Abstract:
Mosquito bed net assembly  10   a - h  includes a mosquito bed net ( 12 ) impregnated with a first insecticide and a barrier member  16   a - h  located above an upper surface ( 14 ) of the bed net ( 12 ) and being impregnated with a second insecticide. In use, bed net assembly  16   a - h  increases the likelihood of delivering a lethal dosage of insecticide to mosquitoes flying in frequently-visited areas of a bed net, without increased attendant health risk to a user.

Description:
[0001]    The present invention relates to a mosquito bed net assembly. More specifically, the invention relates to a mosquito bed net assembly in which the bed net is a box net. 
       BACKGROUND OF THE INVENTION 
       [0002]    Insecticide treated bed nets (ITNs) are one of the most effective tools available for the prevention of malaria. Not only have ITNs proved successful in protecting those who sleep directly underneath them, but widespread use of ITNs has been shown to reduce infection rates in the wider community, including those sleeping without nets. 
         [0003]    The current generation of bed nets, termed long-lasting insecticidal nets (LLINs), remain central to malaria control and elimination in Africa where indoor transmission of malaria is of major significance. However, resistance to pyrethroids, currently the only class of insecticides approved for use on LLINs, is emerging at an alarming rate in  Anopheles gambiae  sensu stricto, the main indoor-biting vector of malaria in Africa, and the species most effectively targeted by LLINs. Accordingly, this resistance to currently-employed bed net insecticides represents a considerable threat for future malaria control. If, therefore, LLINs are to remain central to malaria prevention, new designs or approaches are urgently needed. 
         [0004]    The present invention was devised with the foregoing in mind. 
       SUMMARY OF THE INVENTION 
       [0005]    According to a first aspect of the present invention there is provided a mosquito bed net assembly comprising a mosquito bed net and a barrier member disposed above an upper portion of the bed net, wherein the bed net comprises a first insecticide and the barrier member comprises a second insecticide. The inventor has surprisingly found that for human-baited bed nets (i.e. those bed nets having a prone human beneath) the upper portion of the net, particularly the area directly above a prone human, is the area most visited by mosquitoes intent on feeding. At least one rationale for such a concentration of mosquito activity is the combined effect of bodily stimuli, such as heat and odour, emanating from the human below, which are channelled by the walls of the bed net to a focal point on its upper surface. For LLINs treated with approved pyrethroids, feeding mosquitoes have been demonstrated to adopt oscillating flight paths in the region above the bed net, whether or not they eventually make contact with the treated surface. Other studies have shown that those mosquitoes that do make contact with the upper treated surface of the bed net often go on to make further contacts therewith in a bouncing or hopping manner. The barrier member forming part of the present bed net assembly markedly increases the likelihood of such oscillating and bouncing mosquitoes coming into more frequent contact with an insecticide-treated surface. Additionally, the barrier member forming part of the present invention is located above, and therefore outside, the treated bed net meaning that it is unlikely, if not impossible, for it to come into contact with a human sleeping thereunder. As a consequence, insecticidal alternatives to pyrethroids may be applied to the barrier member, thereby increasing the likelihood of killing mosquitoes that have developed some resistance to pyrethroids. Suitably, the bed net is impregnated with the first insecticide and the barrier member is impregnated with the second insecticide. 
         [0006]    In an embodiment, the first and second insecticides are the same. In view of the observed mosquito flying characteristics, the bed net assembly of the present invention is configured so as to increase the frequency of mosquito-bed net collisions, thereby increasing the likelihood of delivering a fatal dose of a single insecticide. The single insecticide may be any insecticide currently, or eventually, approved by the World Health Organisation Pesticide Evaluation Scheme (WHOPES) for use with LLINs. 
         [0007]    Suitably, the first and second insecticides are different. 
         [0008]    In an embodiment, the first insecticide comprises at least one pyrethroid insecticide. At present, pyrethroids are the only class of insecticides approved by the World Health Organisation Pesticide Evaluation Scheme (WHOPES) for use with LLINs. 
         [0009]    In another embodiment, the second insecticide comprises at least one non-pyrethroid insecticide. The barrier member forming part of the present invention is located above the bed net, such that it is sufficiently distant from a human sleeping thereunder. As a consequence, the barrier member may be impregnated with other, preferably more effective non-pyrethroid insecticides, whose use on standard LLINs would otherwise be barred under the regulations imposed by WHOPES. Optionally, the second insecticide may comprise at least one pyrethroid insecticide in combination with at least one non-pyrethroid insecticide. 
