why it is difficult to discover medicine for Aids?....
Answers
ANSWER:-
Well, I suppose you are referring to HIV (AIDS is a disease, not a virus), so the question is why antiretrovirals (ART) are more difficult to develop than other antivirals? Here I try to give an explanation based on the pharmacology perspective. Actually the mechanism of action of ART is no different than other antivirals, both of which work by interfering with the key enzymes necessary for viral replication (e.g., polymerases, proteases and integrases). As a result, developing an effective inhibitor against HIV should be no more difficult than other viruses like HCV, influenza or dengue.
However, two unique characteristics of retroviruses added additional layers of complexity. The first is that because retroviruses mutate very fast, drug resistance can develop fairly quickly. The polymerases (reverse transcriptase) of retroviruses lack the proofreading mechanism, which resulted in a high mutation rate of retroviruses. As a result, HIV can develop a high degree of diversity after several years of infection, which poses a serious challenge for drug development.
What makes things even worse is that because retroviruses make permanent integrations into the host cell chromosome, retroviral infections are generally incurable, which require lifelong treatments. Such persistent nature of retroviral infections not only makes it difficult to find a cure, but also complicated the treatments. Because most viruses (e.g., measles, influenza or Ebola) don’t form latent reservoirs, they can’t persist indefinitely in our body; instead our immune system will eventually take over and wipe them out. As a result, even partially effective drugs can do a great help, as they can suppress the viruses temporarily, which can buy some time for our immune system. However, that’s not the case of persistent viral infections, as these viruses can evade the immune clearance. Even the vast majority is killed off by the drugs, a few viruses escaping the treatment can still make a comeback. As a result, antiviral drugs against persistent infections must be 100% effective, to which no compromise is acceptable. That’s why HIV is often treated with a three-drug combo, thereby minimizing the risk of drug resistance.
Another implication is that because HIV requires lifelong, multi-drug combined treatments, patients are much less tolerant to toxicity or pharmacokinetics issues. As a result, ART should be extremely well tolerated, with a good absorption and metabolism profile (which means the drugs are taken only once a day) to ensure a good adherence. For example, tenofovir disoproxil (TDF) has largely been phased out due to its long term effects like bone loss and renal problems. However, such long term toxicity would not be an issue for HCV (which is a persistent but curable infection), as HCV can be cured in just 12 weeks, which is simply not long enough for the long term effects to manifest. For some imminently life-threatening infections (e.g., Ebola), drug toxicity is even less an issue and even daily intravenous injections are acceptable (which indicates a poor oral absorption).
So you can understand what kind of challenge we need to overcome when dealing with something like HIV. That’s why despite numerous resources being spent, it took 30 years for ART to perfect. Nevertheless, even though HIV infection is still incurable to date, patients on ART can keep the viruses in check indefinitely, with a virtually indistinguishable lifespan to uninfected people, which is one of the greatest achievements in medicine.
Answer:
HIV stay inactive in T- lymphocyte cells and escape our immune system. So detection is very difficult. Unless detected they cannot be eliminated. Reports by the researchers are positive and we may have a cure in the near future.