Dr. Michelle Kutzler DVM, PhD, DACT
Oregon State University
Experimental West Nile Virus (WNV) Infection in
Vaccinated and Unvaccinated Alpacas
The objectives of this research were to: 1) demonstrate the efficacy
of a killed-virus vaccine against the clinical sequelae associated with WNV
infection; 2) carefully monitor the time course of clinical WNV disease
following an experimental challenge to better enable alpaca practitioners and
owners in identifying and treating this disease; and 3) document end-organ
manifestations of West Nile virus infection in both clinically normal and
affected alpacas.
Two challenge experiments were conducted. In the first experiment,
four vaccinated and eight unvaccinated alpacas were challenged with WNV infected
mosquitoes . The vaccinated animals had received an initial series of three
intramuscular vaccinations with West Nile Innovator (Fort Dodge Animal Health)
given at three-week intervals more than one year prior to the mosquito
challenge. A blood sample was taken to determine the serum neutralizing
antibody titers prior to administering an annual vaccination booster three weeks
before the experimental challenge. All twelve animals were challenged with
infected mosquitoes and not one developed any clinical signs associated with WNV.
Initially, both vaccinated and unvaccinated animals were negative for serum WNV
RNA using reverse transcriptase polymerase chain reaction (RTPCR). Within 1 and
3 days following the mosquito challenge, two of the unvaccinated animals had
detectable virus RNA present in the serum. WNV RNA was never identified in any
of vaccinated animals. A second challenge experiment was then conducted in
which five unvaccinated alpacas received an injection of WNV. Within 3 days
following the challenge, two animals had detectable virus RNA present in the
serum. This experiment allowed us to test the sensitivity of our new camelid-specific
IgM capture ELISA that was developed with Alpaca Research Foundation funding
from another grant. Within 9 days following the challenge, the presence of IgM
antibodies can be detected to confirm acute WNV infection.