Question

Which one of the following diseases is transmitted by a tick?

• A. Rickettsial pox
• B. Epidemic typhus
• C. Q fever
• D. Trench fever

Hint:

Three of these four infections spread through lice or mites; only one has ticks in its natural cycle.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks you to identify, among four rickettsial and rickettsia-like infections, the one whose vector is a tick rather than a louse or a mite.

Step 2: Key Concept or Approach:
Vector identity is the key that separates these look-alike infections. Body lice transmit epidemic typhus and trench fever, a mite transmits rickettsialpox, and ticks transmit Q fever, along with other tick typhus infections such as Rocky Mountain spotted fever and Indian tick typhus. Knowing the vector for each disease, rather than just the causative organism, is what this question tests.

Step 3: Working Through the Options:
Rickettsialpox is caused by Rickettsia akari and spread by the mite Liponyssoides sanguineus that lives on house mice, not a tick. Epidemic typhus, caused by Rickettsia prowazekii, spreads person to person through the body louse, classically in crowded, unhygienic conditions. Trench fever, caused by Bartonella quintana, is also a louse-borne infection, historically notorious among soldiers in the First World War. Q fever, caused by Coxiella burnetii, is maintained in nature in a tick-animal cycle involving cattle, sheep, and goats; humans usually acquire it by inhaling contaminated aerosols from these animals, but the organism's natural transmission cycle among animals runs through ticks, which is why Q fever is grouped with the tick-borne rickettsioses.

Step 4: Conclusion:
Q fever is correct because, unlike rickettsialpox, epidemic typhus, and trench fever, its natural transmission cycle runs through ticks rather than lice or mites.