Bad air or bad bugs?

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Try to imagine yourself in the shoes of Ronald Ross, a British Army surgeon stationed in India in the late 1800s, at the time of the Civil War, when 1.3 million American soldiers died of malaria.

Here are some facts about you:

  • You were born in India

  • Y
    Mid Gut
    ou and your father have contracted malaria, at various times, while living in India

  • You studied medicine, bacteriology and entomology (insects) in England

  • You have treated many soldiers while in India (12 years), who have contracted malaria

  • You have studied other scientists’ experiments (Laveran & Manson), and have seen parasites in different patients’ blood smears

  • You doubt that malaria is caused by “bad air”, and in fact you hypothesize that mosquitoes are spreading the disease

What would you do to prove your hunch? What would be your controls? What would be your variables? And if you were Dr. Ross, what ethical considerations do you face?

These are the materials you will use in your procedure. Do you need them all?

- Uninfected Person

- Infected Person

- Anopheles mosquitoes - male

- Anopheles mosquitoes - female

- Dissecting tools

- Microscope

What did Ross do that linked man and mosquitoes and led to his winning the 1902 Nobel Prize for Medicine, and his eventual knighthood? He dissected mosquitoes that had fed upon a person infected with malaria. On August 20, 1897, “Mosquito Day,” Ross found "some peculiar vacuolated cells” in the stomach of the mosquito. Other experiments followed, that confirmed that the parasite cycles between two hosts – man and mosquito – while meanwhile causing the disease we know as malaria.

Local research facilities such as Seattle BioMed often maintain an insectary on site, where they cultivate Anopheles mosquitoes, the only kind of mosquito to carry the Plasmodium parasite which causes malaria.
Today we will recreate Ross’s steps, by going through the careful process of dissecting a very small organism, and learning where the parasite lives within the mosquito – the midgut and the salivary glands. Mosquito dissection offers an exciting introduction for discussions pertaining to the work being done in laboratories at our own local Seattle Biomedical Research Institute.

  1. Watch a brief video on mosquito dissection.

  2. Working in pairs, receive dead, uninfected mosquitoes in a petri dish.

  3. Get comfortable with the dissecting microscopes (e.g., focus, zoom, eye width).

  4. Put the Petri dish on the scope stage. Tease a single mosquito into the field and focus.

  5. Check out the animals microscopically—inspect the mosquitoes for anatomical differences. Can you see the difference between the males and females? Males have frilly antennae and a smaller abdomen than female anopheline mosquitoes.

  6. Following the actions in the video. Using a pair of tweezers/forceps OR syringe needles, dissect several mosquitoes:

  7. Look for the midgut:

    1. Hold the insect in place, by stabbing the mosquito in the center of the thorax.

    2. Using the second forceps, grab the abdomen and pull slowly. As you do so, the midgut will be pulled from their spot within the mosquito thorax (it looks a lot like panty hose with golf balls in it!). If you are slow enough in your process, you may end up with the reproductive organs (big long tubes) attached to the terminal end of the midgut.

  8. Look for the salivary glands:

    1. Hold the insect in place, by stabbing the mosquito in the center of the thorax.

    2. Using the second forceps, seize the head. Draw the head away from the abdomen. As you do so, the salivary glands will be pulled from their spot at the front of the mosquito thorax (they look a lot like baby’s socks).

Record your observations here:

  • Draw the mosquito head

  • Draw the salivary glands

  • Draw the midgut

  • Draw and highlight the differences between the males and females

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