Ole Skovmand

Background: Despite extensive use of available vector control tools, the burden of malaria and dengue continues to increase throughout sub-Saharan Africa. Gaps in house structures, most especially in eaves and windows, allow vector entry and facilitate indoor vector biting and disease burden. Simple house modification tools that target these structures therefore have the potential to reduce human exposure to bites in the home. This study assessed the performance of Insecticide Treated Screening (ITS) comprising Eave Nets and Window Screens (ITENs & ITWS), incorporated with deltamethrin and piperonyl-butoxide (PBO) in Tanzania. Method: A randomised Latin square (4 X 4) was conducted in four experimental huts built in a semi-field system (SFS). Each hut within each of the chambers of the SFS was covered with a large netting cage to allow recapture of mosquitoes inside and outside of the huts. Four treatment arms were evaluated: 1) new ITS; 2) 12-months naturally-aged ITS; 3) estimated 12 months field-used Olyset® Plus ITNs (Standard-of-Care in Tanzania), and; 4) no treatment. The study was performed for 32 nights using a minimum of 30 mosquitoes per strain per night, that is, a total of 120 (4 x 30) mosquitoes per hut per night. Four laboratory-reared strains were used: transmitters of malaria ( Anopheles arabiensis and An. funestus ) and dengue infection ( Aedes aegypti ) and those known for nuisance biting ( Culex quinquefasciatus ). Recaptured mosquitoes were assessed for mortality at 72 hours (M72), blood feeding and hut entry endpoints. A simulation exercise with a modified mechanistic model tracking Plasmodium falciparum malaria was used to illustrate the potential epidemiological impact from these products. Results: New ITS induced higher M72 than field-used ITNs against all mosquito species tested [OR: 2.25 (95%CI: 1.65-3.06), p<0.0001], while M72 was similar between aged ITS and field-used ITNs [OR: 0.80 (95%CI: 0.59-1.08), p=0.141]. Both new, and aged ITS reduced more mosquito blood feeding and hut entry than field-used ITNs for all mosquito species tested (p<0.0001). Transmission model estimates indicate epidemiological impacts of ITS may supersede those of ITNs at the population level. The model results indicate that the potency of these impacts depends on assumed intervention percentage cover, durability and mosquito bionomics. Conclusions: ITS is an efficacious tool for controlling vectors transmitting malaria, and dengue, and those known for nuisance biting in a semi-field setting. Given the intervention’s simplicity, it should be considered as an additional (or stand-alone) tool alongside behavioural change educational efforts to encourage the repurposing of old ITNs for house screening.

In a recent article in The Lancet, Protopopoff et al. stated that insecticide resistance must be tackled and concluded that adding the insecticide synergist piperonyl butoxide (PBO) to a bed net with a pyrethroid as principal insecticide might be a part of the response. The study in Tanzania compares malaria prevalence between users of two different nets with the principal insecticide permethrin: Olyset and Olyset Plus (Olyset+), the latter also holding the synergist molecule PBO, the first not. The article is based on randomized cluster trial of very high quality, but Olyset+ exposes much more permethrin at the surface so the higher efficacy may not be because of the added PBO. Data published by the World Health Organization (WHO) when evaluating Olyset+ as well of the study of Protopopoff et al. showed that much more permethrin is available on the surface of Olyset+ than on the surface of Olyset and the relatively small and rapidly dwindling dosage of PBO may have nothing to do with the superior effect of Olyset+. The WHO should not change politics for “PBO nets” based on this study alone.

Large ungulates as primary consumers consume variable proportions of herbaceous and woody plants. Recent climate changes modify the herbaceous/woody plant balance. To test their differential effects on ungulate species abundance, we compared large ungulate feeding strategies with climate change patterns, taking the game preferences of local people into account. We analyzed changes in population density of ten species of large ungulates between two census periods (1990–1993 and 1994–1998) in the Niokolo Koba National Park, Senegal. We calculated the cumulative precipitation deficit during the 1989–1997 period. Additionally, we conducted an extensive survey of local people’s game preferences. Results are: 1—in the period 1989–98 all but one year have been drier than the 1940–98 average; 2—this has a cumulative effect on the dryness of the land i.e. produces a water deficit; 3—this pattern favors the growth of woody plants over herbaceous ones; 4—this favors browsers over grazers; 5—grazers are generally preferred by hunters; 6—grazers are therefore disadvantaged both by the drier climate and by preferential hunting; 7—management in the National Park should focus on holding back bush encroachment and encouraging the growth of herbaceous plants.

