Discovered in 1968 in Norwalk, Ohio where it was originally given the name ‘Norwalk virus’ for where it originated

The first strain of norovirus was identified by Albert Kapikian from the US National Institute of Health, after first outbreak spread at a school

Highly contagoius, as a result the virus is worldwide

Norovirus leads to gastroenteritis, inflammation of the intestines and stomach lining due to touching contaminated surfaces or injesting contaminated foods that have the virus on them

Exhibits similar symptoms to stomach flu (vomiting, diarrhea and nausea)

Norovirus evolves through genetic recombination and point mutations

Genetic recombination allows for a wide range of diversity among population and point mutations can occur from only a single nucleotide base alteration

Norovirus phylogeny looks at the evolutionary relationship of different norovirus strains

Phylogeny can be broken down into genotypes and genogroups

There ten genogroups (GI-GX) which account for genetic variation

Genogroups GI and GII are the most prominent in the population

Over 40 genotypes have been classified, the most prominent is GII.4

Norovirus is considered to have a non-enveloped cell structure, meaning it lacks a cell wall, cytoplasmic membrane and outer membrane surrounding it's genetic material

Norovirus has a genome that consists of only single stranded RNA, averaging 7.5kb (kilobases) in length and 30 nm (micrometers) in diameter 

Norovirus's RNA is arranged in three different segments called open reading frames, which are genetic sequences signaling the end of the protein that needs to be translated has completed once the marker is reached (stop codon)

There are three open reading frames (ORF's) in Norovirus:

• ORF1 is responsible for encoding the protein RNA polymerase, which is essential for the viral replication ability of the virus 

• ORF2 and ORF3 are responsible for encoding for the capsid proteins which give the virus the ability to attach to its host cell

When Norovirus is infected within a host cell, it alters the cells metabolism by changing lipid biosynthesis and metabolic pathways to have it work in it’s advantage 

It changes lipid biosynthesis by changing the lipid membrane structure in the cell by having it work for it’s advantage of spreading the disease to other cells 

Norovirus essentially reprograms the metabolic pathways of the cell by increasing it’s glycolysis, oxidative phosphorylation, and pentose phosphate pathway 

These pathways allow the host cell to remain infected with the virus and spread it to other cells, increasing it's transmission

When metabolism within the host cell is inhibited, viral replication is as well-indicating that metabolism, specifically glycolysis, is a key factor in the ability for the virus to spread to other cells

The image shows the structure of a healthy cell in comparison with the virally infected cell

The tropism of Norovirus are epithelial and non-epithelial cells, specifically immune cells (macrophages, dendritic cells, B and T lymphocytes) and intestinal cells (gut-associated lymphoid tissue)

Norovirus consists of a single-stranded RNA molecule as its genetic material

Since plasmids exist inside bacteria and not viruses, Norovirus does not contain any plasmids 

Antibiotic resistance genes are not found in Norovirus since antibiotics do not have any effect on viruses

The genome of Norovirus has been mapped and is 7.5 to 7.7kb in length and is organized into three (can sometimes be four) open reading frames (ORF), as shown in the data

The virulence factors of Norovirus are composed of VP1 and VP2

VP1 is the major capsid protein, making up the outer shell, and VP2 is the minor capsid protein, forming the inner layer of the Noroviruses capsule

Since Norovirus is a virus and not a bacteria, it does not contain any antiobiotic resistant genes and are not considered toxins. However, VP1 and VP2

Since VP1 and VP2 act its structural component, these proteins can help in the viruses ability to infect it's host cell, by first binding to histo-blood group antigens (HGGAs) and allowing entry into it's target cell

In terms of virulence factor 1 (VF1), exoenzymes can help pathogens to invade their host cell by getting released outside the cell, with their primary role being to breakdown larger molecules so absorbance by the cell can occur.

Norovirus envades the immune system by antagonizing cytokine induction to it's host cell, ultimately suppressing it's release of cytokins which are molecules that regulate activity of other immyne cells toward the location of viral infection

Antigenic variation of Norovrius is driven by mutations in the major capsid protein (VP1), allowing the virus to envade host cells more readily by suppressing immune response

The image shows how Noroovirus protein can suppress cytokine induction when VP1 (viral capsid protein) attatches to VF1 (viral factor 1)

Biochemical testing that is done on Norovirus is most commonly done through reverse transcriptase- polymerase chain reaction (RT-PCR)

Norovirus is positive for the viral antigen or viral RNA picked up from real time RT-PCR assay

Since Norovirus is a virus and not a bacteria, it isn't positive for phenol red, IMViC, catalase, oxidase and ETC biochemical testing

Instead, RT-qPCR (as previously menthioned), enzyme immunoassays (EIA) and electron-microscopy (EM) are the methods usually used when testing for the genetic material or viral antigen of Norovirus

As previously mentioned in biochemical tests used to detect Norovirus, RT-qPCR assay's are the preferred method for the diagnosing of Norovirus

RT-qPCR is the preferred method due to its sensitivity in detecting the virus through only a few copies of RNA genetic material or viral antigens needed to show a positive result

RT-qPCR is also very specific, providing information to microbiologist's performing the test on what genogroup (GI or GII) the patient's Norovirus falls into

Another reason it's the preferred method, is due to it's rapid testing- getting results in as little as 30 minutes

RT-qPCR stands for reverse transcription (using RNA to detect genetic material of virus), quantifiable (quantifying gene expression, RNA, and viral pathogen levels), polymerase chain reaction (used to ampify and detect specific viral target- Norovirus)

Another diagnostic test used for detecting Norovrius is is EIA which stands for enzyme immunoassay, which is only used when there is a rise in cases, impacting multiple people in a specific area (outbreak), but should only be used on top of RT-qPCR.

