HEALTH | Mosquitoes: Public enemy number one

Contrary to common notion, crocodiles and sharks are not the deadliest living creatures. Public enemy number one is that tiny speck of a living thing that irritates many Filipinos on a daily basis. It’s called mosquitoes.

Every year, crocodiles kill 1,000 people while sharks manage to take 10 lives, according to studies. In contrast, mosquitoes snatch the lives of 725,000 people each year, reports from the World Health Organization (WHO) show.

It’s no wonder why philanthropist and Microsoft founder Bill Gates posted an infographic on his blog some years back showing mosquitoes at the top of the deadliest animals list.

“Considering their impact, you might expect mosquitoes to get more attention than they do,” Gates wrote on his blog. “Sharks kill fewer than a dozen people every year and in the United States they get a week dedicated to them on television every year. Mosquitoes kill 50,000 times as many people, but if there’s a TV channel that features Mosquito Week, I haven’t heard about it.”

That observation is not debatable. Even in the Philippines, where279 species, subspecies and varieties of mosquitoes can be found, mosquitoes are not given prominence except when there is a dengue outbreak or when never heard before diseases – like chikungunya fever and Zika virus – are reported. All three are spread through the bites of mosquitoes.

Although they don’t live long, they are as old as the dinosaurs, with evidence dating back to the Triassic Period. Remember Jurassic Park, where scientists used the blood found in fossilized mosquitoes to clone the infamous creatures to fill the park?

While the dinosaurs have become extinct, mosquitoes are still here with us. Much as the world wants to exterminate them, these blood-sucking creatures keep on coming back. They are sort of the modern-day version of vampires.

“Few animals on Earth evoke the antipathy that mosquitoes do,” wrote the National Geographic. “Their itchy, irritating bites and nearly ubiquitous presence can ruin a backyard barbecue or a hike in the woods. They have an uncanny ability to sense our murderous intentions, taking flight and disappearing milliseconds before a fatal swat. And in our bedrooms, the persistent, whiny hum of their buzzing wings can wake the soundest of sleepers.”

There are about 2,700 different species (with some reports as high as 3,500) of mosquitoes throughout the world, all of which live in specific habitats, exhibit unique behaviors and bite different types of animals. Though the average mosquito lifespan is only about three weeks, some varieties have been known to live as long as two months in laboratory conditions.

The most common mosquitoes in the Philippines are Aedes aegypti, Anopheles species, and Culex species.

Aedes adults, carriers of the dengue, chikungunya and Zika virus, have black and white markings. They are described as container breeders, preferably those made by man (like flower vase, tires, and buckets) and contain clean water. They prefer darker colors like black and red. The bites peak at the change of light intensity (after sunrise and before sunset).

The adults of Anopheles, responsible for transmitting malaria, have pale and dark marks on its wings. They prefer clean and unpolluted water. They bite at night and rest indoors and outdoors (depends on species). They like darker colors.

The thorax, legs and veins on the wings of adults of Culex, main vector for Japanese encephalitis, are always covered with brown scales. They mainly breed in polluted stagnant water and drains. They also bite at night and usually rest indoors before and after the blood meals. Like the Anopheles, they favor darker colors.

Although mosquitoes are quite small, they do have brains. This organ is simple compared to a human brain but is enough to help them see, move, taste and detect scents or heat. Since they eat and digest blood or nectar, they poop too (either in a semi-solid or liquid form).

“Some mosquitoes have adapted perfectly to urban environments,” says Professor Richard Russell, head of the medical entomology department at the University of Sydney. “We unwittingly provide abundant standing water, from the tin cans and saucers to clogged gutters, septic tanks and drainage ditches.”

Mosquitoes track people down by sensing their body odors and temperature. However, it’s carbon dioxide that gives them the signal that blood is nearby and since human beings exhale carbon dioxide, it’s easier for them to find a person. They are also attracted to lactic acid and octenol found in man’s breath and sweat. They may also have a preference for people drinking beers.

Fortunately, only a couple of hundred mosquito species feast on human blood. Only female mosquitoes bite as they need a blood meal before they can lay eggs. Male mosquitoes make do just fine with plants and those sweat left in the shirts after being worn.

“Only female mosquitoes have the mouth parts necessary for sucking blood,” reports National Geographic. “When biting with their proboscis, they stab two tubes into the skin: one to inject an enzyme that inhibits blood clotting; the other to suck blood into their bodies. They use the blood not for their own nourishment but as a source of protein for their eggs.”

