Swine Hemorrhagic Fever Surveillance 

Evaluation Brief September 2023 

INTRODUCTION 

African swine fever (ASF) continues to spread across the globe as classical swine fever (CSF) 

remains present in the Caribbean and South America. The United States Department of Agriculture’s 

(USDA) Animal and Plant Health Inspection Service (APHIS) has an integrated surveillance plan that 

maintains vigilance for swine hemorrhagic fever diseases and improves the country’s emergency 

preparedness. APHIS recently used a RISKSUR framework to evaluate the effectiveness and 

implementation of this surveillance plan over the past 3 years in the continental United States. 

APHIS expanded surveillance activities in Puerto Rico and the U.S. Virgin Islands in 2021, after 

detection of ASF on the island of Hispaniola. APHIS performed a separate evaluation for surveillance 

activities in those territories and will report those findings separately. 

SURVEILLANCE PLAN GOALS 

To strengthen ASF and CSF detection 

capabilities and enhance outbreak 

preparedness 

by testing high-volume sample 

collection, laboratory capacity, and 

data management capacities prior to 

an outbreak scenario, and establishing 

a baseline of disease absence through 

timely and consistent surveillance. 

Support claims of ASF and CSF disease freedom 

by the diagnostic testing of ASF and CSF in targeted 

subpopulations of swine collected via five surveillance 

components: 

• Foreign Animal Disease (FAD) Investigations 

• Sick Pig Veterinary Diagnostic Lab (VDL) Component 

• Slaughter & Aggregation Point Component 

• Higher Risk Component 

• Feral Swine Component 

SAMPLING 

The evaluation included specimens collected from June 1, 2020, to May 31, 2023, from three 

targeted swine populations: 

• Commercial swine are domestic swine raised primarily for food production and confined to a 

housing facility designed to prevent exposure to feral swine. 

• Higher risk swine are swine raised in non-commercial settings, such as waste feeders, 

outdoor raised swine, swine with known or suspected feral swine exposure, and show swine. 

• Feral swine are free-roaming swine with an increased risk of exposure to ASF and CSF. 

During the past three years, APHIS’ Foreign Animal Disease Diagnostic Laboratory (FADDL) and 

National Animal Health Laboratory Network (NAHLN) laboratories tested approximately 43,533 

specimens for ASF and CSF and 23,524 specimens for CSF only (Figure 1). An average of 1,864 

specimens were tested per month throughout the three-year period. Of note, the average monthly 

specimen counts increased each year, rising from 1,111 specimens in year one of the evaluation 

period to 2,638 specimens in year three. 

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BY THE NUMBERS 

Foreign Animal Disease (FAD) Investigations: 118 investigations, 771 specimens 

Targets swine populations with certain disease symptoms to rule out ASF, CSF, and 

other foreign animal diseases. An FAD investigation is initiated by state and federal 

animal health officials. 

Sick Pig Veterinary Diagnostic Lab (VDL) Component: 20,878 specimens 

Targets clinically ill or dead swine on commercial farms. 

Slaughter & Aggregation Point Component: 10,643 specimens 

Targets clinically ill or dead swine at slaughter facilities and aggregation points such as 

live animal markets. 

Higher Risk Component: 12,385 specimens 

Targets clinically ill or dead higher risk swine; apparently healthy animals may be 

sampled if there are no ill or dead animals available. 

Feral Swine Component: 22,605 specimens 

Targets feral swine in geographic areas APHIS considers to be of higher risk for disease 

introduction and transmission. 

Figure 1: Specimens tested by total and by surveillance component. The number of specimens tested for 

both ASF and CSF or for only CSF varied by surveillance system component and were carried out in accordance with 

the Swine Hemorrhagic Fevers Integrated Surveillance Plan. 

