FIELD OF THE INVENTION

The invention relates to an electrocution-type insect trap, in particular to a portable, battery-powered

electrocution-type trap for catching mosquitoes.

BACKGROUND TO THE INVENTION

Mosquitoes are responsible for huge losses in human and animal life through their role in transmitting infectious diseases. About half of the world's population live in areas where they are at risk of malaria, which the most important insect-borne disease of humans.

The control of malaria and other mosquito-borne disease is critically dependent on accurate surveillance of the abundance and infection of mosquito vectors. Reliable mosquito sampling methods are fundamental for a number of purposes including to governmental agencies that manage and monitor for vector-borne diseases both in tropical countries and temperate regions where they may emerge (including several areas of western Europe and the UK) , to the National Malaria Control Programmes within the 108 countries that have endemic transmission, and to researchers from academia, government and/or industry involved in large-scale mosquito control trials or related research.

Currently, there is only one ^x gold standard' method in use for estimating the number of potentially infectious mosquito bites that a person would be exposed to this. This method is called the "Human Landing Catch" (HLC) , and involves volunteers sitting over night (when most mosquito biting happens) with one of their legs exposed, with the aim of collecting every mosquitoes that lands on them using a mouth aspirator and storing them. The aim is to collect the mosquitoes from their leg before they bite, but that is not always possible.

Obviously, this method involves considerable risk, as it exposes the human subjects that carry it out to the bite of potentially infected mosquitoes. Additionally the method is quite variable and subject to the particular collection skill of the human participant. Due to these risks, some malaria endemic countries are now restricting or banning the use of the HLC method, which is problematic given the lack of suitable alternative methods. Consequently, there is a clear and urgent need within the global mosquito-borne disease community to develop new trapping methods that provide comparably accurate estimate of mosquito biting rates on humans, without exposing participants to any infection risk.

Over the last decade, there have been numerous attempts to develop some exposure-free alternatives to the Human- landing trap, including such approaches as the Bednet trap, and outdoors tent trap. All of these have shown to have limitations in that their performance compares poorly relative to the HLC, either in terms of overall mosquito abundance and/or giving a skewed representation of the types of

mosquitoes that bite people in outdoor environments.

SUMMARY OF THE INVENTION

At its most general, one aspect of the present invention provides a battery-powered electrocution-type insect trap for non-destructive capture of mosquitoes, in which an electric field for mosquito electrocution is optimisable through the provision of a variable voltage power supply.

According to this aspect of the invention, there is provided an electrocution-type insect trap for non-destructive capture of mosquitoes, the insect trap comprising: a DC energy source for producing an input DC voltage; a variable voltage power supply arranged to controllably multiple the input DC voltage to an output DC voltage; and an electrocution grid surrounding an cavity for receiving lure (e.g. a living subject) to attract mosquitoes, wherein the electrocution grid comprises a plurality of parallel spaced-apart conductive elements that are electrically connected to the variable voltage power supply so that the output DC voltage creates an electric field between adjacent conductive elements, and wherein the output DC voltage is selectable to optimise nondestructive capture of mosquitoes. The ability to select the output voltage enables the trap to be usable in a wide variety of different environments and to be tunable to optimise the capture of certain species. Herein the term "non-destructive" means that the electric field is capable of supplying an electric shock that is lethal to mosquitoes, but which does not vaporise or cause combustion or other significant damage to the mosquito carcass, whereby it remains suitable for identification by visual or molecular methods.

The DC energy source may be any suitable portable and/or sustainable energy source, e.g. a battery and/or a solar cell.

The plurality of parallel spaced-apart conductors may have alternating polarities, i.e. alternate conductive elements may be electrically connected to one another to form two sets of mutually interspersed conductors, and those two sets of mutually interspersed conductors may be connected to opposite polarities of the output DC voltage. This

arrangement ensure a uniform electric field presence around the cavity.

The electrocution grid may comprise an insulating frame and the plurality of parallel spaced-apart conductive elements are wires which span across the frame. The wires may extend in a vertical direction, and adjacent wire are preferably separated by 5 mm, which has been found to be optimal for malaria mosquitoes. To ensure uniform separation of the wires, the electrocution grid may include one or more

insulating spacers spanning across the frame in a direction offset from (e.g. orthogonal to) the wires, wherein the wires intersect with and are attached to the insulating spacer at their respective intersection points.

The electrocution grid may comprise a plurality of panels which are arranged to surround the cavity. For example, the electrocution grid may comprise four square panels arranged to form a cube-shaped cavity. The panels may be pivotally connected, e.g. hinged, to one another.

