Mosquito Surveillance & Vector Control

Sri Lanka was certified malaria-free by the World Health Organization (WHO) in 2016 — a landmark public health achievement.

However, the continued presence of Anopheles mosquitoes and increasing travel to and from malaria-endemic countries mean the threat of malaria reintroduction still exists.

The Anti-Malaria Campaign (AMC) carries out continuous entomological surveillance and targeted vector control interventions to maintain zero local transmission and prevent the re-establishment of malaria in Sri Lanka.

1. Entomological Surveillance

Entomological surveillance is the cornerstone of malaria prevention during the Prevention of Reintroduction (PoR) phase.

It involves systematic monitoring of mosquito populations to assess the risk of malaria transmission, known as **receptivity**, and to guide appropriate vector control responses.

Objectives

• Identify and map Anopheles breeding sites and species distribution.
• Detect new or invasive malaria vectors, including Anopheles stephensi.
• Monitor mosquito density, biting behavior, and resting habits.
• Assess susceptibility and resistance to insecticides.
• Evaluate the impact of vector control measures and environmental changes.

Types of Surveillance

• **Extended Sentinel Site Monitoring** – Conducted monthly in high-risk areas to track seasonal trends and vector behavior.
• **Routine Sentinel Site Monitoring** – Conducted quarterly in moderate-risk areas to monitor vector abundance and insecticide resistance.
• **Proactive Spot Checks** – Short-term surveys to assess new or vulnerable areas with potential risk of malaria reintroduction.
• **Reactive Spot Checks** – Conducted within 48 hours of a malaria case report to assess vector presence within a 1 km radius of the patient’s residence.

Techniques Used

• Larval and adult mosquito collection
• Human landing catches and cattle-baited collections
• Resting collection and spray sheet methods
• Parity and infectivity testing
• Insecticide resistance and bioassay testing

Entomological findings are used to determine malaria receptivity levels and decide the most appropriate interventions for each region.

2. Core Vector Control Interventions

Vector control aims to reduce or eliminate mosquito populations capable of transmitting malaria.

The AMC uses a mix of core, supplementary, and personal protection interventions, depending on the ecological setting and risk level.

Indoor Residual Spraying (IRS)

IRS involves applying long-lasting insecticides on interior walls and ceilings where mosquitoes rest. It:

• Reduces mosquito lifespan and density.
• Decreases human–vector contact.
• Provides immediate interruption of transmission in outbreak or case-response situations.

IRS is prioritized where vectors rest indoors (endophilic) and populations predominantly sleep inside houses.

Long-Lasting Insecticidal Nets (LLINs)

LLINs provide both a mechanical barrier and chemical protection against mosquito bites for at least three years. They are distributed to:

• Residents in receptive or vulnerable areas.
• Returnees from malaria-endemic countries.
• Populations in proximity to imported malaria cases.

Before distribution, communities are educated on correct net usage and maintenance. Follow-up visits ensure compliance and longevity.

3. Supplementary Vector Control (LSM)

Larval Source Management (LSM)

LSM targets mosquito larvae before they become adults and includes:

• **Environmental modification:** Permanent alteration of breeding sites (e.g., drainage, filling pits).
• **Environmental manipulation:** Temporary water management (e.g., flushing, cleaning drains).
• **Larviciding:** Application of biological or chemical agents such as Temephos or Bacillus thuringiensis israelensis (Bti) to kill larvae.
• **Biological control:** Introduction of larvivorous fish species like Aplocheilus dayi (“Nalahandaya”) or Poecilia reticulata (guppy) in confined water bodies.

Larval control is especially useful in construction sites, irrigation schemes, or urban habitats where water collections are few, fixed, and findable.

4. Personal Protection and Community Awareness

Personal measures reduce mosquito bites and protect individuals in high-risk settings:

• Use of repellents (creams, sprays, coils).
• Protective clothing covering arms and legs during evening hours.
• LLIN use every night regardless of the season.

Community awareness programs emphasize eliminating mosquito breeding sites and the timely reporting of fever following travel to endemic countries.

5. Vector Control in Special Scenarios

Vector control measures are customized depending on epidemiological and environmental conditions:

These measures are guided by real-time entomological data and coordinated between the AMC Headquarters and Regional Malaria Officers.

6. Insecticide Resistance Monitoring

Regular monitoring of mosquito susceptibility ensures effective insecticide use.

AMC teams conduct annual resistance testing for all major vector species (An. culicifacies, An. subpictus, An. stephensi) using WHO-standard methods.

Findings guide the selection and rotation of insecticides to delay resistance development.

7. Strengthening Surveillance and Partnerships

• Entomological teams operate in every Regional Malaria Office, equipped with trained Health Entomology Officers and field staff.
• All surveillance data are mapped using GPS to identify vector breeding sites and prioritize interventions.
• Collaborations with local authorities, environmental agencies, and communities ensure sustainable vector management and rapid response to any malaria risk.