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Response to and efficacy of vaccination against eastern equine encephalomyelitis virus in emus

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  • 1 Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Vector-Borne Infectious Diseases, Arbovirus Diseases Branch, Foothills Campus-Rampart Rd, Fort Collins, CO 80521.
  • | 2 Present address is the Idaho Department of Health and Welfare, 450 W State St, Boise, ID 83720.
  • | 3 Department of Physiology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 4 Department of Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.
  • | 5 Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Vector-Borne Infectious Diseases, Arbovirus Diseases Branch, Foothills Campus-Rampart Rd, Fort Collins, CO 80521.
  • | 6 Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Vector-Borne Infectious Diseases, Arbovirus Diseases Branch, Foothills Campus-Rampart Rd, Fort Collins, CO 80521.
  • | 7 Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Vector-Borne Infectious Diseases, Arbovirus Diseases Branch, Foothills Campus-Rampart Rd, Fort Collins, CO 80521.

Abstract

Objective—To evaluate humoral immune responses of emus vaccinated with commercially available equine polyvalent or experimental monovalent eastern equine encephalomyelitis (EEE) virus and western equine encephalomyelitis (WEE) virus vaccines and to determine whether vaccinated emus were protected against challenge with EEE virus.

Design—Cohort study.

Animals—25 emus.

Procedure—Birds were randomly assigned to groups (n = 5/group) and vaccinated with 1 of 2 commercially available polyvalent equine vaccines, a monovalent EEE virus vaccine, or a monovalent WEE virus vaccine or were not vaccinated. Neutralizing antibody responses against EEE and WEE viruses were examined at regular intervals for up to 9 months. All emus vaccinated with the equine vaccines and 2 unvaccinated control birds were challenged with EEE virus. An additional unvaccinated bird was housed with the control birds to assess the possibility of contact transmission.

Results—All 4 vaccines induced detectable neutralizing antibody titers, and all birds vaccinated with the equine vaccines were fully protected against an otherwise lethal dose of EEE virus. Unvaccinated challenged birds developed viremia (> 109 plaque-forming units/ml of blood) and shed virus in feces, oral secretions, and regurgitated material. The unvaccinated pen-mate became infected in the absence of mosquito vectors, presumably as a result of direct virus transmission between birds.

Conclusions and Clinical Relevance—Results indicate that emus infected with EEE virus develop a hightiter viremia and suggest that they may serve as important virus reservoirs. Infected emus shed EEE virus in secretions and excretions, making them a direct hazard to pen-mates and attending humans. Commercially available polyvalent equine vaccines protect emus against EEE virus infection. (J Am Vet Med Assoc 2001;218:1469–1473)