How light pollution can cause disease
New research shows that some mosquitos bite more when they are exposed to artificial light
Dr Bernard Coetzee’s light bulb moment about light pollution and its links to infectious disease came while he was drinking tea with a senior colleague. “He confided in me that it was a critical emerging issue in biodiversity conservation and sustainability,” recalls Coetzee, a global change scientist. “And the evidence is compelling.”
Artificial light is “really interesting and really scary”, says Coetzee, a senior lecturer in the department of zoology and entomology at the University of Pretoria. “It’s doing things to the environment that we just don’t think about.”
Coetzee and his colleagues are now unravelling the link between artificial lights and mosquitoes — specifically how artificial lights are used by people, particularly in rural areas across Africa — and how that may alter the biting behaviours of mosquitoes — and affect the transmission rates of vector-borne diseases.
This work is funded and supported by the $150 000 Jennifer Ward Oppenheimer research grant that Coetzee won a year ago for his work on reducing vector-borne disease risk by limiting artificial light
expansion across the continent.
Although Africa remains one of the least light-polluted continents, on which “many Africans may still see the Milky Way”, this is rapidly changing with the expansion of lighting infrastructure, which is closely tied to economic development. “The use of artificial light at night is increasing across Africa,” Coetzee says. “While this increases comfort and work and leisure hours, it may pose a threat to human life.
“Artificial lights can attract insects into homes and, if these are mosquitoes,
they can carry some of the world’s worst vector-borne diseases, such as malaria, dengue fever and the Zika virus, affecting millions of lives in Africa daily.”
It is crucial to understand how artificial lights can be used in ways that are both affordable and energy efficient, but that do not worsen the vector-borne disease burden in Africa, he says.
Humanity has introduced artificial light at night — from cars, houses, buildings, advertising boards, stadiums and factories — to a planet that has historically been exceedingly dark. For most of the planet’s history, almost all organisms have been bound to celestial sources of light — the stars, moon and, particularly, the sun, Coetzee points out.
“In the presence of regular daynight cycles, life has evolved an internal biological clock that physiologically drives our behaviour in response to light levels, telling us when to sleep, eat and more on a 24-hour cycle,” he says. “But with the invention of artificial light, we uncoupled ourselves from the sun, gaining the power to extend our activities long beyond sunset. This relatively new phenomenon has revolutionised the way we work, the way we interact, the way we live.”
Light is an immensely powerful biological driver, and “we are only just beginning to realise how this technology affects ourselves and the planet”, Coetzee notes.
New advancements in artificial light are swift and rapid, says Coetzee, citing how the invention of the blue LEDS that power phones, tablets and computers won the Nobel prize in 2014. “Human activity is so tethered to artificial light that electrical grid infrastructure is now used as an indicator of economic prosperity,” he says.
But artificial light has brought unforeseen adverse effects, with evidence showing that chronic cycle disruption can increase the risk of cancer, obesity and diabetes.
“Light is now a pollutant that can cause drastic changes to the natural patterns of wildlife behaviour, disrupting breeding opportunities and increasing predation risk,” Coetzee says. “Because of artificial light, newly hatched turtles are attracted
away from the sea to their death; nocturnal rodents are less active at night; and bird migrations are disrupted. Insects are affected as well, as carriers of disease; this means that light may be changing human disease risk.
A recent study has found that mosquito species are influenced by light in different ways. The malariaspreading Anopheles mosquito bites in the night-time, so light at the correct spectrum could keep them at bay from the household until occupants are safely installed under their mosquito nets to sleep.
But keeping the lights on doesn’t solve the mosquito problem. A group of mosquitoes that carries dengue and Zika, the Aedes, feeds during the day. “Shine light at them and they will bite more,” Coetzee says.
For their research, Coetzee and his collaborators are conducting a series of lab experiments by placing mosquitos in test tubes and using consumer lights of different kinds to see how this alters their activity and behaviour.
“By combining this lab data with field data on how light is being used in rural areas, we will model and map how artificial light alters disease prevalence,” he says.
Simple changes to people’s lives could help to mitigate vector-borne diseases without compromising the energy expansion that is coupled with much-needed economic development.
Although light influences human physiology and the environment, there isn’t much work being done to deepen the understanding of its effects, particularly in Africa.
“Africa is on the cusp of a developmental revolution, but we don’t have to make the same mistakes as other countries. We can set up light infrastructure in a more sustainable way … We don’t want light bulbs that are more expensive for the consumer, but we also don’t want lights that may increase a mosquito’s propensity for biting you,” Coetzee says.
Research into artificial light at night has received significant attention in some sectors, such as medicine, but less so in others, like the environmental field.
“I think many people take these light rhythms for granted, despite them being so critical to our daily circadian rhythms. So I think, with urban expansion, people are increasingly realising it’s a pollutant that needs attention,” Coetzee says.
Coetzee and his team have just concluded a peer-reviewed paper, setting out how the biology behind their research may all work and what needs to be done about it. “Now the hard work starts,” he says.
‘Artificial lights can attract insects — and they can carry some of the world’s worst diseases’