive and respiratory syndrome (PRRS) has been causing tremendous economic losses in swine farms worldwide (Neumann et al 2005). The economic impact of PRRS virus (PRRSV) on the global swine industry is mainly due to reproductive failure in breeding stock or respiratory disease and reduction of growth performances in piglets and growing/finishing pigs, as well as cost of treatments, such as antibiotics for secondary bacterial co-infections (Brockmeier et al 2002; Cho & Dee 2006).

The severity of PRRSV-associated disease may result from a number of factors such as differences in virulence among the PRRSV isolates, probable recombination among the different isolates within the same farm, immune status, host susceptibility and concurrent infections (other viruses and bacteria) and hygiene-monitoring programme (Papatsiros 2012a). To minimize the risk of PRRSV introduction into swine herds, biosecurity protocols are considered to be very important. It is important to understand the epidemiology of PRRS, before trying to reduce the risk of PRRSV entry to farms and PRRS disease control at the farm level. Such valuable information about PRRSV infection at farm level is shown in Table 1. Routes of PRRSV include introduction of infected pigs, contaminated semen, aerosols, non-porcine species (i.e. rodents and birds), insects, feed/water, trucks, fomites (i.e. clothes and boots), and personnel (Table 1). After the initial PRRSV infection of a swine farm, usually PRRSV tends to circulate in the farm, causing subclinical to clinical disease (Zimmerman et al 2006; Papatsiros 2012b). In commercial farrow-to-finish farms, PRRSV is persistent in the infected herd after the initial outbreak due to a cycle of transmission of the virus from the sows to the piglets, and by direct animal contact at later stages (e.g. at weaning), when infected and naïve pigs are mixed (Papatsiros et al 2006; Papatsiros 2012b) or due to virus transmission from pigs with chronic, persistent infection (Allende et al 2000; Benfield et al 2000). 

Table 1 Information about PRRSV infection, essential for Biosecurity Management Practices (BMPs)

 

BMPs are a fundamental part of porcine herd health management programmes for the prevention of PRRSV infection, as well as for the improvement of the health status and productive performances at herd level (Papatsiros 2012a). According to Albina (1997), Le Potier et al (1997) and Weigel et al (2000), the risk of a herd becoming PRRSV-positive increases with:

The purpose of BMPs is either to stop the introduction of PRRSV into negative herds or limit the introduction of new strains into already PRRSV-infected herds (Dee et al 2001). However, the control of PRRS in a herd, continuously exposed to exogenous infection, is a loss of time and money. Biosecurity measures should be reviewed with regard to both internal and external biosecurity. External biosecurity focuses on the risk of introduction of new PRRS strains or other viral and bacterial co-infections from outside of the farm, while internal biosecurity deals with the spread of PRRSV within the farm, after the initial introduction of PRRSV (Papatsiros 2012a).

The basic elements of BMPs for a commercial farrow-to-finish farm or a sow unit are summarized in Table 2. As infected animals and contaminated semen are the main direct routes of PRRSV transmission, within and between pigs, all replacement animals (boars and gilts) should originate from PRRSV-negative farms (Le Potier et al 1997; Dee 1997). An isolation (quarantine) facility is a critical component of a PRRSV biosecurity programme. Ideally, isolation facilities should be located at distances greater than 120 meters from the breeding herd and ideally offsite, on another farm site. The quarantine period should last a minimum of 30 days, including serological tests and PRRSV vaccinations prior to their introduction into the herd. Blood samples should be collected 24-48 hours after the arrival of replacement animals to the isolation facility as well as 60 days prior to their entry to the breeding herd of the swine farm. 

Table 2 Basic elements of Biosecurity Management Practices (BMPs) for commercial swine farms

All incoming animals should be monitored daily for clinical signs by expert personnel, who must visit the isolation facility at the end of the working day. Moreover, semen for artificial insemination should come from PRRSV-negative boar studs because transmission of PRRSV via semen and boars may occur. Shedding of PRRSV in semen may be intermittent and quite variable in duration between boars; viremia is usually absent; and boars may still harbour infectious virus in tissues even after serum (Christopher-Hennings 2001).

