Annals of Community Health (ISSN 2347-5455, eISSN 2347-5714), Peer Reviewed, Indexed Journal focusing exclusively on Community Medicine and Public Health

Integrated vector management

Plan of presentation

  • Introduction
  • Selection criteria for vector control measures
  • Integrated vector control approach.
  • Evolution of Integrated vector control approach.
  • Integrated vector control approach for mosquito.
  • Key elements of an IVC Strategy.

Introduction

Vectors of public health importance- Mosquito, Housefly, Cockroaches, Sandfly, Louse, Rat flea, Ticks, Itch mite etc.,

Vector-borne diseases- Malaria, Filariasis, Dengue, Chikungunya, JE, Kala-azar, Typhoid, Gastro enteritis, Scabies, Scrub typhus, tick typhus, relapsing fever, bubonic plague etc.,

Transmission of disease- Direct contact, mechanical, biological (propagative, cyclopropagative, cyclodevelopmental).

Control - chemical insecticides which not very successful due to human, technical, operational, ecological and economic factors.

Bionomics of vectors

Essential for effective control of vectors

  1. Vector & its role in disease transmission.
  2. Geographical and seasonal abundance.
  3. Its life cycle in terms of development.
  4. Breeding sites.
  5. Location where adults emerge, mate, feed, rest, hide and lay eggs.
  6. Host preference, feeding behavior, dispersal and migration behavior.
  7. Its life cycle in relation to human habitats.

Selection criteria for vector control measures

  1. Effectiveness.
  2. Safety.
  3. Simplicity of use- indications, contraindications, skills, difficulties in using.
  4. Cost
  5. Time and effort
  6. Type of benefit.
  7. Social acceptability- local context.
  8. Support requirements.

No single method is likely to provide a solution in all situations. The present trend is to adapt a IVC approach.Vector control approach combining two or more methods with a view to obtain maximum results with minimum efforts.

Integrated vector control approach

It is defined as the utilization of all appropriate technological and management techniques to bring about an effective degree of vector suppression in a cost-effective manner".Selection of methods is not possible without detailed field information on the ecology, bionomics of vectors, role in disease transmission.

Evolution of the integrated vector control:

Vector control has been a part of malaria control activities since the early 20th century. During the pre-DDT era, reduction of vector mosquitoes largely relied on larviciding & environmental management of breeding habitats. In 1950s- DDT and other insecticides were extensively used. During 1970s, development of insecticide resistance, poor human acceptance and environmental concerns against the use of insecticides. This led to a rethinking in vector control strategies. During 1980s, WHO proposed an Integrated Vector Control (IVC) strategy based on the principles of Integrated Pest Management in agriculture.

More of the research have gone through Mosquito borne diseases as the mortality and morbidity due to mosquito is too high.

Anti-larval measures

  • Environmental control -The most important step in reducing the number of mosquitoes (Success depends on Community involvement & multisectoral coordination)
    1. Elimination of breeding places (source reduction) like Filling and leveling, Drainage of breeding places.
    2. Proper disposal of refuse other wastes.
    3. Cleanliness in and around the houses .
    4. Observing 'dry day'- intermittent irrigation.

 

  • Chemical Control
    • Insect Growth Regulators: they are highly toxic to insect larvae or pupae, interfering with development into adults. Used in large scales in USA. Costly & have restricted availability -not used in India. Particularly useful if insects have developed resistance to insecticides or because of their environmental effect. Safe to human beings and environment.
      1. Juvenile hormone analogues: prevent development of larvae into pupa or pupae into adult. Ex. Methoprene
      2. Chitin synthesis inhibitors: interfere with moulting process, killing larvae when they moult. Act more rapidly.
      • Ex. Diflubenzuron and Triflumoron.
  • Expanded Polystyrene Beads: Expanded form of polystyrene granules - available commercially with diameter ranging from 0.6 to 2.5 mm. Size is increased by boiling. They do not decay and remain floating for years. Spread on surface of water to form floating layer. A layer of 1-2 cm is sufficient if it covers the surface. Easily blown or washed away- only sites where water remains confined -wells. Can be used safely in drinking water.

 

