Human Landing Catch Method for Mosquito Surveillance: Operational Experiment Protocol and Technical

The human landing catch (HLC) method is the internationally recognized gold-standard technique for quantifying human-vector contact in mosquito surveillance and control programs. This operational experiment guide details the standardized procedures, equipment, safety protocols, and data reporting methods for collecting host-seeking adult mosquitoes under field and semi-field conditions. The technique is essential for dengue, malaria, and arbovirus vector monitoring as well as for evaluating the efficacy of insecticides and repellents.

Technical Overview

The human landing catch method, also referred to as human-baited landing collection, is a direct sampling technique in which trained personnel collect adult female mosquitoes at the moment they land on an exposed human volunteer, before the mosquito takes a blood meal. Because many medically important vector species are strongly anthropophilic, meaning they preferentially seek human hosts, no trap or artificial lure currently matches the sensitivity of a living human bait for these mosquitoes.

The core measurement produced by this experiment is the landing rate, typically expressed as the number of female mosquitoes captured per person per hour or per night. When combined with species identification and pathogen infection testing, the method supports calculation of epidemiological indicators such as the man-biting rate and the entomological inoculation rate. Standard reference procedures are published by the World Health Organization (WHO) and national disease control authorities, and the method remains the benchmark against which alternative sampling tools such as light traps, BG-Sentinel traps, and dual-net human-baited stations are validated.

• Target organisms: host-seeking adult female mosquitoes
• Primary metric: landing density (mosquitoes per person per unit time)
• Standard setting: fixed surveillance stations, indoors and outdoors
• Reference frameworks: WHO test guidelines, national vector surveillance protocols

Testing Samples

Adult Host-Seeking Female Mosquitoes

The experiment specifically samples female mosquitoes in the host-seeking physiological state. Males and non-host-seeking females are generally not attracted to the bait and are excluded from landing-rate calculations. Common target taxa include:

• Aedes aegypti and Aedes albopictus, primary vectors of dengue, Zika, and chikungunya
• Anopheles species, malaria vectors, sampled primarily during nocturnal activity periods
• Culex pipiens complex and Culex tritaeniorhynchus, vectors of filariasis and Japanese encephalitis
• Mansonia and other regional nuisance or vector species

Collection Environments

Samples are collected at fixed surveillance stations selected to represent the epidemiological setting under investigation. Typical environments include residential courtyards, bedrooms, construction sites, urban green spaces, livestock-adjacent areas, and semi-field test cages or chambers used for controlled insecticide and repellent evaluations. Paired indoor and outdoor stations allow comparison of endophagic and exophagic biting behavior.

Human Volunteers Serving as Bait

The human volunteer is an integral part of the experimental system. Volunteers must be healthy adults who have provided written informed consent, received appropriate orientation on the procedure, and, where required by the protocol, completed relevant vaccinations or chemoprophylaxis. Institutional ethics approval must be obtained before any field or laboratory collection begins.

Testing Items

Depending on the surveillance objective, the operational experiment may include one or more of the following measurement items:

• Landing density: number of female mosquitoes landing per person per hour or per standard catch period
• Biting rhythm: circadian activity patterns, including dawn, dusk, daytime, and nocturnal peaks
• Species composition: identification of collected specimens to species level using morphological keys or molecular methods
• Physiological status: classification of females as unfed, freshly fed, half-gravid, or gravid
• Vector infection rate: detection of parasites or viruses in collected specimens by PCR, ELISA, or culture-based assays
• Product efficacy: knockdown and mortality of landing mosquitoes in tests of aerosols, mosquito coils, vaporizing mats, and residual sprays
• Personal protection: effective protection time and landing inhibition rate for topical repellents and treated clothing

All results are reported alongside metadata including collection coordinates, station type, weather conditions, and collector identification to support reproducibility and inter-station comparison.

