Antibodies to West Nile virus in asymptomatic mammals, birds, and reptiles in the Yucatan Peninsula of Mexico.

This research conducted in 2003 and 2004, aimed to assess the prevalence of West Nile virus (WNV) within a diverse range of vertebrates in the Yucatan Peninsula of Mexico. The study found antibodies to the virus in many vertebrates, including 62% of the tested horses and 3% of animals at the Merida Zoo, with all animals healthy despite the presence of these antibodies.

Study Background and Objective

• The study was carried out as a surveillance to understand the pervasiveness of the West Nile virus (WNV) infection in different types of vertebrates in the Yucatan Peninsula of Mexico during 2003 and 2004.
• The primary objective was to study the existence of WNV antibodies in mammals, birds, and reptiles that didn’t show any signs of illness.

Study Design and Methodology

• Blood samples were collected from a total of 144 horses on Cozumel Island, 415 vertebrates (that contained 257 birds, 52 mammals, and 106 reptiles) from around 61 species at the Merida Zoo and 7 farmed crocodiles in Ciudad del Carmen.
• The samples were then tested for antibodies to flaviviruses – a type of viruses that includes WNV – using a blocking enzyme-linked immunosorbent assay (ELISA). If antibodies were detected, the sample was further tested specifically for WNV using the plaque reduction neutralization test (PRNT).

Study Findings

• Out of 144 horses on Cozumel Island, 90 (62%) were found with ELISA antibodies to flaviviruses. Among these 90 horses, 75 (52%) were confirmed seropositive for WNV by PRNT.
• In the Merida Zoo, 13 (3%) of the 415 animals showed the presence of blocking ELISA antibodies to flaviviruses. This group included 7 birds and 2 mammals, a jaguar and coyote, which were found seropositive for WNV via PRNT.
• Out of 7 farmed crocodiles, 6 (86%) were confirmed with WNV infections through PRNT.

Implications of the Study

• All the animals that tested positive for WNV were healthy at the time of blood sample collection, thus indicating the potential for asymptomatic WNV infections in vertebrates.
• The high proportion of seropositive results in the tested populations suggests a wide distribution of WNV in the region and a corresponding risk to other animals and potentially humans.