Can You Close a Border to Disease?

The WTO SPS Agreement and the difficult line between biosecurity and protectionism.

A serious livestock disease appears overseas. Within hours, agriculture officials in neighbouring countries begin assessing the risk: animals may already have moved, and products derived from susceptible species may be travelling through international supply chains. Farmers want protection, importers want certainty, and politicians want to demonstrate that something is being done. Closing the border can seem like the obvious response — stop the animals, stop the products, keep the disease outside. Yet international trade cannot function if every disease report automatically allows governments to prohibit whatever imports they choose for however long they choose; nor can trade rules reasonably require a country to keep importing animals or food when credible evidence indicates that doing so could introduce a serious biological threat.

Somewhere between those positions sits one of the most important and least publicly understood parts of global biosecurity law: the World Trade Organization Agreement on the Application of Sanitary and Phytosanitary Measures, usually known as the SPS Agreement. Its job is difficult — it has to preserve the right of governments to protect human, animal and plant health while preventing health protection from becoming an excuse for arbitrary discrimination or disguised protectionism. That makes the SPS Agreement much more than a trade instrument; it is part of the international architecture governing biological risk, and part of our One Health Security series on the rules of outbreaks.

What does SPS actually mean?

Sanitary and phytosanitary measures are measures intended to protect human, animal or plant life or health from specified biological and food-related risks — including risks arising from pests and diseases, disease-carrying organisms, contaminants, toxins and disease-causing organisms in food, beverages and feed. That brings an enormous range of measures within the SPS world: import restrictions on cattle because of foot-and-mouth disease; controls intended to prevent African swine fever entering through pigs or certain pig products; plant-health requirements designed to keep an invasive pest outside a country; food-safety rules controlling microbiological or chemical hazards; testing and certification requirements; quarantine; treatment requirements; and restrictions applying to particular geographical regions. These measures can protect populations and agricultural systems from serious harm — and they can also stop trade almost instantly. The SPS Agreement therefore asks governments to connect the restriction to the biological risk.

Countries retain the right to protect themselves

The SPS Agreement does not require governments to sacrifice health protection for free trade — quite the opposite. WTO members retain the right to take sanitary and phytosanitary measures necessary to protect human, animal and plant life or health, and this principle is fundamental: a country facing a credible risk of introducing foot-and-mouth disease does not have to wait until infected animals arrive before acting, a government concerned about a serious plant pest can establish import requirements, and food-safety measures can protect consumers against genuine hazards. The difficulty is that a restriction cannot simply be labelled a health measure and thereby escape scrutiny — the SPS Agreement establishes disciplines around how those measures are developed and applied.

Science matters

One of the central principles is that SPS measures should be based on scientific principles and should not be maintained without sufficient scientific evidence, except in circumstances specifically recognised by the Agreement. Risk assessment therefore becomes extremely important. For animal disease, governments may need to consider factors such as the epidemiology of the disease, surveillance information, prevalence in the exporting country or region, the commodity being traded, processing methods, the pathways through which the pathogen could survive and reach susceptible animals, and the consequences of introduction. This is where international trade law becomes surprisingly close to epidemiology: the legal question cannot be answered without understanding the biology.

But science is rarely complete during an outbreak

This creates an immediate problem, because the point at which governments most urgently want to impose controls is often the point at which scientific information is least complete. Imagine a new disease event: cases have been detected in one region, but investigators do not yet know how long transmission has been occurring, the geographical extent is uncertain, laboratory results are still arriving, and animal movements are being reconstructed. The exporting country says the outbreak is localised; the importing country worries that surveillance has not yet revealed the full picture. Waiting for perfect evidence could allow the pathogen to enter, while acting on every possibility could unnecessarily stop trade. The SPS Agreement therefore has to operate in the uncomfortable territory between certainty and precaution.

Provisional measures are possible

The Agreement recognises this problem. Article 5.7 allows members to adopt sanitary or phytosanitary measures provisionally where relevant scientific evidence is insufficient — which is important, because international trade law does not require a government facing an uncertain biological threat to pretend certainty exists before taking action. But provisional does not mean indefinite: a member relying on Article 5.7 is expected to seek the additional information necessary for a more objective assessment of risk and to review the measure within a reasonable period. That creates a sensible governance principle — uncertainty can justify precaution, but uncertainty should also trigger investigation. A temporary restriction should buy time to understand the threat; it should not become a permanent substitute for understanding it.

International standards create a common language

The SPS Agreement does not expect every country to invent biological safety standards independently; it explicitly recognises international standard-setting bodies. For food safety, the principal reference is the Codex Alimentarius Commission, established by FAO and WHO; for animal health and zoonoses, the recognised organisation is the World Organisation for Animal Health (WOAH); and for plant health, it is the framework developed under the International Plant Protection Convention (IPPC). This architecture matters because international trade requires a degree of shared understanding — if every country applied completely different definitions of acceptable disease risk, certification and control, international agricultural trade would become extremely difficult. International standards provide a baseline: countries can base measures on them, and they can also adopt measures resulting in a higher level of protection where there is scientific justification or where this follows from an appropriate risk assessment. The system therefore allows national choice while attempting to anchor that choice in evidence.

