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CM3.6-8 | CM3.6-8 | Vector Biology and Control Measures — SDL Guide (Part 3)
Surveillance, Monitoring, and Programme Evaluation
Effective vector control programmes require two parallel surveillance systems: parasitological surveillance (measuring disease transmission) and entomological surveillance (measuring vector population density and infectivity).
Parasitological indicators for malaria:
- Annual Parasite Incidence (API): total confirmed malaria cases per 1000 population per year. API <1 = low endemicity target for the elimination phase.
- Slide Positivity Rate (SPR): percentage of blood smears positive for malaria parasites among all slides examined. SPR ≥1% triggers enhanced vector control response.
- Annual Blood Examination Rate (ABER): percentage of population whose blood is tested per year; ≥10% is the minimum surveillance target.
Entomological indicators for Aedes (dengue surveillance):
- House Index (HI): percentage of houses positive for Aedes larvae or pupae. HI ≥1% signals dengue transmission risk.
- Container Index (CI): percentage of water-holding containers inspected that are positive for larvae. CI ≥3% is the action threshold.
- Breteau Index (BI): number of positive containers per 100 houses inspected. BI ≥5 indicates a significant dengue risk.
Insecticide susceptibility monitoring: periodic WHO cone bioassay or tube test to assess whether the target mosquito population shows resistance to the operational insecticide. Results guide insecticide rotation decisions. Resistance is defined as <90% mortality in the standard WHO bioassay (susceptibility is ≥98% mortality).
Programme evaluation for vector control uses: vector density trends (before/after IRS, anti-larval operations), disease incidence trends (API, dengue notification), coverage of key interventions (% houses IRS-covered, % households with LLINs), and side-effect monitoring (organophosphate poisoning events among spray operators).
CLINICAL PEARL
Organophosphate insecticide poisoning is common in India — know the antidote sequence. India uses malathion and dichlorvos widely for mosquito control and in agriculture. When a patient presents with profuse sweating, pinpoint pupils, bradycardia, bronchospasm, fasciculations, and altered consciousness—think OP poisoning. The cholinergic toxidrome (SLUDGE/DUMBELS) results from irreversible acetylcholinesterase inhibition. Management: (1) decontaminate (remove clothing, wash skin); (2) atropine in large doses (2-4 mg IV every 5-10 minutes until secretions dry and bronchospasm resolves — you may need 50-100 mg in severe cases); (3) pralidoxime (2-PAM) IV to reactivate AChE — must be given within 24-48 hours before irreversible 'ageing' of the OP-AChE complex. Never give morphine or phenothiazines. Succinylcholine is contraindicated (prolonged paralysis). This clinical scenario bridges your vector control knowledge directly to toxicology.
SELF-CHECK
A malaria control worker presents to the PHC with nausea, excessive sweating, miosis (pinpoint pupils), bradycardia (HR 48), and muscle twitching after an indoor spraying operation using malathion. Which is the correct immediate management?
A. Administer adrenaline IV for the bradycardia and arrange cardiac monitoring
B. Administer atropine IV to counteract the cholinergic crisis, followed by pralidoxime if symptoms persist — decontaminate the patient first by removing clothing and washing with soap and water
C. Administer naloxone — miosis and bradycardia suggest opioid toxidrome
D. Administer thiamine and glucose as this is likely hypoglycaemia from inadequate food intake during field work
Reveal Answer
Answer: B. Administer atropine IV to counteract the cholinergic crisis, followed by pralidoxime if symptoms persist — decontaminate the patient first by removing clothing and washing with soap and water
This is a classic organophosphate (malathion) poisoning presentation: SLUDGE/muscarinic syndrome (sweating, miosis, bradycardia, GI effects) plus nicotinic effects (muscle twitching/fasciculations). Malathion is an OP that irreversibly inhibits AChE. Management sequence: (1) decontaminate immediately—remove contaminated clothing, wash skin thoroughly to prevent ongoing absorption; (2) atropine IV in titrated doses to dry secretions and relieve bronchospasm (start 2 mg, repeat every 5-10 minutes); (3) pralidoxime (2-PAM) to reactivate the OP-AChE complex—effective only if given before 'ageing' (within 24-48 hours). Adrenaline would worsen the situation; naloxone is the opioid antidote (no miosis from opioids typically with bradycardia in this context); thiamine is for Wernicke's.