Mosquitoes and diseases: the deadliest creatures?

Most of the time, a mosquito bite is nothing more than a minor irritant that swells up, itches something strong, then fades and is quickly forgotten. That is, unless that mosquito is carrying an insect of its own.

Mosquitoes kill more than a million people worldwide each year through the transmission of dangerous viruses and parasites. A female mosquito lands on an infected person or animal, sucks up the diseased blood, and passes it on to the next victim she bites.

Simple as that, mosquito-borne diseases like West Nile virus, eastern equine encephalitis, malaria, and even canine heartworms can spread through a population. The infected don’t even realize they have contracted a disease until the symptoms start to show.

According to the Maryland Department of Agriculture, “for the first time in nearly 50 years there are endemic cases of dengue and malaria in the United States. Improvements in global transportation now allow a person infected with a disease to be on a different continent every day “. This allows mosquito-borne diseases to travel from one country to another.”

That ability to spread disease and death across the planet is why the Smithsonian National Zoological Park has declared the female Anopheles mosquito – carrier of malaria – the deadliest animal in the world.

So if you’ve ever wondered what diseases a mosquito can carry and how they’re transmitted, keep reading.

Drawing blood with a mosquito proboscis

First, you need to understand how a mosquito takes your blood.

For the most part, only female mosquitoes feed on the blood of people and animals. They need the protein in their blood to help their eggs develop, so they will usually feed before each batch is laid. A female mosquito can lay up to three batches of eggs before dying.

The mosquito uses a toothed proboscis to pierce the skin to reach a capillary. Through a tube inside the proboscis, the mosquito injects saliva containing a mixture of pain reliever and anticoagulant. Many people are allergic to saliva, which is what causes the swelling and itching around the bite.

Once the saliva is in, the mosquito begins to draw blood through a second tube in the proboscis. The female usually takes about 0.001 to 0.01 milliliters of blood, according to the American Mosquito Control Association.

If the mosquito is a carrier of a disease, it can be transmitted through the small fragments of blood left on the proboscis of the last victim of the mosquito, as well as through saliva, which may contain viruses or parasites.

One bite from the right mosquito at the right time and you’re infected.

That’s why mosquito experts always encourage people to check their yards for standing water where insects can breed, to avoid being outside after dark when hunting, and to use repellent, mosquito traps, and even netting, if necessary. necessary, to avoid being bitten.

mosquitoes bring malaria

Malaria is caused by a parasite that hitchhiks when a Anopheles mosquito drinks the blood of an infected person. only the Anopheles can transmit malaria, according to the Institute of Food and Agricultural Sciences at the University of Florida.

Ronald Ross, a British entomologist, was the first person to make the connection between mosquitoes and malaria, discovering the parasites in 1897.

The parasites live in human red blood cells and reproduce asexually for two to three days until they burst the cell and flood the bloodstream with new parasites. Some develop into male and female gametocytes, which are ingested by the mosquito during feeding.

Gametocytes reproduce within the mosquito over a period of one to three weeks, creating sporozoites that migrate to the insect’s salivary glands. When the mosquito injects saliva into a person, it also transmits the sporozoites, infecting the person with malaria, the Florida researchers report.

The symptoms of malaria are similar to those of the flu, causing fever, chills, and nausea. If left untreated, it can be fatal.

According to the US Centers for Disease Control, nearly half a billion people worldwide contract malaria each year, and more than one million die. Most of the deaths occur among children on the African continent.

The CDC reported that there were 63 malaria outbreaks in the United States between 1957 and 2003. In each case, the outbreaks began with someone who had contracted the disease in a country where it is common and then brought it back to the US.

At least two species of Anopheles Mosquitoes capable of transmitting malaria are frequent in this country.

West Nile virus and mosquito bites

West Nile virus is a relatively mild infection that can sometimes cause severe encephalitis. It was discovered in the blood of a woman living in Uganda in 1937 and is common in Africa, Asia and the Middle East.

It is transmitted when mosquitoes, mainly Culex mosquitoes: feed on infected birds, such as crows, and then pass it on to humans through the injection of saliva in the next feeding. The virus enters the bloodstream and begins to multiply.

Symptoms can start to show between three days and two weeks, and in some cases, the virus reaches the brain, where it can cause inflammation and alter neurological functions, possibly leading to permanent damage to the nervous system.

Those over the age of 50 are most at risk.

But the good news is that about 80 percent of people who get West Nile virus from mosquito bites never develop symptoms. A little less than 20 percent will have fever, headaches, nausea, and sometimes swollen lymph nodes.

And only one in 150 infected people, less than 1 percent, develops encephalitis, the most serious form of the disease. The first signs of encephalitis are usually flu-like symptoms and a stiff neck, leading to high fever, disorientation, seizures, blindness, paralysis and possibly death, according to the CDC.

The mosquito-borne disease first appeared in the United States in 1999 with an outbreak in New York, New Jersey, and Connecticut. Within four years, it had spread to most of the Midwest and had killed 23 people.

In 2007, there were West Nile virus infections in almost every state. The CDC reported 3,598 illnesses and 121 deaths.

Mosquitoes are carriers of other forms of encephalitis

Eastern equine encephalitis is a cousin of West Nile Virus, it is transmitted in the same way: by mosquitoes that have fed on infected birds.

Symptoms are similar and generally appear about 3 to 10 days after transmission by mosquito bite. However, it is a much more serious disease, proving fatal for 30 to 50 percent of those infected, especially among children and the elderly.

“Because of the high mortality rate, it is considered one of the most serious mosquito-borne diseases in the United States,” reports the CDC.

Fortunately, it is also relatively rare. Only 220 cases were reported between 1964 and 2004, mostly in Florida, Georgia, Massachusetts, and New Jersey.

Another particularly dangerous disease in the same family is St. Louis encephalitis, common along the East Coast, the Gulf Coast, and parts of the Midwest. Until West Nile arrived, it was considered the most serious mosquito-borne disease in the country.

As with the other forms of encephalitis, it is acquired by mosquitoes from birds and transmitted to humans, mainly in late summer or early winter. It doesn’t harm birds or insects, but it can be brutal to people.

A little more than half of infected people develop brain inflammation and its accompanying neurological problems, and between 5 and 30 percent die, depending on the age of the infected person. Even those who survive sometimes suffer permanent memory loss or paralysis.

According to the CDC, nearly 5,000 cases have been reported in the past 40 years.

Yes, but what about the mosquito and HIV?

Short answer: it doesn’t happen.

In addition to the diseases already mentioned, mosquito bites can rarely transmit deadly yellow fever and dengue fever to humans, and can pass heartworm larvae to your dog through their saliva; by the way, once infected, the dog is infected for life. , according to the University of Florida agricultural extension office.

But Rutgers University researchers say the only disease that mosquitoes can’t spread from person to person is HIV.

For one thing, the virus that causes AIDS doesn’t live in the body of a mosquito, the way encephalitis does. Mosquitoes actually digest the virus along with the blood a day or two after feeding. It never gets a chance to replicate and migrate to the salivary glands.

And there simply aren’t enough HIV particles in the small amount of blood left on a mosquito’s proboscis after feeding to cause an infection. While encephalitis microbes circulate in large volumes in the bloodstream, traces of HIV are relatively small.

The bottom line is that a person would have to be bitten by 10 million mosquitoes to even have a luck of transmission. And that’s statistically unlikely, say the Rutgers researchers.

Of course, as you’ve seen, mosquito-borne diseases are deadly enough without HIV. Maybe now he understands why those backyard pests are considered one of the most dangerous creatures alive.