After a female-sucking mosquito has bitten, some saliva remains in the wound. The proteins from the saliva (called anticoagulants) evoke an immune response from human’s body. The area swells (the bump around the bite area is called a wheal), and people itch, a response provoked by the saliva. Eventually, the swelling goes away, but the itch remains until man’s immune cells break down the saliva proteins.

To treat mosquito bites, health experts advise that you should wash them with mild soap and water. Avoid scratching the bite area, even though it itches. Some anti-itch medicines or over-the-counter cortisone creams may relieve the itching. Typically, you do not need to seek medical attention (unless you feel dizzy or nauseated, which may indicate a severe allergic reaction to the bite).

But a more serious consequence of some mosquito bites may be transmission of certain serious diseases such as dengue fever, malaria, Japanese encephalitis, chikungunya, Zika virus, and yellow fever.

Dengue is a mosquito-borne viral infection and is caused by one of four dengue viruses that produce a range of illnesses, from viral flu to hemorrhagic fever. About one in four people infected with dengue get sick, according to the US Centers for Disease Control and Prevention (CDC).

“The increase in dengue cases in recent years is the result of the expanding geographical distribution of the mosquitoes which carry the virus,” the WHO reports. “At the same time, the rapid rise in urban populations has increased the number of people exposed to the virus.”

Malaria is a serious and sometimes fatal disease caused by a parasite that grows in your bloodstream and can produce symptoms that develop anywhere from six to eight days to several months after infection. People who get malaria are typically very sick with high fevers, shaking chills, and flu-like illness.

Japanese encephalitis is a mosquito-borne viral disease with a high fatality rate. The virus is found in pigs and birds, and is passed to mosquitoes when they bite infected animals. Most people infected with this disease do not have symptoms or have only mild symptoms. There are over 50,000 reported cases of the disease every year and approximately 4,000 deaths.

Chikungunya occurs mostly in Africa but it has already been reported in the Philippines. An infection causes fever and severe joint pain. According to WHO, joint pain associated with this disease is often debilitating, and can vary in duration. Other symptoms include muscle pain, joint swelling, headache, nausea, fatigue and rash.

Zika virus infection during pregnancy can cause infants to be born with microcephaly and other congenital malformations. Symptoms, which last for 2-7 days, are generally mild and include fever, rash, conjunctivitis, muscle and joint pain, malaise or headache.

Yellow fever, a disease that once plagued Europe and North America, has the potential to spread beyond its present range – into Asia, for example – wherever the mosquito vector exists. Symptoms take 3-6 days to develop and include fever, chills, headache, backache, and muscle aches.

Besides those diseases, mosquitoes have been in the news for carrying a whole host of new and deadly blood-borne diseases. Until 1999, West Nile virus – originating from the Nile River valley – had not previously been documented in the Western Hemisphere. The virus causes encephalitis, an inflammation of the brain, and can be transmitted by mosquitoes.

Mosquitoes are not only deadly, but they’re “powerful,” too. They have been manipulating the course of human history since its very beginning. Around 323 B.C., Alexander the Great was felled by a mosquito, dying from malaria at the age of 33. His dream of a united Greek empire collapsed within a few years, and widespread malarial infection contributed to the decline of Greek civilization.

American President George Washington and his wife Martha suffered from malaria. George contracted the disease when he was a teenager. In the second year of his presidency, he experienced severe hearing loss due to quinine toxicity.

Mosquitoes spread yellow fever to halt a British expedition en route to attack the French in Canada. This was in 1960. In 1802, Napoleon Bonaparte sent troops to reinforce France’s claim to Louisiana and put down a slave rebellion in Haiti. Of the 33,000 soldiers, 29,000 were killed by mosquito-borne yellow fever. Louisiana became part of the U.S. while Haiti became independent.

Bitten by a mosquito, Oliver Cromwell died of malaria in 1658, paving the way for the return of the British monarchy. In 1905, mosquitoes almost succeeded in halting construction of the Panama Canal, as panicked workers fled a yellow fever epidemic.

Meanwhile, what you can do avoid bitten by mosquitoes? There are several ways: Empty standing water in old tires, buckets, plastic covers, toys, or any other container where “wrigglers” and “tumblers” live. Keep swimming pools treated and circulating and rain gutters unclogged. Use mosquito repellents when necessary and follow label directions and precautions closely.

Use head nets, long sleeves and long pants if you venture into areas with high mosquito populations, such as salt marshes. If there is a mosquito-borne disease warning in effect, be sure to stay inside during the evening when mosquitoes are most active. –

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