The variable voltage power supply may comprise a

switched-mode DC-to-DC converter that incorporates a voltage- multiplying rectifier. This arrangement may provide a clean, quiet signal with a low output ripple, whilst also enabling an input voltage of 24 V to be multiplied up to 1 kV.

The variable voltage power supply may be controlled using adjustable peripheral circuitry such as a potentiometer, e.g. arranged to vary the input voltage. The voltage may be controlled within a range up to 1 kV. In order to ensure non- destructive capture of the mosquitoes, the output voltage may be set at or around 600 V.

As a safety feature and to prolong the battery lifetime, the variable voltage power supply may include an output current limiter arranged to limit the current that flows in the plurality of parallel conductive elements. For example, one or more resistors may be used to limit the output current to 10 mA or less.

The variable voltage power supply may include adjustable peripheral circuitry such as a potential divider connected to the output voltage to provide a reduced voltage output for use as a control parameter, e.g. to compare with the input voltage to ensure that the device is operating as intended

The trap preferably includes a display, e.g. low power LCD panel, arranged to show the selected output voltage.

The variable voltage power supply and electrocution grid may be electrically floating, e.g. to reduce the risk of the high voltages causing unwanted electric shocks. The variable voltage power supply may thus be encased in an insulating, and preferably waterproof, housing.

To prevent accidental physical contact with the

electrocution grid, the trap may include an inner shield mounted in front of the electrocution grid inside the cavity and/or an outer shield mounted beyond the electrocution grid outside the cavity.

In one embodiment, the lure is a living subject, e.g. an exposed region of skin on a human or animal subject.

Alternatively or additionally, the lure may be a chemical attractant as known in the art.

In another aspect of the invention, a panel of the electrocution grid discussed above may be used as or

incorporated into a cover for mounting over an aperture.

According to this aspect, there may be provided an

electrocution-type insect barrier for killing mosquitoes, the insect barrier comprising: an energy source for producing an input DC voltage; a variable voltage power supply arranged to controllably multiply the input DC voltage to an output DC voltage; and an electrocution grid panel for covering an opening, wherein the electrocution grid panel comprises a plurality of parallel spaced-apart conductive elements that are electrically connected to the variable voltage power supply so that the output DC voltage creates an electric field between adjacent conductive elements, and wherein the output DC voltage is selectable to kill mosquitoes that attempt to pass through the opening.

Any one or more of the features discussed with respect to the trap aspect discussed above may be applied where

applicable to the barrier aspect. The opening may be a window into a building or similar structure.

The barrier may be battery powered as discussed above, i.e. the energy source may be a DC battery. Alternatively, the energy source may be the mains, and may include a suitable rectifier and/or transformer for converting the main supply to the input DC voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are discussed below with reference to the accompanying drawings, in which:

Fig. 1 is a schematic diagram of the power supply and control system for an electrocution-type insect trap that is an embodiment of the invention;

Fig. 2 is a perspective view of an electrocution-type insect trap that is an embodiment of the invention;

Fig. 3 is a perspective view of the electrifiable grids that are used in the electrocution-type insect trap of Fig. 2;

Fig. 4 is a partly assembled view of the electrocution- type insect trap of Fig. 2; and

Fig. 5 is a selection of charts comparing a mosquito trap that is an embodiment of the present invention with an HLC trap .

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

The present invention aims to provide an electrocution- type insect trap that uses electrifiable grids that are optimized to kill but not destroy mosquitoes on contact (to permit subsequent identification) , and which can be safely located close enough to a living subject, e.g. human or other animal (e.g. livestock), to enable the living subject to be used as means of attracting the mosquitoes, e.g. in the same manner as an HLC. Given the desirability to operate such a trap in remote regions, the present invention provides a battery-powered electrocution-type insect trap with a current-limiting capability that ensures both adequate operational lifetime and user safety. The electrocution-type insect trap of the invention can be used either indoors or outside.

The electrocution-type insect trap of the invention includes a controllable power supply capable of setting an optimal voltage for shocking (i.e. killing without destroying) the two main mosquito vector species of malaria in Africa, i.e. Anopheles arabiensis and Anopheles gambiae s.s.

Fig. 1 is a schematic view of a power supply and control system 100 used in an electrocution-type insect trap that is an embodiment of the invention. The energy source for the power supply is a battery 102, e.g. a pair of 12 V batteries connected in series to provide a 24 V DC input voltage. Any suitable energy source may be used, e.g. solar cells, etc.

