**Core Concept**
Tick-borne diseases are a significant public health concern worldwide, caused by various pathogens transmitted through the bite of infected ticks. These pathogens can be bacteria, viruses, or protozoa, and understanding the specific tick-borne diseases is crucial for diagnosis and treatment.

**Why the Correct Answer is Right**
Chagas disease is not transmitted by ticks but by the bite of an infected triatomine bug, also known as a kissing bug. This disease is caused by the protozoan parasite *Trypanosoma cruzi*. The correct answer is Chagas disease because it is the only option that is not transmitted by ticks. Ticks transmit various diseases, including tick-borne relapsing fever, tick typhus, and viral encephalitis.

**Why Each Wrong Option is Incorrect**
**Option A:** Tick-borne relapsing fever is caused by *Borrelia* species, which are transmitted by soft ticks (genus *Ornithodoros*). This option is incorrect because the question specifically asks about hard ticks, not soft ticks.
**Option B:** Tick typhus is caused by *Rickettsia* species, which are transmitted by hard ticks (genus *Dermacentor*). This option is incorrect because it is indeed transmitted by ticks.
**Option D:** Viral encephalitis, such as tick-borne encephalitis, is caused by flaviviruses, which are transmitted by hard ticks (genus *Ixodes*). This option is incorrect because it is indeed transmitted by ticks.

**Clinical Pearl / High-Yield Fact**
When considering tick-borne diseases, remember that the genus of the tick is often a clue to the specific disease being transmitted. Hard ticks (genus *Dermacentor*, *Ixodes*) typically transmit diseases like tick typhus and viral encephalitis, while soft ticks (genus *Ornithodoros*) transmit diseases like tick-borne relapsing fever.

**✓ Correct Answer: C. Chagas disease**