Chapter 19, Problem 2EDCS

A New Cause of Spots

Fifty-two-year-old David has a good life. After 30 years serving the country as an Army officer, he has retired to the Texas Gulf Coast-a region of large oaks, mild winter weather, and great outdoor spaces. It’s a great place to retire and enjoy hiking through the woods and meadows photographing wildlife. It would be nearly perfect if some of the wildlife didn't bite. Ubiquitous ants, pesky mosquitoes, and bloodsucking ticks seem to always be on the prowl.

It’s a tick that brings him to his doctor today. The thing had bit him on his left shoulder, resulting in a huge boil that swelled and drained pus, though the lesion doesn’t hurt at all. His primary care physician doesn’t appear to be too concerned and prescribes amoxicillin for the boil.

Three days later, David is back but feeling much worse. He has suddenly developed fever, headache, muscle pains, fatigue, and an alarming rash over most of his body. The physician now suspects Rocky Mountain spotted fever (RMSF), though it’s relatively rare in Texas, and orders 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 two weeks.

The rash resolves in a week, and further polymerase chain reaction (PCR) testing on bacteria found in the sample of skin reveals R. parkeri. In the United States, the Gulf Coast tick, Amblyomma maculatum, is the vector for this bacterium that was long thought to be harmless to humans. David is one of the first of several dozen patients to tangle with this pathogen that is emerging as a threat in the southeast United States and in Argentina.

1. 1. Why didn’t the antibody test show infection?
2. 2. What is PCR testing?
3. 3. In a Gram-stained sample of David's skin, what color would the rickettsias be?