Viral and prion pathogens Flashcards
Virus features
- simple micro-organisms
- Not capable of independent existence
- Need a host cell to survive
- Genome in middle, Capsid (protein coat) around, lipid bilayer at superficial surface
Virus life cycle
- Adsorption - onto surface of host cell
- Penetration - endocytosis
- Uncoating - genome released from phagosome
- Synthesis - Genome is replicated by enzymes
- Assembly - virus components assembled
- Release - virus released from host by budding
Viral classification
Viruses are classified by their:
genetic material - DNA vs RNA
presence or absence of an envelope
Herpes viruses
Double stranded enveloped DNA viruses
- 9types
- Characterised by their ability to establish latency and reactivate
HSV - 1
cold sores
- transmitted by direct contact. Latency in sensory nerve ganglion- periodic reactivation
- Shows as vesicles/ulcers and Encephalitis (brain inflammation)
HSV-2
genital herpes
- Transmitted by direct contact. Latency in sensory nerve ganglia - periodic reactivation
- Shows as vesicles/ulcers, Meningitis and neonatal herpes (vertical transmission)
Varicella zoster virus
Causes chicken pox, herpes zoster and shingles.
- Transmitted by direct contact, respiratory droplet.
- Latency established in dorsal root ganglia of CNNS
- Chicken pox = wide rash
- zoster,shingles = unilateral vesicles
Epstein Barr virus
Glandular fever
- Transmitted by saliva and genital secretions
- Infectious mononucleosis is the primary infection - tonsillitis, fever etc
- Reactivation from latency in B cells
Cytomegalovirus
causes CMV
- Transmitted by saliva, donated blood.
- Latency in dendritic cells
- Infectious mononucleosis is primary infection
- Congenital CMV infection- infants with retinitis, microcephaly and deafness
- Reactivation in immunosuppressed patients can cause retinitis and colitis
Rhinovirus
Common cold
- Transmitted by droplets and aerosolised respiratory droplets
- Common cold symptoms
Coronaviruses
- Alpha and beta viruses
- Transmitted airborne/droplets
- causes COVID19, MERS, SARS
Influenza
3 types A,B,C
A = mutates regularly
- 2 important surface proteins H and N have multiple variants
- Transmitted by droplets
- Primary influenza illness = fever, myalgia then cough headache etc
- Secondary infection = bacterial lung infection
Respiratory syncytial virus
- commonest in young children
- Transmitted airborne/droplets
- Causes Bronchiolitis - inflammation of bronchioles - cough, wheeze, hypoxia
HIV - Human immunodeficiency virus
- Transmitted vertically, sexually, needlestick
- HIV targets CD4 cells
- Asymptomatic chronic infection occurs
- AIDS patient become vulnerable as viral load rises and CD4 count falls
Hepatitis A
Faeco-oral
- Nausea, myalgia, fevers
- associated with contaminated water
Hepatitis E
Faeco-oral
- Nausea, myalgia, fever
- associated with pigs/undercooked pork
- causes fulminant hepatitis with high mortality in infected pregnancy women.
Hepatitis B
Vertical, sexual transmission
- After transmission, acute clinical hepatitis may occur
- Hep B is then cleared or chronic - chronicity is inversely related to age at infection
- Chronic hepatitis -> cirrhosis -> hepatocellular carcinoma
Hepatitis C
Transmitted my contaminated instruments (needles)
- can cause acute clinical hepatitis - 85% of which will become chronically infected
- can cause HCC overtime
Norovirus
Transmitted via the GIT, ingestion of aerosolised vomit particles
- Causes a lot of vomiting
Rotavirus
Transmitted via GIT, faeco-oral, contaminated food.
- Causes fever, vomiting and diarrhoea
- It’s a virus of childhood (80-100% infected by 3)
Enteroviruses
- more than 70 types
- Transmitted Faeco-oral, contaminated food/water
- Replicates in gut nut does not act there
-gut -> lymph nodes ->blood
Causes: - fever-rash syndromes
- Meningitis
- Polio
Mumps
Very infectious - droplets, saliva
- causes acute parotitis (salivary glands)
- Orchitis (testes)
- Meningitis
Measles
Highly infectious - droplet transmission
- Primary measles - fever, cough, coryza, conjunctivitis
- acute post infection encephalitis
- Subacute sclerosing pan- encephalitis - degenerative and fatal disease of CNS
Rubella
Droplet transmission
- Primary rubella - mild illness, fever, arthritis in some adults
- Congenital rubella - Classic triad - bilateral cataracts, sensorineural deafness, cardiac defects
Parvovirus B19
Droplet transmission
- causes transient anaemia
- Erythema infectiousum = fever, red rash to cheeks
- Transient aplastic crisis- affects those with high RBC turnover
- Infection in pregnancy - can cause foetal loss in first 20 weeks
what is a prion
A prion is a small infectious particle containing protein but NO NUCLEIC ACID
Human prion diseases share what 4 properties
- manifest in the CNS
- produce spongiform change in brain tissue
- Have long incubation times
- Are progressive and fatal
How are abnormal prions formed
- Inherited from genetic defects
- Transmitted via consumption or direct exposure
Natural prions can be harmful if they do what 4 things
- Gene mutation causes changes in folding pattern
- Prion becomes resistant to protease enzyme
- Prion accumulates abnormally in cell
- Promotes other proteins to abnormally fold
Sporadic Creutzfeld-Jakob disease (CJD)
- very rare 1 in a million
- Gene mutation
- progressive ataxia, depression, dementia then death
nvCJD directly linked to BSE (bovine spongiform encephalopathy)
- same structure prion as normal CJD
- nvCJD cases associated with consumption of contaminated beef