Indirect transmission involves transmission by fomites (boots and coveralls), contaminated equipment (e.g. needles), farm personnel and visitors, transport vehicles (contaminated trailers, coolers, containers), substances (e.g. water, food), insects (e.g. houseflies and mosquitoes), or aerosols (Table 1). For this reason, personnel should change needles often in order to avoid moving the PRRS virus from animal to animal via injection (e.g. sows and boars: discard after one injection / piglets: discard after each litter or pen) (Otake et al 2002b). Moreover, equipment that is used in piglet (i.e. instruments for castration, tooth-clipping or tail-docking) should be disinfected. Personnel should have one set of processing equipment in use and the other should be disinfecting.

PRRSV shedding in saliva, urine, and faeces is a high risk factor for the environmental contamination, creating the potential for transmission via fomites, personnel and vehicles (Table 1). All fomites, such as boots, hand gloves and coveralls should be kept clean plus the washing of hands in designated areas prior to entering the animal air space in order to reduce the risk of PRRSV spread by personnel between sites and buildings, tracking contaminated materials (e.g. manure, urine) of infected animals to naïve animals (Otake et al 2002a).

The use of disposable boots, disposable gloves between litters, bleach boot baths or bag-in-a-box shipping methods was highly efficacious in preventing mechanical transmission of PRRSV (Dee et al 2004a). In addition, separate equipment (shovels, brooms, scrapers) should be used for the manure passage and the feed alley at all times in order to reduce the risk of PRRSV spread. Swine farmers should work closely with veterinarians and regularly audit the compliance of personnel movement between facilities and the sanitation of incoming fomites to reduce the risk of PRRSV spread (Pitkin et al 2009a). Moreover, cleaning - disinfection and drying protocols should be applied in all transport vehicles, including external parts (e.g. wheels, trailer) as well as internal parts (e.g. pedals, floor mats, etc). All organic material (e.g. faeces, urine, feed, etc) should be removed and after the sanitation, it is important to be allowed adequate drying time. Drying appeared to be an important component of a sanitation program for ensuring PRRSV biosecurity of transport vehicles. The use of high volume warm air can decrease the amount of time needed for drying (Dee et al 2004b,c).

Moreover, separate shovels, brooms and scrapers should be used for the manure passage and the feed alley at all times in order to reduce the risk of viral spread from behind affected sows to the at-risk sows via the feed alley. In general, biosecurity efforts should focus on all inputs and outputs of the farms, such as pigs, supplies and materials, feed, water, personnel, removal of manure, and reclaims. In addition, the entry of pests such as rodents, insects, and birds from all buildings should be avoided (Zimmerman et al 2006). Finally, all-in-all-out (AIAO) pig flow is effective in controlling a variety of respiratory pathogens in swine farms (Scheidt et al 1995). This method is very effective in reducing the horizontal spread of PRRSV from older, infected pigs to younger, naïve animals. Although, AIAO does not directly control the transmission of PRRSV, it reduces the impact of secondary bacterial co-infections (Papatsiros 2012a). Furthermore, some pens should serve as hospital pens or recovery pens for sick pigs with clinical respiratory signs. The number of hospital and recovery pens required depends on the individual farm and current health status.

