Disease Vectors

Non-living agents that carry micro-organisms from one place to another include air, water and food.

Living agents that carry micro-organisms from place to place are animals. These animals that carry pathogenic (disease causing) micro-organisms are known as vectors.

Examples of vectors are cockroaches, fleas, mosquitoes, tsetse-flies, black flies, house flies, bed-bugs, ticks, rats, dogs, cats, etc. Vectors may transmit micro-organisms from place to place or person to person either mechanically or biologically.

(a) Mechanical Method: The vectors carry pathogens on various parts of their bodies e.g. legs, wings, mouthparts, hairs, etc. The pathogens do not grow or multiply on the body of the vectors. Pathogens carried in this way include Salmonella typhi, Vibro cholerae and Entamoeba histolytica.

(b) Biological Method: The vector in this case becomes infected with the pathogen when it feeds on the body fluid of an infected person or animal. The pathogen develops and multiplies in the body of the vector which then infects a healthy person when it goes to feed. Thus part of the pathogen’s life cycle takes place in the body of the vector. Examples of such vectors and the pathogen they carry are;

(i) Anopheles mosquito (female) carries plasmodium (protozoan) that causes malaria.

(ii) Tsetse fly carries Trypanosome (protozoan) which causes sleeping sickness (Trypanosomiasis).

(iii) Aedes mosquito carries a virus that causes yellow fever/dengue fever.

Life cycle of Blood fluke:

Life cycle of Malaria Parasite in human host:

Control of Mosquitoes

Mosquitoes can be controlled in the following ways:

1. Draining of swamps: This is done to destroy the breeding ground of mosquitoes.
2. Clearing bushes around houses: This reduces hiding places for the adult mosquitoes.
3. Sleeping in rooms protected by mosquito nets: This help to check the occurrence of mosquito bites.
4. Spraying oil in stagnant water: This is to reduce the surface tension of water and prevent larval stages from breathing.
5. Using insect repellants for the body
6. Use of drugs i.e. to cure/control malaria fever e.g. chloroquine
7. Burying broken pots and empty cans

Control of Vectors

Vectors can be controlled by;

1. Killing the vectorsg. by spraying with insecticides, use of traps and poisons for rats, etc.
2. Use of larvicidesto kill larval stages.
3. Clearing bushesaround houses.
4. Destruction of breeding spotsg. stagnant water should be drained to prevent mosquitoes from breeding.
5. Use of drugsto kill the micro-organism in the host.
6. Keeping the environment clean