Influenza Virus Morphology and Pathogenesis

Influenza Virus Morphology

• Influenza viruses are enveloped, negative-sense, single-stranded RNA viruses.
• They belong to the family Orthomyxoviridae.
• They have a roughly spherical shape, though pleomorphic forms exist.
• The viral envelope is studded with glycoproteins: hemagglutinin (HA) and neuraminidase (NA).
• HA is crucial for viral entry into host cells, binding to sialic acid receptors on the surface of host cells.
• NA facilitates the release of newly formed virions from infected cells by cleaving sialic acid.
• The genome comprises 8 RNA segments, each encoding one or more viral proteins.
• These RNA segments are highly susceptible to mutations, contributing to antigenic drift and shift.

Influenza Virus Pathogenesis

• The virus primarily infects the respiratory tract, starting with the upper respiratory tract (nose, throat).
• Entry of the virus into the body usually takes place through the inhalation of infected droplets produced by coughing or sneezing.
• The virus replicates in the epithelial cells of the respiratory tract.
• Replication causes inflammation and damage to the respiratory surfaces.
• Symptoms of the infection, like fever, cough, sore throat, and muscle aches, are a consequence of the inflammatory response and direct effects of viral replication.
• Viral replication and spread are facilitated by the actions of HA and NA.
• Immune responses, both innate and adaptive, are elicited by viral infection.
• Individuals with compromised immune systems or pre-existing conditions are particularly susceptible to severe complications like pneumonia.
• Secondary bacterial infections can be a serious complication of influenza.
• Cytokine storm may occur in severe cases.

Influenza Virus Laboratory Diagnosis

• Several laboratory methods exist to diagnose influenza virus infection.
• Rapid antigen detection tests (RADTs) are commonly used for quick results. These tests are generally highly sensitive and specific.
• These tests detect viral antigens (HA or NA) in clinical specimens (nasal or throat swabs).
• Molecular assays, such as real-time reverse transcriptase-polymerase chain reaction (rRT-PCR), are highly sensitive and specific for identifying influenza viruses.
• These assays detect viral RNA in clinical specimens. They are considered the gold standard for diagnosing influenza.
• Viral isolation in cell culture is possible but less frequently used due to time constraints and resources required.
• Serological assays, like ELISA, can be used to detect antibodies against influenza viruses in patient samples. These are often employed retrospectively to confirm prior infections or assess immune response.
• Selection of appropriate tests depends on various factors, including the patient's clinical presentation, specimen collection timing, and the resources available.

This quiz covers the morphology and pathogenesis of the influenza virus, detailing its structure, genome, and mechanisms of infection. It highlights the role of glycoproteins in viral entry and release, as well as the processes contributing to mutation and virulence. Test your knowledge on these essential aspects of influenza virology.