In West-Central Texas, the problem results from a dramatic increase of rabies cases among gray foxes. However, in South Texas, the increase in rabies is attributed to infected coyotes. In both areas, infections among other native wildlife and domestic animals also have increased. The first cases in this huge outbreak occurred in the Rio Grande Valley in 1988, and its spread has since advanced to just south of San Antonio. Rabies, in all its strains, is a disease caused by a virus that is carried in the saliva of an infected animal.
Infection usually is transmitted to another mammal through a bite.
After virus particles enter the body, they multiply and invade both the brain and the salivary glands. The cycle repeats as the newly infected animal becomes able to transmit the rabies virus to other animals or humans. Dr. Clark said that animals, whether wild or domestic, may show certain outward signs warning of their infections. One of the most obvious signs in a rabid animal is unnatural behavior. Wildlife with rabies may act disoriented and may also approach, instead of avoid, people.