The disinfection is a crucial point of BMPs in a PRRSV-infected farm. As shown in Table 1, the survival of PRRSV in the environment is affected by factors, such as substrate, pH, temperature, relative humidity, and exposure to ultraviolet light. Improperly cleaned pens are a source of pathogens for the next group of pigs. Rooms should be washed thoroughly using hot water and a high-pressure sprayer, so that all visible organic matter is removed from floors, walls, feeders and drinkers. PRRSV is inactivated by lipid solvents, such as chloroform and ether (Benfield et al 1992). PRRSV is also relatively labile in the environment and particularly susceptible to heating and drying (Pirtle & Beran 1996). The most important step in the sanitation protocol for complete inactivation of PRRSV is the application of adequate downtime or drying time after disinfection. Cleaned and disinfected pens should be left to dry a minimum of 24 hours before pigs are placed, while barns should be allowed to dry for a minimum of 7-14 days between batches. Since PRRSV persists in cold and wet conditions (Dee et al 2002), all equipment and material used at the farm or for transport of pigs must be cleaned and dried (Dee et al 2004b,c). Finally, PRRSV can survive in lagoon effluent for up to 3 days at 20°C and for 7 days at 4°C. Contact with PRRSVpositive effluent can be a source of infection to naïve pigs. Therefore, producers that utilize recycled lagoon water in their waste management protocols may be at higher risk for external PRRSV introduction than those who use deep pits (Zimmerman et al 2006).

Finally, the filtering of air entering pig housing facilities has been proposed as a means to reduce the risk of airborne transmission of PRRSV from infected herds to at-risk populations (Pitkin et al 2009b). Therefore, air filtration is an effective means to reduce the risk of external PRRSV introduction to large breeding herds located in regions of high pig density (Dee et al 2010). Moreover, increased relative humidity may increase the survival time of respiratory pathogens in the room environment and increased ventilation rates may increase air speed, causing chilling. Chilling, due to the wide daily and rapid small temperature fluctuations, contributes significantly to the increased prevalence of disease by increasing stress levels in affected pigs. For this reason, ventilation and temperature controllers should be adjusted so as to ensure that they are set to control temperature fluctuation and daily variability (Papatsiros 2012a). The use of simple environmental testing equipment, such as humidity monitors, data loggers, air speed and gas testers is very important. PRRSV can also be inactivated through composting or incinerating carcasses. 

More than two decades after its emergence, PRRS is still having a major impact on pig health, welfare and production worldwide. Even today, the reduction of economic losses in commercial swine farms is a challenge for farmers and swine veterinarians. The application of BMPs is an essential part of a herd health management programme in order to avoid the introduction of PRRSV strains into swine farms as well as to stop the PRRSV circulation into the herd. The updated knowledge about PRRS disease farm level is considered very important for the best application of BMPs. The implementation and maintaining of BMPs on a regular basis is a beneficial investment for swine farmers. 

Albina E., 1997 Epidemiology of porcine reproductive and respiratory syndrome (PRRS): an overview. Vet Microbiol 55(1-4):309-316.

Allende R., Laegreid W. W., Kutish G. F., Galeota J. A., Wills R. W., Osorio F. A., 2000 Porcine reproductive and respiratory syndrome virus: description of persistence in individual pigs upon experimental infection. J Virol 74:10834-10837.

Benfield D. A., Nelson E., Collins, J. E., Harris L., Goyal S. M., Robison D., Christianson W. T., Morrison R. B., Goryca D., Chladek D., 1992 Characterization of swine infertility and respiratory syndrome (SIRS) virus (isolate ATCC VR-2332). J Vet Diagn Invest 4(2):127-133.

Benfield D., Nelson J., Rossow K., Nelson C., Steffen M., Rowland R., 2000 Diagnosis of persistent or prolonged porcine reproductive and respiratory syndrome virus infections. Vet Res 31(1):71.

Bierk M., Dee S., Rossow K., Otake S., Collins J., Molitor T., 2001 Transmission of porcine reproductive and respiratory syndrome virus from persistently infected sows to contact controls. Can J Vet Res 65(4):261-266.

Bloemraad M., de Kluijver E. P., Petersen A., Burkjardt G. E., Wensvoort G., 1994 Porcine reproductive and respiratory syndrome: temperature and pH stability of Lelystad virus and its survival in tissue specimens from viraemic pigs. Vet Microbiol 42(4):361-371.

