It started with a tickle in your throat. Then, it evolved into congestion, and maybe a little cough. Perhaps you lost your voice.
You might have had a slight fever that went away with ibuprofen, but you never felt bad enough to stay in bed all day.
So, which respiratory virus invaded your cells?
Several types of viruses could be the culprit: respiratory syncytial virus (RSV), influenza, parainfluenza viruses, metapneumovirus, rhinoviruses, coronaviruses, enteroviruses, and adenoviruses are among the most common.
However, most people who are infected will probably never know which one rallied their immune system.
"They are hard to distinguish one from the next because they all have similar respiratory symptoms of congestion, cough, runny nose, fever. They all start that way," said Paul Offit, MD, of Children's Hospital of Philadelphia. "There's really no distinguishing them unless you test."
Testing isn't likely to happen unless you're hospitalized. A typical Quest Diagnostics respiratory panelopens in a new tab or window, for example, includes adenovirus, influenza, parainfluenza, rhinovirus, enterovirus, metapneumovirus, and RSV.
"Typically what we see at Children's Hospital of Philadelphia in winter is RSV, number one; and right behind it is influenza," Offit said. "Then, you'll see things like human metapneumovirus, parainfluenza virus, adenovirus."
Outside of hospitalization, respiratory virus testing isn't as common, which means there's less surveillance data on infections.
"We do not track morbidity or mortality of all of these viruses," said William Schaffner, MD, professor of infectious diseases at Vanderbilt University Medical Center in Nashville, Tennessee. "We know in general that many of them are seasonal, increasing in late fall, winter, and into spring, and they provide the great background of viral infections with which every human on this planet is familiar -- the runny nose, the sore throat, feeling out of sorts for a day or 2 or 3 and then slowly getting better."
While all of these viruses typically prompt similar symptoms, there are a few known to have particular manifestations, such as parainfluenza being responsible for the majority of croup in children, and RSV being a frequent cause of bronchiolitis in infants.
Here are the key features and differences among each of the most common annual respiratory nuisances.
Respiratory Syncytial Virus
RSV is a single-stranded RNA virus in the Pneumoviridae family and the Orthopneumovirus genus. It was first isolated in 1955 from chimpanzees with respiratory illness at the Walter Reed Army Institute of Research, according to a report in Nature Reviews Microbiologyopens in a new tab or window.
It's the most common cause of bronchiolitis in infants, and can be severe in older adults as well. Up to 10,000 adults die each year in the U.S. from RSV, Offit noted.
"RSV has this reputation as a pediatric virus, but over the last 15 years, we've accumulated data that people over 65, particularly those with underlying lung or heart disease, can be affected by RSV just as severely as influenza," Schaffner said. "And in some years the impact of RSV has been as serious as the impact of flu."
In most cases, however, symptoms are usually mild and resemble the common cold. These include congestion, runny nose, sneezing, dry cough, low-grade fever, and sore throat.
Influenza
Influenza is an RNA virus in the Orthomyxoviridae family and its most common subtypes are A and B. Infection typically leads to more severe symptoms than the common cold. These include fever, aches, fatigue, cough, and sore throat.
People infected with influenza are most contagious in the first 3 days after the illness starts, according to the CDCopens in a new tab or window.
The virus can be more severe in young children and in older adults, and the U.S. typically sees some 20,000 to 25,000 influenza deaths per year, though that number can reach as high as 60,000 annually, Offit said.
Parainfluenza Viruses
These single-stranded RNA viruses belong to the Paramyxoviridae family, and fall into two genera: Respirovirus and Rubulavirus, and overall there are four types (1-4) and two subtypes (4a and 4b), according to the CDCopens in a new tab or window.
Parainfluenza viruses are the most common culprit in cases of croupopens in a new tab or window, infamous for terrifying parents with the raspy sound of stridor.
By age 5, almost all children are seropositive, and people can be reinfected multiple times in their lifetime, resulting in mild illness with cold-like symptoms. Older adults and people who are immunocompromised have a higher risk of severe infection, according to the CDC.
Metapneumovirus
This single-stranded RNA virus in the Paramyxoviridae family was discovered in the Netherlands in 2001, but evidence suggests its been in circulation for at least five decades, according to the Encyclopedia of Microbiologyopens in a new tab or window.
Common symptoms include cough, fever, and congestion, but it can lead to more severe disease in young children, older adults, and people who are immunocompromised, according to the CDCopens in a new tab or window.
Rhinoviruses
Rhinoviruses are the most common cause of the common cold, according to the CDCopens in a new tab or window. These single-stranded RNA viruses belong to the Picornaviridae family and have three types: A, B, and C.
They were first isolated in the 1950sopens in a new tab or window by Winston Price, MD, at Johns Hopkins University in Baltimore, during an effort to identify the cause of the common cold.
Coronaviruses
While coronaviruses are now widely known due to the pandemic of SARS-CoV-2, four subtypes previously had been responsible for respiratory disease in the U.S. Those include 229E, OC43, NL63, and HKU1, which have typically been associated with mild cold-like symptoms.
Two other coronaviruses, the original SARS-CoV and MERS-CoV, have caused more severe disease in humansopens in a new tab or window.
These single-stranded RNA viruses are known for their distinct surface spikes, which give them a crown-like appearance.
Enteroviruses
Most people infected with an enterovirus have asymptomatic infections or only mild, cold-like illness. Of the more than 100 non-polio enteroviruses, the most common ones are EV-D68, EV-A71, and coxsackie virus A6 (CV-A6), according to the CDCopens in a new tab or window.
EV-D68 more commonly causes respiratory illness, while EV-A71 and CV-A6 can cause hand, foot, and mouth disease. While EV-D68 is usually asymptomatic or causes only mild symptoms, it can, in rare cases, cause acute flaccid myelitis opens in a new tab or window(AFM).
Adenoviruses
These DNA viruses in the family Adenoviridae are frequently accompanied by small, single-stranded DNA parvoviruses known as adeno-associated viruses, that don't seem to cause any specific disease. In fact, most experimental gene therapiesopens in a new tab or window have switched from using adenoviruses to these adeno-associated viruses to mitigate some of the side effects.
Most adenovirus infections are asymptomatic, and when they do cause symptoms, these are mostly mild. They can also range widely in the type of disease they cause.
"Adenoviruses are interesting. Some are directed more at the respiratory tract, while some have more intestinal symptoms and others like to give us pink eye," Schaffner said. "That viral family is very diverse and often the major impact is quite strain-specific."
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