Fifty-two-year-old David has a good life. After 30 years serving the country as an army officer, he has retired to the coast of North Carolina a region of beautiful trees, moderate winter weather, and great outdoor spaces. It's a great place to retire and enjoy hiking through the woods and meadows photographing wildlife, especially in the early fall. It would be nearly perfect if only some of the wildlife didn't bite. Pervasive ants, pesky mosquitoes, and bloodsucking ticks seem to always be on the prowl.
After one hike he realized he had had a tick latched onto his shoulder for an unknown period of time. He very gently and carefully removed the tick with a pair of tweezers. Within 48 hours, David developed a low-grade fever, severe headache, and generalized malaise. The following day, he began to notice a rash running down his arm and toward his trunk. The rash had very small dark spots that seemed to resemble blood clots. He decided to make an appointment with his doctor.
The physician was able to squeeze David into the schedule the same day. As soon as the physician assessed and inspected David's worsening rash, she suspected Rocky Mountain spotted fever (RMSF), since it is common in the Carolinas, so she ordered a laboratory test using anti-Rickettsia rickettsii antibodies.
The test comes back negative; David is not infected with R. rickettsii. He does not have RMSF.
The doctor takes a skin sample from the infected area and prescribes 100 mg of doxycycline twice daily for seven days, since David's infection is not too severe.
The rash resolves in a week with help from the antibiotic. Polymerase chain reaction (PCR) testing on bacteria found in the sample of skin reveals Rickettsia parkeri, another bacterium that causes spotted fever, though it was long thought to be harmless to humans. David is one of the first of several dozen patients to tangle with this emerging threat in the southeast United States where its vector, the Gulf Coast tick, Amblyomma maculatum, commonly lives.
1. Why didn't the doctor prescribe amoxicillin?
2. Why didn't the antibody test show infection? (Hint: what organism caused the disease?)
3. What is PCR testing? (Hint: tell me what PCR is and how it can be used as a test to identify bacteria)
4. In a Gram-stained sample of David's skin, what color would the rickettsias be? (Hint: you'll need to google search the gram reaction of this microbe)
