Tick species that transmit tick-borne relapsing fever: Ornithodoros hermsii and other Onithodoros tick species.
Tick-borne Relapsing Fever (TBRF) is caused by bacterial spirochete species including Borelliahermsii, Borelliaparkerii, or Borelliaturicatae, with Borelliahermsii being the most common causative agent. The bacteria are transmitted by the bite of soft tick Ornithodoros species. These ticks feed primarily at night. The bite of the tick is usually painless and they feed for only 15 to 30 minutes before dropping off. This makes it difficult to detect the ticks on one’s body. The Ornithodoros soft ticks generally feed on small mammals and rodents including mice, chipmunks, squirrels, rats and rabbits, and in the absence of these hosts they will feed on other warm-blooded mammals including humans.
TBRF can occur in most of the western portion of the US (west of the Mississippi River) with most cases occurring west of the Rocky Mountains. Travelers to these endemic states commonly get the disease as well. A high percentage of cases occur among people vacationing in rodent-infested cabins in wooded and mountainous areas.
Tick-borne relapsing fever is characterized by recurring episodes of fever accompanied by other non-specific symptoms including headaches, muscle pain, joint pain, chills, vomiting, and abdominal pain. Bacterial presence tends to be greater among pregnant women, and may sometimes result in more severe infection. Symptoms tend to develop within 7 days after the tick bite. The symptoms last an average of 3 days (range of 3-7 days) and are then followed by an asymptomatic period (no symptoms present) lasting anywhere from 4 to 14 days. Symptoms relapse an average of 3 times but can recur up to 10 times among untreated patients.
Image obtained from http://www.cdc.gov/ncidod/dvbid/RelapsingFever/Resources/TBRFBrochure1.pdf
A definitive diagnosis of TBRF is made by detecting Borrelia spirochetes in the patient’s smears of blood, bone marrow or cerebrospinal fluid. The best time to detect spirochetes in patient blood samples is when the patient is febrile (feverish).
Symptoms of TBRF often resolve on their own, but treatment with antibiotics can help them resolve much faster. Antibiotics used to treat TBRF include erythromycin, tetracycline, chloramphenicol, and penicillin. The current recommended duration of antibiotic therapy is 7 days. Erythromycin or penicillin antibiotics are recommended for use by young children or pregnant women.
The best way to protect oneself from TBRF is to avoid exposure to rodent and tick-infested dwellings. Homes and vacation cabins should be rodent-proofed and any rodent nesting materials should be removed. Tick exposure can be avoided by fumigating homes with compounds containing permethrins or pyrethrins and using insecticides containing DEET on skin and clothing.