Here's why:
* Vector in biology refers to an organism that carries and transmits an infectious agent (like a virus, bacteria, parasite, etc.) from one host to another.
* Animals and insects can act as vectors in various ways. They can carry the infectious agent on their body, in their saliva, or in their feces.
* Examples:
* Mosquitoes are vectors for malaria, Zika virus, and West Nile virus.
* Tsetse flies transmit sleeping sickness.
* Ticks can carry Lyme disease, Rocky Mountain spotted fever, and other infections.
* Rats can spread diseases like plague and leptospirosis.
Therefore, animals and insects can play a crucial role in the transmission of diseases and are thus considered vectors.