Why Are Mosquitoes So Good at Carrying Disease?

Mosquitoes are Good at Carrying Diseases

Mosquito-Borne Diseases

Most people don’t realize that mosquitoes don’t create the diseases they spread, they are simply carriers.

And of the thousands of mosquito species that exist, only a few are responsible for infecting humans.

Watch the following video and learn why, and how, some mosquitoes are such prolific disease-carrying machines.

Credit: DNews ¹

Video duration: 4:01

The Annoying, Deadly Mosquito

Intro:

“Mosquitoes are one of the most annoying bugs on this planet, but they are also one of the most deadly. Why are they so good at carrying diseases?”

Begin transcript

“Ugh!

Get out of here, you stupid mosquito!

I don’t want your stupid diseases!

Hey guys, Julia here for DNews.

Mosquitoes are often seen as one of the most annoying creatures on this planet and arguably one of the most deadly.

These buzzing nuisances carry deadly diseases like yellow fever, dengue fever, lymphatic filariasis and, famously, malaria.

According to the World Health Organization, malaria infects over 500 million a year and kills 3 million.

So, why are mosquitoes such good carriers of disease, especially malaria?

Well, interestingly, #NotAllMosquitoes!

Of the 3,000 species of mosquitoes, only three seem to be the ones spreading most of the human diseases we’re familiar with.

Anopheles mosquitoes ² carry malaria, filariasis, and encephalitis (an inflammation of the brain).

Culex mosquitoes ³ carry encephalitis, filariasis, and the West Nile Virus.

And Aedes mosquitoes carry encephalitis, yellow fever and dengue fever.

In fact, many species of mosquito aren’t good carriers of disease at all!

According to Dr. Kenneth D. Vernick, a microbiologist at the University of Minnesota, “most mosquitoes are malaria-resistant and the susceptible ones are the oddballs.”

Most mosquitoes actually fight malaria with their immune responses to parasites.

After a mosquito sucks up it’s bloody meal, a peritrophic matrix, (or barrier) forms in-between the bug’s lining of their midgut and the blood.

While it can take a few hours to form, it does trap some parasites inside, possibly providing protection against some of them.

The malaria parasite doesn’t infect mosquitoes at all, it never enters their circulatory system.

Another response mosquitoes have is to coat the parasite in a melanin capsule, but this comes at a cost.

The mosquito has to commit resources to coat the invader, which takes resources away from things like reproduction, resulting in the infected mosquitoes becoming less fertile.

So, though the parasite can enter the mosquito’s body, it often doesn’t make them sick.

Which is good news for the parasite or virus because if their host dies, they die too.

And malaria’s next trick is getting from the mosquito into a human body.

Probably yours.

The parasite uses some of the very things that help a mosquito feed to easily enter the next host.

Mosquitoes have substances in their saliva that weaken blood vessels, promote bleeding, and shut down the human body’s natural first lines of defense.

These evolutionary advantages help invaders slip into their next host; with an injection directly into the bloodstream, they bypass a lot of immune defenses.

And some parasites actually change a mosquito’s behavior to make it easier for them to achieve this goal.

One study in PLOS ONE found that malaria makes humans smell more attractive to mosquitoes.

And another study published in The American Journal of Tropical Medicine and Hygiene found that malaria makes mosquitoes feed longer.

It invades the mosquito’s salivary glands while in the sporozoite stage , which probably helps the parasite get into the next host easier.

But in their invasion, these young viruses interfere with the mosquito’s saliva production which the mosquito needs to locate blood vessels in a host.

With impaired salivary abilities, it takes longer for the mosquitoes to feed to get the same amount of blood.

Which is just fine with the parasite.

It gives them more time to jump to their new host!

So, though mosquitoes are good at ferrying parasites like malaria to our bloodstream, they don’t benefit from their morbid task, and instead put themselves in more danger, and can even become infertile.

The saying goes “don’t kill the messenger“, but in this case… you should totally kill the messenger!

I agree with one Cornell University researcher who called mosquitoes “the most vile and useless species on the planet.”

Why don’t we just get rid of them all?

Well, Trace and Natalia find the answer in this episode right here.

A world without mosquitoes sounds like it doesn’t suck, but what purpose do mosquitoes actually serve?

Don’t they have to have a purpose?

Not really, actually.

They exist because they haven’t gone extinct, yet.’

Alright guys, so how do you feel about mosquitoes?

Would you kill them all or do you think they’re useful in some way?

Let me know down in the comments below and don’t forget to hit those “like” and subscribe buttons and keep coming back to DNews so you don’t miss a single episode.”

End transcript

Footnote(s)

¹ Follow DNews on Google+.

² Learn more about Anopheles mosquitoes on Wikipedia.

³ Visit Wikipedia and learn more about Culex mosquitoes.

Learn more about Aedes mosquitoes on Wikipedia.

What is a “midgut”? Learn more

Learn more about the “sporozoite stage” on Wikipedia.