**Question:** Which of the following ricketsial diseases is transmitted by tick?

A. Lyme disease (transmitted by tick species of the genus Borrelia)
B. Q fever (transmitted by ticks of the genus Amblyomma)
C. Relapsing fever (transmitted by ticks of the genus Borrelia)
D. Ehrlichiosis (transmitted by ticks of the genus Amblyomma)

**Core Concept:** Rickettsial diseases are a group of infectious diseases caused by rickettsiae, gram-negative bacteria that can cause a wide range of symptoms, including fever, headache, muscle pain, and skin rash. These diseases are transmitted by various arthropods, particularly ticks and fleas.

**Why the Correct Answer is Right:** Lyme disease is caused by the bacterium Borrelia burgdorferi and is transmitted by the tick species of the genus Borrelia. The tick species involved is Ixodes scapularis, also known as the black-legged tick. In this case, the correct answer is C, Relapsing fever, which is also transmitted by ticks of the genus Borrelia, specifically Ixodes pacificus (western black-legged tick) and Ixodes scapularis (black-legged tick).

**Why Each Wrong Option is Incorrect:**

A. Q fever is caused by the bacterium Coxiella burnetii and is transmitted by ticks of the genus Amblyomma. The correct answer is not among the options provided, but it is essential to note that this disease is transmitted by Amblyomma ticks.

B. Ehrlichiosis is caused by the bacterium Ehrlichia chaffeensis and is transmitted by ticks of the genus Amblyomma. The correct answer is not among the options provided, but it is essential to note that this disease is transmitted by Amblyomma ticks.

C. Relapsing fever is transmitted by ticks of the genus Borrelia (Ixodes pacificus and Ixodes scapularis), not Amblyomma.

D. Rickettsialpox is caused by the bacterium Rickettsia prowazekii and is transmitted by ticks of the genus Amblyomma. The correct answer is not among the options provided, but it is essential to note that this disease is transmitted by Amblyomma ticks.

**Clinical Pearls:**

1. Understanding the mode of transmission, specifically the arthropod vector (in this case, the tick species), is crucial in differentiating between various rickettsial diseases. This knowledge is essential for accurate diagnosis and appropriate treatment in clinical practice.
2. While the correct answer is not among the options provided, it is crucial to be familiar with the different tick species transmitting various rickettsial diseases to avoid misdiagnosis and inappropriate treatment of patients presenting with similar symptoms.