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The Cochrane Database of Systematic... Jan 2022Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are used to prevent malaria transmission. Both interventions use insecticides to kill mosquitoes that... (Review)
Review
BACKGROUND
Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are used to prevent malaria transmission. Both interventions use insecticides to kill mosquitoes that bite and rest indoors. Adding IRS to ITNs may improve malaria control simply because two interventions can be better than one. Furthermore, IRS may improve malaria control where ITNs are failing due to insecticide resistance. Pyrethroid insecticides are the predominant class of insecticide used for ITNs, as they are more safe than other insecticide classes when in prolonged contact with human skin. While many mosquito populations have developed some resistance to pyrethroid insecticides, a wider range of insecticides can be used for IRS. This review is an update of the previous Cochrane 2019 edition.
OBJECTIVES
To summarize the effect on malaria of additionally implementing IRS, using non-pyrethroid-like or pyrethroid-like insecticides, in communities currently using ITNs.
SEARCH METHODS
We searched the Cochrane Infectious Diseases Group Specialized Register; CENTRAL; MEDLINE; and five other databases for records from 1 January 2000 to 8 November 2021, on the basis that ITN programmes did not begin to be implemented as policy before the year 2000.
SELECTION CRITERIA
We included cluster-randomized controlled trials (cRCTs), interrupted time series (ITS), or controlled before-after studies (CBAs) comparing IRS plus ITNs with ITNs alone. We included studies with at least 50% ITN ownership (defined as the proportion of households owning one or more ITN) in both study arms.
DATA COLLECTION AND ANALYSIS
Two review authors independently assessed studies for eligibility, analyzed risk of bias, and extracted data. We used risk ratio (RR) and 95% confidence intervals (CI). We stratified by type of insecticide, 'pyrethroid-like' and 'non-pyrethroid-like'; the latter could improve malaria control better than adding IRS insecticides that have the same way of working as the insecticide on ITNs ('pyrethroid-like'). We used subgroup analysis of ITN usage in the studies to explore heterogeneity. We assessed the certainty of evidence using the GRADE approach.
MAIN RESULTS
Eight cRCTs (10 comparisons), one CBA, and one ITS study, all conducted since 2008 in sub-Saharan Africa, met our inclusion criteria. The primary vectors in all sites were mosquitoes belonging to the Anopheles gambiae s.l. complex species; five studies in Benin, Mozambique, Ghana, Sudan, and Tanzania also reported the vector Anopheles funestus. Five cRCTs and both quasi-experimental design studies used insecticides with targets different to pyrethroids (two used bendiocarb, three used pirimiphos-methyl, and one used propoxur. Each of these studies were conducted in areas where the vectors were described as resistant or highly resistant to pyrethroids. Two cRCTs used dichloro-diphenyl-trichlorethane (DDT), an insecticide with the same target as pyrethroids. The remaining cRCT used both types of insecticide (pyrethroid deltamethrin in the first year, switching to bendiocarb for the second year). Indoor residual spraying using 'non-pyrethroid-like' insecticides Six studies were included (four cRCTs, one CBA, and one ITS). Our main analysis for prevalence excluded a study at high risk of bias due to repeated sampling of the same population. This risk did not apply to other outcomes. Overall, the addition of IRS reduced malaria parasite prevalence (RR 0.61, 95% CI 0.42 to 0.88; 4 cRCTs, 16,394 participants; high-certainty evidence). IRS may also reduce malaria incidence on average (rate ratio 0.86, 95% CI 0.61 to 1.23; 4 cRCTs, 323,631 child-years; low-certainty evidence) but the effect was absent in two studies. Subgroup analyses did not explain the qualitative heterogeneity between studies. One cRCT reported no effect on malaria incidence or parasite prevalence in the first year, when a pyrethroid-like insecticide was used for IRS, but showed an effect on both outcomes in the second year, when a non-pyrethroid-like IRS was used. The addition of IRS may also reduce anaemia prevalence (RR 0.71, 95% CI 0.38 to 1.31; 3 cRCTs, 4288 participants; low-certainty evidence). Four cRCTs reported the impact of IRS on entomological inoculation rate (EIR), with variable results; overall, we do not know if IRS had any effect on the EIR in communities using ITNs (very low-certainty evidence). Studies also reported the adult mosquito density and the sporozoite rate, but we could not summarize or pool these entomological outcomes due to differences in the reported data. Three studies measured the prevalence of pyrethroid resistance before and after IRS being introduced: there was no difference detected, but these data are limited. Indoor residual spraying using 'pyrethroid-like' insecticides Adding IRS using a pyrethroid-like insecticide did not appear to markedly alter malaria incidence (rate ratio 1.07, 95% CI 0.80 to 1.43; 2 cRCTs, 15,717 child-years; moderate-certainty evidence), parasite prevalence (RR 1.11, 95% CI 0.86 to 1.44; 3 cRCTs, 10,820 participants; moderate-certainty evidence), or anaemia prevalence (RR 1.12, 95% CI 0.89 to 1.40; 1 cRCT, 4186 participants; low-certainty evidence). Data on EIR were limited so no conclusion was made (very low-certainty evidence).
