Typhus: Indian Tick Typhus

Indian tick typhus is usually wrongly diagnosed as Rocky Mountain Spotted Fever (RMSF) due to its similarity with RMSF. In 1925 Megaw identified it as distinct entity. Before that it used to be diagnosed as RMSF.

The causative agent is Rickettsia conorii, which is a member of spotted fever group of rickettsiae. The tick is the reservoir of infection. Transmission of tick to tick is through transplacental mode. Incubation period is 3-7 days.

The mode of transmission: Man is only accidental host. Man acquires infection by tick bite. Contamination of skin by crashed tick can also be a mode of transmission. The transmission cycle is as follows:

 

Tick —–Tick ——- Tick —–Tick

                  |                 |

                Dog            Man

                  |

               Tick ——-Man

Signs and symptoms: The patient generally gives history of tick bite and if examined carefully a lesion or eschar is seen at the site of the bite. After 3-7 days (incubation period) there is acute onset of fever (which may be for 2 to 3 weeks), headache and malaise. On the third day a maculopapular rash may appear. But unlike rashes of other rickettsial diseases the rash appear in the extremities like wrists and ankles first and them spreads it to the rest of the body.

Treatment: Broad spectrum antibiotics like tetracycline, doxycycline and chloramphenicol are the drug of choice for the treatment of Indian tick typhus. 

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