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article imageMosquito spit may limit Dengue virus transmission

By Tim Sandle     Sep 24, 2016 in Science
A key transmission factor with many viral diseases carried by mosquitoes is the saliva of the insects. A new finding, however, suggests that saliva can also help to prevent viral transfer, particularly Dengue virus.
Dengue fever is a serious illness that affects about 50 million people a year. Symptoms include fever, headache, muscle and joint pains and a characteristic skin rash that is similar to measles.
Mosquito salvia can help viral transmission from the mosquito to the host. Here the salvia contains proteins that supress the mammalian immune system. A new finding suggests this isn’t always one way. One salvia protein coded D7 and found in the saliva of the Aedes aegypti mosquito appears to bind to Dengue virus where it functions to inhibit transmission.
However, some people carry antibodies against the D7 protein which means that this inhibitory effect doesn’t take place. The net result is that this can facilitate virus transmission and thus enhance disease severity.
This effect has come to light from research carried out by Dr. Michael Conway of the Central Michigan University College of Medicine. Based on this the research team are attempting to use mosquito saliva or midgut proteins to block transmission of Dengue virus.
The importance of the D7 protein has come from an analysis of a range of different proteins found in mosquito saliva. Such proteins help the mosquito with its blood feeding.
Taking the protein tests showed that, in cells, that D7 significantly reduced Dengue virus RNA levels. This suggests the protein can inhibit viral infection or multiplication. Further studies were then undertaken using mice infected with Dengue. These studies showed that D7 significantly reduced the levels of dengue viral genetic material.
In terms of what is happening it was found that D7 can bind the Dengue virus though the virus's envelope protein (which covers the viral surface). While this is good news in one sense for developing an antiviral, the fact that many people have high levels of anti-D7 antibodies shows the complexity of virus-vector-host interactions and further work is required in order to develop an effective antiviral medicine.
The research has been published in the journal PLOS Neglected Tropical Diseases. The research paper is “Aedes aegypti D7 Saliva Protein Inhibits Dengue Virus Infection.”
More about Dengue fever, Mosquito, Saliva, Virus
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