Air , water and food are non living agents that carry micro organisms from one place to another. Animals are the living agents that carry micro organisms from place to place. The animals that carry pathogenic micro organisms are known as vectors. Important vector include
• insects like house flies , cockroaches, fleas, mosquitoes and tsetse flies, and
• other animals like rats , dogs and cats.
Anal vectors may carry micro organisms from place to place or from person to person mechanically or biologically.
Mechanical Method:
In this method, the animals vector carry pathogens on their bodies. The pathogens are merely carried passively, they do not grow or multiply on the body of the vector. These animal vectors usually breed and live in filthy places like rubbish heaps, faeces and drains. They like to feed on our food and so contaminate it. The housefly with its hairy sticky body and filthy habit is an idea vector that carries pathogens mechanically. Pathogens carried in this way include shigella sp. , salmonella enteriditis, salmonella typhi vibrio cholerae and entamoeba histolytica.
Biological method:
In this method, the vector becomes infected by feeding on the body fluid (e.g blood) of an infected person or animal. The pathogens develops and multiplies in the body of the vector. Latter , the vector infects a healthy person while feeding on his/her body fluids.
In the biological method, a part of the life cycle of the pathogen takes place In the body of the vector. Many viruses and pathogenic protozoa are carried biologically by insect vectors e.g.
• Aedes mosquito carried the virus that causes fever , and • tsetse fly carried the protozoan, trypanosoma, which causes sleeping sickness in humans.