The input voltage is converted to an output voltage (i.e. an output DC voltage) by variable voltage power supply 104, which may be a self-contained IC unit. The structure and function of the variable voltage power supply 104 is discussed in more detail below. A voltage controller 106 is connected to the variable voltage power supply 104 to provide a means of adjusting the output voltage. For example, the voltage controller 106 may include an external circuit having an potentiometer, e.g. with a user-adjustable dial, to enable the output voltage to be adjustable between 0 V and 1 kV. This enables the device to be set to a specific output voltage, e.g. to a predetermined level that is optimal for a particular mosquito species and/or ecological setting, but also has the capability of being altered either higher or lower to optimize performance in different settings.

The output voltage is supplied to one or more

electrocution grids 108. The structure and configuration of the electrocution grid is discussed in more detail below. To ensure the device can be safely used close to a living

subject, the variable voltage power supply 104 includes an output current limiter (e.g. including a resistor having a resistance of 330 Ω or more in series with the output) arranged to limit the output current to 10 mA. The current limiter may be adjustable, e.g. to maintain the power delivered by the device at or below a threshold level for a range of voltages. This ensures the device can be operated safely over a range of voltages.

The variable voltage power supply 104 may comprise a switched-mode DC-to-DC converter that incorporates a voltage- multiplying rectifier. The switched-mode DC-to-DC converter includes a voltage transformer whose primary coil is driven by a power driver stage that receives the input voltage from the battery 102. The power driver stage is typically a solid- state semiconductor switch, e.g. a power MOSFET, that is arranged to receive a switching control signal from a

microcontroller. The secondary coil of the transformed provides an output that is multiplied and rectified by a suitable voltage-multiplying rectifier. This signal is than filtered to give the final output voltage.

The variable voltage power supply 104 may further include an external circuit having a potential divider in the output stage. The potential divider may enable the output voltage to be measured by providing a reduced voltage output suitable for monitoring, etc. In one embodiment, the reduced voltage output may be compared with the input voltage as a means of controlling the control signal for the power driver stage. For example, the difference between the reduced voltage output and the input voltage may generates an error signal used to control the power through the driver stage into the primary of the transformer.

The variable voltage power supply 104 may be a self- contained integrated circuit component. It may enable a wide range of output voltages to be accurately obtained from a single unit.

The power supply and control system 100 further comprises a display, e.g. a digital LCD screen or the like, which is arranged to shown parameters of interest to the user, e.g. the selected output voltage.

The power supply and control system 100 may be

electrically floating, i.e. not connected to ground. It is preferably isolating from the user by being encased in an insulating housing, e.g. plastic box having dimensions 30x20x13 cm. The insulating housing is preferably waterproof, i.e. having an ingress protection rating of IP65 or IP66. The components of the power supply and control system 100 may be chosen to ensure its operational temperature range is 0°C to +50°C, and that it remains operational up to a relative humidity of 80% for temperatures up to 31°C, decreasing linearly to 50% relative humidity at 40°C.

Fig. 2 is a perspective top view of a electrocution-type insect trap that is an embodiment of the invention. Features of the trap that are discussed above with reference to Fig. 1 are given the same reference number. In this embodiment there are four square electrocution grids 108 arranged to enclose a cube-shaped space, but the invention is not limited to this configuration; the trap can work with a variety of frame sizes as dependent on the user needs.

Two different sizes of trap are contemplated:

(i) where each electrocution grid is 30 cm ^χ 30 cm

(i.e. 900 cm ² ) . This trap is designed to be used by a human host who sits in a chair and places their feet in the trap; and

(ii) where each electrocution grid is 1.2 m ^χ 1.2 m, i.e. 1.44 m ² . This trap is designed to be used to encircle an entire host, either a seated human or an animal that fits within the interior space.

Each electrocution grid 108 comprises an outer frame, e.g. made of PVC or other suitably robust insulating material. This material ensures that the system remains electrically floating, i.e. not connected to ground. Moreover, this material may be waterproof, and thereby protect the electrical connections discussed below from water ingress or atmospheric moisture (e.g. if the trap is used outside) . This can improve battery life.

A series of equally spaced holes are fabricated in the top and bottom arms of the each frame. In a preferred

embodiment, the holes each have a diameter of 1.5 mm and adjacent holes are separated by a 5 mm pitch. The holes in the top and bottom of the frame are preferably aligned to form vertically spaced pairs. Each of the vertically spaced pairs of holes receives a respective grid wire 116. Each grid wire may be made of stainless steel and have a diameter of 1.2 mm. The area defined by the frame is therefore filled with an array of parallel conductive wires. Sixty grid wires are fit into the each frame of the small trap, and 240 grid wires are used in each of the frames of the large trap.