Brockmeier S. L., Halbur P., Thacker E. L., 2002 Porcine respiratory disease complex. Brogden K. A. and Guthmiller J. M. (Eds.) Polymicrobial Diseases. Washington (DC), ASM Press, USA.

Cho J. G., Dee S. A., 2006 Porcine reproductive and respiratory syndrome virus. Theriogenology 66(3):655-662.

Christianson W. T., Choi C. S., Collins J. E., Molitor T. W., Morrison R. B., Joo H. S., 1993 Pathogenesis of porcine reproductive and respiratory syndrome virus infection in mid-gestation sows and fetuses. Can J Vet Res 57(4):262-268.

Christopher-Hennings J., Nelson E. A., Hines R. J., Nelson J. K., Swenson S. L., Zimmerman J. J., Chase C. L., Yaeger M. J., Benfield D. A., 1995 Persistence of porcine reproductive and respiratory syndrome virus in serum and semen of adult boars. J Vet Diagn Invest 7(4):456-464.

Christopher-Hennings J., 2001 Monitoring for porcine reproductive and respiratory syndrome virus (PRRSV) in the boar stud. J Swine Health Prod 9(4):186-188.

Dee S. A., 1997 An overview of production systems designed to prepare naïve replacement gilts for impending PRRSV challenge: a global perspective. J Swine Health Prod 5(6):231-239.

Dee S. A., Deen J., Rossow K., Wiese C., Otake S., Joo H. S., Pijoan C., 2002 Mechanical transmission of porcine and respiratory syndrome virus throughout a coordinated sequence of events during cold weather. Can J Vet Res 66(4):232-239.

Dee S., Deen J., Rossow K., Weise C., Eliason R., Otake S., Joo H. S., Pijoan C., 2003 Mechanical transmission of porcine reproductive and respiratory syndrome virus throughout a coordinated sequence of events during warm weather. Can J Vet Res 67(1):12-19.

Dee S. A., Deen J., Pijoan C., 2004a Evaluation of four intervention strategies to prevent the mechanical transmission of porcine reproductive and respiratory syndrome virus. Can J Vet Res 68(1):19-26.

Dee S. A., Deen J., Otake S., Pijoan C., 2004b An experimental model to evaluate the role of transport vehicles as a source of transmission of porcine reproductive and respiratory syndrome virus to susceptible pigs. Can J Vet Res 68(2):128-133.

Dee S., Deen J., Burns D., Douthit G., Pijoan C., 2004c An assessment of sanitation protocols for commercial transport vehicles contaminated with porcine reproductive and respiratory syndrome virus. Can. J Vet Res 68(3):208-214.

Dee S., Spronk G., Reicks D., Ruen P., Deen J., 2010 Further assessment of air filtration for preventing PRRSV infection in large breeding pig herds. Vet Rec 167:976-977.

Dee S., Pitkin A., Otake S., Deen J., 2011 A four-year summary of air filtration system efficacy for preventing airborne spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae. J Swine Health Prod. 19(5):292- 294.

Dee S. A., Torremorell M., Rossow K., Mahlum C., Otake S., Faaberg K., 2011 Identification of genetically diverse sequences (ORF 5) of porcine reproductive and respiratory syndrome virus in a swine herd. Can J Vet Res 65:254-260.

Le Potier M. F., Blanquefort P., Morvan Ε., Albina Ε., 1997 Results of a control programme for the porcine reproductive and respiratory syndrome in the French "Pays de la Loire" region. Vet Microbiol 55(1-4):355-360.

Mortensen S., Stryhn H., Sogaard R., Boklund A., Stark K. D., Christensen J., Willeberg P., 2002 Risk factors for infection of sow herds with porcine reproductive and respiratory syndrome (PRRS) virus. Prev Vet Med 53(1-2):83–101.

