The emergence of pandemic H1N1 2009 (pH1N1) in the spring of 2009 has drawn attention once again to the potential threat of viruses hosted in animals, and is provoking considerable international concern. Humans are affected by the pandemic H1N1 2009 virus. As well as pigs, there are reports of turkeys, ferrets, cats and dogs being infected.

In recent years, viral swine diseases have had a significant impact on human health and people's livelihoods. The introduction of African swine fever to the Caucasus, porcine high fever disease in Asia, and earlier outbreaks of classical swine fever and foot-and-mouth disease in Europe and Taiwan Province of China have all had devastating effects on agricultural economies.

The pandemic H1N1 2009 outbreak and initial uncertainties about the role of pigs in disseminating the virus led the Food and Agricultural Organization of the United Nations (FAO), the World Organisation for Animal Health (OIE) and the World Bank to give the highest priority to developing tools for improving biosecurity in pig production. The biosecurity principles outlined in this paper serve to limit pig-to-pig transmission of disease and reduce the impact of infectious swine diseases, including their economic losses. These principles derive directly from scientific knowledge of the epidemiology and transmission of key swine pathogens.

Routes of Disease Transmission in Pigs

One of the most common routes of transmission for infectious agents is direct pig-to-pig contact: movement of infected pigs in close physical contact with non-infected pigs is decisive in transmitting diseases. Disease transmission through infected semen is well-documented. The role of people in disease transmission has been studied closely over the last decade: they can transport pathogens on footwear, clothing, hands, etc. People can carry viruses on their nasal mucosa (nasal carriers) without being infected. They can also be infected and shed pathogens as healthy or sick carriers. People also determine the movements of domestic animals and products among herds, markets and regions. Economic forces can lead to animals being moved over large distances, which increases the possibility of geographical spread of disease.

Vehicles and equipment can be instrumental in spreading diseases. Airborne transmission is more difficult to document, but has been studied experimentally. As some pathogens can survive in meat waste, specific attention must be paid to the use of food wastes in feeding pigs. Feed, water and bedding can all become contaminated and play a role in maintaining diseases. Faeces from infected pigs can contain large quantities of pathogenic viruses, bacteria or parasites: thus the application of manure to agricultural land may introduce pathogens into the human food chain and ecosystem, if due care is not taken during storage and spreading. Birds, rodents, stray dogs and cats, wildlife and feral pigs, together with arthropods, can all be potential carriers, whether through mechanical transmission or by being infected.

Pig Production Systems

In most countries, a variety of different pig production systems exist, from the simplest, with minimal investment, to large-scale market-oriented enterprises. This paper groups pig production systems into four categories, based on the size of herds, the production goals and husbandry management:

• Scavenging pigs is the most basic traditional system of keeping pigs and the one most commonly reported in both urban and rural areas of developing countries. In this free-range system, pigs roam freely around the household and surrounding area, scavenging and feeding in the street, from garbage dumps or from neighbouring land or forests around villages. Few arrangements are made to provide the pigs with housing. Depending on the local situation, pigs may be free-ranging for most of the year and penned during the rainy season. They may be housed at night in a small shelter, to protect them against theft and predators. Keeping scavenging pigs requires minimal inputs and low investment of labour, with no or limited money invested in concentrated feed or vaccines.
  
  
• Small-scale confined pig production is common in developing and transition countries. Pigs are confined to a shelter, which can range from a simple pen made with local materials to more modern housing. The pigs are completely dependent on their keeper for feed, and receive tree branches, leaves, crop residues, agricultural by-products or prepared feed. Smallholders raise pigs for both subsistence and commercial reasons. Pork is supplied to local markets and to more distant urban markets, through a complex marketing and transport system. Within this system, the financial risks for the producer can be high and there is limited support from organisations and professional bodies for technical inputs or services such as insurance.
  
  
• Large-scale confined pig production systems vary in size, but are generally significantly larger than farms in the previously described categories. Because consumers seek to purchase food at the lowest price, but the price of inputs is rising, the profit margin per pig is decreasing. Producers participating in global commodity pork markets must continually reduce the cost of production per pig to be profitable. Production can be on one site only or on several sites that are all part of the same structure. The major cost reduction measures that can be implemented when moving from small-scale to large-scale confined production are through increased farm size, specialisation of farming activities, consolidation of the different steps of pig production, and adoption of an 'all-in, all-out' production flow at each site, with implementation of some or even extensive biosecurity protocols. Large pig farms may be family-owned, affiliated to companies or corporately owned.
  