         [0010]    Suitably, the upper portion is defined by an upper surface of the net bed. 
         [0011]    In an embodiment, the barrier member is formed from netted, meshed or webbed fabric. For the sake of cost and ease of manufacturing, the barrier member may be made from the same material as the bed net itself. Alternatively, the barrier member may be made from a more, or less, porous material, which may be partially or wholly stiffened depending on the specific form of the barrier member, and the availability of any overhead suspending means. In an embodiment, the bed net assembly is made from polyester. 
         [0012]    In another embodiment, at least a portion of the barrier member is attached to the upper surface of the bed net. The barrier member forming part of the present invention may therefore be integrally formed with the bed net. Suitably, the barrier member is attached to the upper surface by stitching, gluing or any other known attachment means. 
         [0013]    In a further embodiment, at least a portion of the barrier member is suspendable from above the upper surface of the bed net. Depending on the location in which the bed net assembly is to be used, the barrier member, or at least part of it, may be configured so as to be suspendable from above, such as from a ceiling or other overhead object, such that the barrier member is not itself in contact, or in intimate contact, with the bed net. Alternatively, the barrier member may be formed integrally with the bed net, whilst at the same time being configured so as to be suspendable, or partially suspendable, from above. 
         [0014]    Suitably, the barrier member extends substantially perpendicularly to the upper surface of the bed net. The barrier member forming part of the present invention may be configured so as to project upwardly from the plane defined by the bed net&#39;s upper surface. Such a configuration is particularly effective at intercepting such oscillating and low-flying mosquitoes, and delivering to them a fatal dose of an insecticide. 
         [0015]    In an embodiment, the barrier member comprises a first upstanding planar sheet. The barrier member may be a simple rectangular sheet whose bottom edge is associated with the upper surface of the bed net. 
         [0016]    In another embodiment, the first planar sheet extends longitudinally along at least a portion of the length of the bed net. The barrier member may extend along the length of the bed net. Suitably, the longitudinally-extending barrier member is disposed at a substantially medium point along the width of the upper surface of the bed net. More suitably, the first planar sheet extends along the entire length of the bed net. 
         [0017]    In another embodiment, the first planar sheet extends laterally along at least a portion of the width of the bed net. The barrier member may extend along the width of the bed net. Suitably, the laterally-extending barrier member is disposed at a substantially medium point along the length of the upper surface of the bed net. More suitably, the first planar sheet extends along the entire width of the bed net. Optionally, the laterally-extending barrier member is disposed approximately one third along the length of the upper surface of the bed net, such that it lies substantially over the chest area of a sleeping human. 
         [0018]    In a further embodiment, the barrier member further comprises a second upstanding planar sheet, wherein the second planar sheet intersects and is perpendicular to the first planar sheet. The barrier member may therefore be formed from intersecting lateral and longitudinal planar sheets, thereby presenting further surfaces for contact with hostseeking mosquitoes. 
         [0019]    In a further embodiment, the barrier member is conical, frustoconical or cylindrical. Suitably, the barrier member is centrally located on the upper surface of the bed net. Optionally, the barrier member is disposed approximately one third along the length of the upper surface of the bed net, such that it lies substantially over the chest area of a sleeping human. The base of the conical, frustoconical or cylindrical barrier member may define an opening in the upper surface of the bed net, thereby increasing the surface area of the upper surface at the point where bodily stimuli are believed to be most concentrated. Alternatively, where the upper surface of the bed net is unbroken, the conical, frustoconical or cylindrical barrier member may comprise one or more mosquito opening, thereby increasing the likelihood of mosquitoes becoming trapped within the barrier member where they can receive a lethal dose of insecticide. Optionally, the one or more openings define an opening to an internal passage provided within the barrier member. Optionally the internal passage is tapered towards the upper surface. Optionally, only an inner surface of the barrier member comprises the non-pyrethroid insecticide. 
         [0020]    In another embodiment, the barrier member is disposed substantially co-planar to the upper surface of the bed net. Such a configuration is particularly effective at intercepting oscillating and low-flying mosquitoes, and delivering to them a fatal dose of an insecticide. 
         [0021]    Suitably, the barrier member extends across substantially the same area as the upper surface of the bed net. Accordingly, the barrier member may be of substantially identical dimensions to the upper surface of the bed net, such that it may be viewed as a second upper surface. More suitably, the barrier member may be spaced above the upper surface of the bed net by supporting means disposed at its corners. 
