Integrated Vector Control Management

Definition / Concept

• Park's Textbook of Preventive and Social Medicine, p. 871

Principles of Arthropod Control (Four Pillars)

1. Environmental Control

• Offers the best approach because results are likely to be permanent
• Methods include:
  • Elimination of breeding places (source reduction)
  • Filling and drainage operations
  • Carefully planned water management
  • Provision of piped water supply
  • Proper disposal of refuse and wastes
  • Cleanliness in and around houses
• Requires intensive health education of the public and political support

2. Chemical Control

• A wide range of insecticides available: organochlorine, organophosphorus, and carbamate groups
• Limitations:
  • Vector control by insecticides alone is no longer fully effective - resistance has appeared in over 100 species of arthropods of public health importance
  • Danger of environmental contamination has led to restricted use of many insecticides
• Shift from highly persistent compounds (DDT) to biodegradable, less toxic alternatives such as methoxychlor, abate (temephos), and dursban
• Developing countries still largely depend on organochlorine compounds due to lack of equally efficient alternatives

3. Biological Control

• Minimizes environmental pollution from toxic chemicals
• Methods:
  • Larvivorous fish - especially Gambusia - for mosquito control
  • Fungi of genus Coelomomyces (pathogenic to mosquitoes)
  • Other agents under study: bacteria, fungi, nematodes, protozoa, viruses
• Caution: introduction of biological agents may pose direct hazard to human health

4. Genetic Control

• Techniques: sterile male technique, cytoplasmic incompatibility, chromosomal translocations
• Effective in small field trials (WHO/ICMR Research Unit, New Delhi has contributed significantly)
• Not yet ready for large-scale use

5. Newer Methods

• Insect growth regulators
• Chemosterilants
• Sex attractants / pheromones

Integrated Vector Management (IVM) - NVBDCP Framework

"Appropriate biological, chemical and environmental interventions of proven efficacy, separately or in combination as appropriate to the area, through the optimal use of resources."

• Multi-disease integration: Identical vector control methods used to control malaria + leishmaniasis (rural), and malaria + dengue (urban) - achieving cost-effectiveness and synergy
• Safe insecticide use with monitoring of insecticide resistance
• Collaboration with public/private agencies and community participation
• Village as unit of intervention; sub-centre areas classified by risk level where needed

• API ≥ 5 population: covered by LLINs
• API ≥ 2 endemic areas: conventional ITNs + IRS
• IRS preferred where hot summers prevail and ITNs are not accepted by population

• ~80 million population covered by IRS in India
• DDT = insecticide of choice; where resistance exists - malathion or synthetic pyrethroids used
• DDT and synthetic pyrethroids: two rounds per season
• Malathion: three rounds required
• Limitation: low community acceptance (white marks, acrid smell of malathion)

Integrated Control for Specific Vectors

Malaria (Anti-larval component)

• Bioenvironmental measures (source reduction, drainage, biological agents)
• Personal protection measures (nets, repellents)
• This approach is necessary because "there is no single and simple method that would ensure control of transmission"

Filariasis - Four Breakthroughs in Integrated Control

1. Single-dose annual drug treatment (DEC; ivermectin; combined DEC + ivermectin reduces microfilaraemia >95% at 2 years)
2. Intensive local hygiene on affected limbs (with/without antibiotic + antifungal creams) - halts or reverses elephantiasis/lymphoedema
3. DEC-medicated salt - low-concentration DEC in cooking salt to eliminate lymphatic filariasis in communities
4. Insecticide sprays and polystyrene beads to seal latrines and rooftop water-storage tanks - eliminates/reduces urban Culex mosquitoes

Why "Integrated" Approach is Essential

• Insecticide resistance in >100 arthropod species makes chemical control alone insufficient
• Environmental pollution from persistent insecticides limits their long-term use
• No single method is universally effective across all ecological settings
• Cost-effectiveness: targeting multiple diseases with the same vector control tools (e.g., malaria + dengue in urban areas via same anti-larval measures)
• Community participation and multi-sectoral collaboration are needed for sustained impact

Portable (Potable) Water

Introduction

Safe and Wholesome Water (Definition)

• a. Free from pathogenic agents
• b. Free from harmful chemical substances
• c. Pleasant to the taste - free from colour and odour
• d. Usable for domestic purposes

Water Requirement

Uses of Water

1. Domestic - drinking, cooking, washing, bathing, flushing toilets, gardening
2. Public purposes - cleaning streets, recreational (swimming pools, fountains, parks), fire protection
3. Industrial - processing and cooling
4. Agricultural - irrigation
5. Power production - hydropower and steam power
6. Waste carriage - carrying away waste from establishments

Sources of Water Supply

1. Rain Water

• Prime source of all water (feeds both ground water and surface water)
• Characteristics: purest in nature; clear, bright, sparkling; very soft (only 0.0005% dissolved solids); corrosive to lead pipes
• Impurities: picks up dust, soot, microorganisms, CO₂, N₂, O₂, ammonia, and gaseous sulphur/nitrogen oxides from atmosphere
• Bacteriologically clean in unpolluted areas

