Influenza B Viral Infection- Symptoms and Treatment

Influenza B Viral Infection- Symptoms and Treatment

What are the features of influenza B virus?

Influenza B virus is a common virus and it has the following features:

  • Enveloped virus
  • The shape is round but can also be filamentous.
  • 80-120 nm in diameter
  • Segmented negative single-stranded RNA having, linear genome
  • These viruses belong to the family Orthomyxoviridae
  • Capsid containing nucleoprotein with 8 segments which code for 11 proteins.
  • Genome size is 13.5Kb

How influenza B virus expresses its genes?

The genes are expressed via transcription. During transcription, Viral RNA polymerases transcribe the viral RNA. Priming of transcription is done by cap-snatching. Then, polyadenylation of mRNA is done via viral polymerase.

Replication of influenza B virus

Attachment and endocytosis

Virus attaches to receptors (sialic acid) of the host cell through its hemagglutinin (HA) protein proteins ad virus is endocytosed into the host cell by clathrins

Entry into host nucleus

Endosome acidification occurs which helps in the entry of RNA segments into the host nucleus.

Transcription

Transcription of viral genome segments occurs via viral polymerase which produces mRNAs. These produced mRNA are capped, and its polyadenylation has also occurred via viral polymerase.

Replication

Then, the replication of viral genomic segments occurs

Assembly and budding

After the formation of all viral components, viral components are assembled and budding occurs at the plasma membrane of the host cell.

The host of influenza B virus 

Natural host of this virus is human, specifically, it attacks TROPISM epithelial respiratory cells.

Receptors of the influenza B virus

The nature of viral receptors is incompletely defined but more specifically the glycosylated oligosaccharides that terminate in sialic acid residues are attacked by the influenza virus.

Epidemiology and Past studies related to Influenza B virus

Prevalence of Influenza B viruses is found worldwide. These viruses can cause worldwide epidemics leading to the high rates of illness and death. It mostly occurs in the winter season.

In 1940, Influenza B virus was isolated from a child which adapted to humans. It doesn’t require a stable animal reservoir for its infection. The case of influenza B virus causing encephalitis was reported in London in 1946. After most of the initial studies, the viral infection of Influenza B is considered mild as compared to that caused by influenza A.

A total of 4,511 cases of influenza-like illness were reported. Out of 4,511 cases, 1,709 cases were hospitalized. 3,297 cases were patients older than 14 years. The prevalence of Influenza B viruses was found in 56.4% of the cases. The prevalence of influenza B virus was more found in Romania than in the rest of Europe. In 1998–1999, outbreaks of encephalitis/encephalopathy caused by influenza were reported In Japan. in 2006, Eleven cases of neurologic complications were reported in Taiwan. These were caused by influenza B virus infection among children. In Italy, the case of optic neuritis caused by influenza B infection was reported in a 10-year-old boy. In North America, acute necrotizing encephalopathy was caused by influenza B infections in a 3-year-old boy. 25 cases of neurologic disorders caused by influenza B were also reported in the United Kingdom. An increase in influenza activity was observed in Romania during the 2014–15

During this activity, many cases of influenza-like illness and acute respiratory infections were reported. These cases were 3.5 times more acute than the reported infection in previous seasons.

In the present time, influenza B continues to sicken people, especially in the areas of northeastern states. It shows that the infections caused by Influenza B virus can be as severe as those caused by influenza A. It was explained in the latest flu updates given by the Centers for Disease Control and Prevention (CDC).

The CDC also explained that in 2009 influenza B has come out as the potential dominant flu strain. The finding of CDC also challenges the views that consider that the infections caused by influenza B are milder than those caused by influenza A. Unlike influenza A infections, type B infections are found only in humans. Influenza B causes less severe infection than influenza A but still, it can be harmful. Influenza B viral infections do not cause pandemics

Symptoms of influenza B viral infection

Human influenza B viruses can cause acute respiratory infections. The different strains of influenza viruses are reported every year. These viruses emerge because of interspecies gene reassortment and continuous antigenic drift. These drifts cause antigenic shifts and lead to the emergence of new strains with every new season.

The general symptoms associated with influenza B viral infections are followings:

  • Chills
  • Fever
  • Headache
  • Cough
  • Myalgia

Some severe complications associated with this virus are followings:

  • lower respiratory tract (pneumonia)
  • Myocarditis
  • cerebellar ataxia
  • Guillain-Barré syndrome
  • afebrile seizures
  • encephalitis
  • meningitis
  • myelitis

Treatment of influenza B infections

The epidemiology of influenza B viruses is less studied as compared to influenza A viruses. The studies are limited because of its resistance to antiviral drugs like neuraminidase (NA) inhibitors.

The Acute respiratory infections caused by viral infection are one of the main causes of deaths among children and adults worldwide. Influenza is one of the respiratory infections which can be treated via vaccination and antiviral treatment.

Vaccines available

Generally, the following drugs are used for the treatment of influenza:

  • Rimantadine and Amantadine
  • Peramivir, Oseltamivir, and Zanamivir

Challenging treatment

The treatment of influenza B can be a challenging task because of the following reasons:

  • Oseltamivir and zanamivir are the only antivirals which are FDA-approved for its treatment
  • Oseltamivir shows less effectivity than zanamivir in pediatric patients;
  • The use of zanamivir is not prescribed for patients younger than 7 years.
  • The use of NAIs is more effective for the treatment of influenza A infections than that caused by Influenza B viruses.
  • The relationship between NAI phenotypic resistance and molecular markers, transmissibility, the extent of emergence, and the existence of NAI-resistant variants requires more studies to establish understanding.

Advantages of Amantadine and Rimantadine

  • These are less expensive than other antiviral drugs.
  • These are available in various forms like syrup, capsules, and tablets.
  • Amantadine can be used to treat the children of one year or older.
  • These can treat prophylaxis in adults and in children also.
  • These can effectively cure uncomplicated illnesses.

 Disadvantages of Amantadine and Rimantadine:

  • These are most effective against influenza virus A infections.
  • These can cause central nervous system and gastrointestinal side effects
  • These are effective when given within 48 hours of onset of symptoms.
  • Higher risks of drug resistance are associated with these drugs.

The difference between influenza B and A infections

There is very little difference between the infections caused by influenza A and B related to the way these affect. The major difference is related to their classification and their potential to cause epidemics. One is more severe than the other. Influenza B can cause outbreaks of seasonal flu. The outbreaks of influenza B occur less frequently than the outbreaks of influenza A. In the making of seasonal flu vaccine, 1 or 2 strains of influenza B are included every year. This is done to protect people from the strains that are considered most likely to cause illness during the flu seasons.

 

 

Sources:

http://www.cidrap.umn.edu/news-perspective/2014/05/cdc-dont-take-influenza-b-lightly-adults

https://viralzone.expasy.org/80?outline=all_by_species

https://www.aafp.org/afp/2000/1201/p2467.html

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