DISEASE VECTORS ENOTE

WEEK FOUR

SUBJECT: BASIC SCIENCE

CLASS: GRADE 7

TERM: SECOND

TOPIC: DISEASE VECTORS

MEANING OF DISEASES VECTORS AND THE DISEASES THEY TRANSMIT: A disease vector is any living agent that carries and transmits an infectious pathogen to another living organism or from place to place. Agents regarded as vectors are organism such as parasite or microbes.

Vectors	Microorganism	Disease caused
1. Anopheles (female) mosquito	Plasmodium	Malaria
2. Tse-tse fly	Trypanosome	Sleeping Sickness
3. House fly	Vibrio Cholerae	Cholera, typhoid fever, dysentery, diarrhea
4.  Rat flea/body	Ricketsia	Typhus
5. Aedes mosquito	Virus	Yellow fever and dengue fever
6. Rat fleas	Bacterium	Plague

LIFE CYCLES OF ANOPHELES MOSQUITO AND OTHER VECTORS

All mosquito species go through four distinct stages during their life cycle:

Egg: Hatches when exposed to water.

Larva: Lives in water; molts several times; most species surface to breathe air.

Pupa: Does not feed; stage just before emerging as adult.

Adult: Flies short time after emerging and after its body parts has hardened.

The first three stages occur in water, but the adult is an active flying insect. Only the female mosquito bites and feeds on the blood of humans or other animals.

Life cycle of house fly

Eggs: Eggs are laid singly on organic matter. They hatch into white larvae called maggots, after 12-24 hours.

Larva: It has mouth, eyes on its head with soft wriggling body (dull white) containing twelve segments. It eats voraciously and grows rapidly, moulting three times at this stage. It thrives in a dirty and wet environment.

Pupa: At this stage the organism is dormant and changes colour from white to brown. It metamorphoses into a barrel-shaped pupa. This period lasts for about 10 days, after which an adult emerges from the pupa case.

Imago: The period between egg-laying and adulthood takes about 8-9 days. The adult further matures to lay eggs or fertilize eggs in about one month. Metamorphosis is complete.

Life cycle of tse tse fly: Female tsetse mate just once. After 7-9 days she produces a single egg which develops into a larva within her uterus. About nine days later, the mother produces a larva which burrows into the ground where it pupates. The mother continues to produce a single larva at roughly nine day intervals for her entire life. The adult y emerges from the pupa in the ground about 30 days. Over a period of 12- 14 days it matures, mates and if it is a female, deposit its first larva. Thus 50 days elapse between the emergence of one female fly and the subsequent emergence of the first of its progeny.

TRANSMISSION OF MALARIA, RIVER BLINDNESS AND SLEEPING SICKNESS:  Malaria spreads when a mosquito becomes infected with the disease after biting an infected person, and the infected mosquito then bites a non infected person. The malaria parasites enter that person’s bloodstream and travel to the liver. When the parasites mature, they leave the liver and infect red blood cells.

Transmission of river blindness: Onchocerciasis or river blindness, is caused by the parasitic worm Onchocerca volvulus. It is transmitted through repeated bites by blackflies of the genus Simulium. The disease is called river blindness because the blackfly that transmits the infection lives and breeds near fast-flowing streams and rivers, mostly near remote rural villages. The infection can result in visual impairment and sometimes blindness.

Transmission of sleeping sickness: Both forms of sleeping sickness are transmitted by the bite of the tsetse fly (Glossina species). Tse flies inhabit rural areas, living in the woodlands and thickets that dot the East African savannah. In central and West Africa, they live in the forests and vegetation along streams. Tsetse flies bite during daylights hours. Both male and female flies can transmit the infection, but even in areas where the disease is endemic only a very small percentage of flies are infected.

METHODS OF DISEASE VECTORS CONTROL:  The following methods can be use to control disease vectors;

1. Personal prophalactic measures:

·        Use of mosquito repellant creams, liquids, coils, mats, etc.

·        Wearing of full sleeve shirts and full pants with socks.

·        Use of bed nets for sleeping infants and young children during day time to prevent mosquito bite.

2. Biological control:

·        Use of larvivorous fishes in ornamental tanks, fountains, etc.

·        Use of biocides.

3. Chemical control:

·        Use of chemical larvicides like abate in big breeding containers.

·        Aerosol space spray during day time.

4. Environmental management and source reduction methods:

·        Detection and elimination of mosquito breeding sources.

·        Management of roof tops, porticos and sunshades.

·        Proper covering of stored water.

·        Reliable water supply

·        Observation of weekly dry day.

5. Health Education:

·        Impart knowledge to common people regarding the disease and vector through various media sources like TV, Radio, Cinema slides, etc.

·        Involvement of public health organizations such as NAFDAC, Red Cross Society, UNICEF, WHO.

6. Community participation:

·        Sensitilizing and involving the community for detection of aedes mosquito breeding places and their elimination.

ASSIGNMENT

Objectives questions:

1. The stages of life history of mosquito can be represented as A. Adult-Larva-Pupa-Egg B. Adult-Pupa-Larva-Egg C. Egg-Larva-Pupa-Adult D. E-Larva-Pupa-Adult E. Egg-Pupa-Larva-Adult  

2. Malaria parasite is transmitted by A. anopheles mosquito B. aphids C. black fly D. house fly E. tsetse fly

3. The larva of housefly develops into A. eggs B. imago C. maggot D. nymph E. pupa

4. Which of these vectors transmit sleeping sickness? A. Aedes mosquito B. Anopheles mosquito C. Black fly D. House fly E. Tsetse fly

5. The following are public health organizations EXCEPT A. NAFDAC B. Peace Corps C. Red Cross Society D. UNICEF E. WHO

6. An agent that passes pathogen from one living organisms to another is A. air B. food C. soil D. vector E. water

Theory questions:

1. What is disease vector?

2. Explain the life cycle of house fly and anopheles mosquito.

3. List five diseases, the causative microorganisms and caused diseases.