         [0022]    More suitably, the barrier member further comprises a mosquito opening, permitting mosquito access to the space beneath the barrier member. Incoming mosquitoes pass through the barrier member&#39;s opening and contact the upper surface of the bed net. Those which go on to exhibit low-flying characteristics become sandwiched between the bed net&#39;s upper surface and the co-planar barrier member, thereby restricting the mosquitoes&#39; freedom of movement and hence increasing the likelihood of receiving a fatal dose of insecticide. The opening may be centrally-located on the upper surface, or in another region where bodily stimuli are believed to be at their most concentrated. 
         [0023]    In an embodiment, the co-planar barrier member is disposed above the upper surface at a distance of between 0.5 and 10 cm. The narrow gap between the bed net&#39;s upper surface and the barrier member increases the likelihood of delivering a fatal dose of insecticide. Suitably, the edges of the barrier member do not form a closed structure with the respective side walls of the bed net. Accordingly, the upper surface of the bed net is accessible to a user to enable dead mosquitoes to be easily removed by sweeping, blowing or vacuuming. 
         [0024]    In another embodiment, the co-planar barrier member has a top surface and a bottom surface. Suitably, both the top and bottom surfaces are impregnated with the second insecticide. More suitably, only the bottom surface is so impregnated. Such a configuration reduces the risk of human contact with the insecticide. 
         [0025]    In yet another embodiment, the barrier member further comprises stiffening means. Stiffening means may be used in order that the barrier member retains its structure and orientation in use. The stiffening means may be disposed around the edges of the barrier member, as a frame. Alternatively, the stiffening means may be located at regular, or irregular, intervals along the length or width of the barrier member. Suitable stiffening means include ribs, rigid strips, wire frames, wire mesh or support posts. 
         [0026]    In a further embodiment, the first insecticide comprises at least one insecticide selected from the group consisting of allethrin, bifenthrin, cyfluthrin, cypermethrin, cyphenothrin, deltamethrin, esfenvalerate, etofenprox, fenpropathrin, fenvalerate, flucythrinate, flumethrin, imiprothrin, lambda-cyhalothrin, methofluthrin, permethrin, prallethrin, resmethrin, silafluofen, sumithrin, tau-fluvalinate, tefluthrin, tetramethrin, tralomethrin, transfluthrin and pyriproxyfen. At present, pyrethroids are the only class of insecticides approved by the World Health Organisation Pesticide Evaluation Scheme (WHOPES) for use with LLINs, although other, non-pyrethroid insecticides are currently being tested for their suitability. 
         [0027]    In another embodiment, the second insecticide comprises at least one insecticide selected from the group consisting of organophosphates, carbamates, pyrroles, hormone mimics and biological insecticides. In use, the barrier member comprising the second insecticide is sufficiently distant from the user such that more potent, non-pyrethroid insecticides can be used. Suitably, the second insecticide comprises at least one insecticide selected from the group consisting of pirimiphos methyl, propoxur, bendiocarb, indoxycarb, chlorphenapyr, pyriproxyfen, methoprene,  Bacillus thuringiensis  israelensis and entomopathogenic fungi. 
         [0028]    In still another embodiment, the first insecticide further comprises a synergist. When the bed net assembly of the present invention is to be used in those areas where mosquitoes have developed, or are developing, resistance to pyrethroid-type insecticides, a synergist may be used in combination with the first insecticide in order to restore its efficacy. Suitably, the synergist is piperonyl butoxide. 
         [0029]    In a further embodiment, the bed net is a box net. Box nets are among the most common types of mosquito bed net is use and generally take the form of a rectangular box. The flat, upper surface of the box net provides an ideal site on which to locate the barrier member forming part of the present invention. 
         [0030]    According to a second aspect of the present invention, there is provided a kit comprising:
       a. a mosquito bed net, and   b. a barrier member disposed above an upper portion of the bed net, wherein the bed net comprises a first insecticide and the barrier member comprises a second insecticide.       
 
         [0033]    According to a third aspect of the present invention, there is provided a barrier member as herein defined, the barrier member being configured to be associated with an upper portion of a mosquito bed net. 
         [0034]    It will be appreciated that the barrier member may be identical in form any of the barrier members forming part of any of the mosquito bed net assemblies described herein. It will also be appreciated that the barrier member may comprise any insecticide discussed hereinbefore in respect of the barrier members forming part of the mosquito bed net assemblies. 
         [0035]    In one embodiment, the barrier member is configured to be attached to an upper portion of a mosquito bed net. 
     
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
         [0036]    One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures, in which: 
           [0037]      FIG. 1  is a view from the front, one side, and above of one embodiment of the present invention. 
