Pathogenicity of a Venezuelan equine encephalomyelitis serotype IE virus isolate for ponies.

The study examines the pathogenicity of the Venezuelan equine encephalomyelitis (VEE) virus isolated from a 1993 outbreak in Mexico on ponies. The research discovers that the studied strain of VEE, initially considered avirulent, can indeed cause illness in ponies, exhibiting symptoms such as encephalitis and fluctuating body temperature.

Study Context

• VEE is a viral disease endemic in certain parts of the world, widely affecting horses but potentially affecting humans as well.
• Particularly, endemic strains of VEE such as the ID, IE, IF, and II-VI serotypes were thought to be avirulent, meaning they were not capable of causing disease.
• However, outbreaks of encephalitis in the horse populations in the Chiapas and Oaxaca provinces of Mexico in 1993 and 1996 respectively, were associated with VEE virus subserotype IE.

Research Approach

• The study focused on the Chiapas viral isolate from 1993, referred to as NVSL VEE IE 93-42124.
• Three ponies were intradermally inoculated with different quantities of this virus, followed by monitoring of symptoms and diagnostic tests to confirm the presence of the virus and disease.
• The researchers performed microscopic examination of tissue sections stained with hematoxylin and eosin to identify any changes indicative of the disease.
• The presence of antibodies to VEE virus IE was checked using the IgM antibody, which does not distinguish between various subserotypes of VEE I viruses (serotypes IAB, IC, ID, and IF).

Findings

• All infected ponies exhibited signs of infection including fluctuations in body temperature and encephalitis.
• The disease-causing virus was found in the blood of infected ponies from day 1 to 3 post infection.
• Tissue examination revealed signs of mild to moderate nonsuppurative encephalitis, perivascular cuffing by mononuclear cells, gliosis, and meningoencephalitis.
• VEE I virus neutralizing antibody titers were much lower for heterologous VEE I viruses compared to the studied VEE virus NVSL VEE IE 93-42124 and a human isolate of VEE IE virus called Mena II.

Conclusion

• This study established that the NVSL VEE IE 93-42124 virus, isolated during the VEE outbreak in Chiapas, Mexico, is pathogenic for ponies, challenging previous assumptions about its avirulence.