1 | USDA APHIS VS S&P CEAH

Key Results: Illegal entry of swine products and byproducts presents the largest potential pathway 

for the entry of African swine fever virus (Table 1). Port inspection and interception data indicates 

that 1) air passenger baggage and foreign mail are two of the largest illegal pathways and 2) pork, 

ham, and sausage are the products with the highest interception rates. The interception data agrees 

with other studies that demonstrate potential entry of African swine fever virus other swine diseases 

through the air passenger pathway. While there are no studies that look at foreign mail as a pathway 

for entry of animal disease, our interception data, estimate of annual volume of packages entering 

the U.S., and estimate of product concealment in mailed packages indicates that foreign mail is an 

entry pathway that warrants greater analytical scrutiny similar to the air passenger pathway.

TABLE 1. SUMMARY OF EVALUATED LIKELIHOOD RATINGS BY PATHWAY

Pathway Legal Illegal

Live Pigs Negligible, with low uncertainty Negligible to low, with moderate 

uncertainty

Semen Negligible, with low uncertainty Low, with moderate uncertainty

Swine products and by-products Negligible to low, with moderate 

uncertainty

High, with low uncertainty

Wildlife: Meat and Trophies <Not reviewed> Low to moderate, with high 

uncertainty

Feed (animal origin) Low to moderate, with high 

uncertainty

Negligible to low, with high 

uncertainty

Feed (plant origin) Negligible to moderate, with high 

uncertainty

Low, with high uncertainty

Feed (supplements) Negligible to low, with high 

uncertainty

<No data to evaluate>

Fomites <Not reviewed> Negligible to moderate, with high 

uncertainty

Regulated Garbage Low, with moderate uncertainty <Not applicable>

Qualitative Assessment of the likelihood of African swine fever virus 

entry to the United States: Entry Assessment

USDA:APHIS:VS:Center for Epidemiology and Animal Health, Risk Assessment Team. 

Fort Collins, CO
2 | USDA APHIS VS S&P CEAH

The likelihood of African swine fever virus (ASFv) entering the United States (U.S.) is variable 

depending on the pathway assessed. Illegal entry of swine products and byproducts presents 

the largest potential pathway for the entry of ASFv. We qualitatively evaluated the likelihood of 

human-assisted entry of ASFv to the U.S. via legal1 and illegal2 movements of potentially 

infected animals and contaminated products from African swine fever (ASF)-affected 

countries/regions. We evaluated imports of live animal, animal products, and animal feed 

ingredients occurring through commercial cargo, air passenger baggage, cruise ships, 

international mail, border crossings, regulated garbage from ship and airliners coming from 

outside the U.S., and fomites. The purpose of this analysis was to determine the transboundary 

pathways representing the greatest likelihood of entry for ASFv into the U.S., and to identify 

pathways where limited data or high uncertainty occur to highlight areas for future investigation. 

We did not evaluate exposure pathways (how the virus may reach susceptible pigs) or 

probability of infection following potential exposure: therefore, we cannot make any definitive 

statements about how likely the transboundary pathways evaluated would result in an ASF

outbreak in U.S. pig populations.

Animal feed ingredients and fomites have the potential to be pathways associated with a 

moderate likelihood of ASFv entry, but there is high uncertainty because of the lack of data on 

transmission from these sources. Most of the available evidence is based on virus survival in 

fecal matter and a single feed ingredient study. The likelihood of transmission from these 

pathways relies on the assumption that a large enough infectious dose continues to survive 

unadulterated through various processing and shipping steps, none of which are adequately 

described or quantified. While fomite transmission via footwear may have small approach rates, 

the volume of air passenger traffic combined with potential underreporting of declared visits to 

farms elevates the likelihood of fomites entering the U.S. undetected. More research and/or 

data collection on these transmission pathways would reduce the uncertainty of these 

preliminary estimates.