The grid wires 116 are in electrical communication with the power supply 104. The power supply 104 output comprises two polarities. The grid wires are electrically connected to each other so that adjacent grid wires have opposite polarity (so that the output voltage manifests itself as an electric field between all adjacent grid wires) . Thus, adjacent grid wires 116 are not connected to each other, but every

alternative wire is electrically connected. These connections may be made by providing a horizontal conductive connection (e.g. welded rod or solder wiring) at to the top of each frame for the grid wires sharing one polarity, and on the bottom of each frame for the grid wires sharing the opposite polarity. ones. The grid wires 116 may thus be seen as two interlocking sets of fingers having opposite polarity.

To stop adjacent wires short circuiting the power supply, the frames are fitted with horizontal insulating spacers 118, e.g. made from plastic, that hold the grid wires 116 in place. Each small frame is fit with at least one spacer positioned half way down the grid surface. In the large traps, each frame may have at least horizontal three spacers at

equidistant points. The large trap may also have at least one vertical insulating column, e.g. positioned in the middle of the frame, that spans from top to bottom to provide additional structural support.

Holes are drilled along the length of horizontal spacers so that wires going from the top to the bottom of the frame are passed through them. This is done by drilling holes for each wire and inserting wires into the spacer. This

technique ensures that no adjacent wires will touch each other .

The electrocution grids 108 are surrounded on their inner and outer surfaces by an inner shield 114 and an outer shield 112 respectively. The inner shield and outer shield act as physical barriers to prevent accidental touching of the electrified grid wires by the human participant.

In use, a human sits with their legs inside the trapping box which is surrounded by electrocution grids, and the rest of their body is covered in netting which protects them from mosquito bites. The electrocution-type insect trap of the invention is preferably portable, and thus it is desirable for it to have a modular construction. Fig. 3 is a perspective view of the electrocution grids 108 in a partly assembled state. Here it can be seen that a pair of electrocution grids 108 can be pivotally connected along one vertical edge, e.g. using a suitable hinge or hinges, to enable them to be folded flat for transport .

Fig. 4 is a perspective view of the electrocution-type insect trap in a partly assembled state. Here it can be seen that the inner shield 114 and the outer shield 112 comprises separate cages that are assembled from four flat face pieces. Once each cage is assembled it can be moved into position relative to the electrocution grids 108. Although this configuration facilitates transportation of the trap, in other embodiments the shields may be integrally formed with the electrocution grids.

In combination, the current limiting functionality of the variable voltage power supply and the inner and outer shield provide a robust safety precaution against accidental

electrical shocks.

It is also desirable to allow the electrocution grids to discharge, e.g. naturally, before they are handled after use. Ideally the user should wait for 30 seconds after turn off before directly touching the grid surfaces to ensure that all charged components have discharged. In a development of the invention, it may be desirable for the variable voltage power supply to remotely and/or wirelessly controlled, e.g. at ranges of up to 1 km. This may assist in efficient

optimisation of a plurality of traps in a given location if the environment or other circumstances require the output voltage to change.

Results obtained by using a mosquito electrocuting trap (MET) as described above for two species of mosquito,

Anopheles gambiae (AG) and Culex spp. (CS) are presented in Fig. 5 and Table 1.

Unlike previous insect-trapping methods, the data shows that there is no statistical difference between the MET of the present invention and an HLC trap, with regard to their estimates of the proportion of mosquitoes caught indoors (Pi) , the proportion caught during sleeping hours (Po) or the proportion of mosquito bites, occurring indoors, that non- users of bed nets are exposed to (n ₂ ) . The MET of the invention therefore represents a viable exposure-free

alternative to the HLC trap.

Table 1 shows a comparison between MET and HLC for the three mosquito behaviours described above, as analysed using a binomial logistic Generalized Linear Mixed Effect Model, where RR represents the relative risk, and P represents the P-value.

Fig. 5 shows pie charts illustrating the proportions of mosquitoes caught indoors and outdoors (A) , proportions of mosquitoes caught during sleeping hours and outside sleeping hours (B) , and proportion of human exposure to mosquito bites occurring indoors and outdoors as estimated by the HLC and the MET. The white areas represent (for charts (A), and (C) respectively) the proportion of mosquitoes caught outdoors, and the outdoors human exposure. The hatched areas (for charts (A) , and (C) respectively, as shown by the key) represent proportion of mosquitoes caught indoors, and the indoors human exposure. For charts (B) the hatched areas and the dotted areas as shown by the key represent the proportion of mosquitoes caught during sleeping and outside sleeping hours respectively. From the similarity between the two sets of charts, it is clear that the observed behavioural patterns of mosquito biting activity linked with human behaviour are descriptively very similar for MET and HLC .