  • Biological Control
    • Natural enemies into the environment-includes Insects, Viruses, Bacteria, Protozoa, Fungi and Fish.
    • Only two of them have become widely employed. They are Larvivorous fish and Biolarvicides.
      1. Larvivorous fish: Feed on mosquito larvae. Easy, practical, cheap; they have no food value. They should have the following characteristics
        • Preference for mosquito larvae over other types of food
        • Small size
        • High reproduction rate
        • Tolerance to pollution, temperature fluctuation & transportation.
        • Two species are widely used-
          • Gambusia - prefer clean water, tolerate wide range of temperature, pH water salinities.
          • Guppy- can survive in polluted water, cannot withstand temperature <10 degree C.
          • Useful in ornamental tanks, wells, Garden ponds, fountains, swimming pools, large water collection. Approximately 5 fish per sq.m of water surface.
        • Advantages
          • a. Long term effective control measure.
          • b. Cost effective.
          • c. Environmentally safe.
          • d. Controls variety of mosquito species.
        • Disadvantages
          • a. Effective when large numbers eventually establish themselves.
          • b. takes 1-2 months; not suitable - quick anti larval measures are needed.
          • c. less effective in waters with much vegetation or floating garbage.
          • d. Perineal water supply and some times birds eat away fishes.
      2. Biolarvicides: Bacteria are used for the control of mosquito larvae. Bacillus thuringiensis H 14 and Bacillus sphaericus. Available as wettable powder and granules which contain bacteria, spores and toxic crystals. Safe to environment , human being and animals but are expensive.
        • Bacillus thuringiensis H 14 - Gram positive, spore forming bacteria which is specifically acts against mosquito larvae. Produces endotoxin which after ingestion causes gut paralysis & leakage of contents into body cavity leading to death. It is applied at 0.5 gm/sq.m 250gm of B. thuringiensis is mixed with 10 L of water to make 2.5% suspension & sprayed at 1L over 50 sq.m every 2 weeks.
        • Bacillus sphaericus- It also produces toxin which is more effective in polluted water - suitable for treatment of breeding sites of Culex. 500gm of B. sphaericus with 10 L of water to make 5% suspension & it is sprayed at 1 L over 50 sq.m. every 3 weeks.
      3. Others Biolarvicides-
        • Fungi- Coelomyces, Culicinomyces,
        • Nematodes - Romanomermis cluicivorax and R. iyengari.

Anti adult measures

Space sprays

Space sprays are those where the insecticidal formulations is sprayed into the atmosphere in the form of mist or fog.

  1. Thermal fog.
  2. ULV cold aerosols.

Done where immediate results are needed like during outbreak of disease to bring down mosquito population drastically. Useful where exophillic vector species needs to be controlled.

Advantages of space sprays : Immediate effect - suitable for control of disease outbreak. Less insecticide is required for one application. Kills exophillic species of mosquito.

Disadvantages of Space sprays : Effect lasts for shorter period- repeated at least once a week. The cost of equipment, operational and maintenance - high; Needs specially trained staff for maintenance and repair. May cause pollution. Problems with acceptability.

Indoor Residual Sprays:

Application of insecticides to surfaces so that the insecticide particles remain on the surface in the form, size and quantity suitable for insects to pick up on contact and sufficient to exert a lethal effect over a long period. Helpful in endophillic species.

Problems related to house spraying :

  1. May leave visible deposits on walls.
  2. Non acceptability.
  3. Painting or re-plastering of walls after application reduces or eliminates efficacy of insecticides.
  4. People may be reluctant to allow stranger into their houses.

Zooprophylaxis

Reallocation or introduction of cattle or domestic animals between settlements and mosquito breeding i.e. ring of cattle sheds on the outskirts of a village with houses in the center.Many mosquito prefer animal blood than human blood and hence decreases biting of human and transmission of disease. In Japan it is proved to be effective against Culex.

Genetic control:

Today we are mainly depending on insecticides for control of mosquitoes. The problem with this are

  1. Development of Resistance
  2. Environmental Pollution.

Therefore it is desirable to have alternate strategy which overcomes above problem. This lead to the think of genetic control of mosquito.

  1. Sterile Insect Technique
    1. Conventional SIT
    2. Translocation Heterozygotes
    3. Genetic Sexing
    4. Cytoplasmic Incompatibility
  2. Refractoriness to Disease Transmission
    1. Conventional SIT:The mosquitoes are mass- reared & the pupae or adults less than 24 hours are sterilized by radiation or chemosterilants and released into the natural population. The released sterile males compete with the wild males for mating & the females mating with the sterile male produce few or no progeny thus reducing the mosquito population. An attempt to control Culex fatigans is made in India but it was a failure. Field studies also done in Africa and America. It is ideal for the control of Aedes aegypti. The field studies conducted using this method were failed. The reasons were attributed to following.
      1. There is no reduction in fertility in the next generation.
      2. Irradiated males which were competitive in the laboratory but not competitive in the field.
      3. The dose of radiation was too high affecting male fitness.
    2. Translocation Heterozygotes : Breakage of two non homologous chromosomes and reattachment of broken parts to the wrong parts. The Tanslocated Heterozygotes are mass rared and released into the field. The fertility of Translocation heterozygotes reduces to 50 % hence it is also known as Semi-Sterility. The advantage of this method is progeny surviving such crosses also inherit same translocation and in turn passes to their next generation. Field studies were carried using for suppression of Aedes aegypti both in India and Kenya( Rai ,1983; Mcdonald 1977) and also using translocation strains of An.stephensi in India (N.J. Shetty 1984). Both studies result showed translocated males compete higher than the normal males both in laboratory and field and reduction in the mosquito population.
    3. Genetic Sexing : Insecticide resistance gene is introduced into the vector. Malathion resistant gene is linked to Y chromosome in Culex quinquefasciatus which acts as male determining factor. This leads to preferential elimination of females.
    4. Cytoplasmic Incompatibiliy: Sterility in certain crosses between strains of Culex pipens was observed. Study showed males contained Cytoplasmic Incompatibilty resulting no progeny. Similar Cytoplasmic Incompatibilty exists in Aedes albopticus and can be used for genetic control in future.
  3. Refractoriness To Disease Transmission:It means production of mosquitoes refractory to the development of parasite and thus incapable of transmitting disease. Gene coding for the antibody against plasmodium gamete is introduced. When mosquito gets infected, the gametes will be killed as soon as they are formed and no transmission of disease. It is under trail and current focus is on this now. However the use of genetic control for mosquito has achieved little success. The limitations are:
    1. Lack of mating competitiveness released males
    2. Immigration of fertile females from regions close to the release sites.
    3. Political reasons.
    4. Non acceptability by the people.