           [0038]      FIG. 2  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0039]      FIG. 3  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0040]      FIG. 4  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0041]      FIG. 5  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0042]      FIG. 6  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0043]      FIG. 7  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0044]      FIG. 8  is a view from the front, one side, and above of another embodiment of the present invention. 
           [0045]      FIG. 9  shows an example of the frequency of mosquito-net contacts at various points on both insecticide-treated bed nets and untreated bed nets. 
           [0046]      FIG. 10  shows an example of the flight path of multiple mosquitoes over a human-baited bed net. 
           [0047]      FIG. 11  shows an example of the flight path of a single mosquito over a human-baited bed net. 
       
    
    
       [0048]    A mosquito bed net assembly  10   a - h  includes a mosquito bed “box net”  12  impregnated with a pyrethroid insecticide and having a top surface  14 , and a barrier member  16   a - h  impregnated with a non-pyrethroid insecticide and disposed above top surface  14 . 
         [0049]    Referring to  FIG. 1 , barrier member  16   a  is formed from a rectangular planar sheet of netted material, attached to top surface  14  via its lower edge  18  and extending upwardly in a direction perpendicular to top surface  14 . Barrier member  16   a  is located at a middle point along the length of top surface  14 , and extends across its entire width. Barrier member  16   a  is attachable at uppermost corners  20   a,b  to a ceiling or other overhead object. 
         [0050]    Referring to  FIG. 2 , barrier member  16   b  is formed from a rectangular planar sheet of netted material, attached to top surface  14  via its lower edge  22  and extending upwardly in a direction perpendicular to top surface  14 . Barrier member  16   b  is located at a middle point along the width of top surface  14 , and extends across its entire length. Barrier member  16   b  is attachable at uppermost corners  24   a,b  to a ceiling or an overhead object. 
         [0051]    Referring to  FIG. 3 , barrier member  16   c  is formed from first and second rectangular planar sheets  26 ,  28  of netted material, attached to top surface  14  via their lower edge  32  and extending upwardly in a direction perpendicular to top surface  14 . First planar sheet  26  is located at a middle point along the width of top surface  14 , and extends across its entire length. Second planar sheet  28  is located at a middle point along the length of top surface  14 , and extends across its entire width, such that first and second planar sheets  26 ,  28  are arranged perpendicular to one another and intersect one another at a middle point  34  along their lengths. Barrier member  16   c  is attachable at uppermost corners  30   a - d  to a ceiling or other overhead object. 
         [0052]    Referring to  FIG. 4 , cylindrical barrier member  16   d  is formed from stiffened netted material and includes a cylindrical outer wall  38 , extending upwardly from upper surface  14 , and a top wall  40  lying in the same plane as upper surface  14 . Barrier member  16   d  is centrally located on upper surface  14  and is attached thereto via its lower edge  42 . Barrier member  16   d  is open at its bottom face, defining an opening  44  in the upper surface  14 . 
         [0053]    Referring to  FIG. 5 , cylindrical barrier member  16   e  is formed from stiffened netted material having a cylindrical outer wall  46  extending upwardly from upper surface  14 , a top wall  48  lying in the same plane as upper surface  14 , and a bottom wall defined by upper surface  14 . Barrier member  16   e  is centrally located on upper surface  14  and is attached thereto via its lower edge  50 . Only the innermost surfaces of outer wall  46  and top wall  48  are impregnated with the non-pyrethroid insecticide. A plurality of openings  52  are disposed at regular intervals around cylindrical outer wall  46 . Top wall  48  also includes a centrally-disposed opening  54 . Openings  52 ,  54  act as entrance points for mosquitoes. 
         [0054]    Referring to  FIG. 6 , frustoconical barrier member  16   f  is formed from stiffened netted material having a conical outer wall  56  extending generally upwardly from upper surface  14 , a bottom wall defined by upper surface  14 , and an upper edge  58  defining an opening  60  Barrier member  16   f  is centrally located on upper surface  14  and is attached thereto by its lower edge  62 . Only the innermost surface of outer wall  56  is impregnated with the non-pyrethroid insecticide. Opening  60  acts as an entrance point for mosquitoes. 
         [0055]    Referring to  FIG. 7 , cylindrical barrier member  16   g  is formed from stiffened netted material having a cylindrical outer wall  64  extending upwardly from upper surface  14 , a top wall  66  lying in the same plane as upper surface  14 , and a bottom wall defined by upper surface  14 . Barrier member  16   g  is centrally located on upper surface  14  and is attached thereto by its lower edge  68 . Only the innermost surfaces of outer wall  64  and top wall  66  are impregnated with the non-pyrethroid insecticide. Top wall  66  includes a centrally disposed opening  70 , acting as an entrance point for mosquitoes. 
