Medical virology and epidemiology: West Nile virus causes disease in humans and is transmitted from an infected bird to a person by a mosquito vector. This pattern represents which type of disease transmission?

Introduction / Context:
West Nile virus is a classic example of an arbovirus, a term derived from arthropod-borne virus. Understanding vector-mediated transmission is central to infection control, outbreak investigation, and public health messaging.

Given Data / Assumptions:

• Reservoir: birds can carry West Nile virus.
• Vector: mosquitoes acquire virus by feeding on viremic birds.
• Humans are infected when bitten by a competent infected mosquito.
• No direct person-to-person spread via casual contact or fomites is implied.

Concept / Approach:
Transmission categories include endogenous (from a patient’s own flora), fomite borne (via contaminated objects), nosocomial (healthcare-associated), and vector-borne (via arthropods such as mosquitoes or ticks). When a mosquito transmits a pathogen from an animal reservoir to humans, the correct category is arthropod borne.

Step-by-Step Solution:
Identify the vector in the scenario: mosquito. Recognize mosquitoes as arthropods. Match vector involvement to the transmission category: arthropod borne disease. Exclude endogenous, fomite borne, and nosocomial, which do not fit the described chain.

Verification / Alternative check:
Many arboviruses share this pattern (dengue, Zika, chikungunya). The unifying feature is obligatory transmission by an arthropod vector.

Why Other Options Are Wrong:

• Endogenous infection: Originates from a patient’s own microbiota, not via mosquitoes.
• Fomite borne disease: Involves contaminated objects, not blood-feeding arthropods.
• Nosocomial infection: Acquired in healthcare settings, not from wildlife via mosquitoes.
• Zoonosis without a vector: Omits the mosquito step that is essential here.

Common Pitfalls:
Confusing general zoonoses with vector-borne zoonoses; overlooking that arthropod involvement specifically defines the category.

Final Answer:
arthropod borne disease.