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by Mary Garvin
<cont. ...> Kilbourne’s observation that native peoples were not immune to malaria is also interesting and suggests its importation from Europe. Although there is much speculation regarding the first occurrence of malaria in the Western Hemisphere, like many European diseases it may well have first arrived with the colonists (17). The abundance of large populations of Anophelene mosquitoes in America and their close association with humans completed the chain of elements necessary for transmission.
Despite the fact that Anopheles quadrimaculatus, as well as other species of Anopheles are still common in Ohio and throughout North America, we experience little malaria transmission in modern times. For the most part, the malarial cycle was broken when interaction between humans and mosquitoes was reduced. Ironically, drainage of swampland for agriculture, the very activity that originally placed early settlers in close proximity to the Anophelenes, has adequately altered portions of the landscape to sufficiently reduce breeding conditions.
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| Drainage systems, such as this ditch outside of Oberlin, have greatly reduced mosquito breeding habitat and allowed for the agricultural success of northern Ohio. |
Elaborate networks of tile that now drain the low-lying areas and make it possible to efficiently farm there have permanently changed the northern Ohio landscape. The change has come with heavy costs to the environment. Despite the development of no-till agriculture, the rapid run-off of water from tilled land has leached nutrients from the soil, altered the natural hydrology, and created heavy silt deposits in rivers and creeks, reducing the quality of habitat for native plants and animals. Enough of the original Anophelene habitat remains, however, for transmission of malaria to still be possible, because the species is still abundant in the state. Therefore, it is not surprising that occasional cases of malaria are reported when infected people travel through the area and provide a source of infection for foraging mosquitoes. In addition to altering the landscape, mosquito access to humans also has been greatly reduced through the use of window screens that prevent insects from entering homes, and air conditioners that eliminate the need to open windows during the evening when Anophelene species feed. Because the interaction between mosquitoes and humans has been adequately disrupted, the human reservoir of malaria transmission has been depleted and transmission has ceased.
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| Apple trees growing along Middle Ridge Rd. north of Oberlin reflect the agricultural opportunities provided by the sandy ridges. |
Our endless desire to "tame the land" and create order has led to modern land-use patterns that have shifted away from agriculture and limited our daily interaction with the soil and other species living on it. Unlike the residents of early Ohio who encouraged settlement, we now have to create metro parks, zoning ordinances, and policies to control urban sprawl and protect those rural landscapes that remain. Nevertheless, despite our feelings of detachment from the landscape, we interact with it sufficiently to acquire mosquito-borne diseases. Moreover, we actually increase our exposure to these diseases by creating new niches where mosquitoes may breed. For example, here in Oberlin the relatively rare LaCross encephalitis virus is transmitted by the tree-hole mosquito, which breeds as successfully in used tires and other artificial containers as it does in tree holes. Roadside ditches with nutrient-rich agricultural run-off also provide optimal habitat for several species of mosquitoes that transmit West Nile virus.
As Ohio now anxiously awaits the arrival of the relatively benign but much publicized West Nile virus, we’re provided with a stark and interesting contrast to the battle against malaria. Unlike that unavoidable evil of frontier life, the West Nile virus and its cycle are well understood by state health experts who are students of ecology and understand the need to eliminate breeding grounds to reduce our interaction with mosquitoes. Yet because most of the general public knows less about the land and how it can affect us, we find greater satisfaction in less effective but more visible and seemingly proactive means of control, such as insecticides that only momentarily reduce numbers of adult mosquitoes.
Ohio’s changing landscape is likely to always provide numerous rural and urban breeding opportunities for many mosquito species capable of transmitting exotic pathogens. It is our interaction with and understanding of the landscape, however, that will ultimately determine the degree to which we are affected.
MOSQUITOES
Playing
your trumpets
thin as a needle
in my ear,
standing on my finger
or on the back of my neck
like the best arguments
against
pity I know.
You significant vampires
that sip my life
through a straw;
you drops of blood
with wings;
carriers
of insomnia
I search for
with
a lit match...
I had a job once
driving around in a truck
to look for your eggs.
They can be found
in ditches, near
train tracks, outside
of a barn
in an upright piano filled with rainwater.
It is impossible to
kill
all of you,
invisible in the uncut grass
at the edges of the cemetery:
when the dogs go down there it
looks like they’ve gotten into birds.
--Franz Wright, 1977
Please send comments, questions, and suggestions about Oberlin Online news and feature articles to online.news@oberlin.edu.
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