UNITED STATES DEPARTMENT OF AGRICULTURE

ANIMAL AND PLANT HEALTH INSPECTION SERVICE

VETERINARY SERVICES

THE CENTER FOR VETERINARY BIOLOGICS

Environmental Assessment

For Field Testing of a

Porcine Reproductive and Respiratory Syndrome 

Vaccine, Respiratory Form, Modified Live Virus

November 2013

Prepared by:

United States Department of Agriculture

Animal and Plant Health Inspection Service

Veterinary Services

The Center for Veterinary Biologics

_________________________________________________________________________________________________

Environmental Assessment

Field Trial of an Experimental Porcine Reproductive and Respiratory Syndrome Vaccine
Environmental Assessment for Field Testing of a 

Porcine Reproductive and Respiratory Syndrome Vaccine, Respiratory Form, 

Modified Live Virus

I. Proposed Action

APHIS is considering granting authorization to ship an unlicensed Porcine Reproductive 

and Respiratory Syndrome (PRRS) Vaccine, Respiratory Form, Modified Live Virus, for 

field safety testing in pigs. ProtaTek International, Inc., St. Paul, Minnesota, has 

requested authorization to conduct the field safety tests under conditions of husbandry 

that are typical of the commercial swine industry in the United States. The vaccine is

intended for use in healthy pigs, three weeks of age or older, as an aid in the reduction of 

lung lesions caused by PRRS virus (PRRSV). 

Under the provisions of the Virus-Serum-Toxin Act of 1913, as amended in 1985, the 

USDA must ensure that veterinary biologics are pure, safe, potent, and efficacious and 

not worthless, contaminated, dangerous, or harmful. Accordingly, APHIS has conducted 

a risk analysis and has concluded that, regarding intramuscular administration of this

single-dose vaccine in swine, the safety risks to animals, public health, and the 

environment are low. A copy of the firm’s risk analysis with confidential business 

information redacted is available online and by request, as indicated in the Federal 

Register Notice announcing the proposed field testing. APHIS considers the firm’s risk 

analysis, but also reviews other studies and tests conducted by the firm, the confirmatory 

testing completed by APHIS personnel on the Master Seed to confirm the vaccine’s 

purity, sterility, identity, and expression of immunogenic protein, and results of literary 

and regulatory review regarding this and similar previously tested or licensed products. 

Based on APHIS’ analysis of the relevant data, a preliminary determination has been 

reached that field testing this veterinary vaccine will not have a significant impact on the 

quality of the human environment and that an environmental impact statement need not 

be prepared. We intend to authorize shipment of this vaccine for field testing following 

the close of the comment period of the Federal Register Notice announcing the pending 

trial unless new substantial issues bearing on the effects of this action are brought to our 

attention.

II. Background

PRRSV is a positive-stranded RNA virus in the Arteroviridae family, with a genome of 

about 15 kb.1 The virus causes reproductive failure in sows and respiratory disease in 

young pigs postweaning.

2 Treatment options are limited; PRRS continues to be a major 

challenge for swine veterinarians and producers. The best strategy is prevention using 

good management, biosecurity, and vaccination.2, 3 PRRSV is not associated with disease 

in healthy adult humans. 
The vaccine is a chimeric virus constructed from an infectious PRRSV clone backbone 

encoding nonstructural proteins and a portion of a field isolate encoding the structural 

proteins. The chimeric clone contains a genetic marker, i.e. a DNA polylinker that can be 

used to differentiate vaccine virus from field isolates of PRRSV. 

The proposed field safety test will be conducted in at least three different geographical

locations. The product will be used according to instructions on the product circular, and 

in accordance with standard requirements published in Title 9, Code of Federal 

Regulations (CFR), Part 103.3, concerning shipment of experimental biological products 

for use in animals.4 

The potential for escape and dispersal of the experimental vaccine from the proposed 

release sites is low. The personnel to conduct the study are experienced in porcine health 

management. 

