Loss of protection with insecticide-treated nets against pyrethroid-resistant Culex quinquefasciatus mosquitoes once nets become holed: an experimental hut study

Abstract

Background: An important advantage of pyrethroid-treated nets over untreated nets is that once nets become worn or holed a pyrethroid treatment will normally restore protection. The capacity of pyrethroids to kill or irritate any mosquito that comes into contact with the net and prevent penetration of holes or feeding through the sides are the main reasons why treated nets continue to provide protection despite their condition deteriorating over time. Pyrethroid resistance is a growing problem among Anopheline and Culicine mosquitoes in many parts of Africa. When mosquitoes become resistant the capacity of treated nets to provide protection might be diminished, particularly when holed. An experimental hut trial against pyrethroid-resistant Culex quinquefasciatus was therefore undertaken in southern Benin using a series of intact and holed nets, both untreated and treated, to assess any loss of protection as nets deteriorate with use and time.

DDT and pyrethroid resistance status and laboratory evaluation of bio-efficacy of long lasting insecticide treated nets against Culex quinquefasciatus and Culex decens in Ghana

“…Therefore, reduced efficacy of the LLIN against pyrethroid resistant Culex populations observed in this study is worrying. Reduced efficacy of LLIN against C. quinquefasciatus was expected and it is in agreement with other studies carried out in other countries (Ngufor et al, 2014;Irish et al, 2008). However, there is no record on the efficacy of LLIN against pyrethroidresistant C. decens.…”

Physical Durability of Two Types of Long-Lasting Insecticidal Nets (LLINs) Three Years After a Mass LLIN Distribution Campaign in Mozambique, 2008–2011

“…Although we were able to quantify the physical durability of the LLINs after 3 years of follow-up, the degree to which the physical damage of an LLIN impacts its ability to protect the individuals sleeping under it from a malaria-infected mosquito is not well understood. 13,23,24,[28][29][30][31][32][33] The pHI, which provides a standardized measure to compare holes among different LLINs by assigning a weight, which is the midpoint diameter to an estimated hole size, 8,[10][11][12][13]23,34 confirmed differences in durability between these two major brands of LLINs. It would seem obvious that very large holes, such as those 25 cm, would easily allow for a mosquito to enter an LLIN.…”

“…Studies assessing mosquito penetration through different sizes of LLIN holes are necessary to better understand our findings and when LLINs should be replaced if they are to provide protection against malaria. Finally, the effect of the LLIN coverage at the community level on individual protection for persons sleeping under an intact versus damaged LLIN 35 and vector susceptibility 24,31,33 may need to be considered.…”

Insecticidal, acaricidal and repellent effects of DEET- and IR3535-impregnated bed nets using a novel long-lasting polymer-coating technique

“…One new approach aiming at optimisation of antimalarial measures, especially in the light of pyrethroid resistances and damaged netting, can be the development of long-lasting repellent-treated nets (LLRTNs) using highly effective synthetic and/or natural skin repellents (N'Guessan et al 2006;Irish et al 2008). To date, three methods for insecticidebased bed net and fabric impregnation have been devised:…”