We considered the following factors when rating the likelihood of ASFv entry:

1. The overall volume of imports in terms of passengers, animals, shipments, etc. that could 

potentially be contaminated

2. Inspection effort and detection efficiency

3. The number and effectiveness of various regulatory and mitigation actions to reduce 

disease prevalence/transmission along the pathway such as diagnostic testing, treatment, 

disinfection, certificates of animal health, compliance agreements, product 

labeling/traceability, quarantine, regionalization, etc.

4. Available research to quantify viral prevalence, survival, and/or transmission probabilities 

by pathway

 1

The formal entry of shipped goods which has filed appropriate entry documents (entry manifest, 

permits, veterinary certificates, etc), has passed inspection and compliance checklists, is authorized 

for entry by CBP according to various CFRs, and has paid duties to enter the country. 

https://www.cbp.gov/sites/default/files/documents/Importing%20into%20the%20U.S.pdf

2

The informal entry of items under “personal use” that would be rejected entry due to exceeding 

personal allowances for consumption or animal health concerns via various CFRs.

Executive Summary
3 | USDA APHIS VS S&P CEAH

Background

ASF is a highly contagious and deadly viral disease affecting both domestic and feral (wild) pigs 

in all age groups. ASF has been detected in multiple countries on the Asian, European, and 

African continents. Since September 2018, the World Organization for Animal Health (OIE) 

reported the following countries as having new ASF outbreaks in swine or wild boar populations: 

Belgium, Bulgaria, China, Hungary, Latvia, Lithuania, Moldova, Mongolia, Poland, Romania, 

Russia, Ukraine, Vietnam, and Zimbabwe3

. The United States is currently free of ASF.

According to the OIE technical disease card4

, ASFv is extremely stable in the environment 

(Table 2). Some research has documented viral survivability according to different 

environmental conditions. However, this varies according to temperature, humidity, pH, 

presence of organic matter, and exposure to various chemicals.

TABLE 2. ASF RESISTANCE TO PHYSICAL AND CHEMICAL ACTION, FROM THE OIE ASF 

TECHNICAL DISEASE CARD.

Temperature Highly resistant to low temperatures. Heat inactivated by 56°C/70 minutes; 

60°C/20 minutes

pH Inactivated by pH <3.9 or >11.5 in serum-free medium. Serum increases the 

resistance of the virus, e.g. at pH 13.4 – resistance lasts up to 21 hours without 

serum, and 7 days with serum.

Chemicals/Disinfectants Susceptible to ether and chloroform. Inactivated by 8/1000 sodium hydroxide (30 

minutes), hypochlorites – 2.3% chlorine (30 minutes), 3/1000 formalin (30 minutes), 

3% ortho-phenylphenol (30 minutes) and iodine compounds. 

Survival Remains viable for long periods in blood, faeces and tissues; especially infected, 

uncooked or undercooked pork products. Can multiply in vectors (Ornithodoros sp.)

Results

The likelihood that ASFv will enter the U.S. through the legal importation of live pigs is 

negligible with low uncertainty. These estimates are based on:

• All live animal imports are from countries that are currently free of ASF (primarily 

Canada)

• Various regulatory and import requirements relating to animal health mitigate the 

likelihood of ASFv transmission, if properly implemented

• High quality and availability of live animal import data reduces uncertainty of likelihood 

rating

The likelihood that ASFv will enter the U.S. through the illegal importation of live pigs is 

negligible to low with moderate uncertainty. These estimates are based on:

• Available data across three databases report zero interceptions of smuggled live pigs in 

recent years

 3 http://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/Disease_cards/ASF/ 

Report_12_Current_situation_ASF.pdf

4

http://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/Disease_card

s/AFRICAN_SWINE_FEVER.pdf
4 | USDA APHIS VS S&P CEAH

• Increasing U.S. demand for imported wildlife/wildlife products increases the likelihood of 

illegal importation, despite no reports of interceptions

• Imports likely underreported as there may be a bias of inspection toward CITES wildlife 

and wildlife products, increasing likelihood estimate

• Uncertainty with regard to accuracy of data reporting increases uncertainty to moderate

