Biological Vectors

All living vectors, including flies, roaches, mice, rats, etc. can transmit disease. They can be either passive or active.

Passive Biologic Vectors
Passive biologic vectors are not as dangerous because they carry a smaller load of pathogens, and pathogens show decreased virulence due to unfavorable growth conditions. For example, flies carry E. coli and Salmonella from feces by landing on them, but the organisms do not grow on the fly.

Active Biologic Vectors
Active biologic vectors have the infectious pathogen growing in them. They have a larger load and higher virulence because the pathogen can strive inside the host.

For instance, the malaria parasite has a life cycle inside the mosquito and can better infect a human host because it was allowed to grow.

Another example of an active biologic vector is any animal that has rabies. Rabies can grow in humans, but humans are not considered vectors because they do not transmit the disease (biting).