48% 

2% 14% 

12% 

24% 

70% 

30% 

43,533 

specimens 

tested for ASF 

and CSF 

23,524 

specimens 

tested for 

CSF only 

Sick pig VDL FAD investigations Feral 

Higher risk Slaughter & aggregation point 

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EFFECTIVENESS METRICS 

Sample collection over time is displayed in Figure 2. In fall of 2021, the overall number of 

specimens tested increased dramatically. The number of specimens tested in the sick pig VDL 

component increased due to increased stakeholder awareness and engagement with this 

component. APHIS’ 

addition of four states to 

the feral swine ASF 

surveillance in summer 

2022 increased the 

amount of testing that had 

been occurring in those 

states. Two significant 

events––the COVID-19 

pandemic and the 2022– 

2023 highly pathogenic 

avian influenza outbreak–– 

impacted federal, state, 

and industry resources, but 

no appreciable negative 

impacts were observed in 

the number of specimens 

tested nationally. 

Figure 2. Specimens tested by surveillance component. 

The number of specimens tested by surveillance system component by month. 

An effective, targeted surveillance system ensures samples represent the different production types 

and associated risks, as well as the geographic distribution of at-risk populations. Geographic 

representativeness was evaluated through an analysis of the number of specimens tested compared 

to sampling target numbers and state swine populations. 

APHIS provides targets for annual specimen collection to 10 states for the higher risk component 

and 17 states for the slaughter & aggregation point component. Figure 3 shows the proportion of 

these states that met or exceeded 75 percent of their target. APHIS continues to evaluate and 

adjust target sample numbers to reflect potential changes in swine populations and associated 

risks, and to identify where increased sampling may best support surveillance objectives. 

Figure 3. State sampling targets and performance. The proportion of states that met or exceeded 75 percent of 

their sampling target based on APHIS guidelines for the higher risk component (left) and slaughter & aggregation point 

component (right), compared to the proportion that met less than 75 percent of their sampling target. 

Higher Risk Slaughter & Aggregation Point 

100% 100% 

Percentage of States 

(N=10) 

80% 

60% 

Percentage of States 

(N=17) 

80% 

60% 

40% 40% 

20% 20% 

0% 0% 

<75% ≥75% <75% ≥75%

Percentage of Sampling Target Met Percentage of Sampling Target Met 

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To achieve geographic representation, the distribution of animals sampled for the sick pig VDL and 

slaughter & aggregation point components should be proportional to the population distribution of 

commercial U.S. swine. Comparison of the swine population by state (Figure 4a) and the total 

specimens tested from the sick pig VDL and slaughter & aggregation point components (Figure 4b) 

shows that, in general, APHIS, states, and private veterinarians are collecting the most specimens 

from animals originating from those states with larger swine populations. 

Figure 4(a). Average swine population by state. Figure 4(b). Total specimens tested from sick pig 

Map of the United States colored on a gradient VDL and slaughter & aggregation point 

corresponding to total commercial swine population by components. Map of the United States colored on a 

state according to NASS Quarterly Hogs and Pigs gradient corresponding to total specimens tested from the Inventory reports from June 1, 2020, to March 1, 2023. sick pig VDL and slaughter & aggregation point 

components by state from June 1, 2020, to May 31, 2023. 

Surveillance among feral swine is risk-based. States with the heaviest feral swine invasions are 

included in CSF surveillance. Enhancements to feral swine surveillance for ASF were implemented 

in select counties in Florida, Texas, Louisiana, and Georgia in 2022, due to increased risks of 

disease introduction. Evaluation of sample collection by state (Figure 5) shows that surveillance is 

being carried out across the invaded range of feral swine. APHIS will continue to target surveillance 

sampling in feral swine populations most at risk for a disease incursion. 

Figure 5. Total feral swine specimens tested. 

Map of the United States colored on a gradient corresponding 

to total feral swine specimens tested for CSF only or both ASF 

and CSF by state from June 1, 2020, to May 31, 2023. 

Samples collected from Hawaii, Puerto Rico, and Guam are 

not included. 

