**Core Concept**
West Nile virus, Toxoplasma gondii, and Hepatitis B virus (HBV) are examples of pathogens that can be transmitted through blood, posing a risk to patients receiving blood transfusions. Cholera, on the other hand, is primarily a waterborne disease caused by Vibrio cholerae.

**Why the Correct Answer is Right**
Cholera is transmitted through the fecal-oral route, where contaminated water or food is ingested, allowing the bacteria to colonize the small intestine. This route of transmission does not involve the bloodstream. In contrast, West Nile virus is transmitted through the bite of an infected mosquito, which injects the virus into the bloodstream, while Toxoplasma gondii and HBV can be transmitted through blood transfusions or organ transplantation. HBV can also be transmitted through perinatal transmission, sexual contact, and vertical transmission from mother to child during childbirth.

**Why Each Wrong Option is Incorrect**
**Option A:** West Nile virus is indeed transmitted through blood, as it is injected into the bloodstream by an infected mosquito.
**Option C:** Toxoplasma gondii can be transmitted through blood transfusions, making it a bloodborne pathogen.
**Option D:** HBV is also transmitted through blood, as well as other bodily fluids, making it a significant concern for blood transfusions.

**Clinical Pearl / High-Yield Fact**
It is essential to note that while cholera is primarily a waterborne disease, it can also be transmitted through contaminated food or person-to-person contact. In areas where cholera is endemic, it is crucial to maintain proper hygiene practices, such as washing hands frequently and ensuring access to clean water.

**✓ Correct Answer: B. Cholera**