Kathleen Z. Rooney
Demographic factors
Connecticut is much more populated today than it was 60 years ago. The population in Connecticut in 1990 was 3,287,116 contrasted with a population in 1950 of 2,007,280.
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In addition to significant population growth and increased density, the population has shifted to rural areas as a place to live, not to farm. The number of acres converted to developed use from rural use was 40,800 in the 5 year period from 1992-1997.
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These demographic shifts have increased the contact between humans and forested areas and therefore with the insects and mammals that thrive in these forests. Statistically, we can study historical census data to understand the change in residential patterns in Connecticut, and relate them to the growth of Lyme disease.
Social and Behavioral changes
Some of the social attitudes that have caused a rural migration in Connecticut, include a growing affection and protection for wildlife in the face of increased development. As farming has been replaced by other industries in Connecticut, the rural countryside has become a refuge for the urban weary. It is not a working landscape but a pure and bucolic haven for peaceful living. This has also been made possible by inexpensive cars and gas and an increase in commuting. The city is no longer a modernist's haven, but a dirty, toxic environment. The country living is healthy and robust. Outdoor recreation is also very popular, giving more contact among people who are hiking, walking, swimming and the insects that are causing disease. Despite the rise in vector borne illness, this perception of the relative healthfulness of the countryside persists. This was one of the troubling aspects of the original Lyme puzzle. Many who were affected thought that they were raising children in the safest, most natural environment possible: Why were their children being stricken with debilitating illness?
Climate and environmental changes
This may be perhaps the most compelling factor in the evolution of WNV and Lyme disease in CT. The flora of Connecticut has changed drastically in the past 100 years. Young forests have replaced the mostly deforested, agricultural landscape of 19
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century Connecticut. These young forests meet the suburbs and form a transitional environment or ecotone, in which deer, ticks and rodents thrive. According to Arno Karlen, in Biography of a Germ Connecticut is currently two-thirds secondary-growth forests and ecotone.
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Mark Walters' book "Six Modern Plagues" quotes Rutgers ecology professor Edmund Stiles:"Three hundred years ago there were probably about 25 deer [sic] per square mile. Now there are something like 200 per square mile." Stiles goes on to say that generalist species like deer and mice thrive in disrupted forests, while many of their original predators are more specialized and do not. According to Kirby Stafford at CAES, "rates in Connecticut generally run around 30-60 deer per square mile, which is still a lot of deer."
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Additionally, a rise in average temperature and precipitation, attributed to global warming has paralleled a rise in tick population.
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In WNV, global warming has been implicated in the change in avian migratory patterns that have expanded the reach of this disease. With a delay in the onset of winters, the lifespan of mosquitoes can increase and the numbers of infected vectors within the season will increase. Increases in precipitation leads to exponential increases in mosquito breeding and populations. The deaths of large populations of bats due to a fungus called white nose syndrome may lead to a sharp uptick in the mosquito population. Using these factors as predictors for the growth of these diseases, we can draw on climate, rainfall and animal population records as part of our study.
Microbial evolution
The evolution of these pathogens is an area of current scrutiny by scientists. Although it is beyond the scope of this unit to study the microbial evolution of flavivirus and Borrelia burgdorferi, it can be said that evolutionary changes in these pathogens have allowed their adaptation to the vectors and environmental conditions in the Western Hemisphere. Lyme disease may have evolved from a less virulent version of the Borrellia bacterium, or it may be more pervasive as a result of recognition and environmental exposure. We recognize its existence in Europe, the midwest and the West coast as a syndrome caused by a borrelia spirochete. However, in each area it is carried by different vectors. Likewise, WNV is spread by a different set of vectors in Europe and Africa, though the virus is similar enough in both places as to be recognized as the same virus.
