**Tick Fever: Understanding the Cause**

Tick fever, also known as babesiosis, is a tick-borne disease that affects both humans and animals. It is caused by a protozoan parasite belonging to the genus Babesia. Let's delve into the details to understand the cause of tick fever more comprehensively.

**Protozoan Babesia: The Culprit**

The correct answer to the question is option 'A' - Protozoan Babesia.

Babesia is a group of single-celled protozoan parasites that infect red blood cells in mammals. These parasites are transmitted through the bite of infected ticks. When an infected tick feeds on a host, it injects the Babesia parasites into the bloodstream, leading to the development of tick fever.

**Transmission by Ticks: The Role of Vectors**

Ticks are arachnids that belong to the order Parasitiformes. These blood-feeding ectoparasites act as vectors, which means they can transmit pathogens like Babesia to their hosts. Ticks become infected with Babesia when they feed on infected animals, such as deer or mice, that serve as reservoir hosts for the parasite. Once infected, ticks can transmit the parasite to humans or other animals they subsequently bite.

**Life Cycle of Babesia: Understanding the Infection Process**

The life cycle of Babesia involves both the tick vector and the mammalian host. Here is a simplified explanation of how the infection occurs:

1. **Tick Bite:** An infected tick attaches itself to a host and begins to feed on its blood.
2. **Parasite Entry:** While feeding, the tick releases saliva containing Babesia parasites into the host's bloodstream.
3. **Parasite Invasion:** The Babesia parasites invade and multiply within the host's red blood cells.
4. **Symptoms and Disease:** As the parasites replicate, they cause damage to the red blood cells, leading to symptoms of tick fever, such as fever, fatigue, headache, muscle aches, and anemia.
5. **Tick Reproduction:** If the infected tick survives, it can lay eggs, continuing the life cycle.

**Conclusion**

In conclusion, common tick fever, or babesiosis, is caused by the protozoan parasite Babesia. This parasite is transmitted through the bite of infected ticks. Understanding the cause of tick fever is crucial for its diagnosis, treatment, and prevention. It is important to take precautions, such as using tick repellents and wearing protective clothing, when in tick-infested areas to reduce the risk of tick bites and subsequent infection.