Virology - Respiratory Viruses 2022 PDF

Introduction to Virology Dr. Basma Samir (MD)  Viruses are the smallest of all microbes. They lack the characteristics of living things, except the ability to replicate. They are considered neither Prokaryotes nor Eukaryotes.  Viruses are unique because they are only alive and able t...

Introduction to Virology Dr. Basma Samir (MD)  Viruses are the smallest of all microbes. They lack the characteristics of living things, except the ability to replicate. They are considered neither Prokaryotes nor Eukaryotes.  Viruses are unique because they are only alive and able to multiply inside the cells of other living things. The cell they multiply in; is called the host cell. A virus is made up of: a core of genetic material, either DNA or RNA, surrounded by a capsid “protective coat” which is made up of protein. the envelope: sometimes the capsid is surrounded by an additional spikey coat. Viruses are capable of latching onto host cells and getting inside them.  Viruses make copies of themselves to regenerate. They acquire energy (from their hosts).  Are Viruses Alive? Reasons some microbiologists say that viruses are Not Alive: Viruses have no cells (only protein coatings surrounding genetic material). They don't reproduce by themselves; they need host cells.  A viral infection is a proliferation of a harmful virus inside the body. ”Viruses cannot reproduce without the assistance of a host”. They infect a host by introducing their genetic material into the cells and using the cell's internal machinery to make more virus particles.  With an active viral infection, a virus makes a huge number copies of itself resulting in bursting the host cell (killing it) to set the newly-formed virus particles free. New virus particles are then free to infect other cells. Symptoms of the viral illness occur as a result of: Cell damage, Tissue destruction, and Immune system response. Classification of Viruses Based on their type of nucleic acid as genetic material, viruses are classified into DNA or RNA viruses. DNA viruses contain usually double-stranded DNA (dsDNA) and rarely single-stranded DNA (ssDNA). RNA viruses have typically ssRNA, but may also contain dsRNA. Viral Transmission Viruses can be transmitted in a variety of ways. Touch Droplet Air-borne Feco-Oral Contaminated food and water. Contaminated needles Sexual contact Insects including ticks and mosquitoes can act as "vectors," transmitting a virus from one host to another. Respiratory viral infections These viruses are most commonly spread by inhaling droplets containing virus particles. Examples: Rhinovirus (picorna virus) 200 different viruses can cause Common colds. Rhinoviruses (RVs) are the most common cause of common cold. They chiefly cause upper respiratory tract infections (URTIs) but may also infect the lower respiratory tract. Potential complications of infection include otitis media, sinusitis, chronic bronchitis, and exacerbations of reactive airway disease (eg, asthma). Although rhinovirus infections occur all the year-round, the incidence is highest in fall and spring. Cold symptoms like coughing, sneezing, mild headache, and sore throat typically last for up to 2 weeks. Seasonal influenza More than 200,000 people per year are hospitalized annually in the US due to complications of the flu. Flu symptoms are more severe than cold symptoms and often Include body aches and severe fatigue. Influenza viruses belong to the family Orthomyxoviridae. Influenza viruses are classified into types A, B and C on the basis of their nucleoproteins. Only types A and B cause human disease. Seasonal influenza High mutation rates and frequent genetic reassortments of these viruses contribute to great variability of viral antigens. Majority of the currently identified subtypes of influenza A viruses are maintained in wild, aquatic bird populations. Humans are generally infected by viruses of subtypes H1, H2 or H3, and N1 or N2. (Haemagglutinin (HA), Neuraminidase (NA) activity). Minor point mutations causing small changes “antigenic drift” occur relatively often. Antigenic drift enables the virus to escape immune recognition, resulting in repeated influenza outbreaks. Seasonal influenza Major changes in the HA antigen “antigenic shift” are caused by reassortment of genetic material from different A subtypes. Antigenic shifts resulting in new pandemic strains are rare events, occurring through reassortment between animal and human subtypes. In 2009, global outbreaks caused by the A(H1N1) strain attained pandemic proportions, gradually evolving into a seasonal