Studying the life cycle of ticks provided important pieces of the RMSF puzzle. Knowing the life cycle meant that scientists could study questions such as: When did the ticks pick up the bacteria causing RMSF—was it when they were newly hatched? When they were adults? And was the infection passed on to a new generation of ticks through the eggs? The answers to these questions could be used in control efforts and in developing a new vaccine.
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The life cycle of the tick: a fertilized female lays thousands of eggs on the ground. When they hatch as larvae, they attach to small animals and feed. Then they drop off to digest their meal, and molt (shed their old shell) to become nymphs. The first winter they spend as unfed nymphs.
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In spring, the nymphs once again attach to an animal and feed, drop to the ground, and digest their meals. This time they molt to adults, like these Rocky Mountain wood ticks, Dermacentor andersoni. They spend their second winter as unfed adults.
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The next spring they climb grass and bushes to attach to animals.
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But as adults, ticks mate as well as feed. This is when the ticks can get the Rickettsia rickettsii bacteria from the animals they feed on. Even though the bacteria don’t hurt the ticks, it infects all of their cells, and is passed on through the egg. The next generation of ticks will be infected.
Images: Office of NIH History and Stetten Museum, 1554-58
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Environmental studies
To understand the entire picture of RMSF transmission, the entomologists at the Canyon Creek Schoolhouse laboratory began environmental studies of the relationships between the distribution of vegetation, rodents, ticks, and humans.
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“Valuable Experiment: Please Do Not Disturb” reads a sign put up in 1928 by one of the RMSF researchers in one area undergoing an ecological study.
Image: Office of NIH History and Stetten Museum, 1479
