Viruses are not always harmful. 6 ways they are used in health care and pest control

We tend to think of viruses simply in terms of their harmful effects on human health and life. The 1918 flu pandemic killed an estimated 50 million people. Smallpox killed 30% of those who caught it, and those who survived were often scarred and blinded. We are all too familiar with the health and economic impacts of COVID lately.

But viruses can also be used to benefit human health, agriculture and the environment.

Viruses are relatively simple in structure, consisting of a piece of genetic material (RNA or DNA) enclosed in a protein shell (capsid). Some also have an outer envelope.

Viruses enter your cells and use your cellular machinery to copy themselves. Here are six ways we use this for health and pest control.

Read more: How do viruses enter cells? Their infection tactics determine whether they can jump species or cause a pandemic

1. To correct the genes

Viruses are used in some gene therapies to correct malfunctioning genes. Genes are DNA sequences that code for a specific protein needed for the cell to function.

If we remove viral genetic material from the capsid (protein coating), we can use the space to transport “cargo” into cells. These modified viruses are called “viral vectors”.

Viruses consist of a piece of RNA or DNA enclosed in a protein coat called a capsid.

Viral vectors can deliver a functional gene to a person with a genetic disease whose own gene is not working properly.

Some genetic disorders treated in this way include hemophilia, sickle cell anemia, and beta thalassemia.

2. Treat cancer

Viral vectors can be used to treat cancer.

Healthy people have p53, a tumor suppressor gene. About half of cancers are associated with loss of p53.

Replacing the damaged p53 gene using a viral vector stops the cancer cell from replicating and causes it to commit suicide (apoptosis).

Viral vectors can also be used to deliver an inactive drug to a tumor, where it is then activated to kill the tumor cell.

This targeted therapy reduces the side effects that are otherwise seen with cytotoxic (cell-killing) drugs.

This is how a treatment called gene therapy works.

We can also use oncolytic (cancer cell-killing) viruses to treat certain types of cancer.

Tumor cells often lose their antiviral defenses. In the case of melanoma, a modified herpes simplex virus can kill rapidly dividing melanoma cells while leaving non-tumor cells alone.

3. Create immune responses

Viral vectors can create a protective immune response to a specific viral antigen.

One COVID vaccine uses a modified chimpanzee adenovirus (adenoviruses cause the common cold in humans) to transport RNA encoding the spike protein of SARS-CoV-2 into human cells.

Read more: How the viral vector vaccine puzzle was solved, leading to today’s COVID-19 vaccines

The RNA is then used to make spike protein copies that stimulate our immune cells to replicate and “remember” the spike protein.

Then, when you are actually exposed to SARS-CoV-2, your immune system can produce a lot of antibodies and virus-killing cells very quickly to prevent or reduce the severity of the infection.

4. They act like vaccines

Viruses can be modified to act directly as vaccines themselves in several ways.

We can weaken a virus (for an attenuated virus vaccine) so that it does not cause infection in a healthy host, but can still replicate to stimulate an immune response. This is how the chicken pox vaccine works.

Salk’s polio vaccine uses a whole virus that has been inactivated (so it can’t cause disease).

Others use a small part of the virus, such as the capsid protein, to stimulate an immune response (subunit vaccines).

An RNA vaccine packages viral RNA for a specific protein that will stimulate an immune response.

5. Kill the bacteria

Viruses can – in limited situations in Australia – be used to treat antibiotic-resistant bacterial infections.

Bacteriophages are viruses that kill bacteria. Each type of phage usually infects a specific type of bacteria.

Unlike antibiotics—which often kill the “good” bacteria along with the disease-causing ones—phage therapy leaves your normal flora (beneficial microbes) intact.

Bacteriophages (red) are viruses that kill bacteria (green).

6. Target plant, fungal or animal pests

Viruses can be species specific (infecting only one species) and even cell specific (infecting only one type of cell).

This happens because the proteins that viruses use to attach to cells have a shape that binds to a specific type of cell receptor or molecule, like a specific key fits a lock.

The virus can enter cells of all species with this receptor/molecule. For example, the rabies virus can infect all mammals because we share the exact receptor, and mammals have other characteristics that allow infection to occur while other non-mammalian species do not.

When the receptor is found in only one cell type, then the virus will infect that cell type, which can only be found in one or a limited number of species. Hepatitis B virus successfully infects liver cells primarily in humans and chimpanzees.

We can use this property of specificity to target invasive plant species (reducing the need for chemical herbicides) and insect pests (reducing the need for chemical insecticides). Baculoviruses, for example, are used to control caterpillars.

Similarly, bacteriophages can be used to control bacterial diseases of tomatoes and grapevines.

Read more: ‘Phage therapy’ can treat some drug-resistant superbug infections, but comes with unique challenges

Other viruses reduce plant damage from fungal pests.

Myxoma virus and calicivirus reduce rabbit populations and their environmental impact and improve agricultural production.

Just as humans can be protected by vaccination, plants can be “immunized” against a disease-causing virus by being exposed to a milder version.

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