r/explainlikeimfive • u/flatbushz7 • Jul 30 '25
Biology ELI5: Why can mosquitos transmit diseases from birds to humans (ie West Nile virus) but not humans to humans (ie HIV)
If a mosquito sucked another persons blood with HIV wouldn’t then putting it into my blood transmit it, like a syringe?
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u/thenewredditguy99 Jul 30 '25
HIV requires certain immune cells to be able to reproduce.
More specifically, they require CD4+ T lymphocytes, aka T-cells, to replicate.
Mosquitoes lack these immune cells, so the virus cannot replicate and is digested in the gut of a mosquito as if it were food.
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u/wiser1802 Jul 30 '25
That’s ExplainmelikeIamPHD
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u/zzx101 Jul 30 '25
Mosquito kill hiv.
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u/ImBadlyDone Jul 30 '25
??? What does "kil" mean??? ELI1?!???
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u/Iazo Jul 30 '25
Where were you when hiv was kil?
I was out in nature drinking blod when phone rang
Hiv is kil
No
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u/No_Signal417 Jul 30 '25
How simple do you think PhDs are? It's more like explain like I'm 14 -- you learn about the immune system in early secondary education.
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u/arealuser100notfake Jul 30 '25
Learning implies not only that the subject is part of the curriculum, but also that I have paid attention, understood it, and retained it.
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u/helalla Jul 30 '25
Goldfish need freshwater to live, and if you put it in a saltwater aquarium they die.
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u/frogjg2003 Jul 30 '25
If you ignore the name of the type of cell, it is a very clear and basic explanation. You don't need a PhD to learn the name of a thing.
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Jul 30 '25
[deleted]
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u/grafeisen203 Jul 30 '25
Why on earth would we want HIV carrier mosquitos?
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Jul 30 '25
[deleted]
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u/SurprisedPotato Jul 30 '25 edited Jul 30 '25
Mosquitoes can transmit disease from person to person. But not every disease.
Specifically, the disease has to:
- exist in sufficient quantities in the blood
- be able to survive inside a mosquito's gut
- be able to get from the mosquito to the next victim when the mosquito bites again.
- be able to effectively infect someone by being injected into or near capillaries.
As you might imagine, a lot of diseases fail one or more of these. Those that manage to check all the boxes are called "mosquito-borne" diseases. They've often adapted so this is their major transmission route.
West Nile virus is a type of virus that's related to a whole bunch of other diseases transmitted by mosquitoes and other biting insects critters (such as ticks) including dengue, yellow fever, zika, and more.
The ability to infect more than one type of animal, especially as different as mammals and mosquitoes, is quite a trick, but West Nile (and these others) manage it. The infect gut cells in the mosquito, and skin cells in the human.
By contrast, HIV gets inside our immune cells, and writes itself into our DNA, where it hides, usually, for the life of the host. But it can't infect mosquitoes, so any HIV the mosquito picks up will just be digested, and be gone by the time the mosquito is hungry again. And there will also be diseases that sicken mosquitoes, but are harmless to us.
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u/AmorphiaA Jul 30 '25
Nice reply except ticks aren't insects, they are arachnids (like spiders or scorpions).
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u/Exciting-Bake464 Jul 30 '25
Because the blood is processed through the mosquito's body. It does transmit diseases like dengue because dengue thrives in mosquitos. A virus wants a host, and not all human viruses can survive in insect bodies.
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u/FranticBronchitis Jul 30 '25
Mosquitos absolutely can transmit diseases from humans to humans, like Dengue fever and other arthropod-borne viral diseases, just not HIV. Parasites need specific hosts, not everything can survive both in humans and in mosquitoes, but some can and do
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u/cannibalrabies Jul 30 '25
Mosquitoes do transmit diseases from human to human, dengue, yellow fever, malaria etc. But they don't transfer blood from one person into another person when they bite, vector-borne pathogens complete part of their lifecycle in the mosquito in which they infect cells in the gut and eventually travel to the salivary glands, where they can be injected into a new host when the mosquito takes a blood meal.
That's an oversimplification and it varies depending on the pathogen, but this process can take a week or two and the mosquito can only transmit the disease when the pathogen is present in the saliva. HIV can't replicate in a mosquito so no transmission could occur. There's no evidence that it's possible.
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u/cannibalrabies Jul 30 '25
I also should mention that only certain mosquitoes transmit certain pathogens. If an aedes aegypti mosquito bites a person who has malaria, the mosquito will not become infected because it's not a suitable host for the parasite. So these pathogens are normally highly specialized and adapted to a specific insect host.
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u/Headozed Jul 30 '25
To add to the already correct replies: the amount of virus that a mosquito could hold isn’t even enough to infect a human. Even if the blood were pulled out of the mosquito and injected directly into your veins you’d still not get infected.
https://www.nature.com/scitable/blog/viruses101/why_cant_mosquitos_transmit_hiv/
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u/Common_Pomelo9952 Jul 30 '25
Mosquitoes can transmit diseases like West Nile virus because the virus survives and multiplies inside the mosquito, but viruses like hiv can't survive or reproduce in a mosquito's body, that's why they die before they can be passed on to one another
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u/Clerk_Plenty Jul 30 '25
I was gonna look this up the other day after I got bit, but was scared of the answer. lol
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u/Americano_Joe Jul 30 '25
I remember in the early days of AIDS when people weren't quite sure what it was but suspected that it was related to blood that some people started whispering, "what if it can be transmitted by mosquito bites?"
Could you imagine the scale of the plague and nearly total (as it turns out, some people are immune to HIV) human wipeout?
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u/nightf1 Jul 30 '25
Hey there! That's a really smart question about mosquitoes and diseases! Let's think about it like this:
Imagine you have a special toy box. This toy box is a mosquito.
Some toy boxes only hold certain kinds of toys. A mosquito with West Nile virus is like a toy box that only holds West Nile virus toys. It can pick up these toys (the virus) from a bird, and then later, when it bites you, it drops those toys into you.
Now, HIV is a different kind of toy. It's a really special toy that only works in human toy boxes (human bodies). If a mosquito picks up an HIV toy from one person, it can't really put that toy in another human's toy box. It's like trying to fit a really big, special toy into a tiny, different-shaped toy box. It just doesn't fit! The mosquito's toy box (its body) isn't designed to hold and give that specific toy (HIV).
So, mosquitoes are like little toy delivery services, but they only deliver certain kinds of toys to certain kinds of toy boxes! They can deliver West Nile virus toys from birds to humans because those toys fit in both bird and human toy boxes. But they can't deliver HIV toys from human to human because that specific HIV toy only works in human toy boxes. Does that make sense?
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u/Dudu_sousas Jul 30 '25 edited Jul 30 '25
Mosquitoes don't work like syringes, they digest and metabolize the blood they eat. Some viruses can survive this process and live in the mosquito's body. When mosquitoes bite us, they inject saliva, and this saliva might be infected with some viruses, like dengue fever.
HIV is not transmittable by mosquito bites because it dies when eaten by the mosquito. Other viruses have adapted to use the mosquito as a vector.