The Pneumoviruses and Adenoviruses

Kate Kelland

At the Walter Reed Army Institute of Research in the United States in 1955, a group of chimpanzees began suffering respiratory symptoms—runny noses, sneezes, congestion and cough. Having isolated a virus, scientists at the institute identified it as the cause of the chimps’ infection and named it Chimpanzee Coryza Agent Virus, or CCA Virus.  

Within a year or so, an almost identical virus was isolated by a doctor called Robert Chanock who was working with babies suffering severe respiratory symptoms. “From these findings it is clear that viruses that are indistinguishable from CCA Virus are capable of infecting human beings”, Chanock and his co-researcher wrote in a 1957 paper.

Because Chanock and his team also found that human cells infected with this pathogen fused with other infected cells to form large cells known as syncytia, they decided to rename it human Respiratory Syncytial Virus, or RSV.

RSV has since become recognised as a pervasive pathogen that infects nearly all babies and children worldwide at least once—and sometimes twice—before they reach two years old.  

Respiratory Syncytial Virus is classified as a member of the Pneumovirus family, a group of viruses that share some similarities with the Adenovirus family. While both these families are considered relatively low risk in terms of pandemic potential, the viruses within them cause significant burdens of human disease and death—putting them among The Viral Most Wanted. 

compilation of photos about RSV virus

Big Close-Knit Families?

Not really, no. Despite both families of viruses causing respiratory illnesses in people, their genetic makeup and characteristics are quite different. While Pneumoviruses are RNA viruses and have an envelope or cloak, Adenoviruses are non-enveloped DNA viruses. Adenoviruses can also cause a wider range of illnesses, including conjunctivitis, gastroenteritis, hepatitis and myocarditis, although the most common infections they cause are respiratory.


Prime Suspects 

The most notorious and prolific viral attacker in these two families is Respiratory Syncytial Virus. Another prime suspect within the Pneumovirus family is Human Metapneumovirus, which causes respiratory infections a bit like the common cold, but can also lead to bronchitis, bronchiolitis and pneumonia. Within the Adenovirus family there are several suspects, all of which share the same name—Human Adenovirus—but which are known by different species names. Human Adenovirus Species B, for example, causes respiratory illnesses and conjunctivitis, while Human Adenovirus Species F infections are associated with gastroenteritis, particularly in young children. Disease detectives have identified about 50 types of Adenoviruses that can infect humans, but only a small number of them cause serious disease. 

 

Nicknames and Aliases 

Pneumoviruses and Adenoviruses that pose a human disease threat are mainly known just by their acronyms: RSV, for Respiratory Syncytial Virus, hMPV for Human Metapneumovirus and HAdV for the various species of Human Adenoviruses.

Distinguishing Features

Adenoviruses are DNA viruses and have a distinctive appearance when viewed under an electron microscope. They are non-enveloped viruses with an icosahedral shape, meaning they have 20 triangular faces. The diameter of Adenovirus virions, or virus particles, typically ranges from 70 to 100 nanometers.

Pneumoviruses such as Respiratory Syncytial Virus are enveloped and pleomorphic, meaning they have a cloak or fatty membrane around them and can have a variety of shapes. Most often they are spherical or, as is the case with RSV, slim and threadlike. The diameter of spherical Pneumovirus virions is around 200 nanometers. Because the viral envelope, or cloak, is studded with glycoproteins, the surface of the virus often looks like it is covered in small, protruding spikes. 

scientific illustrations of example viruses

Source: Viral Zone by SwissBioPics

Modus Operandi

RSV infects human cells by first attaching to their surface using glycoproteins, or G proteins. Once attached, the fusion or F protein on the surface of the virus helps the viral envelope fuse with the host cell’s membrane, allowing viral RNA to enter. Once inside, the viral RNA hijacks the cell's machinery to produce viral proteins and replicate its RNA to make new virus particles.

Adenoviruses infect human cells by first attaching to the cell surface using their fibre proteins, which bind to specific receptors. After attachment, the virus is first engulfed by the host cell and then goes on to hijack the cell’s machinery to replicate and produce new virus particles. 

