Learning objectives
At the end of this lecture student will be able to : 1-Describe groups of mosquitoes related to disease transmission . 2-Discuss habits of mosquitoes . 3-Classify mosquito-borne diseases . 4-Determine mosquito control measures . 5-Specify house flies habits & ways of disease transmission . 6-Arrange fly control measures . To a level accepted to the accreditation standard of the College .Mosquito *Mosquitoes constitute the most important single family insect from the stand point of human health. *Four important groups of mosquitoes which are related to disease transmission: Anopheles , Culex, Aedes, Mansonia *The body of mosquito consists of three parts: Head , Thorax , Abdomen *There are four stages in the life cycle history of mosquitoes: Egg, Larva , Pupa, Adult
Habits of Mosquitoes
1.Feeding Habits. *Males never bite, they subsist on plant juices. *Females are haematophagous .They require a blood meal, once in (2-3) days for the development of eggs. *Females differ in their feeding habits: Some species prefer human blood (anthrophilic). Some Prefer animal blood (Zoophilic). Some indifferentiate in their choice and feed on both man & animals.2.Time of biting In general mosquitoes bite in the evening or in the early part of night. 3.Resting Habits *Mosquitoes observe themselves during the day in dark and cool corners. a. Some rest indoors (endophilia). b. Some rest outdoors (exophilia). *Indoor resting places are usually the dark corners of houses, upper part of walls ,behind pictures and under furniture. *Outdoor resting places are usually the vegetation shrubs ,tree holes ,cattle sheds and walls.
4.Breeding Habits. *In general anopheline prefer clean water for breeding; culicines prefer dirty and polluted water ,aedes prefer artificial collections of water. Mansonoides breed in water containing certain types of aquatic vegetation. 5.Hibernation. *Mosquitoes are known to hibernate in the adult stage when the environmental conditions are not favorable. *Severe winters are tided over by hibernation.
6.Dispersal. *Mosquitoes do not generally fly far from the place where they breed unless swept by currents of wind. *Range of flight varies with species ,may range up to (11 Km). *Aircrafts and ships have increased the possibility of the dispersal of mosquitoes from country to country and have created fresh problems of public health importance.
7.Life span.*The life span of a mosquito is influenced by temperature and humidity. *Both high & low temperatures are fatal.*The normal life span of mosquitoes varies from (8-34) days .Males as a rule ,are short –lived.
Mosquito-borne diseases:- Anopheles Culex Aedes Mansonoides
Malaria Filaria*Bancroftian Filariasis *Japanese Encephalitis. *West Nile fever. *Viral arthritis (Epidemic poly Arthritis)
Yellow fever Dengue Dengue hemorrhagic fever Rift valley fever
Malayan filariasis
Mosquito Control Measures: * While there are many methods of mosquito control, experts now recommend an “Integrated Approach“ i.e. avoiding excessive use of any one method (combination)*Integrated approach view is to obtain maximum results with minimum inputs to prevent environmental pollution with toxic chemicals and development of insecticide resistance.
*Mosquito Control Methods Classification:1.Anti – Larval Measuresa. Environmental control (source reduction) minor engineering methods e.g. filling, leveling and drainage of breeding places and water management.b. Chemical control Mineral oil ,Paris green, synthetic insecticides.c. Biological control Small fish feed on mosquito larvae (Gambusia affinis and Lebister reticulatus).
2.Anti – Adult Measures.a. Residual sprays. DDT, Lindane, Malathion.b. Space sprays Mist or fog of insecticides (Pyrethrum extract, Residual insecticides).c. Genetic control Sterile male technique, cytoplasm incompatibility , chromosomal translocation, sex distortion. 3.Protection against Mosquito Bites:a. Mosquito Net.b. Screening.c. Repellents. Diethyltoluamide (deet) for (18-20) hours ; Indalone ,dimethyl phthalate, dimethyl carbate.
