Bats, caves, danger and exotic locales. That should catch your students’ attention! The big story here is the co-evolution of viruses and their nonhuman animal hosts, who seem to have a harmless, symbiotic relationship with viruses that cause deadly outbreaks in humans. Though this story is about Marburg virus and a fruit bat, the concepts apply to many virus/host/human infections systems, including H1N1.

On August 2, 2009, ScienceDaily published a story called ‘Ebola Cousin’ Marburg Virus Isolated From African Fruit Bats.

While previous investigations have found antibodies to Marburg virus and virus genetic fragments in bats, the recent study goes significantly further by isolating actual infectious virus directly from bat tissues in otherwise healthy-appearing bats. The new study shows unambiguously that this bat species can carry live Marburg virus. . . . By identifying the natural source of this virus, appropriate public health resources can be directed to prevent future outbreaks. (Emphasis added.)

The blog MicrobiologyBytes also has a post about this finding. The writer notes that ecologists have been looking for this “natural reservoir” for forty years! Now that researchers have found the reservoir, it appears the potential for human disease outbreaks is greater than previously thought.

The original source for ScienceDaily’s  story is found at http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000764.

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

There have been reports of H1N1 flu outbreaks at summer camp. Ask your students who has actually had swine flu recently. How do they know? What do they know about the H1N1 virus and viruses in general? Where do viruses come from? What are they made of? What other viruses have students heard of that can have an even more severe impact on humans than H1N1?

Ask if any students have seen the movie Outbreak? What was the ultimate host for that virus? How is it that animals can host these viruses with no negative impact to their health, yet humans cannot?

Students do not necessarily need to articulate the structure of the virus on a molecular level, but they should understand that the virus is not cellular, has very few parts, and cannot survive except inside the cell of another, benefiting from the host cell’s structures and activities that the virus lacks. Thus, when the virus inhabits some animal bodies, it does no harm, but when the same virus inhabits human cells it causes harm. Can your students construct a reasonable hypothesis to explain this observation?

Show students this eight-slide, narrated animation of how a virus infects a cell: https://www.health.harvard.edu/flu-resource-center/virus/how-a-virus-infects-a-cell_3.htm

This image, which lacks a caption, is for your information. It shows a micrograph of the virus, a labeled schematic, and the corresponding genome, consisting of seven genes.

After students generate some hypotheses about the relationships between viruses and their hosts, have them scrutinize their hypotheses by engaging in scientific argumentation. What is the rationale for the hypothesis? What evidence is there to support the rationale? Can some hypotheses be eliminated? How should others be modified?

Ask students what natural selection means. How might the concept be related to the observation of the apparent symbiotic relationship of viruses and an animal host? Over a very long time, natural selection selected against host animals who lacked the ability to generate antibodies against the virus, leaving survivors who do produce the necessary antibodies. One assumption is that humans, who have inhabited the planet for a very short period of time relatively speaking, have not had enough time for natural selection to eliminate those humans who cannot produce the appropriate antibodies. And at the same time, the necessary random mutations in the human genome that would enable antibody production have not appeared.

The Marburg virus manifests a number of variations in gene base sequence (the order of cytosine guanine, adenine and thymine in the virus’s DNA), suggesting the virus has been around a very long time. Mutations are relatively rare; thus, it takes a very long time to accumulate many. This variation in the virus confers a high degree of fitness on it and increases the probability that at least one or more of the variations will find hospitable environments in which to thrive and reproduce.

H1N1 is subject to the same assumptions. Influenza is naturally hosted by birds. Somewhere in evolutionary history, the bird flu virus acquired a mutation that enabled it to colonize swine, without killing them. In more recent history, the two flu strains were probably inhabiting the same hosts simultaneously, enabling gene mixing of the two viruses and producing H1N1, among other viruses. For the same reasons given earlier, humans do not produce antibodies for the flu virus.

For assessment, have students respond to these inquiries:

1. Why do Egyptian fruit bats hosting Marburg virus

2. Why do you think ecologists were unable to locate the Marburg virus’s natural reservoir for over forty years? (Researchers may not have realized another mammal could host the virus without getting sick. Also, newer technologies are able to differentiate the slightest variations in gene sequences that, although containing some variation, are still the same virus. They may have believed most of these variations, though observed, were not Marburg.)

3. Finally, as a bridge to technology and the application of science findings: What do you think can be done with the fact that the Egyptian fruit bat is a known host to the deadly Marburg virus?

Here are additional resources from the National Science Digital Library Middle School Portal:

Influenza: History, Science, Strains, Detection and Protection; What’s Making You Sick?;

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