Viral Diseases - Microbiology Flashcards
Describe what Baltimore’s classification is
- Based on method of viral synthesis
- Groups viruses into families according to their type of genome
Name all the types of viruses in the baltimore classification of viruses from group I to VII
How do we differentiate between a bacterial and viral cause of infection and course of illness
Some symptoms are pathognomonic
- productive (phlegm) vs non-poductive cough
Course of illness
- Secondary bacterial infection symptoms persist longer than the expected 10 days virus tends to last
- Fever is higher than in viral infections
Diagnostic tests
- To differentiate between the two: CRP, ESR, FBC, PCR and cerebrospinal fluid (CSF count)
What are the moleculer techniques that have allowed multiple, rapid and ofen quantative tests that impact on therapeutic patient managment?
- Nuclei acid-based technonlogies e.g. PCR
- The Next Generation Sequencing (NGS)
- Monoclonal antibodes
- Enzyme immune essays e.g. ELISA
Name the methods used to detect viral infection
- Detection of viral antigens
- Detection of nucleic acids (PCR)
- Electron microscopy
- Virus culture
- Histopathology staining
- Serelogy staining: presence of virus specific antibodoies (lgM and lgG)
Describe the rapid viral diagnostic test - Point of care test (POCT)
- Test for key respiratory viruses
- By the bed side
- Tests for influenza A/B and respiratory syncytial virus (RSV)
- PRC based
- Take 20 mins
How has the huge diversity of viral diagnostic methods made it increasinging complex for clinicians?
Increasing complex to:
- Request the appropriate test
- Interpret the test result
Describe the 3 important variables are the detection of viral pathogens highly dependable on?
- Specimen - obtaining an adequete specimen from the appropriate site
- Collection - Proper timing of speciment collection relative to onset of symptoms
* For many viral infections. viral shedding begins shorty after symptoms peak rapidly after onset and celines steadily as infection resolves (exluding chronic viral infections e.g. HIV) - Processing - Timely processing of samples
* Samples should be collected as soon as possible after the onset of symptoms
What is the duty of all registered medical practioners in the UK regarding infective notfiable diseases?
All have a statutory duty to notify their local health security agency team of suspected cases of certai infectious diseases
What should registered medical practitioners do in regards to urget cases of infective notifiable diseases?
Urgent cases should be reported by phone within 24hrs
What are the possible outcomes of reporting an infective notifialbe disease?
- Isolation
- Exclusion
- Post-exposure prophylaxis
- Immunisation
- Further laboratory testing
- Control measures
What are the considersation for when to notify about an infective disease?
- The nature of suspected infection (how contagious)
- The ease of spread
- The ways in which the spread of the infection can be prevented or controlled
- The patients circuumstances (age, sex, occupation)
Name 10 examples of notifiable diseases
- Covid-19
- SARS CoV-2
What are needlestick injuries?
An incident in which the blood of a patient comes into contact with the blood of a health care worker
What are the three types of exposure in healthcare settings associated with significant risk from blood or higher risk body. Provide examples
- Percutaneous injury - e.g. from needles, sharp instruments, bone fragments, significant bites which break the skin
- Expsoure of broken skin - e.g. abrasions, cuts, eczma
- Exposure of mucous membranes including eyes and mouth
a) What are blood born viruses (BV)?
b) What are the 3 blood born viruses?
c) Put them in order of most infectious to least infectious
d) What are the transmission rates for these blood born viruses?
a) Viruses which can be present in blood or other bodily fluids, and which have high potential for transmission to another person by direct contact with their blood or susceptible fluids
b) Hepatitis B (HBV), Hepatitis C ( HBC), Human immunodefeciency (HIV)
c) 1. Hepatitis B (HBV), Hepatitis C ( HBC), Human immunodefeciency (HIV)
d) HBV = 30% ; HCV = 3% ; HIV = 0.3%
a) Describe the management of exposure to HBV
b) Describe the managment of exposure to HCV
a) Immunisation status is paramount (immune/non-immune recieptant)
Booster dose of HBV vaccine or HBIG
b) No PEP
Follow-up is key to making sure any transmission is detected (blood test, regular follow-up by occupational health referal to viral hepatitis clinic)
a) What is the main infectious material?
b) What are other potential infectious material?
a) Blood
b)
- Amniotic fluid
- Vaginal secretion
- Semen
- Human breast milk
- Cerebrospinal fluid
- Peritoneal fluid (in abdominal cavity)
- Pleural fluid (in layers of pleura that covers the lung and chest cavity)
- Pericardial fluid (secreted by the serous layer of the pericardium in heart muscle)
- Saliva in association with dentistry (likeley to be contaminated with blood even when not visibly so)
a) Which influenza vaccine is used in children?
