Do dirty viruses make you sicker?

 I think we can all safely agree that the immune system is complicated; that viruses are complicated and when you combine the two the overall outcome is more complicated than the sum of its parts. In the current study (Levels of Influenza A Virus Defective Viral Genomes Determine Pathogenesis in the BALB/c Mouse Model) led by Becky Penn in Wendy Barclay’s group at Imperial College London, the question was what happens when the infectious virus (in this study influenza) contains more (or less) junk.

Viruses contain genetic information wrapped up in a protein coat. For a more detailed overview of what viruses are – can I recommend my book Infectious (out now in paperback). The immune system recognises viruses through a number of different ways, but one of them is through recognising the viral genetic material. In the case of influenza this is somewhat more simple because the genetic material is different to human genetic material. Humans pass their genes between different generations using DNA, but influenza uses a related molecule called RNA. Human cells also use RNA, but for different purposes – mostly for transmitting genetic information within the cell. The viral RNA therefore is a clear danger sign to cells that there is an infection. Viruses have evolved to hide their RNA from the immune system. They wrap it around proteins like thread wrapped around a cotton reel. This means the immune system can no longer see the RNA and reduces the response to it.

However, the amount of RNA is not constant. Sometimes individual virus particles fail to hide their RNA, which makes the immune response to them stronger. One factor that affects the packaging of the RNA is how the viruses grow. Becky manipulated the way that she grew her influenza virus, with some of the stocks having much more of these badly packaged viruses and some having neatly packaged genetic material. The theory was that the badly packaged viruses was, because they are more dirty trigger the immune response, what was unknown was how this would effect the outcome. There were 2 possibilities:

1. The immune system would be so fast at seeing the virus, it would kill it before it ever took hold.
2. The immune system would go into overdrive.

Surprisingly, the results were a bit of both. The dirty viruses (also called High DVG because they have more defective viral genomes) were indeed detected quicker by the immune system. This led to the release of signalling molecules called interferon. Interferons trigger an anti-viral state, shutting down the growth of virus within the cells.

The cleaner stocks performed very differently. They were initially able to escape the immune system and set up an infection in the lungs. This infection then, paradoxically, led to the production of the dirty viruses in the lungs of the infected animals. This production in the lungs led to a cycle of inflammation, basically putting fuel on the fire and increasing the severity of disease. This tells us that disease after viral infection is driven by a combination of factors – the damage caused by the virus itself and the immune response to the damage. On a more niche note, it tells us that the quality of experimental virus used is really important in shaping the outcome of the study. Which is one of the almost infinitely complicated variables in doing biological studies with 2 live agents (let’s not even begin talking about time of day, chronobiology and the impact that has!

Infectious now in paperback

 

My book is now out in paperback - available wherever you buy books

Can we save lives by deliberately infecting people?

In the middle of the pandemic, scientists intentionally infected healthy volunteers with SARS-CoV-2, the virus that causes COVID-19. John Tregoning, Reader in Respiratory Infections at the Department of Infectious Disease, explains why these experiments, and the volunteers who take part in them, are critical to modern medicine.

In early March 2021, in the middle of the COVID-19 pandemic, a surprising-sounding set of experiments were taking place. Researchers at Imperial College London (and separately at the University of Oxford) were deliberately infecting healthy volunteers with SARS-CoV-2. This was in fact the latest in a long line of controlled human infection studies – where volunteers are deliberately infected with an infectious pathogen under extremely controlled conditions.

Deliberate human infection for health benefit goes back a long way – the earliest evidence of infection for beneficial use is 10th Century China, deliberately inoculating healthy people with smallpox to make them immune to the disease. This practice continued into the 18th century, when an English doctor, Thomas Dimsdale, deliberately infected Catherine the Great and her son with a very low dose of smallpox virus to protect them against the disease.

This idea of infecting people deliberately to protect them from disease led to Edward Jenner’s famous studies inventing the first ever vaccine. Jenner hypothesised that you didn’t need to use material derived from smallpox to be protected, you could use material from a related virus, cowpox. He proved this worked using a human challenge study; he vaccinated James Phipps (his gardener’s son) with cowpox then deliberately exposed him to smallpox repeatedly, showing that the vaccine worked and Phipps was immune to smallpox.