We studied the effect on malaria incidence, mosquito abundance, net efficacy, net use rate, chemical analysis, and holes of a long lasting insecticide treated bed net (Netprotect) in western Kenya, 2007–2010. Nets were hung in 150 households 6 months before they were hung in a second, 2 km away. Indoor resting densities were monitored by pyrethrum spray catch and malaria cases by passive detection using clinical manifestations and rapid diagnostic test. The probability of findingAn. arabiensisin the control area was 2.6 times higher than that in intervention area during the first 6 months. Human blood feeding index ofAnopheles funestusdeclined 17%. After bed nets were hung in the second area, malaria incidence declined 25% down to the level in the first area. Incidence remained at this low level for 2 years. 90% of collected nets were efficacious after 3-year use. Deltamethrin dosage declined from 1.9 to 0.5 g/kg over 3 years. Attrition rate after 3 years was 21%. WHO hole index changed from 333 to 114 to 381 over the three years. This index summarizes the numbers of holes in size categories and multiplies with the mean hole area per category. It is very sensitive to the impact of big holes in a few nets.

A field test of integrated vector control was conducted in a tropical urban setting with a combination of a floating, slow-release, granular formulation of Bacillus sphaericus and environmental engineering measures (renovation of roads, collective water pumps, and cesspool lids). The targets were Culex quinquefasciatus and Anopheles gambiae in the two biggest towns of Burkina Faso (West Africa). Within the intervention zone, water pumping stations were improved and the surroundings drained to prevent the accumulation of stagnant water. Roads were leveled and given either simple gutters on each side or a concrete channel on one side to drain runoff water. Garbage containers were installed to provide an alternative to the drainage channels for waste disposal. Septic tanks were modified so that they could be emptied without destroying their lid. This study showed that it is possible to implement mosquito control in a tropical urban environment with teams of young people rapidly trained to apply a biological larvicide without any tools other than an iron bar to lift cesspool lids. Environmental improvements were initially costly, but demanded little subsequent expenditure. Local inhabitants' committees were mobilized to provide people with information and monitor the efficacy of the measures. Compared with what people spent individually on mosquito prevention and malaria medicine, these measures were not expensive, but many expected the community to pay for them from existing taxes, e.g., for water treatment and disposal. The necessary funding and logistics require a municipal organization with neighborhood support, if the measures are to be effective.

Bursting strength is a standard method for evaluating mosquito net strength. This article suggests that tension strength with one grab and one hook better represent how holes are generated in bed nets in real life.

Malaria is to-day a tropical disease that especially has major impact in Subsahelian Africa. The current largescale campaign against malaria focuses on better first line use of medication and prevention: (1) the combined use of an Artimisin derivative and one of several synthetic anti-malarials; and (2) the use of insecticidal bednets for transmission prevention, since the disease is transmitted between humans by female mosquitoes. The change from nets that were to be treated and often re-treated to factory pre-treated nets about 7 years ago, made the change from a promising research tool to a major campaign tool. However, once the first line problem of fast disappearance of insecticide treatment was solved, other problems appeared such as physical net durability and low use rate of bednets among people that do not see only the advantages of the nets, but also experience the inconvenience of their use in the daily life. Finally, resistance to insecticides is appearing, probably originating from agricultural use of the same insecticides, but now amplified by the extensive use of insecticides for malaria control. A call for use of common sense and diversified use of insecticides is concluded.

The use of insecticide-treated nets (ITN) is an important tool in the Roll Back Malaria (RBM) strategy. For ITNs to be effective they need to be used correctly. Previous studies have shown that many factors, such as wealth, access to health care, education, ethnicity and gender, determine the ownership and use of ITNs. Some studies showed that free distribution and public awareness campaigns increased the rate of use. However, there have been no evaluations of the short- and long-term impact of such motivation campaigns. A study carried out in a malaria endemic area in south-western Burkina Faso indicated that this increased use declined after several months. The reasons were a combination of the community representation of malaria, the perception of the effectiveness and usefulness of ITNs and also the manner in which households are organized by day and by night.

A floating, slow-release, granular formulation of Bacillus sphaericus (Neide) was used to control mosquito larvae in two suburban areas of two tropic

Insecticide treated bed nets are major tools for the Roll Back Malaria campaign. There are two types of Long-Lasting Insecticide-treated Nets (LNs) on the market: coated nets and insecticide-incorporated nets. Nets provided to this market need a recommendation from the World Health Organization to be purchased by donors and NGOs. During laboratory study (phase I), the first step consists in evaluating the wash resistance of a new LN product. When insecticide-incorporated nets are washed, it takes time to regenerate the insecticidal activity, i.e. insecticide must migrate to the net surface to be accessible to mosquitoes. The interval of time required for regeneration must be carefully determined to ensure the accuracy of further results. WHOPES procedures currently recommend the determination of the regeneration time by using mortality data. However, as mortality cannot exceed 100%, a LN that regenerates a surface concentration exceeding the dosage for 100% mortality, will have its regeneration time underestimated.