Influenza or the flu, a highly contagious respiratory illness, is caused by a group of enveloped, RNA-containing viruses with virions of circular (~100 nm in diam.) or filamentous (~300 nm in length) appearance. They can be zoonotic in nature as they can also infect many species of wild (e.g., aquatic birds) and domesticated animals (e.g., swine, chickens, and ducks).
Influenza viruses are unique as they contain a genome of seven or eight separate RNA segments. The genomic segments from different strains can become reassorted, giving rise to progeny with different antigenic and disease-causing attributes. The intermixing of the genomic segments from different strains can also lead to ‘antigenic shifts’ in the viruses. In addition, influenza viruses continually undergo ‘antigenic drifts’ giving rise to new strains with epidemic potential, thus requiring annual vaccination against the disease.
Influenza D viruses are known to infect pigs and cattle; no human infections from these viruses have been observed.[1]First isolated from pigs in 2011, the viruses were categorized as belonging to a new genus of Orthomyxoviridae in 2016, distinct from the previously-known Influenza virus C genus.
Cases of infections from the Type D viruses are rare compared to Types A, B, and C. Similar to Type C, Type D has 7 RNA segments and encodes 9 proteins, while Types A and B have 8 RNA segments and encode at least 10 proteins.
Influenza virus A is divided into 2 groups based on two proteins on its surface – hemagglutinin (HA) and neuraminidase (NA). Currently, 18 HAs and 11 NAs are known; they can pair up to yield a variety of subtypes (e.g., H1N1, H5N1). Influenza viruses B are more stable and also less virulent. Viruses belonging to the influenza C group generally cause milder illness and not been incriminated in epidemics of influenza in humans.
Influenza viruses are a significant burden on human health 1 resulting in about half a million fatalities globally each year according to the Centers for Disease Control and Prevention (CDC). Timely administration of antiviral medication can help reduce the risk of complications 2. Annual influenza vaccination can also reduce the health impact of these viruses 2 , 3.
In spite of the ancient nature of influenza viruses, we don’t fully understand the means of their spread in nature. However, contaminated hands and indoor air are believed to be among their vehicles.
The relatively large size (about 100 nm in diam.) and enveloped nature of influenza viruses makes them less stable outside hosts and also more susceptible to the action of microbicides. Even mild detergents such as ordinary soap can inactivate them readily.
CREM Co Labs has the facilities for and experience in working with human influenza viruses.
Reference:
Cynthia Nypaver, CNM, PhD, WHNP‐BC,
1 Cynthia Dehlinger, CNM, DNP, NP‐C, 2 and Chelsea Carter, MSN, NP‐C 3
J Midwifery Womens Health. 2021 Jan-Feb; 66(1): 45–53.
Published online 2021 Feb 1. doi: 10.1111/jmwh.13203
Influenza and Influenza Vaccine: A Review – PMC (nih.gov)
Resources to share
• Flu (influenza): Symptoms and treatment – Canada.ca
• https://www.canada.ca/influenza/symptoms
• Stop the spread of the flu and COVID-19 (poster)
• Plan to get your flu shot (poster)
• Flu awareness materials
Related articles:
• A brief review of influenza virus infection (2021)
https://pubmed.ncbi.nlm.nih.gov/33792930/
• Diversity and Complexity of Internally Deleted Viral Genomes in Influenza A Virus Subpopulations with Enhanced Interferon-Inducing Phenotypes (2023)
https://pubmed.ncbi.nlm.nih.gov/37896883/