Viral and Prion Pathogens Flashcards
Layers of the virus
Genome (innermost)
Capsid (protein coat)
Envelope (lipid bilayer)
Some viruses also carry their own enzymes
Classification of viruses
DNA or RNA
Double or single stranded (if single, positive or negative sense)
Envelope or no
Herpes simplex 1
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
Herpes simplex 2
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
Varicella zoster
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
Epstein Barr
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
Cytomegalovirus
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
Rhinovirus
Common cold
Worldwide distribution, in epidemics in autumn, winter and spring
Influenza
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
RSV
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
HIV
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
AIDS defining illnesses
Pneumocystis pneumonia (fungal) Cryptococcal meningitis (fungal) Kaposi's sarcoma (caused by HHV-8)
Faeco-oral spread hepatitises
Hepatitis A
Hepatitis E
Blood borne hepatitises
Hepatitis B
(Hepatitis D, which can only survive with Hepatitis B)
Hepatitis C
Hepatitis A
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
Hepatitis E
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
Hepatitis B
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
Hepatitis C
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
Norovirus
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
Rotavirus
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
Enteroviruses
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
Mumps
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
Measles
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
Rubella
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
