Science Explained: Why HIV is difficult to treat
Columns / September 16, 2015
Why HIV is difficult to treat
The Human Immunodeficiency Virus
HIV fits under a branch of viruses called lentiviruses, and many animals such as cats, cows, horses, and sheep have strains of lentiviruses that typically don’t cause disease. In primates, the lentivirus is called SIV (Simian immunodeficiency virus), and multiple strains exist that are specific to various regions.
Although animals typically survive with a strain of lentivirus, it was found that when an African monkey was infected with an Asian monkey’s strain of SIV, and vice versa, the monkey gets something called Simian AIDS, similar to what humans experience with HIV/AIDS. If humans had a long history of this lentivirus, it would probably not cause such a dramatic illness, suggesting that HIV is fairly new to humans and may have been contracted from trapping, butchering, and eating chimps.
HIV can be transmitted—in descending order of likelihood—via blood transfusion, by birth, by using infected needles and sexual contact. Overtime, HIV destroys vital immune cells that are necessary for fighting common colds and infections, and eventually, individuals will be left with a very low immune cell, specifically CD4 T-cell, count. If their CD4 T-cell count is below 200 cells/mm3, the individual’s condition has reached the final stage of HIV infection, known as AIDS.
HIV can also progress to AIDS if individuals are diagnosed with certain cancers, or opportunistic infections. Such infections, like Tuberculosis or Lymphoma, do not pose a great threat to healthy individuals but can be very dangerous to immunodeficient persons.
The Dangers of Viruses
Unlike bacteria, viruses are not typically considered living organisms, and are typically more complex in their treatment. The virus infects cells by latching onto a host cell, which they take over and use to reproduce. This makes them so much harder to target and kill, because in killing the virus we must also kill the host cell. This is why viruses, such as smallpox, Hepatitis B, Hepatitis C, rabies, HPV and Ebola are difficult to treat, and extremely challenging to cure.
However, most of these viruses have vaccines available that will prevent individuals from contracting them. Bacterial infections and diseases can be cured with a simple antibacterial or antibiotic, though this method can also leave you defenseless due to superbugs. There are an approximated 23,000 people that die every year in the United States from drug-resistant superbugs that have developed from the overuse of antibiotics.
For HIV to enter an immune cell, it must bind to a protein receptor called CD4, as well as a co-receptor CCR5. Once the virus is bound to the receptors, the union of protein and virus are internalized into the cell. Interestingly, some individuals have a mutation in their genes which prevents the CCR5 co-receptor from functioning properly. The dysfunctional CCR5 gene prevents the protein from even making it onto the cell’s surface when your body manufactures these cells. Without it, the virus cannot infect the cell, making some individuals resistant to HIV/AIDS.
In addition, researchers have been able to develop a new class of drugs that alter how the CCR5 protein functions, preventing HIV from taking over the entire immune system and causing AIDS. There are now six classes of HIV drugs, one of those being entry inhibitors, also known as CCR5 antagonists. The drug works by binding the CCR5 co-receptor and causing the co-receptor to change shape. These conformational changes prevent the virus from binding.
HIV/AIDS is arguably one of the most misunderstood epidemics in the world, largely due to the stigmas that surround it. Over 35 million people live with this disease worldwide, and individuals of poor socioeconomic status struggle to access treatment, leaving them with a much higher risk of developing AIDS. By educating ourselves with the science behind a disease, and becoming aware of the social impact misinformation can have, we are better equipped to prevent the spread of HIV altogether.
Danica is a second-year science major. She is passionate about human genetics, physics and neurology.