The Aedes mosquito
Two totally unrelated fields of study are addressing two of the world’s oldest, greatest killers plus a new one: Dengue fever and cancer have been around for eons; The Zika virus is a relative new-comer, but it is related to dengue (pronounced ‘den-gae’).
Actually, assorted studies are separately addressing the dengue and Zika issues, and at least one of them, like one concerned with cancer, have something to do with a bacterial genus called Wolbachia, which live within insects and pass genetic information on to both successor generations and to other insect species.
The connection to dengue anad Zika is more obvious, since those usually fatal afflictions are spread by bites of a species of mosquito. But the one that spreads dengue doesn’t carry or spread Wolbachia, and scientists have been studying how they might make use of that fact, and their knowledge of it, to prevent other insects from passing around the dengue disease.
By the early 2000’s, researchers had uncovered the fact that some bacteria swop bits of DNA with other bacteria. This practice is called lateral gene transfer (LGT).
There also was, at the early part of this decade, early evidence that some such transfers took DNA bits from bacteria into multicellular organisms, and one of the types of bacteria known of being involved in LGT was Wolbachia, which had transferred some of its own DNA to a species of beetle and a parasitic worm.
Then along came Julie Dunning Hotopp, a post-doctoral fellow. She wanted to know more about this phenomenon, and soon did, as she and several colleagues tracked lateral gene transfers from Wolbachia to eight inspect species and nematode worms.
Were these transfers moving genes and traits that could alter the behaviors of the new host? ‘Turns out they were, and confirmation of that, said Dr. Francis Collins, the director of the National Institutes of Health in his blog:
“… put Dunning Hotopp on a research trail that now has taken a sharp turn toward human cancer and earned her a 2015 NIH Director’s Transformative Research Award.”
This award, Dr. Collins noted, “supports exceptionally innovative research projects that are inherently risky and untested but have the potential to change fundamental research paradigms in areas such as cancer and throughout the biomedical sciences.”
It would be pointless to paraphrase the blog post on this, because it’s explained so well there:
Unlike insects and worms, people don’t harbor lots of bacteria in their cells. But the human body does play host to a diverse array of microbes, collectively known as the human microbiome.
Dunning Hotopp, now an associate professor of microbiology and immunology at the University of Maryland School of Medicine, Baltimore, began wondering several years ago while pursuing this new research trail whether it was possible that bacterial DNA might also make its way into the human genome—probably not into the germline (the part that gets passed to future generations), but into various cells of the body (so-called somatic cells).
Dunning Hotopp searched for signs of bacterial gene transfer in publicly available data from the Human Genome Project, the 1000 Genomes Project, and The Cancer Genome Atlas.
There, dispersed within this vast body of data, she found something others had overlooked: thousands of instances in which bacterial DNA had apparently become enmeshed in the DNA within human cells taken from about one out of every three people.
Interestingly, evidence of LGT turned up much more frequently in cancerous cells than in healthy human cells. Microbial sequences were especially frequent in the genomes of acute myeloid leukemias (AML) and stomach cancers, and Dunning Hotopp’s latest NIH award will enable her to conduct additional studies for further confirmation.
It’s not yet clear whether bacterial DNA in human genomes causes cancer, or if cancer cells are somehow more prone to receiving DNA from microbial sources. As a next step, Dunning Hotopp plans to genetically engineer some of the insertions she’s uncovered into human cells in the lab to better understand their functional consequences and potential relationship to cancer.
The search for bacterial DNA in human sequences requires great care to ensure that any findings aren’t due to bacterial contamination of samples. In fact, one reason it’s taken this long to confirm the existence of bacterial DNA in the human genome is because evidence of bacterial sequences, once found, has often been thrown out!
To address this problem and help streamline the search for lateral gene transfer in the human genome, Dunning Hotopp and her colleagues are devising bioinformatics tools, which they intend to share with the scientific community. As these tools become available, I’ll look forward to learning what she and others will uncover.”
Some of the research into causes and possible means of preventing dengue and Zika is spelled out in a WebMd article. Again, there’s little to be gained by me paraphrasing what’s been said there, because I am way less – make that extremely less – knowledgeable about these issues that are the authors of that piece.
So here’s what it said, on February 2nd:
They’re tiny. They attack with supreme stealth, biting in full daylight with no buzz and no sting. And they carry viruses that can be lethal to their preferred food source: us.
The Aedes aegypti, or yellow fever mosquito, killed more soldiers than guns did during the Spanish-American War. And now these black-and-white striped femme fatales — only the females suck blood — are causing misery through Central and South America as they pass the viruses that cause dengue fever, yellow fever, chikungunya and now Zika virus disease from person to person.
Their ancestors lived in the forest where they fed on all manner of warm-blooded creatures, but some time in recent history — no one is sure exactly when — the modern Aedes mosquito developed a preference for just one animal — humans.
“They only live in association with humans. And they have all these physical and behavior adaptations to do it,” says Carolyn McBride, PhD. She’s an assistant professor of ecology and evolutionary biology at Princeton University who specializes in Aedes aegypti.
“They have an amazing ability to recognize human odor,” McBride says. “You can put on a lab glove and cut a little hole in the back so that just an inch of skin is exposed, and they’ll find it.”
