Why is it hard to cure common cold?

Because common cold wears an invisibility cloak.

No.

Firstly, there are more than 200 viruses which cause common cold.

Now, developing 200 vaccines for 200 viruses is impractical.

Secondly, developing a single vaccine for all 200 viruses is proving to be.

Complex, time consuming and expensive as a lot of R&D is required.

Thirdly, we can't make antivirals to kill viruses.

Just like we make antibiotics to kill bacteria.

Why?

Because antibiotics attack the bacteria's protective cell walls.

But as viruses don't have any cell wall, antivirals will be useless.

However, there might be some good news.

Now, a virus survives in human body by hijacking a protein found in human cells.

Researchers have developed a compound which inhibits the virus from doing so.

But as the compound targets human cells, more research is needed to test its safety.

Why is it hard to cure cancer?

Cancer is not a single disease.

It is a name given to a collection of diseases that have some common characteristics.

Cancer usually begins when there is a sudden change.

Or mutation in the genes present in our cells.

This leads to uncontrolled cell division.

Now, it is hard to cure cancer because.

Every cancer is caused by a different set of genetic mutations.

In different types of cells.

Hence, it is a different disease each time due to which.

A treatment which works for an individual doesn't necessarily work for the other.

Now, cancer cells can be killed with treatments like chemotherapy or radiation.

However, sometimes these treatments may not kill all the cancer cells.

Risking a cancer relapse.

Moreover, such treatments even harm healthy cells of our body.

Cancer cells can even metastasize i.e., they can spread to different body parts.

And start growing there, thus making it difficult to eradicate cancer completely.

In addition to this, many cancers are diagnosed at very late stages.

Which makes treatment less likely to succeed.

Thus reducing the chances of survival.

Why is it hard to cure Alzheimer's disease?

Alzheimer's disease is an irreversible, progressive brain disorder.

It basically occurs when proteins in the brain malfunction.

And clump together forming plaques and tangles.

These plaques and tangles block communication in between brain cells.

And even cause cell death.

Thus leading to memory loss, mood changes, hallucinations, etc.

Now, it is hard to cure Alzheimer's because symptoms of the disease.

Begin to show when it has almost irreversibly damaged the brain.

Also, finding candidates for effective clinical trials is difficult.

Because there is no method to identify people with the disease at initial stages.

Thus, it is hard to test the medications and check whether they work or not.

In addition to this, Alzheimer's affects different people in different ways.

Hence, a drug which is somewhat effective on a patient suffering from Alzheimer's.

Might not work on another patient.

In short, due to a lack of fundamental understanding of the disease.

We are unable to cure Alzheimer's.

Why is it hard to cure HIV / AIDS?

HIV or human immunodeficiency virus infects the cells of immune system.

Causing them to produce more copies of the virus and then eventually die.

When too many immune cells of our body die.

And our immune system is unable to fight off diseases.

Then we are said to have AIDS or Acquired immunodeficiency syndrome.

Now, coming back to the question.

It is hard to cure HIV or AIDS.

Because HIV has the ability to mutate extremely quickly.

Hence, a drug which is somewhat effective on a patient suffering from HIV or AIDS.

Might not work on another patient because of the mutated HIV.

Now, there are certain antiretroviral drugs.

That prevent the cells from producing new copies of HIV.

Thus controlling the HIV levels in our body.

But, it is hard to completely eradicate HIV.

Because the virus integrates its DNA into our cell's DNA.

Hence, if we stop taking the drugs.

The DNA of the virus can again cause the cell to produce copies of the virus.

And thus, we are unable to control the level of HIV infected cells in our body.