Porcine Reproductive and Respiratory Syndrome Virus has a significant impact on the global productivity of swine industry. The elimination of economic losses due to PRRS, using management practices in commercial swine farms, is a challenge for swine farmers and veterinarian practitioners. Biosecurity Management Practices (BMPs) are considered as essential key point for the prevention and control of PRRSV infection.
The aim of the present study is to perform briefly the principles of most common BMPs at farm level. BMPs are a fundamental part of a porcine herd health management programme, aiming for the improvement health status and productive performance at herd level. 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. BMPs should be reviewed with attention to both internal and external biosecurity. External biosecurity focus on the risk of introduction of new PRRSV 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.
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In conclusion, the application of BMPs is an essential part of a herd health management programme in order to avoid stopping the introduction of PRRSV strains into swine farms as well as to stop the PRRSV circulation into herd.
Keywords: PRRS, Biosecurity Management Practices (BMPs), control, prevention, pig
Porcine reproductive and respiratory syndrome (PRRS) has been causing tremendous economic losses for swine farms worldwide (Neumann et al. 2005). The economic impact of PRRS virus (PRRSV) on the global swine industry mainly due to reproductive failure in breeding stock or respiratory disease and reduction of growth performance 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 and 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 between 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, protocols of biosecurity 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 control PRRS disease 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, aerosol, 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 virus from the sow to piglets, and then by direct animal contact at later stages (e.g. at weaning), when infected and naÃ¯ve pigs are mixed (Papatsiros et al., 2006; Papatsiros, 2012b) or due to transmission of virus from pig with chronic, persistent infection (Allende et al. 2000, Benfield et al. 2000).
Biosecurity Management Practices (BMPs)
BMPs are a fundamental part of a porcine herd health management programme for the prevention of PRRSV infection, the improvement health status and productive performance at herd level (Papatsiros 2012a). Generally, the risk of a herd becoming PRRSV-positive increases with: a) density of PRRSV-positive neighboring herds, within 500 meters; b) increasing herd size; c) high number of animal introductions; d) purchase of semen for artificial insemination; and e) absence of quarantine for replacement boars and gilts (Albina 1997, Le Potier et al. 1997, Weigel et al. 2000).
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 attention to both internal and external biosecurity. External biosecurity focus 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). Therefore, based on Table 1, BMPs should be reviewed with attention to both internal and external BMPs.
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The basic elements of BMPs for a commercial farrow-to-finish farm or a sow unit are summarized in Table 2. First of all, as infected animals and contaminated semen are the main direct routes of PRRSV transmission within and between pig all replacement animals (boars and gilts) should originate from PRRSV negative farms populations (Le Potier et al. 1997, Dee 1997). Therefore, an isolation (quarantine) facility is a critical component of a PRRSV biosecurity program. Ideally, isolation facilities should be located greater than 120 meters from the breeding herd and ideally offsite, on another farm site. The duration of isolation should be for a minimum of 30 days, including serological tests and PRRSV vaccinations prior to their introduction into the herd. In particularly, blood samples should be collected 24- 48 hours after 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. 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 harbor 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, also, could have one set of processing equipment in use and the other should be disinfecting.
PRRSV shedding in saliva, urine, and feces is a high risk factor for the environmental contamination, creating the potential for transmission via fomites (e.g. boots, coveralls), personnel and vehicles (Table 1). All fomites, such as boots, hands 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 naive 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 controling a variety of respiratory pathogens in swine farm (Scheidt et al. 1995). This method is very effective in reducing the horizontal spread of PRRSV from older, infected pigs to younger, naÃ¯ve 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 be served as hospital pens or recovery pens for sick pigs with clinical respiratory signs. The number of hospital and recovery pens required is depending on the individual farm and current health status.
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The disinfection is crucial point of BMPs in a PRRSV-infected farm. As is 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 and 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 oC and for 7 days at 4 oC. Contact with PRRSVÂpositive effluent can be a source of infection to naÃ¯ve 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 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 are very important. Moreover, PRRSV can be inactivated through the process of composting or incinerating carcasses, so only these methods should be applied.
More than two decades after its emergence, PRRS is still having 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.
In conclusion, the application of BMPs is an essential part of a herd health management programme in order to avoid stopping the introduction of PRRSV strains into swine farms as well as to stop the PRRSV circulation into herd. The update knowledge of PRRS disease at the farm level is considered very important for the best application of BMPs. The application and keeping of BMPs on standard basis is a beneficial investment for swine farmers.