AUTHORS' CONCLUSIONS
in communities using ITNs, the addition of IRS with 'non-pyrethroid-like' insecticides was associated with reduced malaria prevalence. Malaria incidence may also be reduced on average, but there was unexplained qualitative heterogeneity, and the effect may therefore not be observed in all settings. When using 'pyrethroid-like' insecticides, there was no detectable additional benefit of IRS in communities using ITNs.
Topics: Adult; Animals; Humans; Insecticide-Treated Bednets; Insecticides; Malaria; Mosquito Control; Mosquito Vectors; Tanzania
PubMed: 35038163
DOI: 10.1002/14651858.CD012688.pub3 -
Malaria Journal Jul 2020While Iran is on the path to eliminating malaria, the disease with 4.9 million estimated cases and 9300 estimated deaths in 2018 remains a serious health problem in the...
BACKGROUND
While Iran is on the path to eliminating malaria, the disease with 4.9 million estimated cases and 9300 estimated deaths in 2018 remains a serious health problem in the World Health Organization (WHO) Eastern Mediterranean Region. Anopheles stephensi is the main malaria vector in Iran and its range extends from Iraq to western China. Recently, the vector invaded new territories in Sri Lanka and countries in the Horn of Africa. Insecticide resistance in An. stephensi is a potential issue in controlling the spread of this vector.
METHODS
Data were collated from national and international databases, including PubMed, Google Scholar, Scopus, ScienceDirect, SID, and IranMedex using appropriate search terms.
RESULTS
Indoor residual spaying (IRS) with DDT was piloted in Iran in 1945 and subsequently used in the malaria eradication programme. Resistance to DDT in An. stephensi was detected in Iran, Iraq, Pakistan, and Saudi Arabia in the late 1960s. Malathion was used for malaria control in Iran in 1967, then propoxur in 1978, followed by pirimiphos-methyl from 1992 to 1994. The pyrethroid insecticide lambda-cyhalothrin was used from 1994 to 2003 followed by deltamethrin IRS and long-lasting insecticidal nets (LLINs). Some of these insecticides with the same sequence were used in other malaria-endemic countries of the region. Pyrethroid resistance was detected in An. stephensi in Afghanistan in 2010, in 2011 in India and in 2012 in Iran. The newly invaded population of An. stephensi in Ethiopia was resistant to insecticides of all four major insecticide classes. Different mechanisms of insecticide resistance, including metabolic and insecticide target site insensitivity, have been developed in An. stephensi. Resistance to DDT was initially glutathione S-transferase based. Target site knockdown resistance was later selected by pyrethroids. Esterases and altered acetylcholinesterase are the underlying cause of organophosphate resistance and cytochrome p450s were involved in pyrethroid metabolic resistance.
CONCLUSIONS
Anopheles stephensi is a major malaria vector in Iran and many countries in the region and beyond. The species is leading in terms of development of insecticide resistance as well as developing a variety of resistance mechanisms. Knowledge of the evolution of insecticide resistance and their underlying mechanisms, in particular, are important to Iran, considering the final steps the country is taking towards malaria elimination, but also to other countries in the region for their battle against malaria. This systematic review may also be of value to countries and territories newly invaded by this species, especially in the Horn of Africa, where the malaria situation is already dire.
Topics: Africa, Northern; Animals; Anopheles; Asia; Biological Evolution; Evolution, Molecular; Insecticide Resistance; Insecticides; Middle East
PubMed: 32680514
DOI: 10.1186/s12936-020-03335-0