A country is not always one epidemiological unit

For the animal-health stories we have been following, WOAH standards are central: the Terrestrial Animal Health Code contains international standards on disease notification, surveillance, prevention and control, import risk analysis and safe international trade in animals and animal products. These become highly practical, because a disease may be present somewhere within a country without every product from every part of that country presenting the same risk — a processed product may pose a very different risk from a live animal, and a region operating effective surveillance and controls may have a different disease status from an affected region elsewhere in the same state. So suppose African swine fever appears in one part of a large country: should every pig and pork product from the entire country immediately lose access to international markets? Sometimes broad restrictions may be justified; sometimes they may not. The SPS framework therefore recognises concepts of pest- or disease-free areas and areas of low prevalence, while WOAH standards support approaches such as zoning and compartmentalisation — often described as regionalisation. The principle is important: disease controls should reflect the geography of the biological risk where that geography can be established credibly, which allows countries to protect animal health without automatically destroying trade from unaffected regions.

Regionalisation depends on trust

The concept sounds straightforward until an outbreak occurs, because the importing country has to trust the exporting country’s surveillance, its veterinary authority and the effectiveness of its movement controls; it has to understand where infected animals have travelled; and it may need confidence in animal identification and traceability and that the proposed disease-free zone is genuinely epidemiologically separate from the affected area. A line on a map is not enough. Regionalisation therefore depends on system visibility — the better the surveillance, traceability and veterinary governance of the exporting country, the easier it becomes for trading partners to distinguish an affected area from an unaffected one. This creates an important connection between biosecurity infrastructure and trade resilience: investment in surveillance does not merely help detect disease, it can help preserve market access when disease occurs. As we argue elsewhere, trust is biosecurity infrastructure — and here it is trade infrastructure too.

Traceability becomes economic infrastructure

Imagine two countries experiencing identical outbreaks. Country A can rapidly identify affected holdings, reconstruct animal movements, define the likely geographical extent of infection and provide trading partners with detailed surveillance evidence. Country B has fragmented movement records, slow laboratory reporting and limited ability to demonstrate where the disease has or has not spread. The pathogen may be identical, but the rational trade response may not be: trading partners have much stronger grounds for accepting targeted restrictions from Country A, while Country B may face broader controls because uncertainty itself has become part of the risk. This is another reason One Health Security should treat traceability and surveillance as resilience infrastructure rather than simply regulatory administration — better information can reduce both biological and economic damage.

When does biosecurity become protectionism?

Now consider the opposite problem. A domestic livestock industry is struggling economically, a disease appears in an exporting country, and politically an import ban is popular, so the government introduces a broad restriction despite evidence that the particular commodity presents negligible risk. The language is biosecurity; the effect is commercial protection. The SPS Agreement exists partly to constrain this behaviour: measures should not arbitrarily or unjustifiably discriminate between countries where identical or similar conditions prevail, nor be applied in a manner constituting a disguised restriction on international trade. This is why scientific justification matters politically as well as technically — it creates a discipline against using fear of disease as an unlimited trade weapon.

The difficult word is proportionate

The SPS Agreement does not simply apply a general legal test labelled “proportionality” in the way that term appears in some other legal systems, but the underlying policy problem is unmistakable: how much restriction is justified by how much biological risk? A live animal from an infected holding presents one type of risk; a heat-treated product may present another; and an animal originating hundreds of kilometres from an outbreak under verified movement controls may present another. A blanket national ban treats all of those situations similarly — which may sometimes be justified by the uncertainty or epidemiology, but where a more targeted measure can achieve the appropriate level of protection with less disruption to trade, the challenge is matching the intervention to the pathway.

One Health complicates the risk assessment

Some SPS risks sit neatly within one domain; others do not. Imagine a zoonotic pathogen circulating in livestock: the risk assessment may need to consider animal health, occupational human exposure, food safety and potentially wildlife, and a control measure intended to protect livestock might affect food supply, a food-safety measure might alter agricultural production, and a restriction on animal products might change consumer behaviour and trade routes. This is where One Health thinking improves SPS governance, because the correct question is not simply whether the commodity is infected; it may be what biological pathway connects this commodity with harm to humans, animals or plants, and which intervention most effectively interrupts that pathway. That is a systems question.

Borders are only one control point

Disease-related trade discussions naturally concentrate on borders, but the border is often the last opportunity to manage a risk that originated much earlier. Animal-health surveillance in the exporting country matters; farm biosecurity matters; vaccination may matter; traceability matters; processing standards matter; certification matters; and wildlife surveillance may matter. The SPS measure applied at the border therefore sits on top of a much larger risk-management system: strong upstream governance can make downstream trade restrictions more targeted, while weak upstream visibility tends to push importing countries towards caution. The economics of international trade therefore creates another incentive for better One Health surveillance — a point our analysis of the post-Brexit UK border develops for a specific case.

