Viral Infections Flashcards
Viruses are what size?
20-300 nanometres, not visible on light microscope.
Can viruses replicated independently?
No.
How do viruses replicate?
Invade host cells and use their cellular machinery to replicate - intracellular parasites. They do not divide by binary fission.
Examples of viruses?
Influenza, Common cold, Chickenpox (varicella), Herpes and HIV/AIDS.
Viruses are easy/difficult to treat?
May be difficult.
The HIV/AIDS epidemic was caused by which virus?
Human retrovirus HIV.
Morbidity and mortality of HIV epidemic?
25 million died in epidemic and 33 million currently infected.
Swine flu virus is called what?
H1N1.
The current pandemic is?
Swine flu.
Is swine flu easily transmissible?
Yes but not highly pathogenic.
What is a virus?
A piece of genetic information in a protein coat.
How have viruses evolved to transfer genetic information between cells and protect themselves?
Have developed a closed shell to protect nucleic acid.
Capsids are composed of repeating protein units - same or many - what are these called?
Protomers
The protomers must be arranged how?
Platonic structure - A simple regular structure that utilises bonds between same pairs of chemical groups.
Any of the five regular polyhedrons – solids with regular polygon faces and the same number of faces meeting at each corner – that are possible in three dimensions. They are the tetrahedron (a pyramid with triangular faces), the octahedron (an eight-sided figure with triangular faces), the dodecahedron (a 12-sided figure with pentagonal faces), the icosahedron (a 20-sided figure with triangular faces), and the hexahedron or cube.
Why can’t the coat have hexagonal faces?
They would meet at 360 degrees and be planar.
Which is the only closed shell structure that can be made with identical protomers?
The icosahedron - most efficient.
Another structure for the capsid is?
Helix - protomers laid end to end with identical bonds form a ribbon like structure and wrap around axis. Length determined by length of nucleic acid. Diameter determined by characteristics of protomers.
Some viruses also have a…
fatty lipid envelope.
Four types of structure are..
Naked icosahedron, enveloped icosahedron, naked helical and enveloped helical?
Why are bonds looser in enveloped helical structures?
To wind around inside.
How are viruses classified?
Presence or absence of envelope.
Nucleic acid type: DNA or RNA.
Capsid symmetry: helical, icosahedral or complex.
Number of strands of nucleic acid and their construction (single or double stranded, linear, circular, segmented
Yellow fever is what type of infection and what are the symptoms and outcomes? How is it transmitted?
Acute haemmorhagic viral infection. Fever, vomiting, bleeding - recovery or death. Transmitted by mosquitoes rather than fomites.
Previous prevention of yellow fever and current?
Previous: infected people slept in nets.
Current: vaccines.
How are viruses studied?
Electron microscopes to see viruses.
Grown on cell culture (some require animals).
Techniques from molecular biology and immunology.
Proper safety precautions.
How are viruses transmitted?
Through air, direct contact (fomites - any surface where microbes can live), by animals, contaminated food or water, body fluids.
Why is the common cold easier to catch than the flu?
Large particles fall downwards - flu virus is enveloped and therefore bigger, than common cold which will travel far.
Skin transmission diseases include:
Abrasion/injury: HSV1 and 2. Eczema: Papillomavirus Injection/blood: HIV, Hep BCDG Animal bites: Rabies Insect vectors: Yellow fever
Mucous membrane transmission disease include:
Conjuctiva: fingers, instruments; HSV1 an adenovirus
Genitourinary tract: sexual activity; HIV, HSV2, Papillomavirus, Hep B.
Oral: kissing, herpes viruses.
Alimentary tract: faecal-oral, rotavirus, hepititis A, poliovirus.
Respiratory tract: Aesorols, influenza, rhinovirus, measles, mumps and chickenpox.
Rotavirus damages..
villi, reduces surfaces area.
Poliovirus damages..
cells of anterior horn of spinal cord may destroy some motor neuron function resulting in paralysis, loss of muscle tone and deformities.
Herpes virus is latent which means?
Never goes away, can be asymptomatic but can reactivate.
Cytomegalovirus is a..
congenital infection.
Epstein-barr virus and Burkitt’s lymphoma can cause
cancer.
HIV causes..
muscle wasting.
Smallpox shows what signs
lots of spots that turn into blisters filled with fluid which turn into pus. These fall of leaving pitted scars. Now successfully eradicated.
Examples of naked helical virus
tobacco mosaic virus, no human viruses.
Examples of enveloped helical virus
measles, mumps and rabies.
Examples of naked icosahedral virus
polio virus and papillomavirus.
Examples of enveloped icosahedral
herpes virus.
Mosaic tobacco virus experiments important because
discovery that viruses were small and could only be grown in other living cells.
