Tick bite fever is an infection caused by bacteria from the Rickettsial family, transmitted by infected ticks to humans in their saliva when they bite. The bacteria can also infect through small skin abrasions when the tick is crushed on your skin. Bacteria are passed from the infected tick to her eggs, thus propogating the infection in her offspring. The Rickettsial bacteria are not able to survive outside of living cells.
Tick bite fever occurs in many parts of the world and is often given regional or local names (see table).
|African Tick Bite Fever1||Rickettsia conorii||Africa, Mediterranean, India|
|Rocky Mountain Spotted Fever||Rickettsia ricketsii||North and South America (highest infections in south eastern regions) and Russia|
|North Asia Tick Typhus||Rickettsia sibirica||Siberia, Mongolia|
|Queensland Tick Typhus||Rickettsia australis||S.Australia|
|1 Also known as Boutonneuse fever, Marseilles fever, Kenya Tick Typhus, Indian Tick Fever, and Mediterranean spotted fever|
Tick bites most often occur when hiking or camping in wilderness areas, particularly where there is long grass. Hardticks, which have lifecycles that involve dogs, rodents or other animals, are the hosts of the bacteria. Amblyomma ticks will actively seek out humans on which to feed, while Rhipicephalus ticks tend to lie in wait on grass, picked up when you brush past.
The incubation period (time from the infected bite to the appearance of symptoms) is 5-7 days. Symptoms vary depending on the bacterial species, your age and current health status. Typical features include the presence of a black mark at the site of the bite, a fever, severe headache, swollen lymph nodes near the bite site and sometimes a rash. The blackened bite mark is called an eschar. It looks like a small ulcer (2-5mm in diameter) with a black center, similar to a spider bite. The bite site may be difficult to find with the eschar appearing once the other symptoms begin.
A rash is not always present but when it does occur, it consists of small red marks on the skin, raised slightly above the skin’s surface. It will typically start on the arms and legs, spreading to the abdomen and if severe, even to the palms and soles.
African tick bite fever is usually mild, thus serious complications and death are rare. Rocky Mountain Spotted Fever is more severe with a death rate of up to 25% if left untreated.
Should you experience a severe headache, fever, swollen lymph nodes and feel really ill a week or so after a trip away where you hiked or camped (or raced) in a rural or wilderness area, suspect tick bite fever, especially if the area is a known tick bite fever area.
The presence of the eschar or rash is a strong diagnostic sign. Blood tests will confirm the presence of antibodies produced by your immune response cells in reaction to the infection. But, the antibodies may only show up after a few weeks.
In most cases you will get better in about two weeks without treatment. Treatment with the antibiotic doxycycline can shorten the duration of symptoms and reduce the chance of developing a serious complication. Chloramphenicol may be used. There is no vaccine against tick bite fever.
As with most things, prevention is better than cure and early diagnosis speeds recovery.
- AVOID TICK BITES Wear long sleeved shirts, long pants and shoes. Apply insect repellant to exposed skin.
- EARLY DIAGNOSIS If you’ve been in a known tick bite fever area and are suffering from a fever, headache, swollen lymph nodes and have located the eschar, seek medical attention. The eschar is not always visible so don’t rely on its presence as a diagnostic sign.