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  • 1. Introduction to Risk Analysis
  • 2. Terminology and Uncertainty in Pest Risk Analysis
  • 3. Types of Pest Risk Analyses
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  • 1. PRA Initiation Points
  • 2. Organism PRA
  • 3. Pathway PRA
  • 4. Commodity PRA
  • 5. Lesson Summary
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Lesson 3: Types of Pest Risk Analyses

Topic 3: Pathway PRA

Analyzing Pathway Risks

Recall from Lesson 2 that, the ISPM No. 5 definition of pathway is “any means that allows entry or spread of a pest.” Depending on the scope of the pathway PRA, the analysis can be relatively short and simple or long and complex. As we learned earlier, the most common pathways subjected to this type of analysis are imported and exported agricultural commodities such as fruits, vegetables, nursery stock, and other plant products. PRAs that analyze the risk of pests entering an area via a specific commodity, known as commodity PRAs, are covered in the next topic. We will examine other types of pathways in this topic.

As with organism PRAs, a pathway PRA is conducted in order to:

1. Estimate the level of risk posed by a particular situation or activity
2. Determine whether measures:
1. Would be feasible
2. Would be effective
3. Should be applied to manage the identified risk(s)

The scope for a pathway PRAs can be as different as the pathways themselves, although it is possible to make some general statements about them. For example, the most basic unit of analysis is a single pest using a single pathway. Other possibilities include multiple pests using a single pathway, a single pest using multiple pathways, or multiple pests using multiple pathways. The complexity of the analysis increases as more pests and more pathways are considered.

The analysis in some pathway PRAs focus on specific time periods or events. For example, a pathway PRA may examine the likelihood or probability of the entry of any pest by asking the question, “How likely are pests to cross a particular border?” In this example, the analysis does not identify a specific pest. Instead, its focus is on characteristics that make the border a good (or bad) pathway for pests.

Alternatively, a pathway PRA may examine how far a pest might spread once it has entered and established in an area. In this case, the components of a more traditional PRA such as likelihood of entry and establishment would not be considered in the analysis, because those events have already occurred. In this example, the analysis would focus on events related to spread of the pest.

Now let’s consider a graphic representation of a pathway. This graphic can be used to understand the series of hypothetical events that may lead to the introduction and spread of a pest.

Some of the most challenging pathways to characterize and analyze are those resulting from smuggling or illegal importation of goods. A country may make the regulatory decision to prohibit the import of a particular commodity because of its high risk. Smuggling or illegal importation may result if the commodity cannot be legally imported into a country. This outcome presents an even greater risk because smuggled products are not subject to any phytosanitary measures. Furthermore, smuggled products may not be “commercial grade”—that is, they may be of lower quality and carry more pests than products produced specifically for commercial purposes.

The United States suspects that several important quarantine pests were introduced into the country through smuggling. This includes the citrus disease Huanglongbing (HLB) or citrus greening, which was most likely introduced into the state of Florida on smuggled nursery stock (USDA—ARS, 2006).

International travel is an extremely important pathway for pests. More and more people are travelling internationally, and it is common for travelers to bring souvenirs back home. However, some souvenirs may present hidden risks. For example, fresh fruits or flowers may carry important pests. Wooden handicrafts and other souvenirs, such as straw hats and spices, may also carry pests.

Even though international travelers are often required to declare these types of products, many travelers fail to do so. As such, pests that are present in those products may have a high likelihood of surviving transport, particularly air transport, as pests will travel to new countries, over thousands of miles, in a matter of a few hours.

Natural pathways are important but often neglected means of pest movement. Natural pathways include:

• The pest’s ability to disperse on its own—for example, through walking, crawling, flying, sporulation, etc.
• The pest’s ability to use wind, water, or other natural phenomena to aid its dispersal
• Any combination of these factors

A common misconception is that natural pathways do not need to be analyzed in a PRA, because they cannot be managed like human-assisted pathways. However, analyzing a natural pathway establishes the baseline risk for a given pest or situation. Analyzing a natural pathway may be an important component of a pathway PRA.

An example of analysis of natural pathways is that of soybean rust. The PRA demonstrated that this disease would likely spread on air currents from South America to North America. No measures were available that would prevent the spread. As such, it was considered technically unjustified to require measures to prevent the human-assisted spread of soybean rust, because the baseline risk (the risk from natural pathways) was not preventable.

Although natural pathways may be important for many types of pests, human-assisted pathways are of greater concern to NPPOs.

To continue, select Topic 4 from the Topics menu above or click here.