Enzootic and epizootic Venezuelan equine encephalomyelitis virus in horses infected by peripheral and intrathecal routes.

This study investigates the effects of Venezuelan equine encephalomyelitis (VEE) virus on horses, which were infected through peripheral or intrathecal methods. The findings reveal the varying effects and levels of virus in the cerebrospinal fluid as a result of the infection method and VEE strain.

Methodology

• The experiment involved forty-five horses that were infected with either enzootic or epizootic strains of VEE virus.
• These horses were infected by two methods – peripherally (through the skin or mucous membranes) or intrathecally (directly into the spinal cord).

Findings

• After peripheral inoculation of enzootic or epizootic VEE virus strains, low levels of the virus appeared in the cerebrospinal fluid (CSF) – a clear fluid found in the brain and spinal cord.
• Intrathecal infection resulted in higher concentrations of the VEE virus in the CSF, regardless of whether the strain was enzootic or epizootic.
• Interestingly, horses infected intrathecally with enzootic strains endured a more severe outcome than those infected peripherally, often leading to death. This contrasted with peripheral infections where enzootic strains did not cause fatality.
• The animals that died presented extensive histopathologic changes, which involve the microscopic examination of tissue in order to study the manifestations of disease. Additionally, a significant amount of the VEE virus was found in their brain tissue.

Observations with the VEE Virus Vaccine Strain

• The researchers also observed the effects of the TC-83, an attenuated (weakened) VEE virus vaccine strain.
• When inoculated intrathecally, the TC-83 strain too multiplied in the horse’s brain.
• Contrary to the severe impacts observed with the enzootic and epizootic strains, horses infected with the TC-83 strain did not suffer from any clinical disease and experienced minimal histopathologic damage.

This research contributes valuable insights to understanding how different strains of the VEE virus affect horses’ nervous system, including severity based on the method of infection, making it a significant study for the field of veterinary medicine, especially regarding equine neurologic diseases.