Biosecurity programs consist of bioexclusion, surveillance, and biocontainment. It is necessary to clearly identify levels of separation (imagined or physical) between the area considered clean (noninfected, protected) and the area considered dirty (potential source of infection).
Physical separation of areas can be identified by a line referred to as a "line of separation," a "clean/dirty line," or a "cleaning and disinfection" (C&D) line.
Bioexclusion in Biosecurity Programs for Animals
The primary focus of bioexclusion is to prevent or limit the introduction of disease-causing agents into a herd or flock below the threshold for infection or colonization. Bioexclusion requires a systematic approach to preventing pathogen movement across physical or imaginary barriers (protection zones), to eliminate or decrease the number of disease-causing organisms within the animals' environment.
Sound epidemiological principles should be used to establish zone boundaries while making use of existing physical or geographical barriers.
Perspectives on Bioexclusion
Global Perspective on Bioexclusion
The global nature of the animal industry results in daily shipments of animals and animal products throughout the world.
This trade is regulated by the World Organisation for Animal Health (WOAH), and such commerce must comply with WOAH regulations, including those pertaining to farm-level control measures.
Country Perspective on Bioexclusion
To control the spread of disease, WOAH (formerly known as the Office International des Epizooties [International Office of Epizootics], abbreviated OIE) helps to establish international agreements on animal and plant sanitary measures.
The World Trade Organization (WTO) "Agreement on the Application of Sanitary and Phytosanitary Measures" (WTO's SPS Agreement) recognizes WOAH as the relevant international organization responsible for developing and promoting international animal health standards, guidelines, and recommendations affecting trade in live animals and animal products.
The SPS Agreement establishes common definitions and describes WOAH in-house procedures for dealing with international trade disputes. This treaty has also established guidelines and principles governing the transparent, objective, and defensible assessment of disease risk.
More specifically, import risk analysis provides importing countries with an objective and defensible assessment of the disease risks associated with the importation of items such as animals, animal products, biological products, genetic material, feedstuffs, and pathological material.
Region or State Perspective on Bioexclusion
To account for the difficulties in controlling the disease status and management practices of animal populations across the vast expanse of large countries like the US, the Terrestrial Animal Health Code makes allowance for zoning and compartmentalization.
The code defines "subpopulations" by animal health status, enabling member countries to limit damaging trade effects associated with disease outbreaks without exposing the importing country to risk from disease spread. There are also “compartments” based on biosecurity procedures and “zones” based on geography.
The requirements to establish these subpopulations vary with disease specifics and requirements of the trading partners, and they are best decided before disease outbreak. Factors such as disease epidemiology, environmental influences, natural and artificial boundaries, surveillance and monitoring, and applicable biosecurity measures (eg, movement controls and husbandry) are of particular interest.
To establish local zones or compartments, the veterinary services of an exporting country must clearly define subpopulations as stipulated in the terrestrial code. Relevant claims must be reported to the veterinary services of an importing country and supported by official, detailed documentation.
Zone borders are based on natural, artificial, or legal boundaries, making them relatively easy to establish and officially communicate. Compartments based on biosecurity procedures are more difficult to define. The requirements for a compartment include defining adequate biosecurity plans, operating procedures, and management practices that are well documented (including documentation of compliance). This process involves developing a partnership and clearly stipulated responsibilities between animal owners and the appropriate veterinary authority.
Requirements of biosecurity plans include adequate and robust disease surveillance, animal identification, and traceability. These requirements necessitate detailed records for factors such as animal movement and production, feed sources, sources of replacement stock, disease surveillance (including morbidity and mortality), vaccination and medication history, personnel training, and visitor logs.
Risk mitigation also requires that biosecurity plans be regularly audited, reviewed, and adjusted as needed.
Company Perspective on Bioexclusion
For purposes of biosecurity, companies operate as compartments within a country, state, or region. Minimal requirements of international trade require that companies conform to international standards, thereby meeting WOAH requirements.
As compartments within the biosecurity rubric, each trading company, region, state, or country should classify prescribed WOAH diseases according to expected prevalence; design, document, and implement a biosecurity plan to prevent or control these diseases; and provide proof of plan compliance.
This biosecurity plan forms the basis for all disease prevention, diagnosis, and control strategies. The plan should identify potential pathways for disease introduction or spread within the company and describe the measures that are being taken (or will be taken) to minimize risk as prescribed within WOAH's terrestrial code.
