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Treatment as prevention (TasP) is a concept in public health that promotes treatment as a way to prevent and reduce the likelihood of the transmission of an infection from an infected individual to others. The term is primarily used to talk about treating people that are currently living with human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS) to lower the risk of new HIV infection transmissions. In relation to HIV, antiretroviral therapy (ART) is a three or more drug combination therapy that is used to decrease the viral load, or the measured amount of virus, in an infected individual. Such medications are used by HIV-positive individuals to prevent the virus from spreading to their negative partner(s) and improve their health to increase their lifespans. Other names for ART include highly active antiretroviral therapy (HAART), combination antiretroviral therapy (cART), triple therapy and triple drug cocktail.

Through the use of antiretroviral therapy, an individual's viral load is decreased, reducing the amount of HIV-1 virus in both blood and genital secretion samples. A decrease in viral load reduces an individual's chance to transmit the infection. Such effectiveness is evident in HIV Prevention Trials Network's clinical trial, HTPN 052. Although evidence through clinical trials like HTPN 052 reveal positive results in regards to the implementation of antiretroviral drugs as preventative measures against HIV transmission, challenges such as overall cost and drug resistance prevent such initiatives to be put into action. As a result, efforts to find solutions to such challenges and risks have been a focus in research efforts, the goal being to reach a point in time where HIV treatment as prevention becomes a main part of public health initiatives to combat HIV/AIDS.

Today, treatment as prevention has not been implemented permanently into practice.

HIV Prevention Trials Network Clinical Trial 052
The HIV Prevention Trials Network conducted a clinical trial, HPTN 052, that analyzed the effectiveness of antiretroviral drugs on the HIV-1 virus. 1,783 HIV sero-discordant couples, or couples that consist of an HIV-positive individual and an HIV-negative partner, from nine different countries were a part of the study. 97% of the couples were heterosexual. In August of 2011, the HIV Prevention Trials Network concluded that the likelihood of transmission between the couples who were provided early antiretroviral therapy reduced by 96%. When the trial completed, the overall reduction percentage of HIV-1 transmission between couples who were treated early with ART and couples who received the delay-ART treatment was 93%. The study's purpose was to reveal that HIV-1 viral transmission can be prevented through treatment, leading many regions to incorporate a treatment as prevention plan into their public health policy for responding to HIV.

Overall Cost of Treatment
For many countries, especially low- and middle-income countries (LMICS), the overall cost of treatment in the 1990s and early 2000s was too expensive for infected patients to afford it. In addition, individuals with low incomes in the United States struggled to pay high prices set by pharmaceutical companies for antiretroviral drugs. As a result, it is currently implausible for a global treatment system or policy to be put into place since no universal HIV/AIDS test and medication regimen exists because of technology and wealth disparities worldwide.

Side Effects Caused by ART
Antiretroviral drugs can cause patients to experience various side effects including becoming nauseated or suffering from gastrointestinal pains and issues. Such side effects are the result of medications being too toxic for individuals to take. In addition, in LMICs, an increase in the number of side effects expressed in a country leads to the underdeveloped health care systems of said country having to use their limited funds to account for service delivery costs of medications to counter the newly inflicted problems among infected individuals.

HIV-1 Drug Resistance
Beyond side effects, developed countries, when first discussing the implementation of ART in the developing world, believed that the allowance of third-world countries to have early access to antiretroviral drugs would potentially lead to the development of drug resistance. Recently, such resistance has developed in third-world countries as a result of medication combinations failing to diminish the viral load of HIV-1 in infected individuals, the lack of existence of virological testing to discover such failures in patients in these regions of the world, and the lack of different variants of medication regimens to suppress the evolution of the infection.

In the case of resistance to the first-line of combination medications for the HIV-1 virus, mutations occurred within genes of HIV-1 viral RNA that enters T-cells within the human body. Mutations are the result of reverse transcriptase, the enzyme that is responsible for reverse-transcribing the viral RNA into viral DNA, having a high error rate when copying the viral RNA. The mutations occur within the nucleotide bases of the new viral DNA.

After the mutated viral DNA is implemented into the host cell's DNA, the DNA is translated to produce viral proteins that will assist in the infecting of other surrounding cells. When translated, the mutations lead to different amino acids formulating the viral proteins. The primary proteins that are focused upon in relation to HIV-1 are the viral protease and reverse transcriptase because these enzymes are the ones that are inhibited by antiretroviral medications.