  
• Large-scale outdoor pig production, in which animals are confined by fencing, but are mainly outdoors; there is therefore less need for investment in bricks and mortar facilities. These farms can brand and sell pork for higher prices, and will often have a larger portfolio of activities, including agro-tourism or hunting, for example.

Biosecurity

In this paper, biosecurity is defined as the implementation of measures that reduce the risk of disease agents being introduced and spread. It requires that people adopt a set of attitudes and behaviours to reduce risk in all activities involving domestic, captive/exotic and wild animals and their products. Biosecurity measures should be used to avoid the entry of pathogens into a herd or farm (external biosecurity) and to prevent the spread of disease to uninfected animals within a herd or farm and to other farms, when the pathogen is already present (internal biosecurity). This paper does not present vaccination as a biosecurity measure per se.

The following are the three main elements of biosecurity:

1. Segregation – The creation and maintenance of barriers to limit the potential opportunities for infected animals and contaminated materials to enter an uninfected site. When properly applied, this step will prevent most contamination and infection.
2. Cleaning Materials – (e.g. vehicles, equipment) that have to enter (or leave) a site must be thoroughly cleaned to remove visible dirt. This will also remove most of the pathogens that contaminate the materials.
3. Disinfection – When properly applied, disinfection will inactivate any pathogen that is present on materials that have already been thoroughly cleaned.

Within each of these three elements, the measures taken to improve biosecurity depend on the pig production system concerned and the local geographic and socio-economic conditions. Segregation measures include:

• controlling the entry of pigs from outside farms, markets or villages
• implementing quarantine for newly purchased animals
• limiting the number of sources of replacement stocks
• fencing a farm area and controlling access for people, as well as birds, bats, rodents, cats and dogs
• maintaining adequate distances between farms
• providing footwear and clothing to be worn only on the farm, and
• using an all-in-all-out management system.

Cleaning and disinfection measures may involve the use of high-pressure and low-pressure washers, and will be implemented on not only buildings on the premises, but also vehicles, equipment, clothing and footwear.

The willingness to implement measures depends greatly on the investment capacity and social and economic status of the producers and other stakeholders. For meaningful change to take place in rural communities, those involved must have a clear understanding of the economic importance of pig production for their owners' livelihoods and the resource base that enables appropriate sustainable biosecurity measures to be developed; this depends on having a well-designed communication plan.

Good Practices

The implementation of biosecurity measures in scavenging pig production systems is constrained by the producers' limited capacity to invest resources and time, and by the nature of scavenging pig production. However, there are simple measures that can be recommended and that are mainly related to segregation: new pigs introduced into a village must be free of disease, and particular attention is required when they are purchased from a market. The use of quarantine is very important. There is also concern over sows and boars that are moved from one location to another for mating. The health status of the boars needs to be known, particularly regarding diseases of concern. It is common practice for poor pig farmers to sell animals for slaughter as soon as disease is suspected. The marketing of sick animals is a serious disease risk, as these incubating or excreting sick pigs disseminate diseases, particularly when they are sold at live-animal markets. This practice should be prevented. The use of untreated pig swill must be avoided, and is often prohibited by national regulations. In the case of unusual pig deaths, veterinary services should be informed, so that immediate actions can be taken to control disease outbreaks; proper disposal of carcasses by burying, composting or burning is also crucial. Cleaning of night shelters and equipment must be emphasised. Disinfection is unlikely to be practicable.

In small-scale confined pig production, measures will focus on the three elements of biosecurity. An important difference between small-scale confined and scavenging pig production is that confinement facilitates segregation measures. The measures proposed for scavenging pigs are also valid for small-scale confined pig production. Newly purchased pigs should be kept for a minimum of 30 days in a quarantine pen.

In this system, additional measures can be introduced. The location of the pig farm can be controlled. Age-segregated rearing should be encouraged and buildings designed so that commingling among groups of pigs of different health status can easily be avoided. An all-in-all-out management system is possible. Proper fencing and measures to control contact with birds, rodents, cats and dogs can be promoted. It is important to develop protocols for the farm, to which visitors must strictly adhere; with confined pigs, it is possible to control access for vehicles and people, including drivers and feed providers. Authorised visitors, particularly those dealing with pigs – including other farmers – should be provided with specific clothing and clean footwear by the farm being visited, and should wash their hands on entry. All instruments or equipment that is likely to come into contact with pigs should be assigned to the farm and kept clean.