The likelihood that ASFv will enter the U.S. through the legal importation of semen is 

negligible with low uncertainty. These estimates are based on:

• All semen imports are from countries that are currently free of ASF

• Various regulatory requirements and import requirements relating to animal health 

mitigate the likelihood of ASFv transmission, if properly implemented

• High quality and availability of semen import data reduces uncertainty of the likelihood 

rating

The likelihood that ASFv will enter the U.S. through the illegal importation of semen is 

low with moderate uncertainty. These estimates are based on:

• Few occurrences of Customs and Border Protection (CBP) - Emergency Action 

Notification-related semen interceptions, with none from ASF-affected countries

suggests a low volume approach rate along this pathway

• No mechanism for querying semen-only data in the CBP Agricultural Quarantine 

Inspection Monitoring (AQIM) or Work Accomplishment Activity Data System (WADS) 

which increases uncertainty of actual volume of interception

• The relatively low volume of illegal semen interceptions occurring via international mail

with uncertainty of whether the semen is swine-origin

• The relative ease of such shipments evading import restrictions compared to live 

animals due to low mail inspection rates and high mass volume

The likelihood that ASFv will enter the U.S. through the legal importation of swine 

products and by-products is negligible to low with moderate uncertainty. These 

estimates are based on:

• Zero import volume for pork products from ASF-affected countries. Imports are limited to 

swine by-products

• Various regulations in place that either prohibit entry or subject these products to various 

additional processing measures to inactivate disease-causing agents reduces the

likelihood of entry

• Conflicting or insufficient evidence on OIE treatment recommendations to inactive ASF 

virus increases uncertainty and likelihood estimates

• Uncertainty with regard to detailed processing/handling of hog casings imported or reimported from ASF-affected countries

The likelihood that ASFv will enter the U.S. via the illegal entry of swine products and byproducts is high with low uncertainty. These estimates are based on:

• High volume of arrivals and the variety of human-assisted movement pathways increase 

likelihood even with very low prevalence of infectivity

• Low inspection rates at ports of entry increase likelihood that products enter the U.S. 

undetected

• Available interception and inspection databases are either complete or have been 

supplemented to reduce uncertainty
5 | USDA APHIS VS S&P CEAH

• Certain pathways were discontinued from the AQIM surveillance program, so unbiased 

approach rates are no longer available for cruise ships, express couriers, etc. However, 

WADS continues to report high volumes of swine products interception on these 

pathways, reducing uncertainty

• Imperfect detection efficiency of X-ray scanners compared to manual inspection

increases likelihood

• Evidence of ASFv contamination in swine products intercepted at other foreign airports, 

though there is uncertainty in the prevalence of infectivity for U.S. imports

The likelihood that ASFv will enter the U.S. via the illegal entry of swine bush meat or 

wild animal parts is low to moderate with high uncertainty. These estimates are based 

on:

• Low volume of bushmeat/trophies reported as being intercepted compared to other 

pathways

• Increased uncertainty in import volume as there may be bias of inspection toward CITES 

wildlife and wildlife products

• Increasing U.S. demand for imported wildlife/wildlife products might increase likelihood 

of illegal import

• The U.S. and other countries report illegal entry of bush meat from countries affected by 

ASF

• Uncertainty of whether intercepted bush meat or animal parts were of swine origin

• No data available on the detection rate of wildlife import violations, particularly 

undeclared imports

The likelihood that ASFv will enter the U.S. via legal importation of animal-origin feed 

ingredients from ASF countries is low to moderate with high uncertainty. These 

estimates are based on:

• Large percentage of slaughtered animal by-products imported to the U.S. originate from 

ASF-affected countries increases likelihood of entry 

• Uncertainty in the reporting of volume as shipments lines instead of weight makes it 

difficult to estimate entry likelihood relative to other pathway import volumes.