III. Need for the Proposed Action

PRRSV causes widespread disease in both the US and European pig industries, with 

more than $664 million lost annually by US swine producers.5 The firm proposes to 

produce an efficacious, safe vaccine using a chimeric virus, as an aid in the prevention of 

respiratory disease due to PRRSV. 

It is expected that the data from these monitored field trials will confirm the safety of this 

PRRS Vaccine, Respiratory Form, Modified Live Virus, for use in swine at least 3 weeks 

of age within the environment of the United States.

IV. Areas of Concerns

The three areas of concern to APHIS are: 1) animal safety, 2) public health, and 3) 

environmental safety. APHIS has conducted its own risk analysis to assess whether risks 

are associated with the proposal to field test this experimental vaccine. The safety 

characteristics of this vaccine have been thoroughly evaluated. The conclusions derived 

from the risk analysis for each of the areas of concern are summarized below.

A. Animal Safety

The risk to animals is low. 

 Fifteen three-week-old vaccinated pigs and eleven controls from the same litters 

were challenged thirty-five days post-vaccination. Fourteen days later, necropsies 

indicated significant protection in the vaccinated pigs compared to the nonvaccinated controls, average 2.8% lesions vs. average 27.7% lesions, 

respectively.

 The vaccine is attenuated, but the virus can replicate in swine. Vaccination will 

induce a viremia in pigs which is transitory. The firm reports that sentinel pigs 

adjacent to vaccinates remained negative for the PRRS vaccine virus when tested 
by qPCR, virus isolation, or PRRSV-specific antibody test during the course of 

one study.

 Backpassage studies conducted by the firm involved passage five times in threeweek-old pigs. The fifth passage virus was then injected into pregnant sows at 90 

days gestation as well as another group of 3 week-old pigs. No reversion to 

virulence occurred: the pigs did not develop respiratory disease and the sows gave 

birth to healthy piglets.

 The genetic stability of the master seed virus was demonstrated in Marc145 cell 

culture at passages 1 and 15 (the highest used in vaccine production), which 

shared 100% identity for an important structural gene. Genotypic stability in vivo

was shown by inoculation of three pigs with virus that was passaged five times in 

three-week-old pigs previously. After isolation of three virus samples from each 

of the three pigs, gene sequencing of a major structural gene indicated that they 

were 100% identical to the pass five virus, which was 99.6% identical to the 

master seed virus. The genetic polylinker marker was maintained in the viral 

genome.

 Various species including mice, rats, and guinea pigs are resistant to PRRSV. 

However, some species of birds, especially mallard ducks, are susceptible to wild 

type PRRSV.6 The attenuated vaccine virus was not recovered by viral isolation 

or detected by qPCR when injected into mallard ducks during a 28-day study 

conducted by the firm. No lesions were found in tissue samples collected from 

heart, lungs, liver, spleen, kidney, stomach, small intestine, large intestine, lymph 

nodes, thymus and muscle. 

B. Public Health

The risk to public health is likewise low. 

 PRRSV is not considered to be a human pathogen, and does not replicate in 

humans.

 Qualified personnel administering the vaccine could potentially be exposed to it

through accidental injection, with the possibility of a local reaction. 

 Although the safety of this specific vaccine has not been evaluated in humans and 

is therefore unknown, accidental human injection is not expected to cause

significant adverse effects. 

 Many doses of various live PRRSV vaccines have previously been administered 

to swine. No significant adverse events have been reported for those vaccines.

C. Environmental Safety

The risks to the environment are low. 

 Several conventional, attenuated live PRRSV vaccines have been previously 

developed, licensed, and made available for commercial use, without undue 

environmental effects.

