4.3 Implications of Pyrethroid Resistance in the Aquatic
Environment
Pyrethroid resistance in the aquatic environment can have far-reaching implications
that are important from a variety of different perspectives (human and animal health,
evolutionary, ecological, and risk assessment). Below we expand on the consequences of pesticide resistance in aquatic ecosystems, with a particular focus on
the effects resulting from pyrethroid resistance driven by nontarget exposures.
4.3.1 Human and Animal Health Implications
Sea lice, mosquitoes, and black flies are disease vectors. Sea lice transfer salmon
anemia (ISA) between fish, apart from contributing to weakened fish immune
function so that infections are more likely [152]. ISA can cause extreme mortality
in heavily affected populations. One analysis estimated the cost of sea lice infestations on global salmon fisheries to be nearly US $335 million per year
[153]. Increased resistance to pyrethroids among sea lice populations may call for
an increased dosage of pyrethroids during bath treatments, potentially to the detriment of the fish on a sublethal level [154, 155].
Mosquitos and black flies transfer disease to humans. In 2016, 445,000 human
mortalities were documented from malaria, mostly in sub-Saharan Africa [156]. An.
gambiae is a primary vector for Plasmodium parasites that transmit malaria to
humans and livestock in Africa [157]. Burkina Faso, Ghana, and Benin, the same
countries in which nontarget pyrethroid exposures are contributing to resistance
[56, 59, 63, 139], are at high risk for malaria, even in urban regions. Thus, nontarget,
aquatic exposures of larval mosquitoes in urban and agricultural areas pose a great
challenge to the WHO, which relies heavily on pyrethroid-treated bed nets for the
prevention of malaria [158]. Bed net failures have already been attributed to pyrethroid resistance in Benin [159]. Further, selection for L1014F kdr mutations from
pyrethroid overuse also confers DDT resistance, decreasing the efficacy of emergency DDT applications to fight malaria. Urban and agricultural overuse of pyrethroids accelerates the development of pyrethroid (and DDT) resistance, which in
turn may increase the risk of contracting malaria.
Black flies act as disease vectors for Onchocerca volvulus – a nematode that
causes onchocerciasis (river blindness) in Africa and Central and South America
[36]. Nearly 1 million people currently suffer from blindness or visual impairment
due to this parasite [160], and resistance gained from agricultural spray drift and
runoff exposures of pyrethroids can potentially render recommended protective
measures, such as permethrin-treated clothing [156], far less protective. Increased
resistance to pyrethroids means that the prevalence of river blindness may increase.
The Ecological and Evolutionary Implications of Pyrethroid Exposure: A New. . .
131
Environment
Pyrethroid resistance in the aquatic environment can have far-reaching implications
that are important from a variety of different perspectives (human and animal health,
evolutionary, ecological, and risk assessment). Below we expand on the consequences of pesticide resistance in aquatic ecosystems, with a particular focus on
the effects resulting from pyrethroid resistance driven by nontarget exposures.
4.3.1 Human and Animal Health Implications
Sea lice, mosquitoes, and black flies are disease vectors. Sea lice transfer salmon
anemia (ISA) between fish, apart from contributing to weakened fish immune
function so that infections are more likely [152]. ISA can cause extreme mortality
in heavily affected populations. One analysis estimated the cost of sea lice infestations on global salmon fisheries to be nearly US $335 million per year
[153]. Increased resistance to pyrethroids among sea lice populations may call for
an increased dosage of pyrethroids during bath treatments, potentially to the detriment of the fish on a sublethal level [154, 155].
Mosquitos and black flies transfer disease to humans. In 2016, 445,000 human
mortalities were documented from malaria, mostly in sub-Saharan Africa [156]. An.
gambiae is a primary vector for Plasmodium parasites that transmit malaria to
humans and livestock in Africa [157]. Burkina Faso, Ghana, and Benin, the same
countries in which nontarget pyrethroid exposures are contributing to resistance
[56, 59, 63, 139], are at high risk for malaria, even in urban regions. Thus, nontarget,
aquatic exposures of larval mosquitoes in urban and agricultural areas pose a great
challenge to the WHO, which relies heavily on pyrethroid-treated bed nets for the
prevention of malaria [158]. Bed net failures have already been attributed to pyrethroid resistance in Benin [159]. Further, selection for L1014F kdr mutations from
pyrethroid overuse also confers DDT resistance, decreasing the efficacy of emergency DDT applications to fight malaria. Urban and agricultural overuse of pyrethroids accelerates the development of pyrethroid (and DDT) resistance, which in
turn may increase the risk of contracting malaria.
Black flies act as disease vectors for Onchocerca volvulus – a nematode that
causes onchocerciasis (river blindness) in Africa and Central and South America
[36]. Nearly 1 million people currently suffer from blindness or visual impairment
due to this parasite [160], and resistance gained from agricultural spray drift and
runoff exposures of pyrethroids can potentially render recommended protective
measures, such as permethrin-treated clothing [156], far less protective. Increased
resistance to pyrethroids means that the prevalence of river blindness may increase.
The Ecological and Evolutionary Implications of Pyrethroid Exposure: A New. . .
131