2. Surface Water

• More liable to pollution than ground water
• Requires full treatment before use

3. Ground Water

• Advantages: likely free from pathogens; usually requires no treatment; reliable even in dry season; less subject to contamination
• Disadvantages: high mineral content (calcium, magnesium salts - makes water hard); requires pumping

• Consist of a galvanized iron pipe sunk into water-bearing stratum with strainer at bottom and hand-pump at top
• Bacteriologically safe; cheap compared to other sources
• Area within 15 m must be kept free from liquid/solid waste pollution
• Life of tube well: 5-10 years on average (can last up to 30 years)
• Deep tube wells require mechanical drilling; costly but ideal; yield very high

• Ground water that comes to the surface under natural pressure; no pumping needed
• Shallow springs dry up in summer; deep springs are reliable year-round
• Exposed to contamination; protective structures are essential

Water Pollution

• (a) Sewage - decomposable organic matter and pathogenic agents
• (b) Industrial/trade wastes - toxic agents (metal salts, complex synthetic organic chemicals)
• (c) Agricultural pollutants - fertilizers and pesticides
• (d) Physical pollutants - heat (thermal pollution) and radioactive substances

Purification of Water (Three Stages)

Stage I - Storage

• Physical: ~90% of suspended impurities settle by gravity in 24 hours; water becomes clearer
• Chemical: Aerobic bacteria oxidize organic matter; free ammonia reduces; nitrates rise
• Biological: Bacterial count drops by as much as 90% in 5-7 days; pathogens die out
• Optimum storage period for river water: 10-14 days
• Caution: prolonged storage causes algal growth imparting bad smell and colour

Stage II - Filtration

A. Slow Sand (Biological) Filter

• First used in 1804 in Scotland, then London; still the standard method of water purification
• Elements: (1) Supernatant water (1-1.5 m depth providing head), (2) Sand bed (0.2-0.3 mm effective size, 1 m deep), (3) Under-drainage system, (4) Filter control valves
• Schmutzdecke (Biological layer): A layer of organic material and bacteria forming on the sand surface - the actual filtering agent, trapping bacteria, algae, protozoa, viruses
• Rate of filtration: 2-3 million gallons per acre per day (m.g.a.d.)
• Removes 99.9-99.99% of bacteria
• Cleaning: by scraping the sand bed

B. Rapid Sand (Mechanical) Filter

• First installed in 1885 in USA
• Two types: gravity type (Paterson's filter) and pressure type (Candy's filter)
• Steps involved:
  1. Coagulation: Alum added (5-40 mg/L or more depending on turbidity, colour, temperature, pH)
  2. Rapid mixing: In mixing chamber for a few minutes - thorough dissemination of alum
  3. Flocculation: Slow stirring in flocculation chamber for ~30 minutes at 2-4 rpm → forms thick white flocculant precipitate of aluminium hydroxide
  4. Sedimentation: Detained 2-6 hours in sedimentation tanks; ≥95% of flocculant precipitate removed before water enters filters
  5. Filtration: Rapid sand filtration (rate 5-15 m³/m²/hour)
• Sand effective size: 0.4-0.7 mm; sand bed depth 1 m; gravel layer 30-40 cm below
• Cleaning: by back-washing
• Removes 98-99% of bacteria

Stage III - Disinfection

Chlorination

1. Nature of chlorine: Chlorine in water forms hypochlorous acid (HOCl) and hypochlorous ion (OCl⁻). HOCl is the bactericidal agent
2. Chlorine demand: The difference between chlorine added and residual chlorine after 60 min contact. The point where chlorine demand is met = break-point; beyond this, free chlorine (HOCl and OCl⁻) appears in water
3. Contact period: Free residual chlorine for at least 1 hour is essential to kill bacteria and viruses
4. Minimum free residual chlorine: 0.5 mg/L for 1 hour contact
5. Correct dose = chlorine demand of water + 0.5 mg/L free residual chlorine

• Note: Chlorine has no effect on spores, protozoal cysts, and helminthic ova except in higher doses

• (1) Chlorine gas - First choice; cheap, quick, efficient, easy to apply; requires special chlorinating equipment (e.g., Paterson's chloronome)
• (2) Chloramine - Chlorine + ammonia; less taste; more persistent residual; but slower action - not widely used
• (3) Perchloron (High Test Hypochlorite/HTH) - 60-70% available chlorine; more stable than bleaching powder

Small-Scale / Emergency Disinfection

• Must bring to a "rolling boil" for 10-20 minutes
• Kills all bacteria, spores, cysts, and ova
• Also removes temporary hardness
• Drawback: no residual protection against subsequent contamination
• Boil and store in the same container

Water Quality - Criteria and Standards

Physical Criteria (WHO Guidelines)

