L12 Virus Structure And Transmission Flashcards
What does virus structure consist of?
- DNA/RNA genome
- surface protein
- capsid protein
- +/- envelope
- double stranded or single stranded
- linear or circular
What are the characteristics of viruses?
- they are obligate Intracellular parasites so they can only grow in appropriate host cells
- a given virus usually has a specific host
- the virus genome encodes viral proteins
- many viruses are enclosed in one or more lipid membrane envelopes which are derived from host cell by also contain virus-coded proteins
What do virions normally contain?
Numerous copies of one or more different proteins
One or more nucleic acid molecule which acts as the virus genome
What is the virus genome enclosed in?
In a protein shell called a capsid which is made up of many identical capsomeres
What is a genome called when it’s enclosed by a capsid?
Nucleocapsid
What are the 5 basic structural forms of viruses?
1) naked icosahedral e.g. poliovirus
2) naked helical e.g. tobacco mosaic virus
- no human virus with this structure
3) enveloped icosahedral e.g. herpes virus
4) enveloped helical e.g. measles virus
5) complex e.g. pox virus
Why do we study viruses?
- they a major causes of disease and they can infect all known organisms
- virologist want to learn how they operate so they can defeat or lessen the effects of viruses
- they can be exploited for our benefit such as in the Covid-19 vaccine
- oncolytic viruses can be used to treat cancer
What is the cycle of infection for a virus?
Transmission -> entry -> primary site replication -> spread within host -> shedding
What are the 3 modes of virus transmission?
1) horizontal transmission - person to person
2) vertical transmission - mother to baby
3) zoonosis - animal to man
Outline respiratory transmission
A type of HORIZONTAL transmission
- many viruses spread this way cause respiratory disease
- droplets may be directly inhaled, infect conjunctiva, fall onto surfaces and be transferred on fingers to mouth
- droplet size is important in determining the route of transmission
What diseases are a result of faecal-oral transmission?
A type of HORIZONTAL transmission
Rotaviruses : vommiting, diarrhoea and fever
Hepatitis A : inflammation of the liver which leads to jaundice
Poliovirus : 99% of cases result in no symptoms or mild fever and sore throat but 1% develop into irreversible muscle paralysis
Which diseases are spread through sexual transmission?
Human immunodeficiency virus 1 (HIV-1) : leads to AIDS
Hepatitis B virus : hepatitis, liver cirrhosis, liver cancer
Human papilloma virus : type 6&11 - genital warts
Herpes simplex virus - painful blisters on penis, vulva, vagina and cervix
In what ways can viruses be transmitted vertically?
- mother to child transmission
- primary infection of mother while pregnant, or reactivation of a persistent infection
- transplacental e.g. rubella
- during birth - perinatal transmission
- after birth - post natal
What is a reservoir?
The animal in which the virus replicates during zoonosis
What is the vector in zoonosis?
The animal which transmits the virus
