Respiratory viruses Flashcards
explain virus structure and replication
A virus is a microscopic infectious agent that replicates inside living cells of other organisms. Viruses are generally considered non-living as they lack the ability to reproduce on their own and require a host cell to replicate.
Virus Structure:
A typical virus has a simple structure that consists of a genetic material, either DNA or RNA, surrounded by a protective protein coat called a capsid. The capsid may be surrounded by an outer envelope composed of lipids, which are acquired from the host cell membrane during the viral assembly process. The capsid protects the viral genetic material from damage and helps in the attachment of the virus to the host cell.
Replication:
The replication of a virus occurs in multiple steps, which typically involve the following stages:
Attachment: The virus attaches to the surface of the host cell by binding to specific receptors on the cell membrane.
Penetration: The virus injects its genetic material into the host cell or enters the cell by endocytosis.
Uncoating: The virus sheds its protein coat to expose its genetic material inside the host cell.
Replication: The viral genetic material takes over the host cell’s machinery to produce new copies of the virus.
Assembly: The newly synthesized viral components assemble to form complete virus particles.
Release: The newly formed virus particles are released from the host cell either by lysis, which involves the destruction of the host cell membrane, or by budding, which involves the release of the virus through the host cell membrane.
Virology of influenza
Influenza, commonly known as the flu, is an acute respiratory illness caused by the influenza virus. The influenza virus is a member of the Orthomyxoviridae family of RNA viruses, which are characterized by their segmented genome and enveloped structure. There are four types of influenza viruses: A, B, C, and D. Influenza A and B viruses are responsible for seasonal epidemics, while influenza C viruses typically cause mild respiratory illness, and influenza D viruses are found in cattle and not known to cause disease in humans.
The influenza virus is highly contagious and spreads through respiratory droplets when an infected person coughs, sneezes, or talks. The virus can also survive on surfaces and be transmitted through contact with contaminated objects. The incubation period for influenza is typically 1-4 days, and the symptoms can range from mild to severe.
The influenza virus has two major surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA). There are 18 subtypes of HA and 11 subtypes of NA that have been identified in influenza A viruses. The HA protein is responsible for binding the virus to host cells, while the NA protein is responsible for releasing the virus from infected cells and preventing the virus from clumping together.
The influenza virus undergoes frequent mutations, which can result in changes to the HA and NA proteins. This process is known as antigenic drift and is responsible for the annual changes in the circulating strains of influenza. Occasionally, the influenza virus can undergo a major genetic change known as antigenic shift, which can result in the emergence of a novel strain with pandemic potential.
Clinical features of influenza
Fever: A sudden onset of high fever, usually above 38°C (100.4°F), is a typical symptom of influenza. Fever is often accompanied by chills and sweats.
Respiratory symptoms: Influenza typically causes respiratory symptoms, such as cough, sore throat, and runny or stuffy nose.
Muscle and joint pain: Influenza can cause severe muscle and joint pain, especially in the back, arms, and legs.
Fatigue: Fatigue is a common symptom of influenza and can be severe, leading to a feeling of weakness and exhaustion.
Headache: Influenza can cause severe headaches, which are often accompanied by other symptoms such as muscle pain and fever.
Gastrointestinal symptoms: In some cases, influenza can cause gastrointestinal symptoms such as nausea, vomiting, and diarrhea.
Clinical management of influenza
Supportive care: The primary goal of supportive care is to alleviate the symptoms of influenza and prevent complications. This can include getting plenty of rest, staying hydrated by drinking fluids, and using over-the-counter medications to manage fever, cough, and other symptoms.
Antiviral medications: Antiviral medications can help to reduce the severity and duration of influenza symptoms and prevent complications. These medications work by inhibiting the replication of the virus. They are most effective when started within the first 48 hours of symptom onset. Commonly used antiviral medications include oseltamivir (Tamiflu), zanamivir (Relenza), and peramivir (Rapivab).
Prevention measures: Preventing the spread of influenza is important to protect yourself and others from infection. This includes washing your hands frequently with soap and water, avoiding close contact with sick people, covering your nose and mouth when coughing or sneezing, and staying home if you are sick.
