Mosquitoes in the Emirates are becoming resistant to a key insecticide, according to researchers at UAE University in Al Ain.
The research, published in Nature Scientific Reports, was funded by UAE University and carried out in collaboration with Abu Dhabi Public Health Centre. It suggested mosquitoes are becoming immune to the effects of the insecticide known as deltamethrin.
Mosquitoes transmit a variety of deadly diseases, including malaria, which kills about 600,000 people a year, the World Health Organisation has said.
The study, by researchers including postgraduate student Amgd Sayed Ali and co-ordinated by Mohammad Al Deeb, professor of entomology in the university's biology department, involved collecting egg clusters and rearing mosquitoes in a laboratory. DNA was extracted and analysed from 174 adult mosquitoes.
Prof Al Deeb said he and his co-researchers had been “curious about whether resistance had developed” given the long-term use of insecticides in the region.
“Our findings aligned with our expectations, as continuous insecticide exposure tends to exert evolutionary pressure on mosquito populations, leading to resistance,” Prof Al Deeb said. “Resistance means that mosquitoes can no longer be effectively controlled using certain insecticides, leading to increased mosquito populations and a higher risk of disease transmission.
“If resistance spreads across multiple insecticide classes, it can severely limit available control options, making disease outbreaks more difficult to prevent.”
Genetic mutation gives resistance
Analysing the southern house mosquito, or Culex quinquefasciatus, which does not cause illness in the UAE but in other countries spreads a potentially fatal disease called West Nile fever, the scientists found significant levels of resistance.
More than a quarter of mosquitoes grown from eggs collected from coastal sites in Abu Dhabi had two copies of a gene mutation conferring resistance to deltamethrin. At sampling sites near the Omani border, 14.3 per cent of mosquitoes had two copies of the resistance mutation, while at inland sites the figure was 6.3 per cent. Across all locations, 18.4 per cent of the mosquitoes analysed had two copies of the resistance mutation.
It is thought to be the first study to analyse insecticide resistance in mosquitoes in the UAE, although Prof Al Deeb and his colleagues have previously detected insecticide resistance in house flies.
Insecticide use leads to mutation
Resistance evolves because when an insecticide is applied,mosquitoes with alleles (different versions of a gene) that confer resistance are more likely than others to survive and reproduce. This causes resistance alleles to become more common over time and can render insecticides ineffective.
In the case of insecticide resistance in the southern house mosquito, the resistance mutation alters a nerve cell membrane channel through which sodium passes. In susceptible mosquitoes, the insecticide causes the sodium channel to remain open, paralysing and killing the insect.
Elsewhere in the world, the consequences of mosquitoes becoming resistant to insecticides have been significant.
“It’s one of the major concerns about malaria rates,” said Prof Martin Donnelly, of the Liverpool School of Tropical Medicine in the UK, who researches genetic factors that affect resistance. “Since about 2015 the gains we’ve seen in sub-Saharan Africa have stalled. It’s largely as a result of drug resistance and insecticide resistance.”
Prof Al Deeb said that to effectively combat insecticide resistance in the UAE, long-term monitoring programmes should be established. “Our study serves as the first step toward developing resistance management strategies in the country,” he added.
Resistance can be reduced by rotating which insecticides are used, because once any given type is no longer applied, mosquito populations are likely to become susceptible again over time.
The best approach is, Prof Al Deeb said, integrated pest management, which combines various control methods. These include introducing mosquito predators such as fish that eat insect larvae, the use of mosquito traps, the modification of habitats so there are fewer breeding sites, and improvements in sanitation.
Effects of climate change
While the southern house mosquito is not believed to transmit diseases in the UAE, this situation may change, especially as climate change is altering where vector-borne diseases are found.
“Since environmental changes and mosquito behaviour can shift over time, ongoing surveillance is crucial to ensure this species does not become a public health concern in the UAE,” Prof Al Deeb said.
His research group is keen to look at resistance trends over time, resistance in other mosquito species and alternative control strategies. “If funding becomes available, we plan to conduct further research to develop evidence-based mosquito management policies for the UAE,” Prof Al Deeb said.
