**Core Concept**
Q fever is a zoonotic disease caused by the bacterium *Coxiella burnetii*. It is primarily transmitted to humans through inhalation of contaminated particles, often from infected animals or their products.

**Why the Correct Answer is Right**
The correct answer to this question is related to the mode of transmission of Q fever. *Coxiella burnetii* is highly resistant to environmental stressors and can survive for long periods outside of a host. When infected animals shed the bacteria, they can contaminate the air, soil, and water. Humans can become infected by inhaling these contaminated particles, which can be found in dust, aerosols, or on surfaces. This mode of transmission is often referred to as the "inhalation route."

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Q fever is not primarily transmitted through tick bites, although ticks can host *Coxiella burnetii*. While tick bites can transmit other diseases, such as Lyme disease and Rocky Mountain spotted fever, they are not the primary mode of transmission for Q fever.
**Option B:** This option is incorrect because Q fever is not transmitted through blood transfusions. While blood transfusions can transmit other bloodborne pathogens, such as HIV and hepatitis, Q fever is not typically transmitted through this route.
**Option C:** This option is incorrect because Q fever is not primarily transmitted through direct contact with infected animals. While direct contact can increase the risk of transmission, the primary mode of transmission is through inhalation of contaminated particles.

**Clinical Pearl / High-Yield Fact**
Q fever can be treated with antibiotics, but early recognition and treatment are critical to prevent long-term complications, such as endocarditis and hepatitis.

**Correct Answer: D. Inhalation of contaminated particles.**