Disease vectors

Disease means illness or disorder of the body or mind. The agents causing diseases are called pathogens. The science and the study of diseases is called pathology.

Diseases causative agents are viruses, rickettsiae, bacteria, spirochetes, fungi, protozoa, worms.

Diseases Vectors

Diseases vectors are animals which transmit disease causing organisms (pathogen) from an infected person to uninfected person without being infected. They assist in carrying micro organisms or microbes. They are mainly insects, mollusc and some mammals. Examples of vectors are:

1. Mosquito
2. Cockroach
3. Housefly
4. Tsetse fly
5. Dogs and cats
6. Rat
7. Blackflies

Malaria is an infectious diseases caused by a parasite called Plasmodium. The parasite is transmitted to humans when we are bitten by the female Anopheles mosquito. The parasite spends its life cycle partly in humans and partly in mosquitoes. (1) Mosquito infected with the malaria bites a human, transmitting cells known as sporozoites into the human’s bloodstream. (2) These sporozoites travel to the liver. Each of these sporozoites undergoes asexual reproduction and its nucleus divides to form two new daughter cells called merozoites. (3) The merozoites get into the bloodstream and infect red blood cells. (4) In the red blood cells, merozoites grow and split to produce more merozoites, eventually causing the red blood cells to rupture. The newly released merozoites go on to infect other red blood cells. (5) Some merozoites grow and develop into sex cells called male and female gametocytes. (6) Another mosquito bites the infected human, ingesting the gametocytes. (7) In the mosquito’s stomach, the gametocytes mature and undergo asexual reproduction.

Life Cycle of Malaria

The mosquito is the carrier of the micro-organism which causes malaria. The micro-organism is a protozoan called plasmodium. It lives in the blood cells, passes waste matter into them and eventually destroys them. The malaria parasite is carried by the female anopheles. When the mosquito bites a person it passes the parasite into the blood.

The stages in the life cycle of the mosquito: eggs-larva-pupa-adult

The Housefly

This is the common name for the most of familiar species of non-biting muscoid fly. It is found in the vicinity of human habitations throughout the world. It is often a carrier of such diseases as typhoid fever, cholera, dysentery, tracheae and anthrax. The adult fly transmits disease by contaminating food with disease organisms which it has picked up on its hairy legs or has ingested and then regurgitated.

Life Cycle of the Housefly

The female lays an average of 150 white eggs in a mass. The female can live for about two months and can lay between 600 to 1000 eggs during its lifetime. The eggs hatch in about 12 hours into white, legless larvae called maggots which grow to 12.5mm in length. The maggots develop into pupa in five to six days. The pupa develops into a new adult in another four to five days if the weather is warm or in a month or later if weather conditions are favourable.

Life Cycle of the Tsetsefly

Tsetse-fly carries the sleeping sickness parasite. The parasite is trypanosome. The tsetse-fly spread the disease to man and other animals like goats, sheep pigs, horses and donkeys, by biting them. The parasite is passed to the bitten animal through the saliva of the tsetse fly. The bitten animals begin to feel the effects of the parasite after one to three weeks. The human victim suffers fever, headache, and frequent sleeping; hence it is called sleeping sickness or nagana.

Tsetse flies breed in shady, damp places such as the vegetation by the river side. Some breed in open places like the grassland. One mating is sufficient for the tsetse fly to continue to produce new tsetse flies for the rest of her life time. The tsetse fly has a life span of between three weeks and five months. The eggs develops inside the fly and hatch into larvae which are released in a shady place.

The larva then developed into pupa and pupa to adult or imago.

Control Measures of Mosquitoes; Carrier of Malaria

A drop of oil can be put on top of the water containing the larva and pupa stages of the mosquito; this hinders the further development of mosquitoes.

The knowledge of the life cycle of the mosquito will bring insight on how to control its spread. A large number of mosquito eggs and larvae are destroyed by small fish. Mosquito may be controlled by eliminating their breeding places with oil or insecticides. Other ways of controlling the breeding of mosquitoes include clearing the bushes around the houses, removal of all broken bottles and any container that can hold water pouring kerosene on any stagnant water around the houses

Major control measures include the following:

1. Water drainage
2. Insecticide
3. Oil spreading/spraying.
4. Clearing of stagnant water which is a breeding place for the growth of mosquito.
5. Using insect repellent e.g. Raid
6. Using mosquito nets over sleeping beds
7. Clearing bushes around us.

Control Measures of Housefly; Carrier of Dysentery

Apart from the three ways of preventing the spread of diseases by vectors such as:

1. Removing their breeding places
2. Controlling their life cycle
3. Killing the germs in the body of infected person without being harmed;
4. House fly could be controlled in the following ways;
5. Avoid exposing human faeces, kitchen waste and refuse or compost heaps around
6. Always cover your food, do not house fly to land on it.
7. Spraying house fly with insecticides to kill them.

Control of Tsetsefly

Like other vectors, tsetse fly could be controlled by:

1. Controlling their life cycle.
2. Getting rid of their breeding places.
3. Clearing bushes around your houses.
4. Stop the flies from breeding.

EVALUATION

1. What are vectors?
2. Mention diseases cause by vectors
3. Describe the life cycle of mosquitoes