We tend to just think of viruses in terms of their damaging impacts on human health and lives. The 1918 flu pandemic killed around 50 million people. Smallpox claimed 30% of those who caught it, and survivors were often scarred and blinded. More recently, we’re all too familiar with the health and economic impacts of COVID.

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

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

Viruses get into your cells and use your cell machinery to copy themselves.
Here are six ways we’ve harnessed this for health care and pest control.

1. To correct genes

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

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

Viral vectors can deliver a functional gene into someone with a genetic disorder whose own gene is not working properly.

Some genetic diseases treated this way include haemophilia, sickle cell disease and beta thalassaemia.

2. Treat cancer

Viral vectors can be used to treat cancer.

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

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

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

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

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

Tumour cells have often lost their antiviral defences. In the case of melanoma, a modified herpes simplex virus can kill rapidly dividing melanoma cells while largely leaving non-tumour cells alone.

3. Create immune responses

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

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

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

Then, when you are exposed to SARS-CoV-2 for real, your immune system can churn out lots of antibodies and virus-killing cells very quickly to prevent or reduce the severity of infection.

4. Act as 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 it doesn’t cause infection in a healthy host but can still replicate to stimulate the immune response. The chickenpox vaccine works like this.

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

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

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

5. Kill 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 particular species of bacteria.

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

6. Target plant, fungal or animal pests

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

This occurs because the proteins 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 the cells of all species with this receptor/molecule. For example, rabies virus can infect all mammals because we share the right receptor, and mammals have other characteristics that allow infection to occur whereas other non-mammal species don’t.

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

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

Similarly, bacteriophages can be used to control bacterial tomato and grapevine diseases.

Other viruses reduce plant damage from fungal pests.

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

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

Thea van de Mortel, Professor, Nursing, School of Nursing and Midwifery, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

What’s the difference? is a new editorial product that explains the similarities and differences between commonly confused health and medical terms, and why they matter.

The term “man flu” takes a humorous poke at men with minor respiratory infections, such as colds, who supposedly exaggerate their symptoms.

According to the stereotype, a man lies on the sofa with a box of tissues. Meanwhile his female partner, also with a snotty nose, carries on working from home, doing the chores and looking after him.

But is man flu real? Is there a valid biological reason behind men’s symptoms or are men just malingering? And how does man flu differ from flu?

What are the similarities?

Man flu could refer to a number of respiratory infections – a cold, flu, even a mild case of COVID. So it’s difficult to compare man flu with flu.

But for simplicity, let’s say man flu is actually a cold. If that’s the case, man flu and flu have some similar features.

Both are caused by viruses (but different ones). Both are improved with rest, fluids, and if needed painkillers, throat lozenges or decongestants to manage symptoms.

Both can share similar symptoms. Typically, more severe symptoms such as fever, body aches, violent shivering and headaches are more common in flu (but sometimes occur in colds). Meanwhile sore throats, runny noses, congestion and sneezing are more common in colds. A cough is common in both.

What are the differences?

Flu is a more serious and sometimes fatal respiratory infection caused by the influenza virus. Colds are caused by various viruses such as rhinoviruses, adenoviruses, and common cold coronaviruses, and are rarely serious.
Colds tend to start gradually while flu tends to start abruptly.

Flu can be detected with laboratory or at-home tests. Man flu is not an official diagnosis.

Severe flu symptoms may be prevented with a vaccine, while cold symptoms cannot.

Serious flu infections may also be prevented or treated with antiviral drugs such as Tamiflu. There are no antivirals for colds.

OK, but is man flu real?

Again, let’s assume man flu is a cold. Do men really have worse colds than women? The picture is complicated.

One study, with the title “Man flu is not a thing”, did in fact show there were differences in men’s and women’s symptoms.

This study looked at symptoms of acute rhinosinusitis. That’s inflammation of the nasal passages and sinuses, which would explain a runny or stuffy nose, a sinus headache or face pain.

When researchers assessed participants at the start of the study, men and women had similar symptoms. But by days five and eight of the study, women had fewer or less-severe symptoms. In other words, women had recovered faster.

But when participants rated their own symptoms, we saw a somewhat different picture. Women rated their symptoms worse than how the researchers rated them at the start, but said they recovered more quickly.

All this suggests men were not exaggerating their symptoms and did indeed recover more slowly. It also suggests women feel their symptoms more strongly at the start.

Why is this happening?

It’s not straightforward to tease out what’s going on biologically.

There are differences in immune responses between men and women that provide a plausible reason for worse symptoms in men.

For instance, women generally produce antibodies more efficiently, so they respond more effectively to vaccination. Other aspects of women’s immune system also appear to work more strongly.

So why do women tend to have stronger immune responses overall? That’s probably partly because women have two X chromosomes while men have one. X chromosomes carry important immune function genes. This gives women the benefit of immune-related genes from two different chromosomes.

Oestrogen (the female sex hormone) also seems to strengthen the immune response, and as levels vary throughout the lifespan, so does the strength of women’s immune systems.

Men are certainly more likely to die from some infectious diseases, such as COVID. But the picture is less clear with other infections such as the flu, where the incidence and mortality between men and women varies widely between countries and particular flu subtypes and outbreaks.

Infection rates and outcomes in men and women can also depend on the way a virus is transmitted, the person’s age, and social and behavioural factors.

For instance, women seem to be more likely to practice protective behaviours such as washing their hands, wearing masks or avoiding crowded indoor spaces. Women are also more likely to seek medical care when ill.

So men aren’t faking it?

Some evidence suggests men are not over-reporting symptoms, and may take longer to clear an infection. So they may experience man flu more harshly than women with a cold.

So cut the men in your life some slack. If they are sick, gender stereotyping is unhelpful, and may discourage men from seeking medical advice.

Thea van de Mortel, Professor, Nursing, School of Nursing and Midwifery, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.