Many people wonder whether HIV can be passed from human to human by mosquitoes. After all, mosquitoes are more than just annoying pests that buzz in your ear and cause an itchy insect bite. They are actually one of the deadliest animals in the world and a huge public health concern. They are capable of infecting humans with diseases like dengue fever, yellow fever, Zika, West Nile virus, and malaria. Depending on various factors such as climate and preventive measures, mosquito-borne diseases cause hundreds of thousands to millions of deaths each year.
With these statistics, it is understandable that people wonder if HIV is one of those infectious diseases that mosquitoes can transmit. Luckily, the answer is no.
HIV is transmitted from person to person through body fluids, like blood, semen, vaginal fluids, and breast milk. HIV is not transmitted through sweat, saliva, or tears. HIV can only be transmitted if the infected fluids come in contact with someone in one of three ways:
HIV transmission usually occurs during anal or vaginal sex without a condom, or through sharing syringes and hypodermic needles.
Once in lymph glands and the bloodstream, HIV targets a special kind of white blood cell, called a CD4 lymphocyte or a helper T cell. HIV is a specific kind of virus known as a retrovirus. This means that instead of carrying around its genetic information encoded in DNA, it carries RNA. When a retrovirus infects a cell, it forces the healthy cell to convert the RNA message into DNA. The healthy cell is tricked into adding the viral DNA to its own genes and starts making copies of the retrovirus, which are then released into the body, where they infect other healthy cells.
When HIV infects a CD4 cell, it forces the CD4 cell to make copies of the virus. HIV also destroys the CD4 cells it infects. CD4 cells are an important part of the immune system, so as HIV kills CD4 cells, it weakens the immune system and makes it harder for the body to fight off infections and even some types of cancer. A diagnosis of AIDS occurs when the number of CD4 cells (CD4 count, or T-cell count) drops below a specific threshold or when certain complications occur.
According to the World Health Organization, “Vectors are living organisms that can transmit infectious diseases between humans or from animals to humans.” Mosquitoes are one of the best-known and most dangerous vectors. Simply put, mosquitoes bite an infected human or animal, drink their infected blood, and pass on that infection to other humans.
Only female mosquitoes bite humans and other animals to get a blood meal and usually only need a blood meal to produce eggs. The rest of the time, they feed on nectar as male mosquitoes do.
When a female mosquito decides to bite you, it inserts its mouth parts, called a proboscis, into your skin. The proboscis may seem like one long needle, but it’s actually made up of six different parts. One is a tube that drips saliva into the bite. Mosquito saliva contains special chemicals that help keep your blood flowing while the mosquito feeds. A different tube is used to pierce a blood vessel and suck your blood. The saliva tube and the blood-sucking tube are completely separate, so the blood that the mosquito has already consumed won’t go back into your body.
Some parasites and viruses can be found in an infected person’s bloodstream. When a mosquito feeds, the infected blood gets sucked into the mosquito’s stomach. Certain parasites (like malaria) and viruses (like dengue fever, yellow fever, Zika, and West Nile virus) will develop and replicate in the mosquito’s gut tissues and then travel to the salivary glands, where the mosquito’s saliva is made. After that, every time the mosquito bites someone and drips saliva into them, the mosquito will be able to pass on the illness to that person. This is what’s known as biological transmission.
Once you understand how HIV is transmitted and how mosquitoes transmit other diseases, you can understand why transmission of HIV/AIDS through mosquito bites isn’t possible.
First of all, HIV needs CD4 cells for replication. Mosquitoes don’t have CD4 cells, so HIV isn’t able to make copies of itself. Then, because HIV can’t start infecting the mosquito’s tissues, the viruses just get digested inside the mosquito’s gut. This means that HIV is not circulating inside the mosquito’s body, so no viruses make it into the salivary glands. The mosquito can’t pass on HIV the next time they bite someone.
Mechanical transmission happens when a bloodsucking insect has some infected blood on its mouthparts. The infected blood then gets passed along to the next person they bite — just as blood on a used needle can infect the next person to get stuck by it.
Mosquitoes keep drinking blood until they’re full, so if they get interrupted during a blood meal, they will find another human or animal to bite. There will be small amounts of blood from their last meal on the outside of their mouthparts. It is reasonable to ask: If a mosquito is interrupted while biting an HIV-positive person, why doesn’t the next person they bite become infected?
There are multiple reasons. First, HIV cannot live outside the body for very long, so HIV on the outside of the proboscis is probably dead. Another (and more important) reason is that there simply aren’t enough HIV particles to cause infection. Even during acute HIV infection, when viral loads (the amount of virus circulating in the blood) are highest, the tiny amount of HIV-positive blood that would be left on the outside of the mosquito’s proboscis would not contain enough virus to cause infection in the next person.
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Increasing awareness is one of the best ways to reduce the stigma surrounding HIV/AIDS. Have you ever wondered (or been asked) whether mosquitoes could transmit HIV? Share your experience in the comments below, or start a conversation by posting on your Activities page.