Bioexclusion Control Zones
Primary Bioexclusion Control Zone: Animal Confinement Facility
Bioexclusion begins at the animal confinement facility, which is the smallest epidemiological unit within a company or farm. The animals within this facility share a common environment, common management practices, and similar likelihood of pathogen exposure.
The boundaries of animal confinement facilities represent well-defined barriers to entry and an ideal place for implementation of critical control procedures. Every crossing of the facility perimeter should be considered an “event” with potential for pathogen transfer or disease risk.
Decreasing the risk from such events requires an all-in all-out strategy. Thorough cleaning, decontamination, and chemical disinfection should be performed when the facility is empty. After animals arrive, the focus shifts to limiting the number of events (in-house perimeter crossings), as well as the probability of pathogen transmission and infection during unavoidable events.
Secondary Bioexclusion Control Zone: Farm or Site
The secondary zone or compartment in the disease control hierarchy is the farm or site. In this case, the epidemiological unit is the farm rather than the containment facility.
A defined boundary surrounds the farm, and the farm animals share a common environment with common management practices, thereby sharing a common likelihood of exposure to pathogens from nearby containment facilities.
The farm or site establishes physical (eg, fencing) or imaginary boundaries that serve as access points to the secondary control zone, which is a critical zone for disease control. From a biosecurity standpoint, a site can be considered closed, open, or fully open:
In a closed site, the farmer or producer enforces full biosecurity with no uncontrolled access after disinfection.
In an open site, general biosecurity is enforced at the start of transfer or depletion, with access granted only to necessary vehicular traffic.
In a fully open site, routine control is enforced from the point of last animal removal.
Sites involved in an outbreak should remain closed until the responsible veterinarian declares them clean.
Tertiary Bioexclusion Control Zone: Complex
Groups of animals that share a communal animal handling facility (ie, a complex) constitute a tertiary control zone of bioexclusion. The complex represents its own epidemiological unit because sites and farms within it share facilities such as feed mills and processing plants.
Production processes within the complex (eg, rearing farms and grow-out farms) similarly constitute separate epidemiological units. All the defined areas can represent tertiary control zones for biosecurity purposes.
Tertiary zones are seldom fenced, so access boundaries in these zones are typically imaginary.
To save costs, tertiary zones are often established around high-value sectors of the operation, such as the valuable stock used in breeding operations.
To decrease disease transmission risk, critical control points such as transit facilities can be established beyond the site perimeter. At these points, personnel procedures such as showering, changing into protective clothing, and transferring to site- or zone-dedicated transport substantially decrease the probability of disease transmission onto the site.
On-Farm Biosecurity Measures for Animal Health
On-farm biosecurity measures are the last line of defense to protect animal health. The implementation of biosecurity measures varies between different animal industries. To a certain degree, however, all animal industries follow the same principles of segregation, cleaning, and disinfection.
Biosecurity measures need to be part of an overall biosecurity plan, which must be updated and audited regularly. Biosecurity measures are considered external when the measures focus on decreasing the risk of pathogen transmission via elements outside of a population. Internal measures focus on decreasing the risk of transmission within a population.
Having a line of separation (physical or imagined) that clearly demarcates noncontaminated, protected areas from contaminated areas or potential sources of infection helps to establish measures of biosecurity.
Common biosecurity measures include the following:
an isolation or quarantine area to receive incoming replacement animals
perimeter fences
gates
farm-dedicated clothing and footwear
showers
footbaths
dedicated transport vehicles or extensive cleaning and disinfection of transport vehicles between hauls
dedicated farm personnel
visitor log books
clear signage indicating biosecurity practices
dedicated cleaning and disinfection rooms or areas to decontaminate materials introduced into the farm
use of chlorinated water
air filtration (as is popular in pig management in the midwestern US) to prevent the spread of airborne viruses
control of vermin, birds, pets, and insects
Developing a biosecurity plan on an animal farm requires identifying the movements and flows of animals, people, and fomites. Effective biosecurity plans meet the following requirements:
They address disease risks appropriate to the class and type of animals, address risk factors in priority order, state the goals of the plan, and include specifics about how the goals will be achieved.
They include biosecurity procedures deemed appropriate for the farm, should reflect the control points to prevent disease introduction, should be doable, and should instill a biosecurity culture for the animal operation.
They include processes and procedures for implementation, including personnel training and communication with all parties involved.
Their compliance is monitored by a formal or informal auditing process. Biosecurity audits are common in many animal industries, and the main objectives are to evaluate whether the farm is in compliance with established biosecurity measures and to identify areas of risk, given that disease risks are dynamic in nature.
