Slowing the Spread of West Nile Virus: the Robin Vaccination Study
January 1, 2010 by Tina Gheen
For several years, scientists at the University of California Santa Cruz and the Smithsonian Migratory Bird Center have studied infection patterns of West Nile virus in the Washington, D.C., metro area.
They're attempting to determine why West Nile is more prevalent in some areas than in others.
Early findings revealed an interesting discovery—the American robin (Turdus migratorius) plays a key role in spreading the West Nile Virus in the D.C. area.
The American robin happens to be the dish of the day for the northern house mosquito (Culex pipiens), a major carrier of the virus.
The mosquitoes' preference for American robins as well as how quickly an infected robin can transmit of the disease to a new host (within 2-4 days) makes this a particularly effective method for spreading the disease. In fact, the team estimates that 66 to 88% of infected mosquitoes in the study area catch the disease after feeding on a robin.
Based upon this estimation, the team of scientists wondered if they could use a vaccine to slow the spread of the virus. They wanted to break the infection cycle between robins and the northern house mosquito.
The cycle works like this: a mosquito carrying the virus feeds on a robin, and the robin becomes infected with the disease. Within the next week, the virus replicates within the robin, and the disease is transmitted to other mosquitoes when the robin is bitten again. These mosquitoes can then infect more birds, mammals, and people.
So in 2008, the study was expanded to include immunizing robins against the West Nile virus. Working with the researchers from the Centers for Disease Control and the New York State Department of Health, the team used an equine vaccine to immunize robins in a controlled laboratory experiment.
It worked. The vaccinated birds weren’t infectious and would not pass the virus on to mosquitoes. The robins also developed a strong antibody response, which protected them from contracting the disease.
But would vaccinating robins in the wild reduce the transmission of West Nile in larger urban and forested areas? To answer this question, the team set up a pair of research sites in each of 4 locations in the metro D.C. area: Baltimore, Bethesda, Takoma Park, and Foggy Bottom.
One site in each pair was designated as the control site, and one site became the treatment site—the focus of the vaccination effort.
The team used mist nets to capture adult robins for vaccination at the treatment sites. Additionally, previous research indicated juvenile birds were more important in the transmission of West Nile than adults, so the team also vaccinated baby birds in nests 1-3 days before the juvenile birds fledged.
About 50% of the adult robins and 88% of all juvenile birds were vaccinated between April and July of 2008 at the treatment sites.
After reviewing the number of mosquitoes infected at each of the 8 sites from May to October, the scientists found vaccinating robins reduced the fraction of mosquitoes that were infected with West Nile virus by 64%, on average. This was a substantial reduction in the transmission of the disease and a promising solution for the future.
However, capturing and hand-vaccinating birds is time-consuming and labor-intensive. In the future, the team would like to develop a more feasible solution for large-scale vaccination, such as the development of a vaccine the birds find appetizing to eat. Perhaps tasty, nutritious, vaccine-packed worms?
This article summarizes the information in this scientific paper:
DNA Vaccination of American Robins (Turdus migratorius) Against West Nile Virus. 2010. Kilpatrick, A.M., Dupuis II, A.P., Gwong-Jen J. Chang, and Laura D. Kramer. Vector-borne and Zoonotic Diseases 10(4).