How does a mosquito transmit Zika? Why Can't Mosquitoes Transmit HIV?

How mosquitoes spread Zika

1 Mosquito feeds on virus-infected blood.

2 Infected blood travels to the midgut.

3 Virus enters the circulatory system ...

4 ... and travels to the salivary glands.

5 Mosquito bites again, injecting virus-infected saliva into victim before feeding.


By Sarah Almukhtar and Mika Gröndahl | Sources: Dr. W. Augustine Dunn; Oxitec; The Anatomical Life of the Mosquito, R. E. Snodgrass


2.How does a mosquito transmit Zika?

The virus moves from its gut to its salivary glands.

Only female mosquitoes bite people: they need blood to lay eggs, while males drink plant nectar. In the female, the virus travels from the gut to the salivary glands and is injected into the next human victim. When a mosquito bites, it first injects an anti-coagulant saliva so blood does not clog its strawlike proboscis.

http://www.nytimes.com/interactive/2016/health/what-is-zika-virus.html?_r=0

April 01, 2015 | By: Julia Paoli

Why Can't Mosquitoes Transmit HIV?

Currently, I am reading a fabulous book by Bill Bryson entitled A Short History of Nearly Everything. It covers a wide range of scientific topics from the Big Bang to the microbes dwelling in the human body. However, one passage really caught my attention: Bryson noted how HIV, the agent behind the AIDS disease, is not transmissible by mosquitoes (page 312). This fact caught me off guard. I had always known that HIV is not spread by mosquitoes but had never questioned why.

Mosquitoes are carriers for several infamous viruses, most notably malaria and dengue fever. In fact, mosquitoes, through mosquito borne diseases, kill more people per year than any other animal. Luckily for humans, the HIV virus is not carried or spread by mosquitoes. Several reasons account for the inability of mosquitoes to transmit HIV.

1. Mosquitoes' Blood-Sucking Mechanism

As Professor Wayne Crans of Rutgers University so nicely puts it "mosquitoes are not flying hypodermic needles." The "snout" of a mosquito, the part that looks like a needle, is actually composed of six mouthparts. Four of these are used to pierce the skin of the person or animal that the mosquito is biting. The other two parts are composed of two tubes. One of the tubes sends saliva into the host and the other sends blood up to the mosquito. This two tube system is one reason why mosquitoes are unable to transmit HIV. Only saliva is injected into humans when a mosquito bites and thus HIV positive blood that a mosquito may have previously ingested is never transmitted to other humans.

2. The HIV virus gets digested in the mosquito's gut

Unlike mosquito borne diseases, HIV is unable to replicate within the mosquito's gut and therefore is broken down. In humans, HIV binds to T cells and begins replicating. No T cells exist inside the mosquito's gut and so the virus has no way of replicating or migrating to the mosquito's salivary glands. HIV particles are therefore digested by the mosquito alongside the actual blood meal. During the digestion process, the HIV particles are "completely destroyed."

3. HIV circulates at low levels in human blood

In order for mosquito-borne diseases to be spread from person to person, the associated virus needs to circulate within the host's blood at sufficient levels. HIV circulates in human blood at a far lower level than would be necessary to create a new infection. If a mosquito were to inject HIV positive blood into a human (which, as evidenced by reasons 1 and 2, is not possible), then it would take a whopping ten million mosquito bites to transmit one unit of HIV. By comparison, people who are HIV positive generally carry no more than ten units of HIV. Accidentally swallowing a mosquito or squashing one cannot lead to HIV infection either. In these situations the mosquito once again carries an insufficient amount of HIV positive blood to cause a new infection.

http://www.nature.com/scitable/blog/viruses101/why_cant_mosquitos_transmit_hiv