Now here’s a relationship not many middle school students would stop to consider: bird species diversity and West Nile virus incidence. A press release dated October 6, 2008, indicates researchers at Washington University in St. Louis have collected evidence that shows an inverse relationship between bird species diversity and West Nile virus. Thus, urban and suburban areas are likely to host more cases of West Nile virus than forested or rural areas perhaps. At first, that seems counterintuitive. How can an urban area, presumably low in trees and thus birds, be a more likely host site than a rural one for the bird-harbored West Nile virus?

An understanding of systems — as described by the National Science Education Standards content standard dealing with systems, order and organization — offers insight. In this case an understanding of the systems, order and organization of viral life cycles and transmission modes is needed. First, we understand the disease is caused by a virus. Next, we know a unifying characteristic of viruses is their inability to reproduce outside a hijacked cell. Finally, we note West Nile virus can be transferred from bird to human via the salivary glands of biting mosquitoes.

The next system to consider is the natural history of birds. Their habitat, competition for food and shelter, and their niche are this system’s parameters. This system naturally intersects with the natural history of mosquitoes and the tag-along West Nile virus. Likewise, this system of mosquito and West Nile virus commensalism intersects with the Homo sapiens natural history when the mosquitoes infect humans.

Okay, so we see how systems intersect and impact each other, but what accounts for the inverse relationship these researchers reported?

Most bird species are not good hosts for the virus. However a few are. Those few happen to tolerate urban and suburban conditions well. Those few species include robins and crows, for example. Even if there were 10 species of birds found in a suburban area, you could expect a high incidence of West Nile virus under the following scenario. The raw number of all birds is 1000. Nine hundred are robins. One hundred are split evenly among nine other species. Robins are particularly good West Nile virus hosts.

How to Turn This News Event into an Inquiry-Based, Standards-Related Science Lesson

Students are likely to agree that forested areas would host a greater number of birds and a greater diversity of bird species than urban or suburban areas. Challenge students to explain why. Explain to them that West Nile virus is transmitted from birds to humans through mosquito bites and that the virus can make people sick, sometimes very seriously. Ask them to predict what kind of areas would likely have the highest human incidence of West Nile virus — urban, suburban or rural/forested?  Have them support their prediction with solid logic. Have a student volunteer to verbalize his or her prediction and supporting logic. Then ask other students if they agree or disagree with the prediction and logic (as opposed to agreeing/disagreeing with the student) and why. Encourage respondents to elaborate on their thinking by allowing plenty of wait time.

When all of the students are secure in their stance, and there will likely be two different stances, ask them to brainstorm some methods that should/could be used to test their ideas. What kinds of evidence would they need? How would they go about obtaining it? Again, facilitate some peer review by asking students to evaluate the generated ideas for tests, and to provide methodological improvements where they can. Finally, share with them the methods and findings of these researchers. Are the students surprised? Why or why not? How does the evidence impact arguments for conservation?

The lesson described connects to both the History and Nature of Science and the Science as Inquiry content standards of the National Science Education Standards. In the AAAS’s Project 2061 benchmarks, students in grades 6-8 are expected to acquire knowledge of systems thinking.

Here are additional related resources from the National Science Digital Library Middle School Portal: Structure and function in living systems; The big picture book of viruses; and Zoonotic diseases go global

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