Viruses and Disease

Question 1

Properties of a virus

Answer 1

Piece of genetic material (DNA/RNA) surrounded by a protein coat - simple structure
Unlike parasites they can’t replicate outside a host cell
Do not divide by binary fission
Much smaller than bacteria - not visible with light microscope

Question 2

What are the 4 different virus structures, giving examples.

Answer 2

1. Naked icosahedral eg. HIV, Polio virus, papillomavirus
2. Naked helical eg. tabacco mosaic virus
3. Enveloped icosahedral eg. all Herpes viruses
4. Enveloped helical eg. Measles, Mumps, Rabies virus

Question 3

What are the routes of viral transmission?

Answer 3

Respiratory - through the air by coughing or sneezing, eg. Influenza
Direct contact - eg. Adenovirus
Faecal-oral - Hepatitis A
Animal vectors - birds, insects, bats eg. Rabies
Sexual - eg. HIV

Question 4

Why was the discovery of the tobacco mosaic virus so important?

Answer 4

Shows that viruses can pass through filters that retain bacteria - much smaller

Question 5

Why were Walter Reed’s Yellow Fever experiments so important?

Answer 5

Reed showed that Yellow Fever was transmitted by mosquitos, therefore mosquito nets eradicated the virus

Question 6

What virus causes acute infection with full recovery of the patient?

Answer 6

Rotavirus - causes vomiting and diarrhoea, damage to villi and mucosal layer in stomach

Question 7

What virus causes acute infection with permanent damage?

Answer 7

Poliovirus - damage to the cells of the anterior horn of the spinal chord may destroy some motor neurone function = paralysis
Loss of muscle tone and function = deformities

Question 8

What virus causes recurrent infection that persists for the life of the patient?

Answer 8

Herpes Simplex Virus type 1 - causes cold sores which establish latency
Whilst remaining latent there are no symptoms, but virus can reactivate causing cold sores

Question 9

Which viruses cause congenital infection?

Answer 9

Cytomegalovirus - type of herpes, 1 in a 100 babies born with it, 10% severe infection
or Rubella

Question 10

Which viruses can cause cancer?

Answer 10

Epstein-Barr virus & Burkitt’s lymphoma - tumour in the jaw, mainly present where malaria is (Africa)

Question 11

Which virus is an emerging virus?

Answer 11

HIV - causes AIDS = muscle wasting (common symptom in advanced stages of the disease)

Question 12

Which virus has been successfully eradicated?

Answer 12

Smallpox

Question 13

Herpes Simplex Virus - type 1 (HSV-1)

Answer 13

Primary HSV-1 lesion with gingivostomatitis and secondary bacterial infection
Effects children 9 months - 5 years
Symptomatic reactivation = cold sores (latency)
Complications = become immunocompromised, excema
Treatment is Acyclovir (orally/intravenously/topically)

Question 14

Herpes Simplex Virus - type 2 (HSV-2)

Answer 14

Primary HSV-2 infection genital herpes
Fever and pain, in women lesions cover cervix, in men lesions cover bum and thighs
Symptomatic reactivation 8/9 times a year, can be asymptomatic
Neonatal herpes: on the skin/eye/mouth, neurological, disseminated
Treatment is Acyclovir (orally/intravenously/topically)

Question 15

HSE (encephalitis)

Answer 15

History of flue like symptoms, neurological symptoms can lead to coma and death
Treatment is Acyclovir (orally/intravenously/topically)

Question 16

Varicella-zoster virus (VZV)

Answer 16

Primary infection of chicken pox spread by direct contact/respiratory
Fever, mild general malaise (2-4 days), centripetal spread of vesicular rash, pruritic (itchy), on skin and mucous membranes, disease lasts for 1 week
Symptomatic reactivation = shingles, mainly in elderly
Uncomplicated unless immunocompromised = pneumonia, hepatitis, encephalitis
Dangerous in pregnancy, especially in first 20 weeks, last week before delivery
Treatment is Zoster Immune Globulin (ZIG)

Question 17

Epstein-Barr Virua (EBV)

Answer 17

Primary infection is asymptomatic, infectious mononucleosis causing a sore throat, fever, fatigue, swollen lymph glands
Symptomatic reactivation - oncogenic associations:
- non-Hodgkin’s lymphoma in AIDS patients
- Burkitt’s lymphoma

Question 18

Human cytomegalovirus

Answer 18

Primary infection is usually asymptomatic, occassionally an infectious mononucleosis like illness may be seen
Reactivations or re-infections common
Serious disease in immunocomprimised patients: fever; pneumonitis, hepatitis
Congenitally infected

Question 19

Human herpes virus 6 and 7

Answer 19

Roseola infantum affects 6mth-2yrs
High fever, rash, 1-2 day course, usually mild
Occassional complications - respiratory tract symptoms, meningitis, encephalitis

Question 20

Human herpes virus 8 - HSV-8

Answer 20

Kaposi’s sarcoma associated herpes virus
Endothelial cell tumour
Sexual/non-sexual transmission

Question 21

What are the 5 major paramyxoviruses?

Answer 21

Parainfluenza
Measles
Mumps
Respiratory syncitial virus 
Human metapneumovirus

Question 22

Describe the symptoms and complications of mumps

Answer 22

Swelling of salivary glands

Complications: architis in post-puberty males (can cause sterility), meningitis, encephalitis, first trimester infection

Question 23

Describe the symptoms and complications of measles

Answer 23

Patient is infected before rash appears (highly contagious)
Conjunctivitus, dry cough, sore throat, headache, low fever which intensify as rash spreads
Complications: bronchopneumonia, encephalomyelitis

Question 24

Togaviridae (Rubella virus)

Answer 24

Pale, red rash, centripetal spread, mild fever, runny nose
Problems in pregnancy if contracted in first 16 weeks
Congenital rubella - cause spontaneous abortion, congenital rubella syndrome:
- eyes = cataracts/blindness
- ears = hearing loss
- heart = malformation
- mental retardation
- diabetes

Question 25

Retroviridae

Answer 25

Human immunodeficiency virus 1 and 2
Causes AIDS - arises as a direct result of depletion of T-helper lymphocytes
Patients vulnerable to opportunistic infections
Severe thrush, pneumonia, tuberculosis all symptoms of AIDS