Testing Methods

Preparation and Safety Measures

Before field deployment, the protocol must be reviewed and approved by an ethics committee. Volunteers receive training in mosquito recognition, aspiration technique, and record keeping. Each team is equipped with mechanical aspirators or mouth aspirators fitted with filtration barriers, labeled collection cups with mesh screens, absorbent cotton and sugar solution for specimen maintenance, timers, flashlights or headlamps with red filters, and standardized data sheets. Safety measures include prohibition of alcohol consumption, verification that collectors have no insect-sting allergies that would disqualify them, and arrangements for medical follow-up after the collection period.

Field Collection Procedure

The standard operational sequence is as follows:

• Confirm the activity window of the target species, for example early morning and late afternoon peaks for Aedes, or overnight cycles for Anopheles
• Position the volunteer at the fixed station, exposing the lower legs and forearms while keeping the remainder of the body clothed
• Observe continuously and aspirate each mosquito at the moment it settles on exposed skin, always before it begins probing or feeding
• Transfer captured specimens into the labeled collection cup assigned to that station and time interval
• Record capture time, station code, indoor or outdoor position, and collector identity for every session
• Rotate collectors between stations at defined intervals, commonly using 15-minute catching periods within each hour, to distribute collector skill bias evenly
• Terminate collection at the end of the scheduled window and place cups in insulated carriers for transport

Laboratory Processing and Reporting

Captured mosquitoes are immobilized by brief chilling or triethylamine exposure, sorted by sex and species under a stereomicroscope, and counted. Landing rate is calculated by dividing the total number of females captured by the number of catchers and the number of catching hours. When pathogen testing is required, specimens are pooled by species, station, and date before molecular analysis. All raw and processed data are archived in the surveillance database with chain-of-custody documentation.

Applications

The human landing catch experiment is deployed across a broad range of public health and research contexts:

• Routine vector surveillance in dengue and malaria endemic areas, guiding larval source management and adulticide interventions
• Estimation of the entomological inoculation rate to prioritize districts for indoor residual spraying or insecticide-treated net distribution
• Efficacy evaluation of household insecticide products, including aerosol sprays, coils, mats, and spatial repellents, under WHO test guideline conditions
• Assessment of personal protection products such as DEET, icaridin, and IR3535 repellents, including determination of complete protection time
• Outbreak investigation, where rapid characterization of vector density supports emergency vector control decisions
• Baseline and endpoint measurements in clinical trials, vaccine efficacy studies, and vector control program evaluations
• Calibration and validation of alternative sampling devices, for which HLC results serve as the reference standard

FAQ

Is the human landing catch method safe for volunteers?

When conducted under an approved protocol, the risk is minimized because mosquitoes are captured immediately upon landing and before they bite, so volunteers are not fed upon. Additional safeguards include pre-collection health screening, vaccination or chemoprophylaxis where epidemiologically justified, and post-collection medical monitoring.

Why use humans as bait instead of traps?

Anthropophilic vectors such as Aedes aegypti and many Anopheles species locate hosts through species-specific human odor cues that artificial lures only partially reproduce. Traps frequently underestimate true human-biting rates, so HLC remains the reference method for measuring human-vector contact.

What is the standard collection duration?

Durations are species- and protocol-dependent. Daytime Aedes surveys commonly use 30-minute to 1-hour catches at morning and dusk peaks, while Anopheles surveys may run hourly 15-minute catches across a full 12-hour night cycle to characterize biting rhythm.

How is the landing rate reported?

The landing rate is expressed as females per person-hour or females per person-night, calculated from total captures divided by catchers and catching time. Comparative studies report confidence intervals and standardized station metadata.

Are there alternatives when ethics approval cannot be obtained?

Yes. The human-baited double net trap, in which the volunteer is protected inside an inner net while mosquitoes are trapped in the outer compartment, and the Centers for Disease Control light trap are accepted alternatives, although each has known species-specific bias relative to the landing catch standard.