b) Which influenza vaccine is used in ages over 65
c) Which type of influenza vaccine is used for quadrivalent: H1N1, H3N2, influenza B two subtypes?
a) Live attenuated (LAIV) quadrivalent
b) Trivalent adjuvanted inactivated vaccine
c) Inactivated influenzas vaccine
Name the non-infectious bodily fluids if there is no blood
- Urine
- Vomit
- Saliva
- Faeces
Describe the management of needle stick injury
- Encourage the wound to bleed, ideally by holding it under running water
- Wash the wound using running water and plenty of soap
- Do not scrub the wound while you’re washing it
- Do not suck the wound
- Dry the wound and cover it with a waterproof plaster or dressing
- Contact site nurse from operative centre - assess risk and requirements for attendance
- If high risk for HIV - attend A&E for assessment staff member
What HIV Art drugs to prescribe for PEP?
- Tenofovir disoproxil 245mg/emtricitabine 200mg and Raltegravir 1200mg once daily
- PEP should be initiated as soon as possible after exposure, preferably within 24 hrs, but can be considered up to 72hrs
Describe how viruses infect human cells
- Attachment
* Virus attaches to a specific human cell-surface receptor via their capsids or envelope proteins - Penetration
* Fusion: attachment to the receptor causes a change in the viral envelope, allowing the membranes to fuse.
* Viropexis: Virus taken up in an endocytic vesicle and the virus enters the cytoplasm. If the virus has an envelope, this fuses with the vesicle membrane, from within the cell.
* Receptor-mediated endocytosis: Virus particles are transported through the plasma membrane to clathrin-coated pits and enter the cell as the clathrin-coated pit invaginations. These vesicle fuses with an acidic endosome allowing uncoating to take place. - Uncoating
* Enzymes from the virus or host degrade the capsid and release the genomic material into the host cell cytoplasm. - Replication
* DNA-dependent DNA polymerase- makes a complementary strand of DNA, converting a single strand into a double strand.
* DNA-dependent RNA polymerase- uses viral DNA to produce mRNA, which can then be translated into proteins and other enzymes on host ribosomes.
* RNA-dependent DNA polymerase (reverse transcriptase)- makes a complementary strand of DNA from RNA strands.
* RNA-dependent RNA polymerase- makes a complementary strand of RNA. - Assembly
* Some of the mRNA produced is translated on host ribosomes into viral proteins
* Viral proteins assemble into new nucleocapsids with replicated viral genomic material.
* May be followed by modification (or maturation) of the viral protein, which may take place after the virus has been released from the host cell, such as in HIV.
Release
- Some viruses are released through lysis of the host cell, enveloped viruses bud off.
- New virions accumulate near the cell membrane, which then envelopes them and forms a bud that breaks off from the host cell, releasing the virions into the environment.
a) What is influenza?
b) State the 3 types
c) Which types are responsibe for most clinical cases?
d) What is the usual incubation period of inflenza?
a) An acute viral infection of the respiratory tract with frequent antigenic changes
b) A, B and C
c) A and B
d) 1-3 days
a) Which family do the 3 types of influenza virus belong to?
b) How many different RNA segments do infleunza A and B carry? and how many different proteins do they code for?
c) Which infleunza virus do subtypes only occur in?
a) Orthomyxoviridae family
b) A and B carry 8 different RNA segments that code for 11 different proteins types
c) Subtypes only occur in A viruses
a) Where is the initial site of influenza infection?
b) Which receptors do human influenza viruses prefer?
c) What does infection result?
a) mucosa in respiratory tract
b) a2, 6-linked sialic acid receptors present in the upper and lower respiratory tract
c) Degeneration of respiratory epithelial cells with loss of ciliated tufts
Desquamation (shedding of the outer layers of the skin)
Oedema (Swelling in the ankles, feet and legs)
Hyperaemia (excess of blood in the vessels supplying oropharynx)
Mononuclear cell infiltrates in lamina propria in respiratory tract
Describe the pathogenesis of RSV
- Necrosis of bronchiolar epithelium with denudation (loss of surface layers) of the ciliated epithelial cells
- Lymphocytes migrate into affected tissue
- The submucosa and adventitia become oedematous
- Increased secretion from mucous-producing cells –> mucus builds up
- Plugs consisiting of mucous, cellular debris, fibrin strands occulade the smaller bronchioles