epidemiological pattern in 2010. Transmission Droplets by unprotected coughs and sneezes. Airborne transmission of influenza viruses occurs particularly in crowded spaces. Hand contamination followed by direct mucosal inoculation of virus is another possible source of transmission. Respiratory Syncytial Virus (RSV) can cause both: Upper respiratory infections (like colds) and Lower respiratory infections (like pneumonia and bronchiolitis). Usually, RSV symptoms are mild and typically mimic the common cold. Self-care measures are usually all that's needed to relieve any discomfort. But, RSV can cause severe infection in some people, especially premature babies, older adults, infants and adults with heart and lung disease, or anyone with a very weak immune system (immunocompromised). SARS-COV-2  SARS-COV-2 is a respiratory coronavirus that causes COVID-19 infection. COVID-19 caused a global pandemic in 2020, shutting down schools, businesses, and public life in nations across the world, infecting millions of people and killing over 1 million worldwide and 210,000 in the US as of early Fall. The first reports of this virus came from Wuhan, China in Dec., 2019. SARS-COV-2 An enveloped β-coronavirus, with a genetic sequence very similar to SARS-CoV-1 (80%) and bat coronavirus RaTG13 (96.2%). The viral envelope is coated by spike (S) glycoprotein, envelope (E), and membrane (M) proteins. Host cell binding and entry are mediated by the S protein. The first step in infection is: virus binding to a host cell through its target receptor. SARS-COV-2 The S1 sub-unit of the S protein contains the receptor that binds to angiotensin-converting enzyme 2 (ACE 2) in host cell. In SARS-CoV-2 the S2 sub-unit is considered a potential antiviral target. Symptoms include cough, fever, shortness of breath and pneumonia. Delta - B.1.617.2 First identified: India Spread: Spreads more easily than other variants. Severe illness and death: May cause more severe cases than the other variants Vaccine: Breakthrough infections in people who are fully vaccinated are expected, but vaccines are effective at preventing severe illness, hospitalizations, and death. Treatments: Nearly all variants circulating in the United States respond to treatment with FDA-authorized monoclonal antibody treatments. Omicron - B.1.1.529 First identified: South Africa Spread: May spread more easily than other variants, including Delta. Severe illness and death: Due to the small number of cases, the current severity of illness and death associated with this variant is unclear. Vaccine: Breakthrough infections in people who are fully vaccinated are expected, but vaccines are effective at preventing severe illness, hospitalizations, and death. Treatments: Some monoclonal antibody treatments may not be as effective against infection with Omicron.  Early evidence suggests that fully vaccinated people who become infected with the Delta variant or the Omicron variant can spread the virus to others. All FDA-approved or authorized vaccines are effective against severe illness, hospitalization, and death. The recent emergence of the Omicron variant further emphasizes the importance of vaccination and boosters.  Risk factors associated with the development of Severe Disease, Admission to intensive care unit, and Mortality??  Underlying condition Older age Hypertension Cardiovascular disease Chronic obstructive pulmonary disease Diabetes. Obesity Malignancy Clinical Presentation High fever (≥39°C on admission) Dyspnoea on admission Higher qSOFA score (Quick SOFA) Altered mental status · Respiratory rate ≥22 · Systolic BP ≤100.)  Diagnosis Laboratory markers Neutrophilia/lymphopenia Raised lactate and lactate dehydrogenase Raised C reactive protein level in serum Raised ferritin level in serum Raised IL-6 level in serum Raised ACE2 level in serum D-dimer >1 μg/mL in blood PCR Radiologic studies Chest plain X-ray Chest CT  Prevention Frequent hand-washing Social distancing Covering the nose and mouth when coughing or sneezing Avoiding contact with infected individuals Disinfecting hard surfaces and not touching the eyes, nose and mouth can help reduce transmission as well. Discussed Topics General characteristics of Viruses. Viral structure Viral replication. Viruses according to Nucleic acid core (DNA & RNA viruses)  Respiratory Viral Infections. Picorna viruses (Rhinovirus) Orthomyxovirus (Influenza Viruses) RSV SARS viruses SARS-COV-2 (COVID-19) Manifestations of COVID-19 disease. Virulence factors of COVID-19 Variants of COVID-19 Laboratory diagnosis of COVID-19 Preventive measures of COCID-19