Deliberate infection

The practice of deliberate infection for scientific benefit really took off after the demonstration by Pasteur, Koch and others that microbes cause disease. In the early 1900’s, Walter Reed, the American public health pioneer, was trying to understand where yellow fever came from – he had a suspicion that it came from mosquitos. This was important because identifying the source could alter behaviour and reduce the incidence. To test his hypothesis, Reed recruited 11 volunteers to be bitten by mosquitos that had previously bitten a yellow fever patient; two of the volunteers contracted yellow fever, strongly supporting his idea. One important development in Reed’s infection studies was the concept of ‘informed consent’. The volunteers were informed about the risk to themselves of participation, before they gave their consent to take part. Sadly, later in the 20th century, some human infection studies entered a darker chapter, with the horrific experimentation on prisoners in Nazi Germany and Imperial Japan without their consent.

Informed consent is the bedrock upon which all modern research involving volunteers is built, and it is crucial for infection studies. The landscape of human infection studies has changed dramatically since the middle of the 20th century; now, ensuring the health and safety of participants is of paramount importance and trials are carefully designed to minimise any potential risks. Studies are only performed following extensive ethical review by an external body, for example all human infection studies carried out at Imperial College London have ethical approval from the UK Health Research Authority. There is ongoing debate about whether infection studies can ever be ethical, in terms of deliberately exposing someone to the risk of harm; even in the context of minimising the risk. However, there are many benefits to the studies and when volunteers understand the risk and choose to participate for the greater good, they can achieve important things.

Vaccines

One of the ways in which deliberate human infection studies (or ‘challenge studies’) are most beneficial is in the testing of vaccines. Vaccines are tested in the same way as any drug and the first studies involve a small number of participants who receive a dose of vaccine and are closely monitored to check first and foremost whether the vaccines are safe. These early studies (called Phase I clinical trials) can also inform about whether the vaccine is making an immune response. However, in order to demonstrate that the vaccine can prevent disease, much larger studies are needed. These studies (phase III) are often very large, because you can’t be sure how many of your vaccinated volunteers will then be exposed to the infectious agent. This means that you need huge numbers of subjects to get to statistically meaningful numbers to compare infection rates with and without a vaccine.

Infectious challenge studies can help to overcome this barrier, especially when the pathogen being tested is rare. One example of this is typhoid, a bacterial infection that causes diarrhoea in approximately 10-20 million people a year, mostly in low- and middle-income countries. A research team in Oxford gave volunteers a typhoid infection and tracked them untill they had clinical symptoms before treating them with antibiotics. Again, pausing to think of the volunteers – knowing that you are likely to get a bout of diarrhoea and going ahead with it anyway, for other people’s benefit, takes a special mindset.

Indeed, without volunteers, modern medicine would falter, so we all owe a large debt of thanks to these selfless individuals. Having shown it was possible to infect people in a controlled way, the Oxford group tested whether two new vaccines could reduce disease. They showed that whilst 77% of the volunteers without a vaccine developed typhoid, only 35% of the vaccinated volunteers did. Deliberate infection studies have also been used to support the rollout of vaccines for cholera, malaria and shigella.

Measuring antibodies

Another important benefit of deliberate human infection studies is in understanding how specific viruses cause disease and how we can be protected against them. The Common Cold Unit was a British research centre operating on Salisbury plain between 1946 and 1989. It set out to understand respiratory infections; being somewhat isolated it was able to look at transmission of colds, by infecting one volunteer and then housing them together with other uninfected volunteers. It also provided us with important information about the levels of immunity required to protect against influenza. By measuring antibodies in the blood of people before they were infected it was possible to identify a threshold above which infection was unlikely to occur; this threshold is still in use for the development of influenza vaccines.

Some diseases have more challenges than others in setting up the infections. Whilst respiratory viruses can be grown and dripped into the nose, other infections get into our bodies through a third organism, called a vector. In the case of schistosomiasis (sometimes called bilharzia), the disease-causing parasites live in snails (the vector) before infecting people. To help develop drugs and vaccines for this neglected tropical disease, researchers have had to learn snail husbandry!

Returning to the coronavirus human challenge studies, these look to address both the development of vaccines and improve our understanding about infection. In the earliest results from the Imperial-led study, the team showed symptoms start to develop very fast, on average about two days after contact with the virus. The infection first appears in the throat; infectious virus peaks about five days into infection and, at that stage, is significantly more abundant in the nose than the throat. It was seen that volunteers who had not had COVID-19 before could be infected with an extremely low dose of the virus, which might help to explain why SARS-CoV-2 is so infectious. It can also inform more generally about the behaviour of respiratory viruses. These studies are now progressing to help in the design and testing of the next generation of vaccines and drugs.

As we have seen in the last two years, infections can be extraordinarily disruptive. Studying how they behave, why we get infected and how to prevent this is extremely important – when performed safely and ethically, human infection studies are an important part of our toolkit.

 This first appeared on the Imperial College, Faculty of Medicine Blog