Viral and Prion Pathogens

Question 1

Layers of the virus

Answer 1

Genome (innermost)
Capsid (protein coat)
Envelope (lipid bilayer)

Some viruses also carry their own enzymes

Question 2

Classification of viruses

Answer 2

DNA or RNA
Double or single stranded (if single, positive or negative sense)
Envelope or no

Question 3

Herpes simplex 1

Answer 3

Coldsores
80% of UK population experience HSV-1
Direct contact with vesicle fluid for transmission
Latency in trigeminal nerve ganglion w/ periodic reactivations
Can also cause encephalitis which can be fatal

Question 4

Herpes simplex 2

Answer 4

Often called genital herpes
10-20% of population
Direct contact with vesicle fluid for transmission
Latency in sensory nerve ganglia w/ periodic reactivations
Causes vesicles or ulcers (typically genitals/ buttocks)
Can cause meningitis
Vertical transmission at birth can cause life-threatening severe disseminated viraemia in neonates

Question 5

Varicella zoster

Answer 5

Still herpes
1st infection = chickenpox
Reactivation = shingles
Respiratory droplet tranmission in chickenpox or vesicle fluid contact
Latency in dorsal root ganglion of whole CNS
Shingles is found in one dermatome at a reactivation due to its latency in nerve roots

Question 6

Epstein Barr

Answer 6

More herpes!
Glandular fever or infectious mononucleosis
90-95% infected by age 25 in UK
Saliva and genital secretion transmission
Primary infection: tonsilitis, fever, lymphadenopathy, hepatosplenomegaly. Atypical lymphocytes

Question 7

Cytomegalovirus

Answer 7

Also known as CMV
Transmitted by saliva/genital secretions, donated blood/stem cells/solid organs, or latency in myeloid progenitors/monocytes/dendritic cells
Can cause infectious mononucleosis, congenital CMV via vertical transmission (possibly leading to congenital retinitis, deafness, microcephaly, hepatosplenomegaly)
Can reactivate in immunosuppressed patients, possibly causing retinitis, colitis and pneumonia

Question 8

Rhinovirus

Answer 8

Common cold

Worldwide distribution, in epidemics in autumn, winter and spring

Question 9

Influenza

Answer 9

Cross-species (e.g. swine flu)
Peaks in winter
3 distinct types - A, B and C
A mutates regularly
Surface proteins H and N have different variants used in nomenclature e.g. H1N1 (twin flu) or H3N2 (seasonal)
Primary influenza illness = fever, myalgia, headache, cough, sore throat, nasal discharge
Post-influenza secondary bacterial lung infection - S.pneumoniae, H. influenzae, S. aureus

Question 10

RSV

Answer 10

Respiratory syncytial virus
Most common in young children (70% infected, 30& have had clinical illness in first year of life)
Passed by coughs and sneezes
Can cause bronchiolitis in children under 2 causing cough, wheeze, hypoxia and apnoeas

Question 11

HIV

Answer 11

Transmitted via blood, genital secretions and breastmilk (needlestick, sexual, vertical)
HIV targets CD4+ helper T cells
Acute seroconversion flu-like illness can occur 2-6 weeks after transmission
Asymptomatic chronic infection followed for 5-15 years before onset of AIDS where viral load increases and CD4+ count drops, with patient become immunocompromised and susceptible to opportunistic infection

Question 12

AIDS defining illnesses

Answer 12

Pneumocystis pneumonia (fungal)
Cryptococcal meningitis (fungal)
Kaposi's sarcoma (caused by HHV-8)

Question 13

Faeco-oral spread hepatitises

Answer 13

Hepatitis A

Hepatitis E

Question 14

Blood borne hepatitises

Answer 14

Hepatitis B
(Hepatitis D, which can only survive with Hepatitis B)
Hepatitis C

Question 15

Hepatitis A

Answer 15

Faeco-oral spread
Nausea, myalgia, fever, jaundice, right upper quadrant pain
Usually self-limiting
Usually asymptomatic in children
Around 50% symptomatic in adults
Associated with lower socioeconomic groups, returning tourists and MSM

Question 16

Hepatitis E

Answer 16

Faeco-oral spread
Nausea, myalgia, fever, jaundice, right upper quadrant pain
Usually self-limiting
Associated with pigs/undercooked pork
95% of cases are asymptomatic
Fulminant hepatitis 25% mortality in infected pregnant women