Where They Hide Out
Experts who have spent some time studying Aedes mosquitoes are amazed at how well they’ve adapted to feeding on people.
Take, for instance, their habitat. They don’t have a lot of stamina in the air. Their flight range is just 300 to 600 feet. As a result, insecticidal sprays mostly don’t work on this breed, because it’s hard to catch them airborne.
To feed, they have to stick close to their intended targets, a.k.a. us. They live under decks, patio furniture, and in homes that don’t have cool air — they don’t much like air conditioning. They especially love the drip trays that collect extra water under potted plants. But that’s not the only place you’ll find them.
They “can breed in incredibly small amounts of water,” says Joe Conlon, spokesman for the American Mosquito Control Association.
“When I was in Suriname, South America, several years ago, I saw them breeding very happily in discarded soda bottle caps,” he says.
In New Jersey, researchers at Rutgers University found them breeding in water that had pooled in discarded snack-size potato chip bags.
“These mosquitoes are in people’s backyards,” says Dina Fonseca, PhD, an entomologist and associate professor at Rutgers. They live in containers, she says, and are “urban, domestic mosquitoes.”
In 2009, Fonseca and her team went house to house through neighborhoods around Trenton, N.J., trying to understand exactly where these mosquitoes and their close relatives, Aedes albopictus, live and lay their eggs.
(In lab experiments, albopictus mosquitoes have also been shown to carry Zika.)
They dumped and checked out more than 20,000 different water-holding containers for the study.
They found these mosquitoes mainly in buckets, in the drip trays under potted plants, and in little pools of water than collect in the crevices of outdoor equipment like lawn mowers and air conditioners.
Even in the most manicured, clutter-free yards, they found infestations. One place that was a reliable hideout? The corrugated extenders that people attach to downspouts to direct rainwater away from homes.
“Sometimes they are so long that you always have water inside of those accordion folds. We’ve gotten 500 larvae out of those little folds before,” Fonseca says.
And Margaret Chan, MD, director-general of the World Health Organization, warned that many areas could see their number of mosquitoes boom this year because of the El Nino weather pattern — the strongest in almost two decades. El Nino often brings warmer, wetter winter weather, which allows these insects to hatch earlier and breed longer.
How to Protect Yourself
The Zika virus is spread when a mosquito bites an infected person, then bites an uninfected person and passes the virus. Most infected people don’t show symptoms. But the virus is suspected of causing microcephaly in babies of infected pregnant women, although a cause-and-effect link hasn’t been definitely established.
Microcephaly causes devastating, sometimes-fatal brain damage, and can result in miscarriage or stillbirth.
The CDC has warned women who are pregnant or may become pregnant to consider postponing travel to more than 25 countries and territories in Central and South America, and the Caribbean.
In Brazil, the situation is so desperate that they’re trying an experiment: releasing genetically engineered male mosquitoes into the wild. When they breed with females, they pass a self-destruct gene to their offspring that causes them to die before they reach adulthood.
Oxitec, the British company that produces that mosquito, claims in tests that it cut wild Aedes populations by as much as 90%.
The company says it has been in talks with the FDA to test its mosquitoes in the Florida Keys, but hasn’t yet received approval to try it there.
Supporters say the Oxitec mosquito could end the menace of Zika and other mosquito-borne viruses without the toxic after-effects of pesticides. But critics worry about the unintended consequences of releasing a genetically modified insect into the wild.
While we wait to see if science can save us, warm, wet weather is on the way.
Fonseca says the first Aedes mosquitoes will hatch in an area after the temperature has been above 50 degrees for at least 16 days.
To protect yourself, experts agree that the most important thing to do is to get rid of standing water in and around your house. But the mosquitoes aren’t always where you might think.
In her house-to-house survey, Fonseca didn’t often find them up high in places like roof gutters or in ornamental ponds or in swimming pools, even when they’d been left untreated and neglected. Instead, she says, think low and small.
Fonseca and Conlon offer these suggestions:
- Empty buckets or watering cans. If you have a rain barrel, treat it with a non-toxic product designed to kill mosquito larvae.
- Drill holes in your trash or recycling bins so they don’t collect water.
- Even though it’s a pain to disconnect them, unscrew and empty downspout extenders at least once every 5 days. That’s how long it takes mosquito eggs to hatch.
- If you’ve got plants in containers, empty their drip trays at least once a week. Same goes for outdoor-furniture covers that may hold pockets of water after a rainstorm.
- Try to cover any outdoor equipment, like a barbecue grill, so it doesn’t collect water in places you can’t see or reach.
- Aedes mosquitoes like to bite below the knees, so long pants and socks are important. Wear long sleeves as well.
- Use a mosquito repellent. Conlon says the active ingredients DEET or a slightly less sticky, greasy alternative called picaridin both work well.
Here’s another tip from Conlon, who isn’t just a professional mosquito fighter, but also a Florida resident who has to deal with them year-round: If you’re sitting on a porch or patio, use box fans to create a strong breeze around your feet and legs. Since mosquitoes don’t do well in wind, a draft helps set up a mechanical barrier, and it also helps blow away all the human odors that cue them to your warm-blooded presence.
The more we learn, the more we realize how little, overall, we understand about the sometimes weird workings of nature!