Notifications matter too

The WTO SPS system includes transparency obligations: members notify certain proposed SPS measures and provide information through designated enquiry points and notification authorities. During fast-moving disease events, however, there can be a significant difference between a formal notification system and the speed at which epidemiological intelligence changes, producing another possible form of governance latency. The biological situation may change on Monday, veterinary authorities may reassess the risk on Tuesday, and a border measure may change on Wednesday — after which businesses throughout the supply chain have to understand what has changed, which consignments are affected and what documentation is now required. The faster the biology moves, the more important clear communication becomes.

Disease measures should have an exit

Emergency controls are relatively easy to introduce politically; removing them can be harder, because once a restriction exists governments may face pressure to maintain it until there is absolute certainty that risk has disappeared — and absolute certainty is rarely available. Good SPS governance therefore requires exit criteria: what evidence would justify reducing the restriction, what surveillance period is required, what disease status must be demonstrated, could regionalisation replace a national restriction, and can testing or treatment reduce risk sufficiently? Without predefined questions such as these, temporary biosecurity measures can acquire institutional inertia. This is another place where governance latency can run in reverse — the system can be too slow not only to impose necessary controls, but also to remove controls that are no longer justified.

The cost of getting it wrong runs both ways

Under-react to a disease threat and the consequences can be enormous: an introduced livestock disease can lead to animal losses, movement restrictions, control costs, welfare consequences and long-term disruption of agricultural markets. Over-react and the damage can also be substantial: farmers in unaffected regions lose export markets, food prices may change, supply chains are disrupted, governments may have to provide economic support, trading partners may retaliate or challenge measures, and trust deteriorates. The objective is therefore not maximum restriction; it is maximum risk reduction consistent with the evidence and the chosen level of protection — a much harder standard.

What should better disease-trade governance look like?

The first requirement is rapid epidemiological visibility: trading partners should not have to choose between accepting assurances and imposing broad restrictions because detailed information is unavailable. The second is pre-agreed data exchange: disease status, surveillance, laboratory results, movement information and the basis for regionalisation should be capable of being shared rapidly during significant events. The third is dynamic risk assessment: controls introduced at the beginning of an uncertain outbreak should change as evidence improves. The fourth is explicit exit planning: emergency restrictions should identify what evidence would allow them to be narrowed or removed. And the fifth is cross-sector assessment: animal-health, public-health, food-safety and trade officials should understand the same biological risk rather than producing separate assessments around institutional boundaries.

There is a practical idea hiding here. During a significant transboundary animal or foodborne disease event, governments could create a temporary common operating picture combining outbreak locations, affected species, relevant commodity pathways, animal movements, laboratory confirmation, surveillance zones, trade flows, current import restrictions and the evidence supporting regionalisation. This would not determine whether trade should continue; it would allow epidemiologists, veterinary authorities and trade officials to reason from the same representation of the system, reducing the gap between what the biology is doing and what the trade regime thinks the biology is doing. That gap can be economically enormous.

Can you close a border to disease?

Yes. International trade law does not prevent governments from protecting human, animal or plant health; sometimes restrictions are necessary, and sometimes rapid provisional action is entirely rational because waiting for complete scientific certainty would allow a serious biological threat to spread. But the right question is not simply whether a border can be closed. It is which pathway needs to be interrupted, how much restriction is necessary to interrupt it, and how quickly the measure can change when the evidence changes. The SPS Agreement attempts to place those decisions within an international framework of science, risk assessment, transparency and non-discrimination — a framework that matters because disease creates fear, and fear creates political incentives for visible action. Sometimes the strongest biosecurity measure is also the correct one; sometimes it is not. The challenge is knowing the difference quickly enough to protect both biological systems and the economic systems built around them. A pathogen does not care whether a measure is called trade policy or disease control; One Health Security should care whether it actually interrupts the biological risk.

Related One Health Security analysis

This piece is part of our Rules of Outbreaks series on global health law. It connects to Who Governs a Global Outbreak? (the architecture), One Pathogen, Four Legal Systems (the journey through regimes) and Outside the System, Inside the Risk (the post-Brexit UK border).

Questions & Answers

References and further reading

1. World Trade Organization. Agreement on the Application of Sanitary and Phytosanitary Measures (full text).
2. World Trade Organization. Understanding the WTO Agreement on Sanitary and Phytosanitary Measures; and the WTO SPS information and notifications gateway.
3. World Organisation for Animal Health. Terrestrial Animal Health Code and WOAH international standards.
4. Codex Alimentarius Commission (FAO/WHO), international food standards; and the International Plant Protection Convention, international standards for phytosanitary measures.