# Isolation of Madariaga Virus (MADV) in a Horse Coinfected with Equine Infectious Anemia in Venezuela: A Review of MADV Circulation in the Country

## TL;DR

Madariaga virus, which causes severe disease in horses and can infect humans, has been continuously circulating in Venezuela since 1975 and is now reported in a new case from 2024.

## Contribution

The study reports the isolation and molecular characterization of a new Madariaga virus strain from a horse in Venezuela and shows its genetic similarity to a human case and a Colombian horse isolate.

## Key findings

- The 2024 Madariaga virus isolate from Venezuela is highly similar to a 2016 human case and a 2002 Colombian horse isolate.
- The virus has been continuously circulating in Venezuela since its first identification in 1975.
- The infected horse was co-infected with Equine Infectious Anemia virus.

## Abstract

Madariaga virus causes severe encephalitis in equids in South America and may also affect humans. This study reports the isolation and molecular characterization of a Madariaga virus isolated from a horse in Venezuela in December 2024 in the context of the viral cases reported in Venezuela. The sequence of this virus was highly similar to that of the only human case reported in the country in 2016, as well as to a sequence of a virus isolated from a horse in Colombia in 2002. The virus has been found continuously circulating in Venezuela since its first identification in 1975.

Background: Madariaga virus (MADV), formerly known as the South American variant of Eastern Equine Encephalitis virus (EEEV), is an alphavirus that belongs to the Togaviridae family and has been periodically infecting equids in Venezuela since its first identification in 1975. This study reports the isolation and molecular characterization of MADV isolated from a horse in December 2024 in the context of MADV cases reported in Venezuela. Methods: Antibodies to the rabies virus were detected by indirect immunofluorescence, and to the Equine Infectious Anemia virus (EIAV) by passive immunodiffusion. MADV RNA was detected by qRT-PCR. The sequence of the complete viral genome was obtained by next-generation sequencing. Results: The sequence of this virus was highly similar to that of the only human case of MADV reported in the country in 2016, as well as to a sequence of a virus isolated from a horse in Colombia in 2002. The horse was found to be co-infected with EIAV. Conclusions: The continuous circulation of MADV in Venezuela warrants reinforcing the preventive measures against these alphaviruses, which ignore borders, and may cause important animal and human health concerns.