         [0056]    Referring to  FIG. 8 , barrier member  16   h  is formed from a rectangular planar sheet of netted material arranged to lie above, and in an identical plane to, upper surface  14 , and spaced apart therefrom at a distance of approximately 2-3 cm. Barrier member  16   h  is of identical dimensions to upper surface  14 , and is held apart therefrom by vertical support posts  72   a - d  extending between the respective four corners of barrier member  16   h  and upper surface  14 . Barrier member  16   h  also includes a centrally disposed circular opening  74 , approximately 30-40 cm in diameter, acting as an entrance point for mosquitoes The distance between upper surface  14  and barrier member  16   h  is maintained in the region of opening  74  by a plurality of vertical support posts  76  extending between the edge of opening  74  and upper surface  14 . Only the underside surface of barrier member  16   h  is impregnated with the non-pyrethroid insecticide. 
         [0057]    In use, and referring to  FIG. 9 , mosquito bed net assembly  10   a - h  addresses the findings that for human-baited bed nets, the upper portion of the net, particularly the area directly above a prone human, is the area most visited by mosquitoes intent on feeding. 
         [0058]    Referring to  FIG. 10 , an experiment conducted in total darkness using IR lighting and IR-sensitive cameras demonstrates the flight path of 25 female  Anopheles gambiae  mosquitoes over a standard, human-baited bed bet.  FIG. 9  clearly shows a density of mosquito activity on the upper surface of the bed net, particularly in a central portion, with little to no activity occurring at the side walls.  FIG. 9  further demonstrates mosquitoes&#39; tendency to adopt oscillating flight paths within this densely populated region. By virtue of barrier member  16 , which comprises a non-pyrethroid, and therefore comparatively more potent, insecticide, mosquito bed net assembly  10   a - h , in particular bed net assembly  10   a - g , provides improved protection against those mosquitoes having a tendency to adopt such oscillating flight paths over the upper surface of the bed net. Barrier member  16  is therefore ideally located to maximize contacts with such mosquitoes and deliver to them a lethal dose of insecticide. 
         [0059]    Referring to  FIG. 11 , other experiments conducted in total darkness using IR lighting and IR-sensitive cameras demonstrate the tendency of  Anopheles gambiae  mosquitoes to exhibit low-flying trajectories over the upper surface of a standard, human-baited bed net, often making frequent contact with the upper surface. By virtue of barrier member  16 , which comprises a non-pyrethroid, and therefore comparatively more potent, insecticide, mosquito bed net assembly  10   a - h , in particular bed net assembly  10   h , provides improved protection against those mosquitoes having a tendency to adopt these so-called “bouncing” flight trajectories over the upper surface of the bed net. Barrier member  16   a - h , in particular barrier member  16   h , is therefore ideally located to maximize contacts with such bouncing mosquitoes and deliver to them a lethal dose of insecticide. 
         [0060]    The improved mosquito-killing efficacy of bed net assembly  10   a - h  does not compromise the health of a user, since when using mosquito bed net assembly  10   a - h , a user is protected from non-pyrethroid-containing barrier member  16   a - h  by upper surface  14  of box net  12 . Accordingly, bed net assembly  10   a - h  adheres to the stringent requirements imposed by WHOPES, yet offers markedly improved mosquito killing potential. 
         [0061]    After using bed net assembly  10   a - h , a user simply removes dead mosquitoes from upper surface  14  by known means, including brushing, blowing or vacuuming. 
         [0062]    While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, barrier member  16   a - h , which has been described as being formed from netted material, may equally be formed from other meshed or webbed fabrics. Whilst barrier member  16   a - g  has been described as being attached to upper surface  14  via its lower edge, it is equally envisagable that barrier member  16   a - g  be suspended entirely from a ceiling or other overhead object, without therefore making intimate contact with upper surface  14 . Similarly, barrier member  16   a,b , which has been described as having portions attachable to a ceiling or other overhead object, may equally comprise one or more rigid support member so as to render it free-standing. Moreover, the positions of barrier member  16   a - g  on upper surface  14 , or its general shape, may vary depending on the flight trajectory tendencies of the surrounding mosquitoes. For example, barrier member  16  may be located in the region approximately one third along the length of upper surface  14 , such that it is provided substantially above the chest of a user.