Option D.7 – Antivirals
D.7.1 – State how viruses differ from bacteria
Viruses act as parasites by inserting their DNA into a host cell, and using their machinery to reproduce. This is to the detriment of the cell.
D.7.2 – Describe the different ways in which antiviral drugs work
Some antiviral drugs are given in the form of vaccines, which are weakened or inactive forms of the virus. When this enters the body, the immune system recognises the antigens on the vaccine and produces the antibodies to fight it. Since antibodies permanently remain in the body, if the actual virus enters the body, it can respond immediately to overcome it and prevent infection. Using this method, many lethal diseases have been almost or completely eradicated.
Some antiviral drugs will block the ribosomes so that the virus cannot use its reproductive enzymes. Although the virus can still enter the cell, it will not be able to use it to replicate.
Other drugs will have fake nucleosides that will be incorporated into the genome of the virus when it replicates.
These nucleosides prevent viral DNA polymerase from replicating again, thus stopping any more production of the virus. The drug acyclovir is used to fight off herpes, and replaces the nucleoside guanine. This same drug can also be used against chickenpox and shingles.
Finally, some drugs will prevent the virus from entering the cell, such as to prevent the influenza virus.
D.7.3 – Discuss the difficulties associated with solving the AIDS problem
HIV (Human Immunodeficiency Virus) is a retrovirus, which means that it contains RNA. It works by fusing with the receptors on a T cell (part of the immune system) and releasing RNA and enzymes into it. Using these enzymes, including reverse transcriptase, the RNA is made into DNA and placed into the DNA of the host cell. The host cell will then start producing the virus, allowing it to spread throughout the body. HIV is difficult to treat because it will easily mutate and has a metabolism that is close linked to that of human cells, making antiviral drugs ineffective. In addition, treatment and control of the virus is made more difficult because antiretroviral agents are very expensive, and there are many sociocultural issues surrounding HIV. Since HIV attacks cells of the immune system, an infection causes it to be severely weakened, until other diseases that are normally easy to fight off can become lethal.
Viruses reproduce very quickly once they have invaded a cell, and their mutations allow them to adapt as their environment changes. Even when a vaccine for HIV is developed, new strains are constantly being formed that are not affected by it. Also, the fact that it contains RNA and changes its surface proteins so quickly means that it cannot be stored in the organism’s immune memory. Many vaccines have been tested, but are practically redundant against this constantly evolving virus – retroviruses have the highest mutation rates ever measured.
In terms of other possible drugs to destroy HIV, the way the virus integrates itself into the cell means that any drug that harms the virus will likewise harm the cell. There are not yet any known drugs that can solely target HIV alone, and leave the host cell undamaged.