National Veterinary Services Laboratories 

Equine Arteritis Virus Antibody

Proficiency Test Summary 

1. Composition of proficiency test panel: The equine arteritis virus antibody panel consists of 

twenty 0.6 ml samples of equine serum. The disease caused by equine arteritis virus is termed 

equine viral arteritis (EVA) and the panel name is abbreviated as EVA. The panel contains 

negative, weak positive and strong positive samples, and includes blind duplicates. The samples 

are labeled with the test acronym and calendar year (e.g., EVA 2010), a panel set number (e.g., 

Set 11), and a code number (codes 1 through 20). The codes are scrambled between sets. 

2. Cost of proficiency test: Click here to view current NVSL Catalog of Reagents. Additional 

information on diagnostic reagents, including ordering, payments, shipping details and fees, is 

located at www.aphis.usda.gov/nvsl. Then click on the Reagents and Proficiency Tests link.

3. Storage conditions: Short term (up to 7 days) store at 4° ± 2° C. Long term (over 7 days) 

store at <-20° C in a non-frost free freezer.

4. Sample preparation/selection criteria: Samples with high, medium, and low concentrations 

of EVA antibody are chosen for incorporation into the panel. Antibody levels arise from 

naturally and experimentally acquired infections. Each panel member is tested at least three (3) 

times, by a minimum of three NVSL technicians, in the OIE prescribed virus neutralization test 

for EVA. In addition, prior to distribution, the panel is examined by the University of Kentucky 

OIE reference laboratory for EVA to determine expected titers for each panel member. 

5. Panel quality control: Samples are monitored for stability and reproducibility. Stability 

testing of the panel has determined that normal shipping and handling conditions do not change 

the end values of the components. Two panel sets of each lot of proficiency panels are used to 

confirm stability after final preparation. 

6. Timing of the proficiency test distribution and data collection: The NVSL does not 

regulate which laboratories offer EVA serology testing. A list of laboratories that have 

successfully completed the EVA proficiency test is maintained by NVSL as a courtesy to 

countries that require EVA serology testing by an approved laboratory for international 

movement of horses or equine products. The EVA proficiency test is administered 

approximately once every two years. Advance notice is provided through the AAVLD website. 

7. Test method: Performance and interpretation of the EVA virus neutralization proficiency 

test should be conducted using methods as described in the current OIE Manual of Diagnostic 

Tests and Vaccines for Terrestrial Animals. The NVSL SOP for this method is SOP-EO-2108. 

The EVA virus neutralization test at NVSL is ISO17025 accredited.

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8. Submitting test results: Participating laboratories are required to have data submitted for 

scoring no more than four (4) weeks after panel distribution. Results are reported to the NVSL 

by fax or mail. One set of results is reported from each laboratory. 

9. Scoring of individual panel samples: For each sample, a titer result is reported. The 

international standard for the lower limit of antibody detection for EVA is a serum titer of 1:4. 

Scoring is based on two criteria: proper identification of positive and negative samples (with 

respect to EVA antibody) and accuracy of reported titers. 

10. Laboratory pass/fail criteria: Identity scores are determined by assigning one point per 

sample correctly identified as negative (antibody titer less than 1:4) or positive (any titer). 

Accuracy scoring is determined by assigning one point per sample for the expected titer. 

Reported titers within one two-fold dilution of the expected titer are also assigned one point. For 

a four-fold difference in titer from the expected result, 0.33 point is subtracted and for an eightfold difference 0.67 point is subtracted. Reported titers that differ more than eight-fold from the 

expected titer receive zero points for accuracy. Satisfactory results for identity and accuracy are 

determined after examination of panel performance at participating laboratories. Historically, 

approximately 20 laboratories have participated in the EVA panel. 

11. Reporting laboratory test scores: Results for each laboratory are reported to the individual 

laboratory director and to the appropriate AVIC for the laboratory’s location. Reports include 

individual laboratory results for each sample as well as summary results of participants in the 

proficiency test. Results are compiled and reported within 30-60 days of the receipt of 

participants’ results.

12. Remedial actions required for failing laboratories: Laboratories that fail the proficiency 

test are encouraged to contact subject matter experts at NVSL for discussion of methods and 

resolution of potential areas of concern. Laboratories have the option of obtaining a second 

panel set to attempt a retest. If a failing laboratory declines to take, or does not pass, the retest 

the laboratory is removed from the list of approved laboratories for EVA serology. The NVSL 

offers training in the performance of the EVA virus neutralization test. 

13. Special requirements: Restrictions - Owing to the requirements for maintenance of cell 

culture and propagating equine arteritis virus, the EVA VN test has been limited to federal, state, 

and university laboratories. Successful completion of the proficiency test is required prior to 

inclusion on the list of approved laboratories for this test. At present, there are approximately 20 

laboratories approved to conduct EVA serology for export testing. 

The current list of approved laboratories can be found at: 

http://www.aphis.usda.gov/animal_health/lab_info_services/approved_labs.shtml

International requests for the EVA proficiency panel are considered on a case-by-case basis and 

must follow applicable authorization and permit requirements. 

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