Contraceptive developed for stray cats

Experts estimate that anywhere from 30 million to 60 million stray cats roam the United States

By ENN staff

Experts estimate that anywhere from 30 million to 60 million stray cats roam the United States. These feral cats are wreaking havoc on the nation's songbird population and raising public health concerns as they spread infectious diseases and alter delicate ecological balances.

To deal with this problem, a Virginia-Maryland Regional College of Veterinary Medicine student has come up with a new way to control the birth rate of feral cats. Utilizing the prestigious Geraldine R. Dodge Foundation grant, Michelle Meister-Weisbarth has developed a genetically engineered bacterium to serve as an oral contraceptive to control the unwanted cat population.

Working with faculty mentor and molecular biologist Dr. Stephen Boyle, Meister-Weisbarth used genetic engineering technology to modify a strain of the bacterium salmonella, which could then be delivered to feral cats in the wild via a vaccine-laden bait.

According to Boyle, work in other laboratories around the world has demonstrated the viability of using genetically altered strains of salmonella as vehicles for delivering vaccines, including oral contraceptives. Controlling the birth rates of feral cats has been difficult in the past, since conventional spay and neuter techniques require surgery in a controlled environment. In addition, animal control experts note that eliminating or removing the cats does not work well since others seem to migrate into the recently vacated niches.

The new technique starts with the utilization of genetic engineering techniques to remove specific genes on the salmonella genome, making it unable to cause disease. Meister-Weisbarth then introduced a gene encoding a protein derived from the zona pellucida surrounding the vertebrate egg into the salmonella. The bacterial vaccine is capable of inducing the production of antibodies which recognize the zona pellucida and block the ability of a sperm to fertilize the egg.

Boyle says the attenuated strain cannot cause disease, making it especially useful as a vehicle for delivering an immuno-contraceptive agent since once ingested it survives in the stomach and crosses the intestinal tract to cells in the immune system. Once in the cells of the immune system, the salmonella are killed and the zona pellucida antigen is released and stimulates production of antibodies. Because these antibodies bind to the zona pellucida surrounding the egg, they inhibit the binding of sperm and thus block fertilization.

Scientists have been working on various ways of delivering vaccines for rabies into wild populations in the form of bait. Boyle and Meister-Weisbarth both believe these methods can be modified to deliver the genetically engineered salmonella as an oral immuno-contraceptive.

The next phase of research, for which the team is soliciting funding, will involve testing the attenuated salmonella on lab animals.

For more information, contact Jeffrey S. Douglas, (540) 231-7911, email: jdouglas@vt.edu.

Copyright 1998, Environmental News Network, All Rights Reserved

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