Personal Prophylaxis

  1. Mosquito Nets: They are used to protect against mosquito bite during sleep. They also protect against other creatures like spiders, cockroaches, lizards, snake and rats. The material should be white.The best pattern is rectangular net, Others are Circular nets, wedge shaped nets, self supporting nets(babies and infants). The size of the openings in the net is at most importance, the size should not exceed 0.0475 inch in any diameter. The number of holes in one square inch is usually 150.
    • Disadvantages of Untreated Nets : Mosquito can feed when body makes contact with the net. Hungry mosquito wait on or near the net untill net is opened. After failing to get through the net Mosquito are diverted to unprotected people sleeping nearby.
    • Insecticides Treated Mosquito Nets : They provide better and effective protection by not only preventing mosquito bites & also killing them. Thus it reduces Mosquito population. They are prepared by soaking the net in insecticidal solution & dried. Nylon nets are preferred over cotton nets because they are more durable, insecticide stays longer duration and quicker in drying after impregnation. Synthetic Pyrethroids are used for impregnation. Permethrin, Deltamethrin,Cyfluthrin and Lambdacyhalothrin are used.
    • Dosage of Insecticides:
      • 25 mg per sq.m in case of deltamethrin(2.5%) and Lmbdacyhalothrin (10%)
      • 50 mg per sq.m in case of cyfluthrin(10%).
      • They have effect up to 6 months when not washed. Under the programme Long lasting inscecticide treated bed nets are provided free of cost in endemic areas.
  2. Repellents : They are mainly used for application on exposed parts of skin. They act by preventing human-insect contact and do not knock down or kill. Chief advantage is short duration of protection. So it is useful for Plantation workers, Army people, Labors who work outdoor at night and Travelers. N,N-Diethyl-3-toluamide (DEET), indalone, dimethyl phthalate, dimethyl carbate. DEET is best available product; the repellent effect last for 4-6 hours. Some people can develop allergy on application.
  3. Screening: Screening of buildings with copper or bronze having 16 meshes to the inch is recommended. They are costly.
  4. Others- Mosquito hitting swatter, full cover of hands and legs, use of fan at high speed.
    • Insecticide Vaporizers: They are used in the form of coils, mats, liquid vaporizers and aerosols/spray. They protect against mosquito and biting flies by,
      1. Irritating and disturbing them after contact and preventing them from biting and also preventing them entering room.
      2. Paralyzing or killing them.

Key elements of an IVC Strategy:

  1. Advocacy, social mobilization and legislation :Promotion and inclusion of IVC principles. Empowerment of communities for sustainability. Establishment or strengthening - regulatory & legislative control for public health.
  2. Collaboration within the health sector and other sectors: Agriculture and agriculture development projects, Urban sector; Industrial development; Infrastructure development projects; Water resources development projects; Housing projects;
  3. Integrated approach : IRS in high risk areas and in epidemic situations based on vector behavior and community acceptance. Use of insecticide-treated nets/long-lasting insecticidal nets and other personal protection methods. Environmental management and Biological control needs to be given importance.
  4. Evidence-based decision making : IVC strategy requires assessment of the vector control needs based on the local factors. Demands efficient surveillance/ information management system that highlights targets for vector control interventions.
  5. Operational and implementation research : Strong operational and implementation research support for development of new and modified tools
  6. Capacity building : expertise at the central, as well as peripheral levels. Developing tools and guidelines in local languages and training of personnel for vector control.
  7. Monitoring and evaluation - indicators as per the local requirements and targets set. Inputs, costs & outcome of different interventions, when used singly or in combination & simultaneously or consecutively in a defined area, must be monitored. 


References

  1. Integrated vector control approach TRS series. World health organization 1983.{http://whqlibdoc.who.int/trs/WHO_TRS_688.pdf}
  2. Hand book for integrated vector management. World health organization. 2012.
  3. Community participation for disease vector control. ICMR/WHO proceedings. Malaria research centre- 1986.
  4. Shaukat Kamal. Control of mosquito's . Advances in medical entomology and human welfare; 1998,67-76.
  5. Park K. Park's Textbook of preventive and social medicine. 21th ed. Jabalpur: M/s Banarasidas Bhanot Publishers; 2010. 708 - 28.
  6. A Guide To Malaria & Its Control For PHC Medical Officer of Karnataka. Directorate of Health And Family Welfare Services.
  7. Operational manual for malaria action programme (MAP) . NMEP. 2nd ed. Delhi: Government of India; 1995.


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