Neumann E. J., Kliebenstein J. B., Johnson C. D., Mabry J. W., Bush E. J., Seitzinger A. H., Green A. L., Zimmerman J. J., 2005 Assessment of the economic impact of porcine reproductive and respiratory syndrome on swine production in the United States. J Am Vet Med Assoc 227(3):385-392.

Otake S., Dee S. A., Rossow K. D., Deen J., Joo H. S., Molitor T. W., Pijoan C., 2002a Transmission of porcine reproductive and respiratory syndrome virus by fomites (boots and coveralls). . J Swine Health Prod 10(2):59–65.

Otake S., Dee S. A., Rossow K. D., Joo H. S., Deen J., Molitor T. W., Pijoan C., 2002b Transmission of porcine reproductive and respiratory syndrome virus by needles. Vet Rec 150:114-115.

Otake S., Dee S. A., Rossow K. D., Moon R., Pijoan C., 2002c Mechanical transmission of porcine reproductive and respiratory syndrome virus by mosquitoes, Aedes vexans (Meigen). Can J Vet Res 66:191-195.

Otake S., Dee S. A., Jacobson L., Torremorell M., Pijoan C., 2002d Evaluation of aerosol transmission of porcine reproductive and respiratory syndrome virus under controlled field conditions. Vet Rec 150:804-808.

Otake S., Dee S. A., Rossow K. D., Moon R. D., Trincado C., Pijoan C., 2003a Transmission of porcine reproductive and respiratory syndrome virus by houseflies (Musca domestica). Vet Rec 152:73-76.

Otake S., Dee S. A., Moon R. D., Rossow K. D., Trincado C., Farnham M., Pijoan C., 2003b Survival of porcine reproductive and respiratory syndrome virus in houseflies (Musca domestica Linnaeus). Can J Vet Res 67:198-203.

Papatsiros V. G., Alexopoulos C., Kritas S. K., Koptopoulos G., Nauwynck H. J., Pensaert M. B., Kyriakis S. C., 2006 Long-term administration of a commercial porcine reproductive and respiratory syndrome virus (PRRSV)-inactivated vaccine in PRRSVendemically infected sows. J Vet Med B Infect Dis Vet Public Health 53(6):266-272.

Papatsiros V. G., 2011 PRRSV and PCV-2 infections in Greek swine farms: Clinical forms and vaccination programmes. VetScan 6(1): article 73.

Papatsiros V. G., 2012a Porcine herd health management practices for the control of PRRSV infection. Perez-Marin C. C. (Ed.) A Bird's-Eye View of Veterinary Medicine. InTech Europe, Croatia 281-300.

Papatsiros V. G., 2012b Impact of a killed PRRSV vaccine on sow longevity in a PRRSV infected swine herd. J Appl Anim Res doi:10.1080/09712119.2012.692323.

Pirtle E. C., Beran G. W., 1996 Stability of porcine reproductive and respiratory syndrome virus in the presence of fomites commonly found on farms. J Am Vet Med Assoc 208 (3):390-392.

Pitkin A., John D., Scott D., 2009a Further assessment of fomites and personnel as vehicles for the mechanical transport and transmission of porcine reproductive and respiratory syndrome virus. Can J Vet Res 73(4):298–302.

Pitkin A., Deen J., Dee S., 2009b Use of a production region model to assess the airborne spread of porcine reproductive and respiratory syndrome virus. Vet Microbiol 136(1- 2):1-7.

Pitkin A., Otake S., Dee S., 2011 A one-night downtime period prevents the spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae by personnel and fomites (boots and coveralls). J Swine Health Prod 19(6):345-8.

Prieto C., Suárez P., Simarro I., Garcia C., Martin-Rillo S., Castro J. M., 1997a Insemination of susceptible and preimmunized gilts with boar semen containing porcine reproductive and respiratory syndrome virus. Theriogenology 47:647-654.

Prieto C., Suárez P., Simarro I., García C., Fernández A., Castro J. M., 1997b Transplacental infection following exposure of gilts to porcine reproductive and respiratory syndrome virus at the onset of gestation. Vet Microbiol 57:301-311.