The importance of regular and thorough cleaning of the pig unit is often not fully understood: manure should be removed from the pens every day, unless there are slatted floors or an equivalent. Contact with manure, urine and straw bedding from sick and dead animals should be avoided. After cleaning, the use of disinfectant should be promoted. When a group (batch) of same-aged pigs leaves a building, the room should be thoroughly cleaned and disinfected. Vehicles, especially those used to transport pigs, should be thoroughly cleaned and disinfected before returning to or visiting other farms. A safe pig loading bay will limit movement of vehicles on the farm.

In large-scale confined production systems the same principles apply as for the previously discussed systems but the impact of disease has the potential to be proportionally higher. The physical location of herds should be planned to maintain adequate distances from neighbouring farms and frequently used roads. For aerosol transmission, the same rules apply as for the previous system. For units where significant investment in livestock health has occurred, filtration of incoming air is sometimes employed in an attempt to reduce the risk of airborne infection. Standards should be developed for the purchase of incoming genetic material. When practising artificial insemination (AI), the health status of the AI unit should match that of the recipient herd, and its biosecurity protocols should be adequate. The control of visitors and fomites is a major focus, as both can bring pathogens to the farm. Training and updating of staff by veterinarians and technicians specialized in disease control is necessary.

A number of disease control measures and techniques are now available to control relevant pathogens in commercial farms. The biggest challenge is often to ensure proper implementation of good husbandry practices. Progressive eradication of pathogens contributes to regional biosecurity by lowering the regional disease risk. Followed to its logical conclusion, this process can result in eradication of disease from the region or country.

Biosecurity for large-scale outdoor production systems needs to focus on the control of feedstuffs, water and pasture contamination, wildlife and human visitors. Other factors such as transportation, fomites and sources of breeding stock also need to be considered, as the risks are the same as in the other production systems.

Intermediaries, service providers and transporters are the key links along pig production and marketing chains. Their potential roles in disease transmission – but also as champions for biosecurity – is important; they must therefore be fully involved in the implementation of biosecurity programmes.

Slaughterhouses are another important element in the marketing chain where all three elements of biosecurity must be implemented, with a major focus on bio-containment. To maintain a high health status at AI centres, it is essential that the boars purchased are of verified disease-free status. The implementation of a quality assurance scheme in these enterprises should be a priority.

Live-animal markets are obvious mixing points and a potential source of disease spread: bio-containment is crucial at these sites, and contact among animals of different origins must be controlled. To limit the risk of disease spread, animals that have not been sold should not be reintroduced back into the home herd without a quarantine period. Wastewater and slurries need to be managed properly. However, such markets are also a useful location for disseminating and collecting information.

Conclusion

Pigs are susceptible to a wide range of diseases that affect productivity and, de facto, the producer's income – whether he/she is a large-scale commercial producer or has only one scavenging pig. The 2009 influenza pandemic, caused by a new strain of swine-origin H1N1, was a timely reminder of the risks for human health related to livestock production – the same livestock, including pigs, that supports the livelihoods and food security of almost a billion people, most of whom are poor.

Among the solutions required to minimise the risk of disease spread, the strengthening of biosecurity is a priority. It does not reduce the need for appropriate preparedness plans and adequate resources to control disease outbreaks once they occur, but it is proactive, has a preventive impact and enables producers to protect their assets.

A thorough knowledge of pig disease epidemiology and the routes of disease transmission has enabled authorities and producers to develop adequate biosecurity measures for the pig sector. Some of these measures are applicable across all production systems, while others are not. Each production system requires specific biosecurity measures, and although decision-makers should not compromise on public health, the measures to strengthen biosecurity in pig production must take into consideration the technical and financial capacity of stakeholders to implement them. The social and economic impacts of closing farms that cannot comply with the required level of biosecurity must also be carefully assessed.

The key to changing behaviours/practices in relation to enhanced biosecurity lies in people's perceptions of risk and the resources available at the production level. For meaningful change to take place in rural communities, a holistic, multi-sectoral approach is required to identify critical risk points for disease spread and to understand the evolution of diseases in specific environments, the impact of disease on people, and the impact that people have or can have on disease. The promotion of appropriate sustainable biosecurity measures goes hand-in-hand with the use of participatory methodologies and a well-designed communication strategy.

Further efforts are required to find the appropriate balance between what the private sector can and will voluntarily implement – based on cost/benefit ratios – and the requirements of regulations. Mutual trust between the public and private sectors is essential. In the case of zoonotic diseases, pre-emptive discussions among public health agencies, agricultural departments, veterinary services and the pig industry should take place to ensure common understanding and good cooperation in the interest of society in general. Strengthened collaboration between public services and the private sector is crucial for better disease control.

Further Reading

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April 2010