Which term describes the animal that maintains a disease organism in nature (e.g., birds for WNV and EEE)?

• A. Bridge Vector
• B. Reservoir Host
• C. Pathogen
• D. Host

Answer: (B)

In disease ecology, the term reservoir host refers to the animal that maintains a pathogen in nature, providing a persistent source of infection for vectors. Birds serve as reservoir hosts for West Nile Virus and Eastern Equine Encephalitis because they can carry the virus for periods that allow mosquitoes to become infected and continue transmission cycles. This maintenance happens even if disease signs in the birds are not obvious, so the pathogen remains in the ecosystem across seasons and populations.

A bridge vector is a vector that moves the pathogen from the reservoir to other hosts, such as humans, but it is not the organism that maintains the pathogen in nature. A pathogen is the disease-causing organism itself, not the animal that harbors it. A host is any organism that can be infected by the pathogen, but without implying long-term maintenance in nature. So the best term for the animal that keeps the disease organism going in the natural environment is reservoir host.