Scheidt A. B., Cline T. R., Clark L. K., Mayrose V. B., Van Alstine W. G., Diekman M. A., Singleton W. L., 1995 The effect of all-in-all-out growing-finishing on the health of pigs. J Swine Health Prod 3(5):202-205.

Schurrer J. A., Dee S. A., Moon R. D., Rossow K. D., Mahlum C., Mondaca E., Otake S., Fano E., Collins J. E., Pijoan C., 2004 Spatial dispersal of porcine reproductive and respiratory syndrome virus contaminated flies after contact with experimentally infected pigs. Am J Vet Res 65(9):1284-1292.

Shirai J., Kanno T., Tsuchiya Y., Mitsubayashi S., Seki R., 2000 Effects of chlorine, iodine, and quaternary ammonium compound disinfectants on several exotic disease viruses. J Vet Med Sci 62(1):85-92.

Swenson S. L., Hill H. T., Zimmerman J. J., Evans L. E., Landgraf J. G., Wills R. W., Sanderson T. P., McGinley J. M., Brevik A. J., Ciszewski D. K., Frey M. L., 1994a Excretion of porcine reproductive and respiratory syndrome virus in semen after experimentally induced infection in boars. J Am Vet Med Assoc 204:1943-1948.

Swenson S. L., Hill H. T., Zimmerman J. J., Evans L. E., Wills R. W., Yoon K. J., Schwartz K. J., Althouse G. C., McGinley M. J., Brevik A. K., 1994b Artificial insemination of gilts with porcine reproductive and respiratory syndrome (PRRS) virus-contaminated semen. J Swine Health Prod 2(6):19-23.

Wagstrom E. A., Chang C. C., Yoon K. J., Zimmerman J. J., 2001 Shedding of porcine reproductive and respiratory syndrome virus in mammary gland secretions of sows. Am J Vet Res 62:1876-1880.

Weigel R. M., Firkins L. D., Scherba G., 2000 Prevalence and risk factors for infection with porcine reproductive and respiratory syndrome virus (PRRSV) in swine herds in Illinois (USA). Vet Res 31(1):87-88.

Wills R. W., Zimmerman J. J., Yoon K. J., Swenson S. L., Hoffman L. J., McGinley M. J., Hill H. T., Platt K. B., 1997a Porcine reproductive and respiratory syndrome virus: routes of excretion. Vet Microbiol 57(1):69-81.

Wills R. W., Zimmerman J. J., Swenson S. L., Yoon K. J., Hill H. T., Bundy D. S., McGinley M. J., 1997b Transmission of porcine reproductive and respiratory syndrome virus by direct close or indirect contact. J Swine Health Prod 5:213-218.

Wills R. W., Zimmerman J. J., Yoon K. J., Swenson S. L., McGinley M. J., Hill H. T., Platt K. B., Christopher-Hennings J., Nelson E. A., 1997c Porcine reproductive and respiratory syndrome virus: a persistent infection. Vet Microbiol 55(1-4):231-240.

Wills R. W., Doster A. R., Osorio F. A. 2002 Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) to age-matched sentinel pigs. J Swine Health Prod 10(4):161-165.

Yoon I. J., Joo H. S., Christenson W. T., Morrison R. B., Dial G. D., 1993 Persistent and contact information in nursery pigs experimentally infected with porcine reproductive and respiratory syndrome (PRRS) virus. J Swine Health Prod 1(4):5-8.

Zimmerman J. J., Benfield D. A., Murtaugh M. P., Osorio F. A., Stevenson G. W., Torremorell M., 2006 Straw B. E., Zimmerman J. J., D’Allaire S., Taylor D. J. (Eds.) Diseases of Swine (9th ed.), Porcine Reproductive and Respiratory Syndrome Virus (Porcine Arterivirus). Blackwell Publishing, Ames IA, USA PP 387-417.