• Survivability of ASFv in raw pork products and high ASFv titers in blood from infected 

animals suggest similar survivability in slaughtered animal by-products if insufficiently 

treated

• Persistence of ASFv in blood (a relatively high protein matrix) for extended periods in the 

environment

• Rendering and other manufacturing processes may inactivate ASFv (lowering the 

likelihood rating), but there is insufficient information available to evaluate the sufficiency 

of these practices

• Uncertainty associated with data for slaughtered mammal by-product imports which do 

not indicate a processing step that could inactive ASFv (such as heat treatment)

• Uncertainty introduced by the inclusion of mixed or prepared feeds to the analysis which 

have unknown processing standards (such as during pelletization)

The overall likelihood that ASFv will enter the U.S. via illegal entry of animal-origin feed 

ingredients is negligible to low with high uncertainty. The overall rating is due to:

• Extremely low approach rates for prepared animal feeds and no interception volume for 

slaughtered animal by-products from AQIM.
6 | USDA APHIS VS S&P CEAH

• Uncertainty introduced by non-specific reporting of slaughtered animal by-products/feed 

ingredients in WADS. Closest category of interest may be inedible swine products which 

includes many non-target commodities.

• Uncertainty introduced by AQIM database reporting issues that required supplemental 

datasets for negative data

• Certain pathways were discontinued from the AQIM surveillance program and are no 

longer available for analysis

• Uncertainty introduced by the assumption that personally transported/smuggled animal 

blood, parts, skins, or carcasses could be treated as food scraps for backyard feeding or 

as ingredient for making a mixed feed

• Uncertainty of the level of ASFv infectivity of prepared animal feeds, if any

The likelihood that ASFv will enter the U.S. via the legal importation of plant-origin feed 

ingredients from ASF countries is negligible to moderate with high uncertainty. These 

estimates are based on:

• Moderate to high percentage of soybean imported to the U.S. originate from ASFaffected countries increases likelihood

• Low percentage of mixed/prepared animal feeds imported to the U.S. originate from 

ASF-affected countries reduces likelihood

• Uncertainty in the reporting of volume as shipments lines instead of weight makes it 

difficult to estimate entry likelihood relative to other pathway import volumes

• Likelihood estimates rely on assumption of plant contamination from viral shedding in the 

fields:

• Variability in the degree of shedding of ASF viruses in feces depending on the virus 

strain, where higher titers in feces could be reached for some virus strains in a small 

proportion of infected pigs 

• Uncertainty in the rate of inactivation of ASF viruses in moist or dry feces at different 

temperatures over time

• The relatively higher dose required for oral transmission of ASF viruses and 

outcomes from oral feeding trials from several studies

• A single study indicates potential for ASFv (Georgia 2007 isolate) to persist postinoculation in various feed ingredients under a 30-day simulated shipping model.

• Uncertainty due to unknown processing and manufacturing processes at feed mills that 

would affect ASFv survivability in prepared feeds

The overall likelihood that ASFv will enter the U.S. via an illegal plant-origin feed pathway

to be low with high uncertainty. The overall rating is due to:

• Extremely low approach rates for pathways with available data in AQIM

• Uncertainty introduced by AQIM database reporting issues which required supplemental 

datasets for negative data

• Certain pathways were discontinued from the AQIM surveillance program and are no 

longer available for analysis

• Uncertainty as to whether the intent of the intercepted plant products was for animal feed

• Uncertainty of rate of ASF contamination of intercepted feed ingredients, if any
7 | USDA APHIS VS S&P CEAH

The likelihood that ASFv will enter the U.S. via the legal import of animal feed 

supplements is negligible to moderate with high uncertainty. These estimates are based 

on:

