Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies.

This study investigates the pattern of Venezuelan equine encephalitis (VEE) spread among wild and domestic animals during a 1971 epidemic in southern Texas, identifying horses as a significant amplifier and distributor of the virus.

Overview of the Study

• The research was conducted in 1971 during an outbreak of Venezuelan equine encephalitis (VEE) in southern Texas.
• The researchers selected the lower Rio Grande Valley, specifically the Boca Chica area of Cameron County, as their point of investigation due to a high level of VEE activity among horses, humans, and mosquitoes.

Investigation Approach and Findings

• The researchers examined a total of 4739 wild and domestic non-equine (non-horse) vertebrates for signs of VEE virus.
• Only a single instance of VEE virus was isolated from these species, despite much higher rates of isolation from concurrent studies on horses and humans.
• According to antibody studies, large domestic animals experienced significantly more VEE virus activity than wild birds, mammals, or reptiles.
• In 1972, VEE antibodies were found exclusively in rabbits, indicating that the epidemic virus had failed to establish a new, sustainable cycle within the wild vertebrate population in southern Texas.

Key Factors in the Ceasing of VEE Transmission

• The cessation of the VEE transmission has been attributed to four key factors:
• Firstly, the elimination of the horse population as a source of VEE, which happened due to death, naturally acquired antibodies, or vaccination.
• Secondly, the implementation of quarantines.
• Thirdly, control measures to reduce mosquito populations were put in place as mosquitos are known vectors for the disease.
• Lastly, the virus failed to establish a new cycle within the wild vertebrate population.
• As a result, equines (horses) were highlighted as the most significant vertebrate host in the virus amplification and spread during a VEE epidemic.