Severe Winter Freezes Enhance St. Louis Encephalitis Virus Amplification and Epidemic Transmission in Peninsular Florida

Abstract

Mosquito-borne arboviral epidemics tend to strike without warning. The driving force for these epidemics is a combination of biotic (vector, amplification host, and virus) and abiotic (meteorological conditions, especially rainfall and temperature) factors. Abiotic factors that facilitate the synchronization and interaction of vector and amplification host populations favor epidemic amplification and transmission. In Florida, epidemics of St. Louis encephalitis (SLE) virus (family Flaviviridae, genus Flavivirus, SLEV) have been preceded by major freezes one or two winters before the onset of human cases. Here, we analyze the relationship between severe winter freezes and epidemic SLEV transmission in peninsular Florida and show that there is a significant relationship between the transmission of SLEV and these severe freezes. We propose that by killing cold-sensitive understory vegetation in the mid-peninsular region of Florida, freezes enhance the reproductive success of ground-feeding avian amplification hosts, especially mourning doves and common grackles. In conjunction with other appropriate environmental signals, increased avian reproductive success may enhance SLEV and West Nile (WN) virus amplification and result in SLE and WN epidemics during years when all of the biological cycles are properly synchronized. The knowledge that winter freezes in Florida may enhance the amplification and epidemic transmission of SLE and WN viruses facilitates arboviral tracking and prediction of human risk of SLE and WN infection during the transmission season.

Risk Factors Associated with Death in In-Hospital Pediatric Convulsive Status Epilepticus

“…More research will be needed to verify these data and to identify possible causes. Seasonal variations in infections such as bacterial meningitis [20] and viral encephalitis [21] and other respiratory tract infections may have played a role in this annual variation.…”

Mosquito-Borne Arboviral Surveillance and the Prediction of Disease Outbreaks

“…nigripalpus oviposition sites that allow the mosquitoes to begin reproducing early in the year, during the spring dry season, a period when there would normally be no available oviposition sites. In addition, it has also been shown (Day and Shaman 2009) that there is a significant relationship between severe south Florida winter freezes and avian reproduction during the three breeding seasons following the freeze. It is proposed that severe winter freezes clear cold-sensitive vegetation from the understories of woodland habitats.…”

“…Environmental temperatures may also impact avian nesting behavior and reproductive success (Day and Stark 1999). Severe winter freezes in south Florida have been shown to enhance avian nesting, foraging, and reproductive success during the following spring (Day and Shaman, 2009). The exact ways in which winter freezes in south Florida impact avian nesting success the following spring will be discussed in detail in the SLEV in Florida section below.…”

“…Similarly, the age structure and infectivity status of known amplification hosts can be monitored and used to measure arboviral transmission risk (Day and Stark, 1999). Finally, the environmental conditions that influence vector and amplification host population structures can be tracked and used to predict how and when vector, amplification host, and viral populations will synchronize and escalate to a point where epidemic disease transmission is inevitable Day and Shaman, 2009). A thorough knowledge of the three biological cycles (virus, vector, and amplification host) and the environmental factors that drive these cycles can allow the skillful prediction of when and where mosquito-borne arboviral disease outbreaks will occur (i.e.…”

Research Contributing to Improvements in Controlling Florida’s Mosquitoes and Mosquito-borne Diseases

“…Florida’s climate—which features a wide range of weather conditions, including winter freezes—also influences the risk for subsequent transmission by species of Culex [58,59]. Research on Culex vectors led to the establishment of Florida’s sentinel chicken surveillance program with hundreds of sentinel chicken flocks located throughout much of Florida.…”