Common & important viral diseases Flashcards
What causes chicken pox? How is it spread? Incubation period? Symptoms?
Varicella zoster virus (VZV)
- Highly infectious
Spread by aerosol and direct contact
- Primary infection usually produced in childhood
Incubation period 11-20 days
Presents as a vesicular eruption (rash) - small pink macules (spots) that progress into vesicles and pustules
- Diagnosis by recognition of the rash
What causes shingles? Symptoms?
Herpes zoster virus:
- After initial infection (chicken pox), varicella zoster virus persists in latent form in the dorsal root ganglion of sensory nerves & can reactivate in later life
Presents w/ pain described as burning or stabbing, followed by vesicular rash in the affected dermatome
What is influenza & what are the 3 types of influenza virus?
Acute viral infection of respiratory tract
3 types: A, B & C.
Influenza A & B are responsible for most cases.
What is the incubation period?
1-3 days
Why is influenza unique among respiratory viruses?
Frequent antigen changes
Seasonality
- changes in hemagglutinin neuraminidase (HN) glycoproteins on surface of virus
Impact on general pop.
- can cause explosive outbreaks & can cause substantial mortality (particularly in people with chronic illnesses).
Explain the pathogenesis (how a disease develops) of influenza infection.
Initial site of infection is mucosa in the respiratory tract.
- Infection is caused by HA binding to syalilated glycans on epithelial cells.
Infection causes degeneration of respiratory epithelial cells w/ loss of:
- ciliated tufts, desquamation, oedema, hyperemia (an excess of blood in the vessels supplying an organ) & mononuclear cell infiltrates.
What are the symptoms & complications of influenza?
Symptoms:
- Cough
- Fever & chills
- Malaise
Complications
- Lower respiratory tract infection
- Admission to hospital
- Death
NOTE: All depends on factors such as age, co-morbidities & type of co-morbidity.
At risk groups for influenza?
a) Chronic respiratory system diseases e.g. COPD, asthma
b) Cardiovascular system diseases e.g. Heart disease
c) Endocrine system diseases e.g. diabetes
d) Hepatic system disease e.g. Liver failure, jaundice, Hepatitis
e) Renal system diseases e.g. Chronic kidney disease
f) Neurological/neuromuscular conditions e.g. MS
h)Immunosuppression - due to HIV, cancer, blood conditions
i) Pregnant women
Influenza in pregnant women?
PHE recommends immunisation.
Mortality in pregnancy w/ flu usually due to overwhelming pulmonary disease
x 2-4 fold increased risk of complications w/ increasing stage of pregnancy —> pneumonia, preterm delivery, perinatal mortality, foetal distress.
How is influenza managed in at risk groups?
Immunisation w/ inactive vaccine
Clinicians should suspect flu in at risk patients w/ lower respiratory tract infections
treat using ‘educated guess’ whilst waiting for PCR results i.e. don’t wait to treat!
Treatments for influenza?
Neuraminidase inhibitors- antiviral drugs:
- Oseltamivir
- Zanamivir
What influenza vaccines are available?
Live attenuated vaccine (LAIV) - quadrivalent - children
Inactivated influenza vaccine(quadrivalent: H1N1, H3N2, influenza B two subtypes).
Trivalent adjuvanted inactivated vaccine - age over 65+.
What is Norovirus caused by? Incubation period? What does it cause? Symptoms? Diagnosis?
- Virus - norovirus
- Incubation period= 24-48 hours
- Most common cause of infectious gastroenteritis
- Symptoms= vomiting, diarrhoea & stomach cramping
- Diagnosis may be achieved by electron microscopy, antigen or DNA detection (PCR) in stool samples
Virus is highly infectious& cases should be isolated & environmental surfaces cleaned w/ detergents & disinfected w/ bleach
What causes measles?
- Caused by a Morbillivirus of the Paramyxoviridae family
- Spread by airborne or droplet transmission
- Acute viral illness
- Highly contagious
Why does measles still cause death?
Largely due to an increased susceptibility to secondary bacterial & viral infections because of a prolonged state of immunosuppression.
Clinical features of measles?
1.Prodromal stage
- Fever
- Malaise- generally feeling unwell
- Coryza - irritation & inflammation of mucous membranes inside nose → runny nose, sneezing…
- Conjunctivitis
- Cough
- Koplik’s Spots
- Small red spots w/ blueish-white centres
- Occur inside cheeks
- May appear on mucous membranes of mouth 1-2 days before the rash appears
- May be seen for a further 1-2 days afterwards. - . Rash
- Erythematous - abnormal redness
- Maculopapular - rash that contains both macules (flat discoloured area) & papules (small raised bump).
- Starts at head & spreads to trunk & limbs over 3-4 days
NOTE- view images on notes
When are people infectious w/ measles?
- From beginning of prodromal period
- To 4 days after appearance of the rash
What is the incubation period of measles?
- 7-18 days
- Average = 10 days
- W/ further 2 days before the rash appears
What are the complications of measles?
- Otitis media- infection of middle ear
-Pneumonia - Diarrhoea
- Convulsions
- Encephalitis - inflammation of active tissues of the brain- Can lead to headache, stiff neck, light sensitivity, seizures, confusion.
- Subacute sclerosing pan-encephalitis (SSPE) - progressive neurological disorder in children & young adults that affects CNS.
What are the 3 different forms of measles encephalitis?
- Post-infectious encephalomyelitis - occurs at 1 week after onset of rash.
- Measles inclusion body encephalitis - occurs in immunocompromised patients.
- Characterised by acute neurological compromise & deterioration of consciousness, seizures & progressive neurological damage - SSPE - rare, fatal, late complication of measles infection - 1/25,000 measles infections.
Treatment for measles?
MMR vaccine- in 1988
- 2 dose MMR schedules introduced in 1996
Cases rising due to Wakefield
What is HIV?
Progressive deterioration of the immune system that be fatal if untreated
Virology of HIV?
2 types:
- HIV-1
- HIV-2
Enveloped viruses
RNA viruses
- reverse transcribe their genome to form double-stranded DNA which integrates into host’s DNA.
Explain the HIV life cycle?
- HIV approaches a CD4 T-cell.
- Binding: HIV binds w/ glycoproteins to CD4 receptor
- Fusion: virus fuses to host cell & releases RNA into it.
- Reverse transcription: HIV enzyme reverse transcriptase converts single stranded HIV RNA into double stranded HIV DNA
- Integration: HIV DNA enters host’s nucleus & is integrated into host’s DNA using integrase enzyme. Creates a provirus.
- Transcription: the provirus becomes active & uses RNA polymerase & mRNA to create copies of HIV genomic material. - mRNA is used as blueprint to make long chains of HIV proteins.
- Assembly: the enzyme protease cuts long chains of HIV into individual proteins & assemble a virus particle containing HIV RNA.
- Budding: the newly assemble virus buds form the host cell taking w/ it a part of the cell’s outer envelope
-This covering is a mixture of protein & sugar forming the HIV glycoproteins. - The immature virus breaks free of infected cell.
- Maturation: protease completes cutting the HIV protein chains into individual proteins & newly formed copy of HIV can now infect other cells.