7

 The stability and identity of the master seed was tested by the firm at passages 1 

and 15 in Marc 145 cell culture, using RT-PCR and sequencing of a major 

structural gene to demonstrate 100% equivalence. APHIS testing at the Center 
for Veterinary Biologics (CVB) showed a high degree of stability and identity 

between passages 1 and 15 in four significant genomic regions of interest that 

were sequenced. APHIS-CVB testing also demonstrated excellent protein 

expression by the master seed at passages 1 and 15, using both fluorescent 

antibody in tissue culture and Western blot analysis.

 The master seed and another chimeric virus were co-cultured in Marc145 cells by 

the firm for 4-5 days and viral RNA extracted. RT-PCR and analysis of PCR 

products indicated that recombination and horizontal gene transfer did not occur. 

 Shed/spread studies in pigs were conducted by the firm. Using virus isolation, 

qPCR, and ELISA testing on blood samples, four pigs housed adjacent to the 

vaccinated pigs and three of four commingled pigs were negative by all three 

tests. One commingled pig was positive on day 28 only by qPCR and virus 

isolation, but negative by ELISA. All nasal, fecal, and urine samples collected 

were negative by virus isolation. All samples from the sixteen vaccinated pigs 

were negative on day 28. 

 The vaccine virus was evaluated by the firm for survival at room temperature. 

After 24 hours, no virus was detected under dry conditions. Under liquid 

conditions, virus titer was reduced by ~2.4 logs and not detected at all after 4 

days. Risks associated with surviving virus are further reduced given the narrow 

host range, attenuation, and reduced transmission to commingled or adjacent pigs, 

noted previously. 

The information above provides support to the claims made regarding the safety of the 

PRRS vaccine to animals, public health, and the environment. There are no apparent 

substantial issues with adverse environmental impacts concerning use of this vaccine.

V. Alternatives

Two alternatives were considered. The only alternative considered other than the 

preferred action alternative is not to approve the proposed field tests, the “no action” 

alternative. We have considered the applicants’ goals in light of the agency’s public 

interest and responsibilities and any potential environmental impact. Based upon the 

results of our risk analysis and the potential applications for this vaccine in disease 

control, APHIS adopts the alternative that the proposed field tests be approved.

VI. Conclusion

Based upon the risk analysis documented in this EA, APHIS has determined that 

implementation of the proposal would not significantly affect the quality of the human 

environment and that the preparation of an Environmental Impact Statement is not 

required (Finding of No Significant Impact).
References

1. Dea, S., Gagnon, C.A., Maardassi, B., et al. 2000. Current knowledge on the 

structural proteins of porcine reproductive and respiratory syndrome (PRRS) virus: 

comparison of the North American and European isolates. Arch Virol 145:659-688.

2. Overview of Porcine Reproductive and Respiratory Syndrome. In: The Merck 

Veterinary Manual, Tenth Edition, 2010. S.E. Aiello & M.A. Moses (Eds), Merck & 

Co., Inc., Whitehouse Station, N.J. Available online: 

http://www.merckmanuals.com/vet/index.html

3. Overview of Health-Management Interaction: Pigs. In: The Merck Veterinary 

Manual, Tenth Edition, 2010. S.E. Aiello & M.A. Moses (Eds), Merck & Co., Inc., 

Whitehouse Station, N.J. Available online:

http://www.merckmanuals.com/vet/index.html

4. Code of Federal Regulations, Washington, DC. Available online: 

http://www.gpoaccess.gov/cfr/index.html

5. Swine vets, researchers encouraged to submit PRRS proposals. 2013. Pork Network. 

Available online: 

http://www.porknetwork.com/pork-news/Swine-vets-researchers-encouraged-tosubmit-PRRS-proposals-219274431.html

6. Zimmerman, J.J., Yoon, K.-J., Pirtle, E.C., et al. 1997. Studies of porcine 

reproductive and respiratory syndrome virus infection in avian species. Vet Micro 

55:329-336.

7. USDA Veterinary Biological Products, Licensees and Permittees. 2013, p45. 

Available online: 

http://www.aphis.usda.gov/animal_health/vet_biologics/publications/CurrentProdCod

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