• Low import volume relative to other feed ingredients but high variety of supplement types

increases likelihood

• Uncertainty in the reporting of volume as shipments lines instead of weight makes it 

difficult to estimate entry likelihood relative to other pathway import volumes

• Uncertainty associated with a single study of ASFv persistence in animal feed 

ingredients which indicated potential persistence in choline inoculated with ASFv, but not 

lysine or Vitamin D

• Uncertainty due to lack of ASFv persistence studies in other types of feed supplements

• Uncertainty due to unknown processing and manufacturing processes at feed mills that 

would affect ASFv survivability in prepared feeds

• Uncertainty due to lack of data on infectious dose via contaminated feed supplements

The likelihood that ASFv will enter the U.S. via fomites is negligible to moderate with high 

uncertainty. These estimates are based on:

• An extremely low approach rate for air passengers with shoes or clothing contaminated 

with soil or other substances that requires cleaning/disinfection from all countries of 

origin decreases likelihood

• Approach rate for air passengers with contaminated shoes or possessions is zero from 

ASF-affected countries of origin decreases likelihood

• Targeting efficiency of intercepting passengers with soiled footwear appears to be 

declining in recent years, which may also underreport the approach rate, potentially 

increasing the likelihood

• Potential underreporting of contaminated footwear based on bias toward passenger 

declaration of farm visitation, which would underestimate the approach rate.

• Lack of available data for other fomite vectors (cloth, contact surfaces, etc), which would 

underreport the likelihood for this pathway

• Variability in the degree of shedding of ASF viruses in feces depending on the virus 

strain, where higher titers in feces could be reached for some virus strains in a small 

proportion of infected pigs 

• ASFv remains infectious in pig faeces for up to 5 days at 70°F or 14 days at 40°F, 

indicating potential for temporal windows of transport via shoes/clothing, increasing the 

likelihood. However, there is a lack of data on ASFv persistence in soil contaminated 

with excreta and on various media (clothing, shoes, tires, etc)

The likelihood that ASFv will enter the U.S. via regulated garbage from countries where 

ASF is present is low with moderate uncertainty. These estimates are based on:

• Stringent regulations from the Code of Federal Regulations and the Swine Health 

Protection Act mitigates the likelihood of entry

• The low rate of inspection on vessels and aircraft for regulatory garbage compliance

increases likelihood that contaminated garbage could enter the U.S. undetected

• The combination of the high volume of ship arrivals and a low violation rate on 

aircraft/vessels combined with a high compliance rate of garbage handling facilities that 

handle removal, transport, and treatment suggests a low likelihood of ASFv entry

• Uncertainty introduced via unknown process for targeting spot inspections for ships and 

aircraft most likely to be in violation of regulations

• Uncertainty introduced due to unknown false negative detection rate of inspectors
8 | USDA APHIS VS S&P CEAH

TABLE 3. DEFINITION OF LIKELIHOOD CATEGORIES FOR THIS QUALITATIVE ASSESSMENT

Term Definition

Negligible This event would almost certainly never occur

Low This event would be unlikely to occur

Moderate This event would be nearly as likely to occur as not to occur

High This event would be likely to occur

Very High This event is almost certain to occur

TABLE 4. DEFINITION OF LEVELS OF UNCERTAINTY

Term Definition

Low Available data is well supported, reliable, complete, accessible from multiple sources or 

published references, and are in general agreement.

Moderate Data is available, and has few issues with interpretability, potential biases, reliability, 

insufficient attribute resolution, and/or underreporting. 

High A complete lack of available data OR some data is available but may be incomplete, 

unreliable, from a small number of published sources, and/or demonstrates conflicting 

evidence. Includes the combination of anecdotal evidence, personal communications, and 

expert opinion with available published data.

Questions or comments on data analysis, contact: CEAH at 970-494-7000 

vs.ceah@aphis.usda.gov

Definitions of Categories

For the purposes of this qualitative assessment, we assigned a qualitative likelihood 

rating. Tables 3 and 4 define the terminology that were applied for expressing likelihoods.