Can HIV be Transmitted by Mosquitoes?

21 March 2017

Question

Is it possible to get HIV from a mosquito that has drawn blood from an infected person and passed it onto a healthy person?

Answer

Ricky Nathvani put Mehran's question to Peter Bull at the Department of Pathology at the University of Cambridge...

Peter - The short answer to this question is very clearly stated by The Centre for Disease Control in Atlanta on their website. No, HIV is not transmitted by mosquitoes, ticks, or any other insects.

Ricky - Phew! Well that’s a relief... but why?

Peter - Several viruses are transmitted by insects. For example: dengue, zika, yellow fever, and the parasites responsible for malaria and sleeping sickness. If all these diseases are transmitted by insects, why not HIV?

What all these infections have in common is the ability to reproduce and multiply within specific insects and then be reinjected into another person. By contrast, HIV is immediately rendered harmless once it gets digested in the insect’s gut.

Ricky - So, it turns out that HIV in infected blood just gets digested inside mosquitoes and can’t do much from there. But how do all those other nasty diseases end up surviving?

Peter - Viruses like dengue, that I just mentioned, are all in the same biological group called flaviviruses. They can all reprogramme insect cells to manufacture copies of themselves. This is an enormous feat of nanoengineering involving specific interactions between many virus and insect molecules. And the viruses genetic software, if you like, only works with compatible insect’s cellular hardware.

Similarly, the parasite responsible for malaria has evolved to infect insects over millions of years. Instead of being destroyed by mosquito digestive juices, which is what happens to HIV, the parasite’s sex cells picked up from an infected human fuse to form a new immature form of the parasite. After escaping through the wall of the gut, this divides to produce thousands of new malaria parasites which make their way to the mosquito's salivary glands ready to be injected with saliva through a dedicated tube into another human when the mosquito next takes a blood meal.

Ricky - So certain diseases can hijack the mosquito cells to make thousands of copies of itself. But thankfully, other blood borne viruses like HIV can’t really do this…

Peter - There are a lot of stages a virus or a parasite has to go through to be transmitted between humans. HIV isn’t capable of surviving and replicating in a mosquito so it can be transmitted because it gets destroyed in the mosquito’s gut. Nor is it able to infect or multiply in insect cells. Insects are not like flying syringe needles or blood bags, and only a handful of infectious agents have evolved the specialised ability to reproduce in insects and then spread to another person.

Ricky - So malaria and yellow fever might find it’s way into you from a mosquito, but at least HIV won’t. Cheers for the answer Peter.

Comments

There are a large number of biting flies that transmit infections purely mechanically (the infective organism doesn't develop within the insect, but the interupted feeding habits of the fly means there is blood on the insects mouthparts as it goes from host to host. For example Trypanosoma Vivax infections spread by species of Stomoxys, Chrysops and other flies. Probably not important but could they be responsible for some transmission?

No, it's highly unlikely. The infecting dose from a bite alone, without amplifying the bug numbers within the fly vector, is so vanishingly small as to be negligible.

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