Houseflies*Houseflies are the commonest and most familiar of all insects which live close to man.*They occur in abundance all the year round.*Majority are non- biting.*Houseflies should be regarded as a sign of insanitation and their number is an index of that insanitation.*The common housefly (Musca domestica) is mouse –gray in color.*The body is divided into head, thorax and abdomen.*The housefly undergoes a complete metamorphosis with four stages in its life cycle: Egg, Larva (maggot), Pupa, Adult
In one setting the female lays about 120 -150eggs in moist decaying organic matter. Habits: 1.Breeding habits: The most important breeding places of flies are:- a. Fresh horse manure. b. Human excreta. c. Manure of other animals. d. Garbage. e. Decaying fruits and vegetables. f. Rubbish dumps containing organic matter. g. Ground where liquid wastes are spilled.
2.Feeding habits: *Housefly doesn't bite. *It is attracted to food by its sense of smell. *It cannot eat solid food. *It vomits on solid food to make a solution of it and sucks it in a liquid state. *Adults delight in sputum, feces , discharges from wounds and open sores. 3.Restlessness: The fly is a restless insect and moves back and forth between food and filth. This helps in the spread of infection mechanically.
4.Vomit drop:The fly vomits frequently .The “vomit drop “ is often a culture of disease agents.5.Defecation:The housefly has the habit of defecating constantly all the day. Thus it deposits countless bacteria on exposed food.6.Resting habits:*Flies have a tendency to rest on vertical surfaces and hanging objects.*They have a tendency to fly towards light.
7.Dispersal: Normally houseflies remain close to their breeding places ,but they disperse frequently up to 4 miles, and sometimes even more from the point of their origin. Transmission of disease: Flies are potential vectors of many diseases. Flies transmit disease in the following ways:- 1/Mechanical transmission *Houseflies are exceptionally efficient mechanical spreaders of disease. *They transport micro-organisms on their feet and hairy legs.
*Pathogenic organisms, ova and cysts have been recovered from the bodies of common housefly. *Houseflies are therefore called “Porters of infection”.2/Vomit drop The regurgitated stomach contents or “vomit drop” is a rich bacterial cultural.3/DefecationThe excrement of housefly has been found to contain numerous microorganisms as well as cysts and ova of intestinal parasites.
Fly Control Measures
1.Environmental control*The best way is to eliminate their breeding places and to bring about an overall improvement in the environmental sanitation on a community – wide basis.*It include:1.Storing garbage, kitchen wastes and other refuse in bins with tight lids, pending disposal.2.Efficient collection ,removal and disposal of refuse by incineration ,composting or sanitary landfill.3.Provision of sanitary latrines. 4.Stopping open air defecation. 5.Sanitary disposal of animal excreta. 6.Stepping up general sanitation. *A clean house with clean surrounding is the best answer to fly problem. 2.Insecticidal control 1.Residual control *The addition of sugar to insecticidal formulations enhances their effectiveness. *proper care should be taken to prevent contamination of food or water during spraying operations.
Solid Baits 2.Baits Liquid Baits Poisoned baits containing 1-2 % Diazinon, Malathion, Dichlorvos, Ronnel and Dimethoate have been tried with success. 3.Cords and Ribbons *Cords and strips impregnated with Diazinon , Fenthion or Dimethoate have been tried with success. *These are hung like festoons from ceilings. *Period of effectiveness is 1-6 months.
4.Space spraying. * These may be applied indoors or outdoors using hand or power sprayers. *Space sprays in general have little or no residual action. *They produce only a temporary effect on adult fly populations. *Repeated applications are necessary. 5.Larvicides. *Used for treating fly breeding places. *It is found that they cause or accelerate the development of resistance.
Insecticides ,at best , are only a supplement , but not a substitute for sanitation. 3.Fly papers *Sticky fly papers are useful adjuncts to other methods of control. *Adhesive mixture can also be applied to strips of wire and hung up in places where flies abound.
4.Protection against flies*Screening of houses , hospitals , food markets , restaurants and all other similar establishments .*Screens with 14 meshes to inch keep out house flies , but finer screens also keep out other insects .5.Health education*It is difficult to achieve fly control without the willing cooperation of the people .*A “fly consciousness” should be created among people through health education .*Fly control campaigns require organized individual and community effort which is the basis of a successful public health program .*It is only through health education that people can be motivated with a desire to get rid of flies permanently .