Virology Flashcards
What are the three requirements for classification as a virus?
- Sub-microscopic entity
- Single nucleic acid surrounded by a protein coat
- Obligate intracellular parasite
What are the 6 stages in virus life cycle?
Attachment, entry, replication and protein synthesis, assembly and release
Define viral pathogenicity
The severity of disease caused by different viruses
Define viral virulence
The severity of disease caused by different strains of the same virus
5 types of viral replication (ie single strand RNA, double strand DNA etc)
- Single strand RNA positive sense-the viral RNA can be used directly to make protein
- Single strand RNA negative sense-the viral RNA must be transcribed to positive sense (complimentary base pairing) and then is used to make protein
- Double stranded DNA-same as human replication but using viral enzymes (important in antivirals)
- Double stranded RNA-only example is rotavirus
- Retrovirus-genome is transcribed to double stranded DNA using reverse transcriptase then integrated into the host genome using integrase
What is the stage of the viral life cycle most commonly targeted by antivirals?
Replication
Define incubation period
The time between becoming infected with virus and symptom onset
Define generation time
The time between virus exposure and becoming infected to others
Define reproductive number
The number of subsequent infections in a susceptible population that can be caused by a viral illness in 1 individual during the infective period
What are the 5 patterns of viral illness?
Acute, subclinical, persistent and chronic, latent (acute and then persistent latent) and slowly progressive (the disease takes years to manifest)
What are the two types of rash and the relevance of them in diagnosis?
Maculopapular rash-the rash is caused by the immune response to the virus rather than the virus itself so cannot be used in diagnosis
Vesicular rash-can diagnose from the rash alone based on location, stage etc
What nucleic acid are measles, mumps and rubella? How are they transmitted?
All are single stranded RNA viruses (measles and mumps are negative sense and rubella is positive sense)
Respiratory transmission
What is the prodrome of measles?
What else will you see in an infected individual?
The 3C’s-conjunctivitis, cough and coryza.
Koplik spots, person will be very unwell(fever, malaise and anorexia)
What is the incubation period of measles?
What is the infectious period?
Incubation period-10 to 14 days
Infectious period-2 days before the rash until 10 days after
Complications of Measles infection
Secondary bacterial infection, encephalitis (10 days after) and sub-acute sclerosing encephalitis (6-8years after infection)
What are the risk groups in measles infection?
Immunocompromised, pregnancy and neonates
What is the incubation period of rubella?
What is the infectious period?
IP-14 to 21 days
Infectious 7 days before the rash until 7 days after
What are the complications of rubella?
Congenital rubella syndrome!-before 12 weeks risks serious malformation (so termination is offered) and 13-16weeks risks sensorineural hearing loss
arthralgia
What are the other names for Parvovirus B19?
Slapped cheek disease, fifth disease, erythema infectiosum
What is the incubation period for Parvovirus B19?
What is the infectious period?
IP-14 to 21 days
Infectious 7 days before the rash until the day the rash appears (so infection control is impossible)
What type of virus is Parvovirus B19?
Single stranded DNA
What does Parvovirus B19 infect, in that case who is at risk in infection?
Infects RBC progenitors, therefore risk in haemolytic disorders where it can precipitate an aplastic crisis
Risk groups in Parvovirus B19 infection
Haemolytic disorders-aplastic crisis
Immunocompromised
Pregnancy-if infection at less than 20weeks hydrops foetalis
What are the complications of HHV6 and HHV7?
Encephalitis and in transplant
What is the clinical presentation of mumps infection?
Parotiditis, fever, malaise and thyroiditis
What are the possible complications of mumps infection?
Pancreatitis, orchitis, oophoritis and aseptic meningitis
What is the viral classification of Herpes Viruses?
All are double stranded DNA viruses with an envelope.
Part of the herpesviridae family
What is the life cycle of HSV1 and HSV2?
infection in epithelial cells, latent in nerve cell bodies and then reinfection in the same epithelial cells
What is the general life cycle of herpes viruses?
Initial infection, latency and then reactivation
What are the complications of HHV1 and HHV2 infection?
Secondary bacterial infection, corneal ulceration, meningitis (HSV2) and herpes simplex encephalitis (HSV1)
What are the risk groups in HHV1 and HHV2 infection?
Immunocompromised and neonates
What is the life cycle of Varicella Zoster Virus?
Primary infection in lymph nodes, moves to organs and then disseminates in skin.
Latent in nerve cell bodies and then reactivation in the skin.
