Risk Assessment Methodologies for Imports of Products of Animal Origin: A Systematic Review of Formal and Informal Trade Pathways

Every time a shipment of meat, milk, or eggs crosses a border, it carries more than just food; it carries the potential for invisible travelers. These travelers are disease-causing agents like viruses and bacteria that can survive inside animal products long after the animal is gone. When these products enter a country free of such diseases, they can spark outbreaks that devastate local farms, disrupt food supplies, and cost billions of dollars. To stop this, governments rely on import risk assessments. Think of these assessments as a detailed map that helps officials predict where a disease might enter, how it might spread, and what damage it could cause. This map is drawn using data about the type of product, the route it takes, and the specific germs it might carry. The goal is to build a wall of safety around a country's livestock, but the strength of that wall depends entirely on how accurately the map is drawn.

A team of researchers recently decided to check the quality of these maps. They wanted to know how well scientists and officials are currently assessing the risks associated with bringing animal products into a country. They focused on two very different ways these products move: the formal, legal trade that happens through official ports with health certificates, and the informal, often illegal trade that happens when people bring food in their suitcases or when goods are smuggled across borders without inspection. The researchers gathered every study they could find that tried to measure the risk of disease entering a country through these pathways. They looked at 51 different studies published over the last thirty years to see what methods were used, what diseases were studied, and where the biggest gaps in knowledge might be hiding.

What they found was a landscape dominated by a few specific threats and a few specific routes. The most common diseases examined were African swine fever, foot-and-mouth disease, and classical swine fever. These three viruses are the heavyweights of animal disease risk, largely because they can survive for months or even years inside meat and meat products. The studies showed that meat and meat products, particularly those from pigs and cattle, are the most frequently analyzed items. This makes sense, as these are the products most likely to carry these resilient viruses. In contrast, milk and dairy products were studied much less often, and other items like bushmeat or fish were rarely considered at all. The researchers noted that while milk can carry disease, the processes used to make it safe, like pasteurization, and the strict conditions required to keep it cold, make it less likely to be a major vector for these specific outbreaks compared to raw or cured meats.

The way these risks are calculated varies significantly depending on the data available. Some studies use simple, descriptive categories to say a risk is "low" or "high," while others use complex mathematical models to calculate exact probabilities. The researchers found that nearly half of the studies used these detailed mathematical models, but a large portion still relied on descriptive methods. This difference often comes down to the availability of numbers. To build a precise mathematical model, you need hard data on how many people are traveling, how much meat they are carrying, and how many animals are sick in the country of origin. When that data is missing, scientists have to fall back on expert opinions and general estimates.

A striking pattern emerged regarding the routes of entry. The vast majority of the studies focused on formal trade, the legal shipments that pass through official checkpoints. This is largely because official trade leaves a paper trail; governments know exactly how many tons of beef arrived last month and from which port. Informal trade, however, is a ghost in the machine. It includes the meat hidden in a traveler's luggage, the packages sent through the mail, or the goods moved across borders by people who do not declare them. The researchers found that while informal trade is widely recognized as a dangerous pathway, it is rarely the main focus of risk studies. When it is studied, it is almost always about passengers carrying food in their personal bags. Other informal routes, like postal shipments or courier services, are almost completely ignored in the current literature.

This gap in knowledge is significant because the informal route is often where the most dangerous surprises happen. A traveler might carry a piece of cured sausage from a country with an active outbreak, and because it was not declared, it bypasses all the safety checks. The researchers pointed out that we simply do not have enough data on how often this happens, what kinds of products are involved, or where they come from. Without this information, the risk maps are incomplete. They show the main highways clearly but leave the back roads and hidden paths largely blank. The studies also revealed that most assessments stop at the point of entry. They calculate the chance of a virus arriving at the border, but fewer studies follow the virus to see what happens next: how it might reach a farm, how it could spread to other animals, or what the economic consequences would be if an outbreak occurred.

The researchers concluded that while we have made great progress in understanding the risks of legal trade, our understanding of informal trade remains fragile. The current system relies heavily on data that is easy to find, which means the invisible flows of illegal or unreported trade are underestimated. To fix this, the authors suggest that countries need to invest in better surveillance at the borders, specifically looking for what travelers are bringing in and what is being smuggled. They also call for more international cooperation to share data on these hidden pathways. Until we can map the informal routes with the same clarity as the formal ones, our defenses against animal diseases will remain incomplete, leaving the door slightly ajar for the next outbreak.