Overall, the transmitted drug resistance (TDR) among resource-limited setting (RLS) adults in regions such as Africa, Asia and Brazil has increased. The calculated rate of TDR was 6.6% as of 2015. In addition, studies that were conducted within these regions revealed a correlation between the length of time ART was implemented as a method of treatment and the likelihood of the establishment of TDR. The studies concluded that the likelihood of TDR in LMICs is 1.7 times greater if ART is implemented for equal to or more than five years.

Necessity for Adherence
Antiretroviral therapy requires HIV-positive individuals to abide by strict adherence and thrives when countries have the necessary HIV services available for infected individuals to access. Management of HIV/AIDS includes services such as HIV testing and diagnosing, consistent HIV care and treatment, education lessons regarding how to use ART effectively and distribution methods to ensure individuals receive their medications. In LMICs, the lack of HIV testing, which, in turn, creates a lack of HIV diagnosing, limits the opportunity for the initiation of treatment as a preventative method because most infected individuals are unaware of their current condition.

Global Fund
In 2002, The Global Fund to Fight AIDS, Tuberculosis and Malaria (Global Fund) was a financial initiative developed to raise and provide funding to the developing world in an attempt to enhance their care and treatment programs for individuals who are living with HIV/AIDS, tuberculosis (TB) and malaria. For the international organization to be successful, developed countries must work in conjunction with third-world countries, private organizations, civil society and afflicted communities to ease the impact of the epidemics. In an attempt to prevent the misuse of funding provided by the Global Fund, a system was set in place for countries to apply for funding through submission of proposals and implementation plans. As a result of the impact of the Global Fund, seventeen and a half million people are being treated with antiretroviral therapy as of 2017.

PEPFAR
In 2003, in an attempt to promote the importance of HIV research and funding, George W. Bush enacted the President's Emergency Plan for AIDS Relief (PEPFAR/Emergency Plan), committing the United States government to authorize $15 billion dollars to support HIV/AIDS, tuberculosis (TB) and malaria over a five year period in third-world countries. With the improvement of ART treatment as a result of PEPFAR, the number of new infections declined by 51-76% worldwide since the enactment of the Emergency Plan. In addition, the funding received from PEPFAR allowed developing countries to treat millions, prevented millions of new infections and provided other care services to millions of already infected individuals.

Generic Drugs
Antiretroviral generic drugs are medications that are identical to brand names drugs. Pharmaceutical companies in Brazil and India like Cipla and Farmanguinhos dedicated their efforts to reduce the prices of ART drugs. For example, Cipla reduced prices of antiretroviral drugs for poor third-world countries to practically zero. Through their initatives in combination with pharmaceutical companies in Brazil, individuals in third-world countries are being provided access to antiretroviral treatment regimens that they could not afford before. Today, ART drug combinations cost $75 dollars in Africa.

With the providing of generic drugs at such low costs in the developing world brings about turmoil regarding the current expensive prices of antiretroviral drugs in the United States. Antiretroviral drug regimens in the United States range in price from $10,000 to $40,000 as a result of pharmaceutical companies having control of price regulation. With this, the future of price reduction in the United States depends on pharmaceutical competition and negotiation to make antiretroviral drugs available to all low- and middle-income individuals despite where they may live in the world.

"Community-Based Care"
"Community-based care" refers to communities with high rates of HIV transmission and infected individuals taking the initiative to end the spread of HIV within their own community. Community based care services include access to:


 * HIV testing
 * directly observed therapy with HAART (DOT-HAART)
 * DOT-HAART refers to the administration and delivery of antiretroviral drugs by community members to ensure individuals adhere to drug regimens. Such community members observe the taking of medications to provide guidance and clarify any questions infected individuals may have.
 * educational services regarding HIV transmission and prevention methods
 * condoms and other barrier methods
 * maternal-child transmission packages
 * social services for families and orphaned children
 * other services to ensure suppression of HIV transmission

The utilization of community-based care assists in the efforts to diminish HIV transmission to reduce the number of new infections annually.

Cost-Effectiveness
In South Africa and India, a clinical trial was completed to determine the cost-effectiveness of administering antiretroviral drugs early to treat HIV. Sero-discordant couples were used in the study and each couple was provided either early or delayed antiretroviral treatment. Over a five-year period, researchers concluded that early ART was cost-saving in South Africa and cost-effective in India. Over a lifetime, early ART was determined to be very cost-effective in both countries. After the release of such results, other countries have concluded that it is cost-effective to utilize combination therapy resources especially when implementing them early into practice.

