Detection of eastern equine encephalomyelitis virus RNA in North American snakes

Abstract

The role of non-avian vertebrates in the ecology of eastern equine encephalomyelitis virus (EEEV) is unresolved, but mounting evidence supports a potential role for snakes in the EEEV transmission cycle, especially as over-wintering hosts. To determine rates of exposure and infection, we examined serum samples from wild snakes at a focus of EEEV in Alabama for viral RNA using quantitative reverse transcription polymerase chain reaction. Two species of vipers, the copperhead (Agkistrodon contortrix) and the cottonmouth (Agkistrodon piscivorus), were found to be positive for EEEV RNA using this assay. Prevalence of EEEV RNA was more frequent in seropositive snakes than seronegative snakes. Positivity for the quantitative reverse transcription polymerase chain reaction in cottonmouths peaked in April and September. Body size and sex ratios were not significantly different between infected and uninfected snakes. These results support the hypothesis that snakes are involved in the ecology of EEEV in North America, possibly as over-wintering hosts for the virus.

Figure 1.

Exposure to (Antibody +) and infection with (polymerase chain reaction [PCR] +) eastern equine encephalomyelitis virus in cottonmouth snakes (Agkistrodon piscivorus) from Tuskegee National Forest, Alabama, USA. Data on seropositivity rates were taken from previously published sources.

Figure 2.

Body size (snout-vent length) of male and female cottonmouth snakes (Agkistrodon piscivorus) exposed to (A) and infected with (B) eastern equine encephalomyelitis virus from Tuskegee National Forest, Alabama, USA. Error bars show SD.

Figure 3.

Sex ratio of eastern equine encephalomyelitis virus (EEEV) quantitative reverse transcription polymerase chain reaction (qRT-PCR)–positive (A) and EEEV qRT-PCR–negative (B) cottonmouth snakes (Agkistrodon piscivorus) from Tuskegee National Forest, Alabama, USA.