**Core Concept**
Frisch bacillus, also known as *Francisella tularensis*, is a Gram-negative bacterium that causes tularemia, a zoonotic infection. The bacterium is typically acquired through contact with infected animals, contaminated water, or vectors like ticks and mosquitoes.

**Why the Correct Answer is Right**
Tularemia can manifest in various forms, including ulceroglandular, glandular, oculoglandular, oropharyngeal, and pneumonic, depending on the route of exposure. *Francisella tularensis* is highly infectious and can be transmitted through contact with infected animals, such as rabbits and rodents, or through contaminated water and soil.

**Why Each Wrong Option is Incorrect**
**Option A:**
* *Yersinia pestis*, the causative agent of plague, is a different bacterium that affects humans through the bites of infected fleas or direct contact with infected animals.

**Option B:**
* *Bartonella henselae*, the causative agent of cat-scratch disease, is another distinct bacterium that affects humans primarily through scratches or bites from infected cats.

**Option C:**
* *Brucella melitensis*, the causative agent of brucellosis, is a different bacterium that affects humans through contact with infected animals, such as sheep and goats.

**Clinical Pearl / High-Yield Fact**
Tularemia can be effectively treated with antibiotics such as streptomycin or doxycycline, and early treatment can prevent complications and improve patient outcomes.

**Correct Answer: D. Francisella tularensis**