An Overview of Equine Influenza in South America

Abstract

Equine influenza virus (EIV) is one of the most important respiratory pathogens of horses as outbreaks of the disease lead to significant economic losses worldwide. In this review, we summarize the information available on equine influenza (EI) in South America. In the region, the major events of EI occurred almost in the same period in the different countries, and the EIV isolated showed high genetic identity at the hemagglutinin gene level. It is highly likely that the continuous movement of horses, some of them subclinically infected, among South American countries, facilitated the spread of the virus. Although EI vaccination is mandatory for mobile or congregates equine populations in the region, EI outbreaks continuously threaten the equine industry. Vaccine breakdown could be related to the fact that many of the commercial vaccines available in the region contain out-of-date EIV strains, and some of them even lack reliable information about immunogenicity and efficacy. This review highlights the importance of disease surveillance and reinforces the need to harmonize quarantine and biosecurity protocols, and encourage vaccine manufacturer companies to carry out quality control procedures and update the EIV strains in their products.

Keywords: H3N8; H7N7; South America; equine influenza.

Figure 1

Geographical localization of the countries where EIV was reported in South America.

Figure 2

Maximum likelihood phylogenetic tree of the HA gene of H3N8 EIV. Bootstrap values obtained after 1000 replicates are shown at major nodes. Magenta boxes enclose South American strains. Colored diamonds (♦) represents the strains detected in South America: pre-divergent lineage (black), American lineage (blue), Florida clade 1 (green).