Surveillance in Biosecurity Programs for Animals
The terms monitoring and surveillance are both used to describe ongoing data collection to estimate disease prevalence and severity in a population. However, a monitoring program is typically geared toward collecting statistically reliable prevalence data that can be used to track trends in disease incidence and severity over time.
A surveillance program is based on prevalence data from a readily available sample of the population, with the goal of timely action to correct perceived increases in disease incidence. The importance of these programs increases when remote management control is needed to keep up with increases in herd or flock size and production.
When catastrophic outbreaks require disease eradication, the surveillance program should be focused on detecting source cases and on enabling biocontainment through quarantine and slaughter. When eradication is not required or is not possible, collection of prevalence data should be adjusted to differentiate from other factors contributing to losses, not from effects of the disease itself.
The data collection system should be designed to provide insightful and epidemiologically informative disease indicators. During design, it is good to keep in mind the need for important parameters (eg, sample size) that can be used to calculate other animal health estimates, such as prevalence, incidence, morbidity, mortality, and herd or flock immunity (as indicated by antibody titers, farm production records, etc). In the absence of random sampling, such statistical estimates cannot be taken as absolutely accurate; however, they might be adequate markers of the need for intervention.
For disease eradication and trade, it might be necessary to demonstrate freedom from infection in a country, zone, or compartment/company. Although there might be no obvious evidence of infection in the population, it is impossible to definitively prove freedom from infection unless a perfect (100% sensitive/specific) test is used to examine every member of the population. In this situation, the surveillance system should be able to statistically estimate to an acceptable level of confidence that infection is below a specified prevalence level.
As part of health tracking, individual animals should be monitored for disease at regular intervals. Any change in prevalence suggests a change in the disease conditions that could require corrective action to prevent disease spread.
How often animals are monitored depends on disease epidemiology and the level of biocontainment (eg, need for quarantine or slaughter). Factors such as latent period, mode of transmission (eg, vertical or horizontal), potential for animal dispersion and tracking, and test sensitivity are important considerations.
Biocontainment in Biosecurity Programs for Animals
Biocontainment strategies decrease the consequence of disease challenge by limiting the opportunity for challenge (bioexclusion), enhancing resistance (immunization), and preventing spread (quarantine). When eradication is required, quarantine is usually followed by emergency slaughter.
Pearls & Pitfalls
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Control measures are applied routinely for endemic diseases, but more sporadically for epidemic outbreaks.
The term quarantine refers to the practice of enforced isolation of animals exposed to infectious agents, as well as the place in which these animals are isolated and the time period of isolation. Quarantine is routinely required when live animals or their products are imported. To avoid disease entry into a country, region, zone, compartment, or population, potentially infectious animals or material must be isolated until shown to be disease free.
Enforced isolation is the first biocontainment step when potentially infected animals are brought to a production setting. Movement within or through the control area is restricted and monitored. The size and nature of the control zone depend on disease risk; it usually involves a containment facility, farm, site, or complex within a particular company. The control zone can be expanded to a 3.2-kilometer (2-mile) radius for diseases of national or regional importance.
Disease monitoring is used to establish the extent of an outbreak—first within the quarantine zone, and then in a well-defined surrounding contact zone. The relevant veterinary authority assumes control in cases of foreign or notifiable disease. All vested parties (eg, countries, states, regions, companies, owners) should prearrange an emergency response plan sufficient to address relevant details of containment and eradication.
Other biocontainment measures that focus on decreasing the risk of disease transmission within a population include the use of vaccines, management practices such as all-in all-out, isolation of sick animals, and basic cleaning and disinfection protocols.
Vaccination is commonly used to decrease the risk and/or consequence of infection among exposed individuals or populations. Vaccinations can be used to protect individuals from disease or to protect the next generation by limiting direct vertical transmission and enhancing maternal antibody transfer.
Medication can also be added to feed or drinking water to decrease disease risk.
Key Points
Implementing basic biosecurity practices is key to bioexclusion and biocontainment.
Basic components of a biosecurity program include appropriate procedures such as using physical barriers and protocols to keep disease agents out; implementation of procedures, which require personnel training and communication; and compliance with protocols, which usually requires formal or informal auditing processes.
The line of separation helps clearly demarcate noncontaminated from contaminated areas.
For More Information
Alarcón LV, Allepuz A, Mateu E. Biosecurity in pig farms: a review. Porcine Health Manag. 2021;7(1):5.
Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine. 12th ed. Wiley-Blackwell; 2025.
