Deltamethrin is a highly effective insecticide. It is used, among other applications, for the production of Long-lasting insecticidal nets, which, along with indoor residual spraying, are the main vector control strategies recommended by the World Health Organization for the management of malaria. As such, this insecticide has helped prevent hundreds of millions of cases of malaria globally. Among the other uses of deltamethrin are agricultural use and home pest control. Deltamethrin has been instrumental in preventing the spread of diseases carried by tick-infested prairie dogs, rodents and other burrowing animals. It is helpful in eliminating and preventing a wide variety of household pests, especially spiders, fleas, ticks, carpenter ants, carpenter bees, cockroaches and bed bugs. Deltamethrin is also one of the primary ingredients in ant chalk. Deltamethrin belongs to a group of pesticides called synthetic pyrethroids. This pesticide is toxic to aquatic life, particularly fish, and therefore must be used with extreme caution around water. Although generally considered safe to use around humans, it is still neurotoxic to humans. Deltamethrin is able to pass from a woman's skin through her blood and into her breast milk, although breastfeeding remains safe under prevailing conditions. It is an allergen and causes asthma in some people.
Production
Deltamethrin is a pyrethroid composed of a single stereoisomer, of a possible 8 stereoisomers, selectively prepared by the esterification of - or cis-2,2-dimethyl-3-cyclopropanecarboxylic acid with - or -alpha-cyano-3-phenoxybenzyl alcohol or by selective recrystallization of the racemic esters obtained by esterification of the - or cis-acid with the racemic or - or + or − alcohol.
Malaria control
Deltamethrin plays a key role in controlling malaria vectors, and is used in the manufacture of long-lasting insecticidal mosquito nets. It is used as one of a battery of pyrethroid insecticides in control of malarial vectors, particularly Anopheles gambiae, and whilst being the most employed pyrethroid insecticide, can be used in conjunction with, or as an alternative to, permethrin, cypermethrin and organophosphate-based insecticides, such as malathion and fenthion. Resistance to deltamethrin is now extremely widespread and threatens the success of worldwide vector control programmes.
Resistance to deltamethrin
Resistance has been characterised in several insects, including important vectors of malaria like the mosquito Anopheles gambiae as well as non-disease carrying pests like bed bugs.
Mosquitoes
Methods of resistance include thickening of the cuticle of the insect to limit permeation of the insecticide, metabolic resistance via overexpression of metabolizing cytochrome P450 mono-oxygenases and glutathione-S-transferases, and the knockdown resistancesodium channel mutations which render the action of insecticides ineffectual, even when co-administered with piperonyl butoxide. Characterization of the different forms of resistance among mosquitoes has become a top priority in groups studying tropical medicine due to the high mortality of those who reside in endemic areas.
Bed bugs
Two mutations, the valine to leucine mutation and the leucine to isoleucine mutation in voltage-gated sodium channel α-subunit gene, have been identified as responsible for knockdown resistance to deltamethrin in bed bugs. One study found that 88% of bed bug populations in the US had at least one of the two mutations, if not both, meaning that deltamethrin resistance among bed bugs is currently making this insecticide obsolete.
Poisoning
In humans
Since deltamethrin is a neurotoxin, it temporarily attacks the nervous system of any animal with which it comes into contact. Skin contact can lead to tingling or reddening of the skin local to the application. If taken in through the eyes or mouth, the most common symptom is facial paraesthesia, which can feel like many different abnormal sensations, including burning, partial numbness, "pins and needles", skin crawling, etc. There are no reports indicating that chronic intoxication from pyrethroid insecticides causes motor neuron disease. Recently, in South Africa, residues of deltamethrin were found in breast milk, together with DDT, in an area that used DDT treatment for malaria control, as well as pyrethroids in small-scale agriculture. There are no antidotes, and treatment must be symptomatic, as approved by a physician. Over time, deltamethrin is metabolized, with a rapid loss of toxicity, and passed from the body. A poison control center should be contacted in the event of an accidental poisoning. A 2015 study conducted in Brittany, France found a negative correlation between deltamethrin exposure and cognitive scores in infants.
Cases of toxicity have been observed in cattle following use of agricultural deltamethrin preparation in external application for tick control. It has also commonly known as having severe poisoning effects on the cat which is vulnerable to the pyrethroid.