Pre- and Post-Exposure Prophylaxis
Antiretroviral chemoprophylaxis, or pre-exposure prophylaxis (PrEP), refers to the use of antiretroviral drugs prior to exposure of HIV as a precaution against transmission. PrEP is prescribed to individuals who are at high risk of contracting HIV and must be used daily to be effective. The most common regimen of PrEP is emtricitabine and tenofovir disoproxil fumarate (FTC-TDF), two oral antiretroviral medications. Around the world, PrEP has proven to diminish the chances of a HIV-negative individual from getting the disease and protects against the development and spreading of the virus within an individual's cells.

Post-exposure prophylaxis (PEP) refers to the temporary use of antiretroviral drugs when an HIV-negative individual has been potentially exposed to HIV. PEP must be taken 36-72 hours after exposure to prevent viral replication and acquisition of the virus. The medication must be taken daily for 28 days to ensure the elimination of HIV. One of the most common PEP regimens is Truvada. When determining whether to prescribe PEP, doctors analyze the HIV status and viral load of the infected partner in addition to the type of HIV exposure to draw conclusions regarding the amount of risk the non-infected partner faces regarding the development of the infection. It has been concluded that individuals who experience blood or mucosal exposure to an HIV-infected individual who has a high viral load experience the greatest risk to HIV transmission. Even though such risk exists in society and PEP has been used to prevent the transmission of HIV to non-infected individuals in certain scenarios—an example being the use of PEP by nurses who accidentally become exposed to HIV—there are currently no clinical trials to analyze the efficacy of PEP due to ethical reasons such as the ethics surrounding withholding treatment or PEP from individuals who have potentially been infected with the virus. Although this may be the case, PEP has the potential to prevent the spreading of HIV to individuals who are not on PrEP and have been exposed to the virus.

Single-tablet Regimens
When doctors prescribe antiretroviral drugs to patients, the initial prescriptions consist of drug regimens that contain multiple pills of different classes that must be taken daily. Although triple therapy is most commonly used, there are single-tablet regimens (STRs) that exist to treat AIDS. STRs are created through combining three antiretroviral drugs into one pill. Single-tablet regimens are only available at specific clinics around the world—meaning there is limited access to these regimens—and are only prescribed if a doctor feels a patient will struggle with the treatment schedule of antiretroviral therapy. The implementation of STRs worldwide could serve as a replacement for the triple-drug antiretroviral therapy and allow patients to have a less strict ART schedule to abide by.

Injectable HIV-1 Treatment
The greatest struggle faced by HIV-positive individuals is maintaining compliance of taking the ART pills every day. The lack of compliance can lead to drug failure or drug resistance. In July of 2017, The Lancet released an article revealing the results of a study conducted involving an injectable HIV-1 treatment to serve as a future replacement for the three-drug oral combination therapy. This new treatment would consist of two drugs: cabotegravir and rilpivirine and injections would occur every four to eight weeks for each patient. Thus far, the treatment has passed Phase II of the clinical trial and has been proven to be just as effective as the oral regimen.

Microbicides
In an attempt to prevent the spread of HIV to an HIV-negative individual, HIV-specific microbicides can be utilized to interrupt the viral life cycle. As a result of the interruption by the microbicides, the viral DNA transcribed from HIV RNA cannot be integrated into a host cell's genome by the enzyme integrase. The inability of HIV to infect host cells allows an individual to be safe from contracting the infection. In relation to the viral life cycle, microbicides can be used to disrupt the absorption of the virus into the body, the fusion of the viral and host cell's membranes, transcription of viral DNA and the integration of viral DNA into the genome of the host cell. For example, to prevent the fusion of the viral and host cell's membrane, monoclonal antibodies, which are virus entry inhibitors, can be placed into the human body to prevent the interaction between the CD4 receptors and the viral HIV envelope protein gp120. Post-entry inhibitors can be placed into the body to block the virus once it has entered the host cell. To be utilized, post-entry inhibitors must be released when viral reverse transcriptase or viral integrase are inhibited and replicated rapidly to combat the virus.

In addition, prior to intercourse, a topical microbicide product can be inserted in the vagina or rectum to prevent the spread of HIV/AIDs between partners.