Walter Reed’s yellow fever experiment is important because
discovery that viruses can be transmitted by insects.
What are the 8 herpes viruses?
HSV1, HSV2, CMV, VZV, EBV, HHV6, HHV7, HHV8.
Facts about herpes viruses?
Very common, cause a variety of diseases, all establish latency.
Who is most susceptible to HSV1 and what does it cause?
Coldsore virus.
Uncommon in babies up to 6-9 months due to maternal antibody.
Normally contracted between 9 months to 5 years or adolescence and early adulthood due to kissing.
Rare after 30 years.
Lower socioeconomic groups tend to have an earlier primary infection.
Where do latent viruses live and how do they reactivate?
Lives in nerve cells, latent until ganglia triggered where it moves back up neurone to skin and forms blisters. Reactivation triggered by a variety of stimuli such as stress, infection, UV light and menstruation.
Symptoms of HSV1
Symptomatic recurrence in 60% cases. Tingling, itching, eruption of blisters, crusting.
How long does each infection of HSV1 last?
10 days.
HSV1 complications
Can affect skin if sufferers have eczema. Can spread on immunocompromised patients. Can cause blindness if reaches eye.
What does HSV2 cause
Genital herpes
Primary infection of genital herpes may be severe - true or false
True
Where can lesions of HSV2 spread?
Cervix in females and buttocks and thigh in males.
What percentage of patients develop meningitis from HSV2?
25%
How long do fever and pain associated with HSV2 last??
3 weeks
HSV2 explain
Starts with small macules and papules in infected area, develops into diverse vesicles which develop into ulcers.
Symptoms of HSV2
Differs between the sexes, for females - painful lesions on vulva and cervix. 10-15% may develop urinary retention syndrome. Up to 25% will develop aseptic meningitis. Males - Lesions occur on glans penis or penile shaft but can also occur on buttocks, thighs and perineum. In severe primary infection, sacral radiculomyelitis may occur leading to urinary retention and meningoencephalitis.
Frequency and healing of HSV2
During recurrence new lesions appearing delays healing by up to 15 days.
Up to 8-9 recurrences a year for 1/3 patients but recurrence is milder than primary infection.
HSV1 causes 30% primary genital infection in developed countries and recurrence is less likely with this strain.
60-80% of patients recurrence is asymptomatic.
Neonatal herpes incidence and mortality
UK 1/60,000 deliveries USA 1/2000-5000 deliveries Skin/eye/mouth - low mortality Neurological in CNS - 50% mortality or neurologically impaired Disseminated - 80% mortality
HSEncephalitis incidence and mortality
1/200,000 10^6
Untreated patients about 70%, only 2% of those who recover will return to normal neurological function.
Symptoms of HSE
Flu like symptoms for 2 weeks preceding onset of neurological symptoms
Fever continues with neurological symptoms including altered consciousness that increases in severity and may result in coma and death.
Affects the temporal lobe - function and memory.
Treatment for HSV
Acyclovir IV, tablet or cream
Prompt treatment needed for HSE
Also effective against VZV, less so against beta and gamma herpes infections (CMV, EBV)
Acyclovir molecules enter cell and converted to acyclovir monophosphate by the HSV enzyme thymidine kinase (TK). Enzymes in human cell add two more phosphates to eventually form the active drug acyclovir triphosphate which competes with 2-deoxyguanosine triphosphate (dGTP) as a substrate for viral DNA polymerase, as well as acting as a chain terminator. In actual infection the HSV releases its naked capsid that delivers DNA to the human nucleus, the active drug acyclovir triphosphate exerts its action on the viral DNA located in the nucleus.
Varicella zoster virus causes what?
Primary: Chickenpox
Recurrent: Zoster/shingles
How is chickenpox spread?
Direct contact or respiratory
What is the incubation period for chickenpox?
10-21 days
Symptoms of chicken pox
Fever, general malaise for 2- 4 days followed by a centripetal spread of vesicular rash, itchy, on skin and mucous membranes. Vesicles appear in crops for 2-4 days, 100-300 lesions.
Complications of chickenpox
Usually uncomplicated but can cause complications if immuncompromised such as pneumonia, hepatitis, pancreatitis, encephalitis, secondary skin infections such as s.aureus.
If pregnant:
First 20 weeks: Congenital (fetal) varicella syndrome (limb hypoplasia, microcephaly, cataracts, growth retardation and skin scarring) - incidence 1% in first 12 weeks and 2% in weeks 13-20.
In 2nd and 3rd trimester - Herpes zoster in an otherwise healthy infant
A week before to a week after delivery - neonatal chickenpox - severe and even fatal disease in the neonate.
Treatment for neonatal chickenpox
Zoster immune globulin given to neonate, possible aciclovir.
Where is EBV latent?
B-Lymphocytes
