Most viral infections can only be fought off by the body's immune system. In fact, the only viral infections that science has cured has been through the use of vaccinations. This raises the obvious question: Why isn't a vaccination being developed? There are several reasons. The first is that a vaccination against one strain of the DEN virus would protect the individual from that strain, but would mean that invasion by a different strain of DEN would result in Dengue Hemorrhagic Fever. So a vaccination would have to be used for all forms of the virus. Even if this were to occur, there would still be one other severe problem with the vaccination. The effectiveness of the body's immunity through the use of vaccinations declines over time. However, it would not be possible to determine at what point the body's immunity would require a booster without running human trials. If the immunity did get too low, the patient would again acquire DHF, because of the minimal resistance still being afforded by the body's system.

Genetic Engineering Offers A Possible Solution

Overview:

Using a modified retrovirus, scientists were able to transduce a mosquito with an antisense RNA sequence. Because antisense RNA is complementary to Sense RNA, it binds to it, preventing tRNA from binding to the sense RNA and producing the protein.

In Detail:

1. It was first determined that it would be possible to use a modified avian retrovirus (dsSIN) to insert specific DNA sequences into certain mosquito cells. The cells infected in the salivary glands of the mosquito by the avian virus were the same cells of the salivary gland infected by the DEN virus. This meant that it would be possible to program antisense RNA strands to crucial RNA coding strands of the DEN virus.
2. A dsSIN virus was modified to include a 567-base antisense RNA that was targeted to disrupt a premembrane protein in the DEN-2 (DEN-2 is one of the 4 types of DEN virus mutations.) viral genome. Inhibition of the transcription of this protein prevented the formation of the virus.
3. The exact sequence of the 567 bases was determined by sequencing the promoter region of the viral genome. The complementary RNA bases to this sequence determined the code of the antisense RNA strand.
4. To determine whether they had inserted the 567-bases, researchers performed a Northern blot analysis on a control of the avian virus and of the target cells of the virus. The target cells that contained the antisense RNA coding were 567 base pairs longer, and thus could be differentiatied by their location on the agarose gel.
5. Once the recombinant viruses were isolated. Two groups of female mosquitoes were created. The target group were intrathoracically injected with both the recombinant avian virus and the DEN-2 virus. The control group received only the DEN-2 virus.
6. After 11 days, tissue samples of the salivary glands and the midguts are taken from the target group and the control group.
7. A rabbit antiserum that binds to the DEN virus is applied to the tissues.
8. Then a goat antirabbit antibody is applied to the tissues. This factor binds to the rabbit antiserum. The goat antirabbit antiserum has immunoflourescent properties, so if the DEN virus is present, it can be detected because it will be glowing.
9. The mosquitoes that were genetically altered with the antisense RNA do not produce Dengue virus in their salivary glands.