Will Climate Change Boost Mosquito-Borne Disease?
Will climate change cause an increase in diseases like Zika? Probably, but it won't be the only factor. Continue reading →
The immense amount of coverage of the Zika virus outbreak has focused attention on the health care situation in Brazil, particularly with the Rio Olympics almost upon us. Most recently, U.S. women's soccer goalkeeper Hope Solo has said that, because of the virus, she is unsure about whether she will participate in the games.
A recent PBS Frontline report showed how Zika strained the country's health care system - the largest in the world - which was already overwhelmed by a huge increase in two other mosquito-borne illnesses: dengue fever and chikungunya. Pouring gasoline on the fire is an economic crisis resulting in fewer doctors and nurses to a combat greater numbers of cases.
And of course, it isn't just Brazil. The spread of Zika across the Americas has prompted the World Health Organization to declare a public health emergency.
One of the questions raised about the outbreak is whether climate change is involved. After all, it has to varying degrees also been implicated in the spread of other mosquito-borne diseases. There have been big increases in cases of West Nile Virus and dengue in the United States, while chikungunya has recently been reported in western Europe.
And if climate change is responsible, it's easy to understand why. As temperatures around the country rise, the areas that are conducive to such mosquitoes could expand, and the insects could start to emerge earlier in the year, meaning more opportunities for bites that could spread disease. It's notable that the 2012 West Nile Virus outbreak in the United States followed an unseasonably warm late, spring, summer and early fall. But within that overall trend, there some nuance.
For example, temperatures more conducive to mosquitoes won't necessarily mean conditions that are more conducive to the pathogens they transmit. There are a lot of Aedes aegeypti mosquitoes, an invasive species, in Arizona, but no dengue fever, which they often carry. It's possible that because A. aegypti thrives in environments that are moist as well as warm, Arizona's desert climate doesn't allow the mosquito to live long enough for the dengue parasite to go through its full life cycle.
So, as climate change increases drought in some areas, should those places cross dengue fever off their lists of things to be worried about? Not so fast, because as with many diseases, human behavior also plays a role. Because A. aegypti often breed in containers used for household water storage, and because the need for such water storage containers will increase in areas projected to be more prone to drought as climate continues to change, there may ultimately be more opportunities for dengue-carrying mosquitoes in arid environments.
There are other factors, as well. Australia, for example, has seen increased cases of the Ross River Virus, which is the most common mosquito-borne disease in that country. And while climate may be part of the reason for this increase, so too are land-use changes: Newly-constructed wetlands in urban fringe areas are increase mosquito habitat, and efforts to control foxes in those areas have led to increases in wallabies. This is significant because in order to become vectors of the virus, mosquitoes must first bite an infected animal, normally a wallaby or kangaroo.
The Ross River Virus issue is a little different, because it's an Australian disease that may be increasing its range within that country. The likes of dengue and chikungunya are appearing in countries far from where they have traditionally been found. And a big part of the reason for that is that people have brought them there.
The extent to which humans are transporting themselves, and their belongings, across the globe, is continuing to expand, and invasive species are coming along for the ride. The Asian tiger mosquito, the vector for chikungunya, made its way to Europe and North America via eggs attached to used tires and lucky bamboo. This increased movement of people is likely for now the single greatest factor behind the spread of infectious diseases, including those transmitted by mosquitoes.
Of course, the mosquitoes would not be able to thrive in their new countries were conditions not suitable for them, and by and large, the picture is that, overall, a warmer, wetter environment can be expected to increase mosquitoes' range and the time available to them to complete their life cycles. The WHO has even concluded that a global temperature rise of 2-3 degrees C will increase the number of people worldwide at risk from malaria by 3-5 percent, which works out at several hundred million.
But on local and regional levels, such predictions are harder to make, complicated by such factors as human behavior, land use changes, wildlife populations and the particular nature of existing climatic conditions.
The Aedes aegypti mosquito, seen here biting a human, is a vector of dengue fever.
Ticks resemble little bumps on skin, but a closer look reveals the barbed mouthpart (hypostome) that's inserted in human flesh and can't easily slip out. Dania Richter of the Technical University of Braunschweig watched, under very high magnification, ticks using other mouthparts to pierce skin, generating “a toehold,” before a breaststroke-like action pulled in the barbed hypostome. The study is published in the latest Proceedings of the Royal Society B.
This scanning electron micrograph image of a southern house mosquito (foreground) makes evident the straw-like mouthpart used to suck human -- and other -- blood. The red and black additions highlight smelling activity. It’s believed that a mosquito can smell a person from 100 feet away.
Spiders in the genus Loxosceles, including the brown recluse, are among the few common spiders whose bites can seriously hurt people. Greta Binford, an associate professor of biology at Lewis and Clark College, recently studied the spiders, including the one shown here from South America. The spider bites can cause our skin to die. "Our bodies are basically committing tissue suicide," she explained. "That can be very minor to pretty major, like losing a big chunk of skin. The only treatment in that case is usually to have a skin graft done by a plastic surgeon."
Older workers within a rainforest termite species,
, have built-in “explosive backpacks” that become bigger and more deadly over time. The blue in this image -- showing several workers and a soldier termite -- is actually a sack of toxic blue liquid. Jan Šobotnik at Academy of Sciences of the Czech Republic in Prague found that worker termites could explode this toxin onto enemies during suicide missions that help their colonies.
Entomologist Michael Caterina and his team studied clown beetles, which munch on fly larvae found in decomposing bodies He snapped this shot, which shows one such beetle’s mandibles. It’s apparently a bug-eat-bug world, even in the remains of the deceased.
Slimy slugs are the bane of gardeners, but a recently discovered slug species makes others seem tame. The ‘ghost slug,’ found in Cardiff, Wales, lives on land, is carnivorous and possesses blade-like teeth. It’s out all year round -- not just on Halloween.
This fly was photographed after it became stuck in a glob of hand sanitizer, so it was likely frozen in this image seconds before its demise. The photo reveals the fly’s compound eyes, which have the fastest visual responses in the animal kingdom. The tongue-like proboscis is also sticking out.
Leeches are predominantly bloodsuckers that feed on blood from humans and other animals. When leeches bite into a victim, their saliva prevents blood from clotting, causing victims to bleed from the wound for hours. The good news is that this effect has beneficial microsurgery applications, such as helping doctors reattach tiny veins.
The zombie-ant fungus invades an ant’s brain, causing the insect to march to its death at a mass grave near the ant colony. The fungus winds up the winner, since it then erupts via spores that come out of the ant’s head. A parasitic fungus, however -- the white and yellow material in this image -- can castrate the zombie-ant fungus, allowing the ant to live.
Photographer Linda Tanner spotted this black widow spider in an old, dark barn, heading for a front porch. Black widows are very common, and are often found in garage door slats, hiding in dark corners, under woodpiles and in other places in and around homes. Usually they mind their own business, focusing on their insect prey, but their venom can cause human victims to experience nausea, muscle aches and paralysis of the diaphragm, which can lead to breathing difficulties.