Rabies is a fatal disease. Without vaccination, rabies infection is nearly 100% fatal once a person develops symptoms. Since 1988, Texas has experienced two animal rabies epidemics: one involving coyotes and dogs in south Texas, and the other involving gray foxes in west central Texas. These outbreaks, which affected 74 counties, resulted in thousands of people potentially exposed, two human deaths, and countless animal lives lost.
In 1994, Governor Ann Richards declared rabies a state emergency. The Texas Department of State Health Services responded by launching the Oral Rabies Vaccination Program to control the spread of these outbreaks of rabies in wildlife.
Since 1995, the program has distributed more than 53 million doses of rabies vaccine across 758,100 square miles (nearly 2 million square kilometers) of Texas, by hand and by air. The number of rabies cases in dogs and coyotes went from 141 to 0 in 2005, and the number of rabies cases in foxes went from 101 to 0 in 2014. By 2004, one strain of canine rabies had been effectively eliminated from Texas, and another strain had been substantially controlled.
We are researchers who began studying rabies in wildlife and oral vaccination in the 1980s. From providing proof of concept in the use of oral vaccines in raccoons to being among the first to use novel rabies vaccines in the 1990s, we have been at the forefront of efforts to contain this deadly virus.
Decades of vaccine research led to one of the most successful public health projects in Texas. And we hope it can provide a roadmap for using mass vaccination of wildlife to prevent future outbreaks.
Development of the oral rabies vaccine
The Texas Oral Rabies Vaccination Program has benefited greatly from the work of several researchers over the past decades.
The mid-20th century saw several important developments in the control of rabies. When attempts to poison or capture infected animals failed, virologist and veterinarian George Baer of the U.S. Centers for Disease Control and Prevention recognized the need for another strategy to prevent and control rabies in wildlife. His and his colleagues’ work in the 1960s led to the concept of oral rabies vaccination. Although oral vaccination of wildlife would help control infection at the source, it was previously thought to be logistically impractical given the large number of target animals.
In the late 1970s, European researchers began the first field trials of orally vaccinating foxes against rabies. Small plastic containers were filled with vaccine and placed in baits, such as chicken heads. More than 50,000 of these vaccine-laden baits were distributed over four years in fox habitats in forests and fields.
Researchers in Canada also began similar field trials in Ontario. In the 1980s, an average of 235 rabid foxes were reported in the area each year. Bait containing oral rabies vaccine was dropped annually from 1989 to 1995 and successfully eliminated the fox variant of rabies from the entire area.
Recombinant oral rabies vaccine
The first generation of these vaccines used live viruses that had been modified not to cause serious disease. Although effective and generally safe, the original rabies vaccines had to be stored at cool temperatures and had the rare risk of causing rabies in animals.
In the early 1980s, scientists developed recombinant rabies vaccines, which use a separate virus to express the genes of the rabies virus. A collaboration between a nonprofit organization, the U.S. government, and the pharmaceutical industry led to the development of a recombinant viral vaccine that produced a rapid immune response to rabies without the potential to cause rabies.
In 1984, preliminary work in laboratory animals showed promise for using an oral form of the recombinant vaccine to vaccinate animals. However, the concept of using genetically modified organisms was still in its infancy, both among scientists and the general public. Although the vaccine was safe and effective in captive raccoons and foxes, major questions arose about how it might affect other species once released into the environment.
After years of work to improve the vaccine design and test its safety in several non-human species, the first European trial was conducted at a military base in Belgium. With data supporting that it could safely and effectively control wildlife in Luxembourg and France, the vaccine was approved in 1995 to control rabies in foxes.
Similar studies of the oral recombinant rabies vaccine were conducted in the United States. The first trial began in 1990 on Parramore Island off the coast of Virginia, and a year of intensive monitoring found no significant adverse effects on the environment or any animal species. A second year-long study on the mainland near Williamsport, Pennsylvania, had similarly positive results.
After the vaccine was successfully used to control rabies in raccoons in several other East Coast states, it was approved for use in raccoons in 1997.
In 1998, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service and the U.S. Fish and Wildlife Service received funding to expand existing oral wildlife vaccination projects to states of strategic importance to prevent the spread of specific rabies viruses and to coordinate projects between states.
Results in Texas
In Texas, the oral recombinant vaccine is now distributed primarily by hand and via approximately 75 separate helicopter flights per year.
The Texas Department of State Health Services rabies laboratory worked with the CDC to establish the Regional Rabies Virus Reference Typing Laboratory. One of us was recruited to distribute the vaccine in the field and to develop molecular typing tools to distinguish between different types of rabies virus variants in the lab. These techniques allowed us to identify where different rabies virus variants were emerging at a given time.
Our lab was also the first in the country outside of the CDC to help other U.S. states and countries test their samples for variants of the rabies virus. These techniques helped researchers monitor where the rabies epidemic was ongoing or in retreat due to wildlife vaccination and new modes of transmission.
With the constant threat of emerging and re-emerging infectious diseases such as COVID-19 and influenza, the prospect of mass vaccination of wildlife may provide a way to address future pandemics. While much work remains to be done, we are hopeful that one day we will have the option to use mass vaccination of wildlife to reduce or eliminate infectious diseases such as rabies.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Rodney E. Rohde, University of Texas and Charles Rupprecht, Auburn University
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Rodney E. Rohde has received funding from the American Society of Clinical Pathologists, American Society for Clinical Laboratory Science, US Department of Labor (OSHA), and other public and private entities/foundations. Rohde is affiliated with ASCP, ASCLS, ASM, and serves on several scientific advisory boards.
Charles E. Rupprecht consults for academic, government, industry, and NGO organizations worldwide. He receives funding from academic, government, industry, and NGO sources.