Basic Science JSS 1 Week 8

Topic: Disease Vectors

Introduction

Vectors are animals that transmit diseases from one living thing to another. Their mode of transmission may be feeding, biting, stinging, sucking, etc. The most common vectors include, insects such as mosquitoes, houseflies, tsetse flies, rodents, black flies, fleas, ticks; rodents such as rats; reptiles such as snakes and carnivores such as dogs and cats.

Life Cycle of Some Insect Vectors

Mosquitoes

There are three types of mosquitoes that spread serious diseases. These are the female anopheles, culex and aedes.

Mosquitoes undergo complete metamorphoisis (i.e. they pass through four stages of metamorphosis which are egg, larval, pupal and adult stages).

The adults female mosquito lays her eggs in stagnant water. This hatches in two to five days into larva. The larval stage lasts between two to fourteen days. This proceeds into pupal stage which lasts between hours and day. The pupal finally releases the imago or adult.

lifeDiagram of the Life Cycle of Mosquito

Houseflies

Houseflies also undergo complete metamorphosis. The adult female lays its eggs on decaying organic matter. The eggs hatch into larvae (maggots) within one day. These feed on decaying matter between three and six days, and then develop into pupae. The pupal stage lasts up to five days and releases the adult housefly or imago.

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Diagram of the Life Cycle of Housefly

Tsetse fly

The tsetse fly breeds in shady, damp places (vegetation by the riverside). The eggs are fertilized within the body of the female tsetse fly after mating with the male. The larvae hatch while still inside the body of the female and are released after eight days. The entire process of development of the tsetse fly form the egg to adult takes place between three weeks and five months.

Blackfly

The insect, though usually called blackfly, is often grey or yellow in colour and transmits a worm called Onchocerca volvulus that causes river blindness. The larvae and pupae of the blackfly are found in fast flowing water. The tiny worms, known as microfilarae, pass from the blood and migrate to the person’s eyes and attack them causing inflammation of the eyes which may result in total blindness, hence the name river blindness.

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Diagram of the Life Cycle of Blackfly

Control Measures of Vectors

These control measures can be done through the following:

  1. Clearing of Drainage Systems: This involves removing or drying the water medium in which the vectors breed. This helps to stop the multiplication of vectors like mosquitoes.
  2. Spraying of Insecticides: This is done to kill the insect vectors. Insecticides affect the insects’ respiratory systems.
  3. Spraying of Oil: Oil spread on water covers the surface of water, preventing the passage of oxygen. This makes organisms in the water to die because of suffocation since oxygen is lacking.
  4. Covering our foods always,
  5. Improvement in personal and environmental sanitation,
  6. Clearing of bushes around our homes as well as vegetations by the sides of streams and rivers.

Some Diseases Transmitted by Vectors

Malaria: is caused by a protozoan called Plasmodium species. Plasmodium is transmitted in the blood of the host by the bite of the female anopheles mosquito.

River Blindness: This disease is mostly suffered by people living in riverine areas. The pathogen is transmitted through the bite of the blackfly.

Sleeping Sickness: This is also called trypanosomiasis. This disease is transmitted into the blood of the host through the bite of the tsetse fly.