1. Turbidity: Should be below 1 NTU (nephelometric turbidity units); 5 NTU acceptable in rural areas
2. Colour: Should not exceed 15 TCU (true colour units)
3. Temperature: Palatably cold; should not exceed 25°C; higher temperatures compromise disinfection efficiency and cause taste/odour problems
4. pH: Acceptable range 6.5 to 8.5; pH <7 causes corrosion of metal pipes (elevated lead levels); pH >8 decreases chlorine disinfection efficiency
5. Hydrogen sulphide: Taste/odour threshold 0.05-0.1 mg/L ("rotten eggs" smell); immediate corrective action required
6. Iron: Should not exceed 0.3 mg/L; above this, stains laundry and promotes iron bacteria growth
7. Sodium: Average taste threshold ~200 mg/L
8. Sulphate: Taste impairment minimal below 250 mg/L
9. Total Dissolved Solids (TDS): <600 mg/L = good palatability; >1,200 mg/L = increasingly unpalatable; <1,000 mg/L generally acceptable
10. Zinc: Taste threshold 4 mg/L; >5 mg/L water appears opalescent

Bacteriological Standards (WHO Guidelines)

Biological Hazards

• Protozoa: Slow and rapid sand filtration effectively remove a high proportion; standard routine monitoring methods not available
• Helminths: Infective stages can be transmitted via drinking water; particularly important for Dracunculus medinensis (guinea worm) and human schistosomes; source protection is the best approach
• Free-living organisms (fungi, algae): Mainly interfere with treatment processes, and cause colour, turbidity, taste, and odour problems

Chemical Aspects

• Chemical contaminants rarely cause acute problems except in massive accidental contamination
• Primary concern: cumulative toxic properties after prolonged exposure - especially heavy metals and carcinogens

Biological (Microbiological) Aspects of Standards of Drinking Water

Overview

• Not contain any microorganisms known to be pathogenic
• Be free from bacteria indicative of pollution with excreta

"The potential consequences of microbial contamination are such that its control must always be of paramount importance and must never be compromised."

• Infants and young children
• People who are debilitated or living under insanitary conditions
• The sick and the elderly

• (a) Bacteriological
• (b) Virological
• (c) Biological (protozoa, helminths, free-living organisms)

(a) Bacteriological Aspects

Primary Indicator - Coliform Group

• Faecal streptococci
• Sulphite-reducing clostridia

(1) Coliform Organisms

• Aerobic and facultative anaerobic
• Gram-negative
• Non-sporing
• Motile and non-motile rods
• Capable of fermenting lactose at 35-37°C in less than 48 hours

• Faecal group (E. coli) - the most important indicator
• Non-faecal group - e.g., Klebsiella aerogenes

Why Coliforms Are Chosen as Indicators (Not Pathogens Directly)

(2) Faecal Streptococci

• Regularly occur in faeces, but in much smaller numbers than E. coli
• Finding faecal streptococci = important confirmatory evidence of recent faecal pollution
• Highly resistant to drying
• Valuable for:
  • Routine control testing after laying new mains or making repairs in distribution systems
  • Detecting pollution by surface run-off to ground or surface waters

(3) Clostridium perfringens (Cl. perfringens)

• Also occurs regularly in faeces, though generally in much smaller numbers than E. coli
• Spores are capable of surviving in water for a longer time than organisms of the coliform group
• Spores usually resist chlorination at doses normally used in waterworks practice
• Interpretation of findings:
  • Presence of spores in natural water = faecal contamination has occurred
  • Presence in absence of coliform group = faecal contamination occurred at some remote time in the past
  • Presence in filtered supplies = may indicate deficiency in filtration practice

Bacteriological Standards (WHO Guideline Values - Table 5)

These guideline values provide guidance required to ensure bacteriologically safe supplies of drinking water - whether piped, unpiped, or bottled.

(b) Virological Aspects

• Drinking water should be free from any viruses infectious for man
• Disinfection standard for virus inactivation:
  • 0.5 mg/L of free chlorine residual after a contact period of at least 30 minutes at pH 8.0 - sufficient to inactivate viruses
  • This free chlorine residual is mandatory in all disinfected supplies in areas suspected of endemicity of hepatitis A (incidentally also takes care of bacteriological safety)
  • For other areas: 0.2 mg/L free residual chlorine is considered adequate

(c) Biological Aspects (Protozoa, Helminths, Free-living Organisms)

(i) Protozoa

• Standard methods are not currently available for routine detection of pathogenic protozoa in water supplies in routine monitoring programmes
• Rapid or slow sand filtration have been shown to be effective in removing a high proportion of pathogenic protozoa
• Detection remains a limitation for routine water quality monitoring

(ii) Helminths

• Infective stages of many parasitic roundworms and flatworms can be transmitted to humans through drinking water
• A single mature larva or fertilized egg can cause infection - such infective stages should be absent from drinking water
• The water route is relatively unimportant except for:
  • Dracunculus medinensis (Guinea worm) - primarily a hazard of unpiped water supplies
  • Human schistosomes - also primarily hazard of unpiped water
• Methods for detection of these parasites are unsuited for routine monitoring
• Source protection is the best approach to prevention

(iii) Free-living Organisms

• Include fungi, algae, etc.
• Do not typically cause direct infection
• Main problems are their interference in the operation of water-treatment processes, and causing:
  • Colour
  • Turbidity
  • Taste and odour problems in finished water

Summary Table