Question 17

Hepatitis B

Answer 17

Vertical, sexual and parenteral transmission
After transmission, there can be acute clinical hepatitis, but 90% children and 50% young adults are asymptomatic
Can clear or become chronic
Risk of chronicity is inversely related to age at infection
Over time, chronic hepatitis can turn to cirrhosis which can turn to hepatocellular carcinoma

Question 18

Hepatitis C

Answer 18

Sharing needles, needlestick injury, transfusion of contaminated products. Vertical and sexual possible but less common
Approximately 25% of people have acute clinical hepatitis after transmission
15% will clear the virus, 85% chronically infected
Chronic hepatitis can become cirrhosis, becoming hepatocellular carcinoma

Question 19

Norovirus

Answer 19

90% of adults infected at some time, short lived immunity (<1 year)
Associated with point-source outbreaks (e.g. cruise ships, hospitals, military)
Transmitted via ingested/inhaled vomit particles
Mainly just a lot of vomiting

Question 20

Rotavirus

Answer 20

80-100% of children infected in 1st 3 years of life
Mainly winter
Major cause of infant mortality in developing world
Faeco-oral transmission and aerosolised faeces/vomit
Fever, vomiting and watery diarrhoea

Question 21

Enteroviruses

Answer 21

A whole genus with over 70 serotypes
Main peak in summer/autumn
75% of cases in under 15-year-olds
90% of cases are asymptomatic or have mild febrile illness
Enteric transmission
Replicate in gut but do not cause GI symptoms
From gut -> lymph nodes -> blood
Can cause meningitis - over 50% of viral meningitis is caused by enteroviruses!
Hand foot and mouth can occur in children
Severe disseminated disease in neonate

Question 22

Mumps

Answer 22

Mainly a childhood illness
Transmitted in saliva or respiratory secretions
Very infectious
Acute parotitis - unilateral or bilateral
Orchitis - 20-30% of males, typically 4-5 days after parotitis
Meningitis occurs in up to 15% of mumps cases
Can lead to meningoencephalitis and sensorineural deafness
Was a main cause of meningitis prior to MMR

Question 23

Measles

Answer 23

Currently occurs in clusters of unvaccinated
Respiratory droplet transmission
Highly infectious - environment still infectious after 2 hours
Primary measles - fever, coryza (nose mucous membrane inflammation), conjunctivitis, Koplik’s spots, then maculopapular rash
For 1:1000, acute post infectious measles encephalitis - occurs 7-10 days after infection, high mortality rate, immune mediated
For 1:1,000,000, subacute sclerosing pan-encephalitis SSPE - 7-10 years after infection, progressive, degenerate and fatal disease of CNS

Question 24

Rubella

Answer 24

German measles
Rare due to vaccine
Respiratory droplet transmission
Primary rubella - mild illness, fever and maculopapular rash. Arthralgia/arthritis occurs in 30% adults
Congenital rubella - classic triad of bilateral cataracts, sensorineural deafness, microcephaly. Risk highest in first 12 weeks of pregnancy

Question 25

Parvovirus B19

Answer 25

Slapped cheek
Mainly in spring
50% infected by 15, 90% by 90
Respiratory droplet transmission
Infects and kills erythrocyte progenitor cells, causing transient anaemia
Erythema infectiosum = fever, coryza, red rash on cheeks, lacy rash on body
Transient aplastic crisis affecting those with high erythrocyte turnover e.g. sickle cell, thalassaemia
Infection in pregnancy if in first 20 weeks has a 7-10% chance of foetal loss and 2-3% chance of hydrops fetalis (severe anaemia -> heart failure -> oedema, ascites)

Question 26

Definition of a prion

Answer 26

Particle including protein with no nucleic acid
Gene mutation can cause changes to folding pattern, which becomes resistant to protease, accumulates and promotes other proteins to fold abnormally
Abonormal prions are either inherited genetically or transmitted via consumption to direct exposure

Question 27

4 properties shared by prion disease

Answer 27

1) Manifest in CNS
2) Produce spongiform change in brain tissue
3) Long incubation times (up to 30 years)
4) Are progressive and fatal

Question 28

nvCJD

Answer 28

New variant Creutzfeld-Jakob disease
Directly linked to BSE (bovine spongiform encephalopathy)
Same structure as sporadic CJD
nvCJD associated with consumption of infected beef

Question 29

CJD

Answer 29

Sporadic Creutzfeld-Jakob disease
1 in 1,000,000
Gene mutation
Progressive ataxia, depression, dementia, then death