Norovirus is directly transmitted through person to person contact with the infected individual through contact with their skin (skin-on-skin contact) or by accidentally getting infected by their feces (fecal-oral route)

Indirect contact of Norovirus is through viral particles being expelled by a infected person to another individual through inhalation of viral particles- exposing a new individual to virus

Indirect transmission of Norovirus is also acquired through ingesting contaminated food or touching contaminated surfaces that are infected by the virus 

Fomites are objects that can be infected by the agent Norovirus through contaminated surfaces (tables, door knobs, etc.)

Vectors of Norovirus are through getting tiny fece or vomit particles in exposed individuals mouth

The pathology of Norovirus shows up through the following symptoms (what the patient is experiencing internally) and signs (what is externally apparent to others):

• Symptoms: 

  • Stomach pain 

  • Nausea 

  • Body aches 

  • Fatigue 

  • Dehydration

• Signs:

  • Vomiting

  • Diarrhea 

  • Fever 

Damage done by Norovirus:

• Leading cause of gastrointestinal illness in the united states 

• Causes 58% of food-borne illnesses 

• Person-to-person contact is usually how the virus spreads, but contaminated surfaces also spread Norovirus as well 

• Vaccination and proper aseptic techniques and precautionary measures taken in hospitals inhibit the spread of Norovirus 

• In healthy individuals, they can usually recover from the illness in 3-5 days without any intervention, but for chilrden, immunocompromised individuals and the elderly, staying in a hospital may need to occur to prevent dehydration and promote a full recovery 

The immune response of Norovirus occurs through the following physiological processes within the body:

• At the site of infection, cytokines trigger inflammatory response and recruit immune cells (lymphocytes, macrophages, dendritic cells, etc.) to be up-regulated to fight the virus

• Norovirus does not rely on antibodies, making it a virus that triggers a cell-mediated response to fighting infection by utilizing T cells (T lymphocytes) and other immune cells to get rid of the antigen (Norovirus)

• Humeral immunity relies mainly on antibodies to get rid of the antigen, specifically B cells (B lymphocytes), since Norovirus relies on immune cells more than antibodies, it doesn't elicit this immune response (humeral or antibody-mediated response) like it does for the cell-mediated immune response 

• Norovirus is usually acute, but in immunocompromised individuals, it can become chronic. However, it doesn't seem to cause an autoimmunity post-infection, which is when the body mistakes it's own healthy cells for an invaders and destroys them.

Depending on the health of ones immune system, a full recovery can be achieved through resting for a few days and rehydration of fluids lost through vomiting and diarrhea by drinking plenty of fluids to restore electrolytes

However, those with a compromised immune systems may require more extensive treatment protocols in order to recover from Norovirus, including through anti-microbial medication and immunoglobulin therapy

Some anti-viral and immunoglobulin treatments have proven to be ineffective, such as through the anti-microbial drug ribovirin, and through taking oral immunoglobulins

Other chemotherapy treatments have been proven to be successful, like through the anti-viral drug Nitazoxanide, which has provided relief to patients suffering from constant, severe diarrhea to reduce output- allowing for the fluids and electrolytes that would've been lost, to be restored. 

While oral immunoglobulins aren’t effective, intravenous immunoglobulins (IVIG) therapy, which has provided patients suffering from immunodeficiency diseases to experience a faster recovery time, so that Norovirus does not become chronic 

Using anti-viral medication and immunoglobulin IV chemotherapy treatments allows for individuals unable to recover from the virus within a few days through rest and rehydration a faster recovery time, reducing the chances that the virus becomes chronic, however, they do come with side effects:

• Anti-viral medication (Nitazoxanide):

  • Nausea 

  • stomach pain

  • vomiting

• Immunoglobulin IV administration:

  • Fever 

  • Chills

  • Headaches

This is why chemotherapy treatments are only used in those who's immune systems aren't strong enough to recover from the virus by time (a few days), rest and rehydration (water and electrolytes) due to immunodeficiency and severe, constant diarrhea 

Generally, recovery is achieved through:

• Nitazoxanide:

  • Using 500mg/twice daily for seven day to fourteen days.

• Immunoglobulin IV treatment:

  • Administering 25mg/kg for three consecutive days. 

Norovirus is the leading cause of acute gastroenteritis outbreaks world-wide

Gastroenteritis is the inflammation and of the mucous membranes lining digestive tract, leading to nausea, vomiting and diarrhea 

Outbreaks can occur throughout the year but most commonly occur between November-April 

Since Norovirus is extremely contagious and can be spread through person-to-person contact, contaminated surfaces and contaminated foods, it has the ability to become an epidemic or pandemic

To classify a disease as an epidemic, there must be an increase in the number of cases than expected for a particular area. In January of 2025, the CDC stated that Norovirus cases have doubled what they were this time last year in the US, making Norovirus fall under the classification of an epidemic. 

During COVID-19, Norovirus cases fell to an all time low, indicating that the protective measures of significantly reducing person-to-person contact helped reduce the spread of Norovirus. Therefore, Norovirus has the potential of becoming a pandemic as well if people don't stay home when they are sick, clean surfaces and practice proper food preparing techniques.

Prevalence rate is determined by comparing the number of people infected with the disease to the number of people in the entire population for a specific period of time. 

Worldwide, there are an estimated 685 million Norovirus cases annually

In the US, an average of 2,500 cases are reported to the CDC per year. This number doesn't reflect the estimated amount of people infected with the virus, which is much higher-which is estimated to be closer to 20 million morbidity rate.

The mortality of Norovirus is close to 200,000 death per year worldwide, especially in impoverished nations, the elderly and immunocompromised populations.

In the US, the mortality rate of Norovirus is 900 deaths/year