RSV, hMPV, CoV… these may all sound like random acronyms, but they are influenza’s less well-known viral cousins. In fact, studies have shown that a lot of illness that we think of being caused by the “flu” is actually due to these other viruses.
Some of them are seasonal, such as respiratory syncytial virus (RSV) and parainfluenza virus. While others, such as coronaviruses (CoV) and rhinoviruses, are found all year around.
And others still are found living in your nose, throat or windpipe, but it isn’t clear whether they do much. These include respiratory polyomaviruses WU and KI (known to those in the field as the “Wookie” viruses). But why is all this important?
For most of us, respiratory viral infections are an annoyance that, at worst, require us to take a day or so off work. Occasionally, complications ensue in otherwise healthy people for reasons that aren’t entirely clear to doctors.
In recent years, we’ve found that around a quarter of the people are admitted to hospital with influenza don’t have an obvious reason for ending up there (that is, they don’t have an identifiable medical risk factor).
In addition to secondary bacterial pneumonia, which is known as a complication of the flu, some studies suggest that influenza might trigger heart attacks and strokes.
In some people, “ordinary” respiratory viruses are known to be dangerous. These include asthmatics, those whose underlying severe medical problems, and those with impaired immune systems.
In young children, viral infections can cause diseases such as croup, which sometimes requires hospitalisation. In Indigenous children, we think that there’s an interplay between viral infections and more serious bacterial infections such as middle ear disease, an important cause of impaired hearing.
So, there’s clearly a real need for effective vaccines and treatments for some of these other viruses.
Indeed, some of these respiratory viruses are really nasty. SARS, a coronavirus that emerged in China, was known to have affected 8,096 people and resulted in the deaths of at least 775 (including many health-care workers caring for infected patients). It was estimated to cost around A$40 billion.
On a different scale, a related novel coronavirus is currently the focus on attention in the Middle East, where a hospital outbreak in Saudi Arabia has been known to involve 13 patients. Seven of these people have died and over 50 cases have been reported in total.
For most of us, what we think of as “the flu” (fever, with a runny nose, sore throat or cough, and body aches and pains) is actually not due to influenza virus infections. In fact, studies have shown that of those with this syndrome, only about 40 per cent have influenza – even in the middle of winter.
There don’t appear to be any simple ways to tell what’s due to the influenza virus and what’s due to other viral infections. The currently available tests aren’t that useful because they’re relatively expensive and the results aren’t available for at least a day or so.
This is important for our perception of the effectiveness of influenza vaccines and treatment. While this vaccine is reasonably effective in preventing influenza, it isn’t anywhere as good at preventing flu-like symptoms generally (because it only prevents those due to influenza).
There is some evidence that the protection of influenza vaccines may be inferior to that produced by natural infection. This is the rationale for a new generation of “live attenuated” vaccines that provide protection but without causing significant illness.
Antivirals are also only effective for influenza and some would say that even this is debatable. To have any effect, they need to be started soon after the onset of symptoms – both these factors dilute out the effectiveness of treatment.
Other than influenza, there’s no proven effective treatment against respiratory viruses, although there are some expensive preventative agents and antivirals we often try for patients who are critically ill or who are at very high risk of getting really ill.
Remarkably, respiratory viruses, which are essentially little particles of genetic material that arguably aren’t even alive, continue to cause all this misery.
Associate Professor Allen Cheng works in the Department of Epidemiology and Preventative Medicine at Monash University.
This article has appeared in The Conversation.