What is the clinical presentation of primary VZV infection?
Chickenpox-a vesicular rash in a centripetal distribution with crops of lesions at different stages
How is primary VZV infection transmitted?
Respiratory transmission or through close, direct contact with the rash
What is the incubation period and infectious period of primary VZV infection?
IP-8 to 21 days.
Infectious from 2 days before the rash until the vesicles crust over.
What are the possible complications of primary VZV infection?
Sepsis, Varicella pneumonia, cerebellar ataxia (because latent in nerve cell bodies) and varicella encephalitis
What are the at risk groups in primary VZV infection?
Immunocompromised, neonates and pregnancy
What is clinical presentation of VZV reactivation?
Shingles-a dermatomal rash. Opthalmic Zoster.
What are the complications of VZV reactivation?
Neuralgia, sepsis, ocular problems (Opthalmic zoster), encephalitis, meningitis and myelitis
What is the single risk group for VZV reactivation?
Immunocompromised-multi-dermatomal rash
When is the VZV indicated?
IgG negative contacts of immunocompromised children, healthcare workers and those over 70 (for shingles)
What is a complication/risk group for CMV infection?
Pregnancy-congenital CMV (7% born with symptoms)
What is the histological identifier of CMV infection?
Owl’s eye inclusions
What does EBV infect?
B lymphocytes
What is the clinical presentation of EBV infection? What is the implication of this?
In adolescence infectious mononucleosis (glandular fever) and splenomegaly.
Cannot let them play contact sport for around 6 weeks afterwards because of the risk of splenic rupture
How is EBV diagnosed?
Monospot test-heterophile antibodies
What can EBV be associated with?
Cancers-lymphoproliferative (eg Burkitt’s lymphoma) and also nasopharyngeal
What is the other name for HHV8?
Kaposi’s sarcoma associated HHV.
What is the clinical presentation of infection with HHV6and HHV7?
A rash as fever settles
What are the complications/risk groups for HHV6 and 7?
Febrile convulsions and encephalitis. Risk of generalised infection including neutropenia in the immunocompromised
What is the clinical presentation of infection with chlamydia trachomatis?
Most are asymptomatic.
D-K serotypes-nongonococcal urethritis (mucoid discharge), cervicitis, vaginal discharge, endometriotis
L serotype-lymphogranuloma venerum (an invasive STI)-transient papules and painful inguinal and perirectal lymph swellings
What is the treatment for Chlamydia?
Single dose of azithromycin 1mg. OR
Doxycycline 100mg twice daily for 7 days
What is the classification of Nisseria Gonorrhoea?
Gram negative diplococci
What is the clinical presentation of nisseria gonorrhoea?
50% women and 5% are asymptomatic
Men-urethritis and dysuria
Women-endocervical infection (discharge) and pelvic inflammatory disease
Neonatal Conjunctivitis
What is the treatment for nisseria gonorrhoea?
Ceftriaxone and azithromycin
What is the causative organism of syphilis?
Treponema Pallidum-a gram negative spirochete
What is the clinical presentation of syphilis?
A systemic disease!
Primary syphilis-primary chancre 3 weeks post infection
Secondary syphilis-red, maculopapular rash (including on the hands and feet), 6 weeks after the primary chancre
Tertiary syphilis-dementia and gummata (small soft swelling that can effect any organ)
What are the 4 most clinically relevant serotypes of HPV?
6 and 11-associated with warts
16 and 18-association with cervical cancer
Two main causes of viral gastroenteritis? Which do we vaccinate against?
Rotavirus and norovirus. Vaccinate against rotavirus.
What is the incubation periods of rotavirus and norovirus?
Rotavirus-48 hours and symptoms last 4-8days
Norovirus-1to2days and symptoms last 1to2days
What is antigenic shift?
Influenza A.
Re-assortment of the segmented genome in a non-human host causes HA and NA surface proteins completely different to those seen before.
Causes pandemics eg Swine flu, Spanish flu
What is antigenic drift?
Small point mutations in the HA and NA genes causes gradual changes in the proteins.
The cause of yearly epidemics
What is the major population group to be concerned about in RSV?
Under 6 months
What type of virus is influenza?
Negative strand RNA
What type of virus is RSV?
Enveloped RNA
What do the different parainfluenza strains cause?
hPIV 1 and 2-croup
hPIV III-bronchiolitis and pneumonia
What is the patient group you worry about in PIV?
T-cell defective patients.
