Eastern equine encephalomyelitis virus in relation to the avian community of a coastal cedar swamp.

This research examines how the Eastern equine encephalomyelitis virus (EEEV) spreads within bird populations and local mosquitoes in a coastal cedar swamp in southern New Jersey, and its findings highlight the role of birds, particularly permanent and summer resident species, in perpetuating this virus transmission cycle.

Research Purpose and Methods

• In this study, the researchers aim to better understand the mechanisms that initiate annual outbreaks of the EEEV, a virus that is primarily spread between mosquitoes and birds in eastern North America. The mosquito Culiseta melanura acts as the main vector, carrying the virus, and passerine birds are the primary hosts where the virus multiplies.
• The research was conducted in a coastal cedar swamp community in southern New Jersey, an area known for high annual cycles of the virus. For the study, the researchers captured and sampled both birds and mosquitoes during three epidemics and one season of limited virus activity.

Analysis of Birds and EEEV

• The researchers analysed antibody prevalence (the presence of virus fighting proteins that indicate a previous infection) in birds, in relation to eight physical and natural history characteristics. This data offered insights into the members of the bird community that had evidence of previous EEEV infection.
• In the study, it was found that resident status of birds is closely linked to their participation in the EEEV cycle. Species spending a significant amount of time at the research site (permanent residents or summer residents), had the highest rates of EEEV antibody prevalence. These birds included the Blue Jay (62% prevalence), Wood Thrush (60% prevalence), and Tufted Titmouse (44% prevalence).

Insights into EEEV Transmission

• The research showed that this bird community could be infected with the virus and start spreading it among each other and local mosquitoes before the virus could be detected in the mosquito population.
• The researchers found evidence of a previously undetected, or ‘cryptic,’ cycle where the virus activity in the bird population rises weeks before it’s detected in C. melanura mosquitoes through traditional laboratory techniques.
• This study provides essential insights, suggesting that the annual outbreaks of the disease might be initiated by the reactivation (‘recrudescence’) of latent (inactive) virus in previously infected birds, rather than a new spread of the disease from the insect vector.