Accomplices

All human viruses in the Pneumovirus and Adenovirus families are highly contagious, but they do not use vectors or intermediaries to spread from one person to another. Instead, they can spread through the air in droplets from an infected person’s coughs and sneezes as well as through close personal contact or touching contaminated surfaces.  

 

Common Victims

Human Pneumoviruses and Adenoviruses pose a significantly increased risk to babies, the elderly and people whose immune systems are weak or compromised. These groups are much more likely to develop severe complications from RSV infection, such as pneumonia or bronchiolitis, and to develop more severe eye infections or gastroenteritis if infected with an Adenovirus.

polaroid photos of people

Infamous Outbreaks

Respiratory Syncytial Virus

Respiratory Syncytial Virus is a major cause of disease among babies, children and the elderly across the world. Disease experts estimate that this Pneumovirus alone causes up to 200,000 deaths a year globally.  

As well as its death and disease toll, RSV is also a heavy burden on healthcare infrastructure and spending. In the United States, for example, its estimated economic burden is more than $6 billion a year. Even though most people are infected with RSV in their first two years of life, re-infection again and again throughout life is very common—even within the same season and sometimes with the same strain. 

line chart showing positive tests for respiratory viruses

Data sourced from the CDC National Respiratory and Enteric Virus Surveillance System

Common Harms

RSV infection can inflict a full range of harms on its victims, from relatively mild common cold symptoms such as runny nose, to flu-like symptoms including fever, cough and sore throat, to severe bronchiolitis or pneumonia with breathlessness, chest pain and acute respiratory failure.

Adenovirus infections typically bring with them milder symptoms, but they are also wide-ranging depending on which of the Adenovirus species is on the attack. The most common respiratory symptoms include cough, runny nose, sore throat, fever, bronchitis and pneumonia. Some Adenovirus infections cause eye symptoms such as conjunctivitis, also known as pink eye, while others cause gastrointestinal symptoms such as diarrhoea, stomach pain, nausea and vomiting. 

scientific illustrations of symptoms of RSV and adenovirus

Lines of Enquiry

Disease detectives’ efforts to develop a vaccine for Respiratory Syncytial Virus have involved many decades of research and multiple lines of enquiry. Their initial attempts, in the 1960s, were with an inactivated vaccine, but this approach was abandoned after it was found to cause a dangerous phenomenon known as “enhanced disease” in babies who had been vaccinated and were later exposed to the virus.

It wasn’t until the 1980s that RSV vaccine researchers were able to make a major step forward—when they discovered that antibodies passed down from mothers to their babies were able to protect or partially protect against RSV infection.  

While it still took another four decades of dedicated research and development work, the world’s first safe and effective vaccine against RSV was finally approved by U.S. medicines regulators in 2023 for use in people aged 60 and older. The following year a second RSV vaccine was licensed for use in both elderly people and in pregnant women to help protect their babies. RSV vaccines have since been approved for at risk groups in more than 50 countries, including Japan and across Europe.

In some wealthy countries such as the United States, there is also an approved monoclonal antibody treatment for RSV which is licensed for preventative in babies under the age of two years old who are particularly vulnerable to becoming infected.  

Adenoviruses are often used as “vectors” in the development of vaccines against other diseases, in part because they are very good at infecting human cells and generating an immune response. But, aside from a vaccine that is licensed only for very limited use to try to prevent outbreaks of Adenovirus infection among military recruits in the United States, there are currently no approved Adenovirus vaccines. 

compilation of images related to RSV vaccinations

Editor's note:
The naming and classification of viruses into various families and sub-families is an ever-evolving and sometimes controversial field of science. 

As scientific understanding deepens, viruses currently classified as members of one family may be switched or adopted into another family, or be put into a completely new family of their own. 

CEPI’s series on The Viral Most Wanted seeks to reflect the most widespread scientific consensus on viral families and their members, and is cross-referenced with the latest reports by the International Committee on Taxonomy of Viruses (ICTV). 

 

The Viral Most Wanted homepage

Related articles

Related articles

Related articles