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FUNCTIONAL METRICS 

The ease of sampling protocol adoption, variety of accepted sample types, and robust data 

collection system contribute to the overall functionality of this surveillance plan. Laboratory 

engagement is demonstrated through the involvement of 12 NAHLN laboratories, 4 of which were 

added during the 3-year evaluation period. The addition of approved sample types for ASF and 

CSF surveillance has also increased acceptability and engagement. For example, whole blood was 

added for the higher risk component, which led to increased specimen volume. 

During the last evaluation in 2020, 5.2 percent of specimens were unable to be matched to field 

data and were therefore not reportable. Since then, plan partners invested significant time and 

resources to develop tools to support matching processes to address this gap successfully. At the 

end of this evaluation period, only 0.2 percent (n=569) of specimens were not matched and there 

are clear processes to quickly get unmatched specimens resolved. Efforts are underway to build out 

additional capability to link field data to laboratory results and improve the functional metrics. 

ACCOMPLISHMENTS AND CHALLENGES 

The evaluation identified program successes and areas for improvement as outlined below. 

Accomplishments: 

• Increased awareness and engagement with the sick pig VDL component, resulting in a 

fivefold increase in the number of case-compatible specimens tested per month. 

• Added 3 sample types to improve sample collection flexibility and efficiency. 

• Increased availability of flexible, scalable, and timely surveillance through the addition of 

four NAHLN laboratories to active surveillance programs. 

• Increased data fidelity through automated identification and management of duplicate 

records, pooled specimens, and other factors impacting data quality. 

• Provided consistent sampling from all targeted surveillance components across time and 

location though effective coordination of federal, state, and industry partners. 

• Maintained stable testing rates in the face of significant stresses on personnel and 

resources during the COVID-19 pandemic and the 2022–2023 highly pathogenic avian 

influenza outbreaks. 

Challenges: 

• Limitations among data collection systems to consistently capture clinical signs, 

age/production type, and premises identification number have been an ongoing challenge 

since the plan’s inception in 2019. Accurate and consistent availability of these data would 

better support surveillance evaluations and other epidemiologic analysis. 

• Data quality issues occasionally delayed linking laboratory results with epidemiologic 

information gathered by specimen submitters. 

• Geographic representativeness could be improved through participation of additional 

premises and a re-evaluation of state-level sample targets to best support current needs 

and animal movement patterns. 

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COLLABORATIVE GOALS FOR IMPROVING THE SURVEILLANCE SYSTEM 

Ongoing success of the surveillance plan requires continued collaboration among federal, state, 

and industry partners, particularly in the following focus areas: 

1. Enhance risk-based targeting of swine subpopulations through ongoing disease introduction 

risk analyses. 

2. Re-evaluate state sample target numbers, encourage sample collection from 

underrepresented states, and identify resource needs to efficiently execute geographically 

representative disease surveillance. 

3. Continue to develop and expand the use of tools to capture and share electronic information 

through all surveillance components and through all stages of specimen collection, 

processing, and reporting. 

CONCLUSION 

The Swine Hemorrhagic Fevers Integrated Surveillance Plan continues to meet its goals by providing 

ongoing active surveillance for hemorrhagic fevers among the most at-risk animals and populations. 

By adding approved sample types, expanding surveillance within the NAHLN, and improving data 

systems, this surveillance plan continues to provide timely and accurate surveillance. For the most 

recent year assessed, the system tested more than double the number of specimens for ASF and/or 

CSF when compared to the first year of implementation. The investment in electronic data collection 

and management systems has allowed real-time monitoring and analysis of surveillance data. Finally, 

the risk-based, targeted nature of the surveillance system continues to provide an efficient means of 

achieving the objectives of supporting disease freedom, strengthening detection capabilities, and 

improving outbreak preparedness. 

For more information about CSF and ASF surveillance in the U.S., please view the Swine 

Hemorrhagic Fevers Integrated Surveillance Plan. 

For information about the RISKSUR framework, please visit the RISKSUR website. 

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