Lecture 17 - Viral diseases I

Question 1

Name some emerging diseases.

Answer 1

• Russian Flu (1977 – since around 1000)
  
  • HSV-2 (1978 – for hundreds of thousands of years)
  • HIV-1 (1981 – since late 19th century)
  • Hepatitis C (1989 - first identified – since Middle Ages)
  • West Nile Virus - transmitted by insect bites (1999)
  • SARS (2003)
  • Chikungunya (2005)
  • H1N1 pandemic influenza (pandemic in 2009)
  • MERS (Middle east respiratory syndrome - 2012)(outbreak in Korea -2015)
  • Ebola (2013 – since 1976)
  • Zika (2015 – 1947, pandemic since 2007)
  • There are many more such as cholera, typhoid, meningitis etc.
    Many of the first outbreaks are likely not actually the first and have been around for much longer. Phylogenetic calculations is used to find when the virus actually first appeared but more recently ancient viral DNA has been extracted from ancient remains.

Question 2

Discuss a rhinovirus infection progression.

Answer 2

Mild Rhinovirus infection in humans
Virus is first inoculated
Incubation period - From inoculation to appearance of first symptoms (3 days in Rhinovirus)
Prodromal period - when infectious but still have no symptoms (about a day)??????????
Neutralising antibody - binds to virus and stops it being infections. Fractions mean that in a serum ample it can only be diluted so much (50%) until it can no longer neutralise virus. The sample after the illness can be diluted much further (250 fold).

Question 3

Discuss the incubation period of EVD.

Answer 3

• The time from contracting the virus to development of symptoms
  ○ Average 11 days – range 2-21 days
  
  • Average symptoms to hospitalization period – 5 days
  • Average serial interval – 15 days
    Serial interval is the time between one infection and when they can infect another person. Difficult to calculate as cant accurately calculate when or who someone infects.
  • Average time to death – 10 days
    Average time to recovery – 17 days

Question 4

Discuss hepatitis A infection in humans

Answer 4

Hepatitis A has a long infection period.
The virus causes liver damage that begins functioning at 1 week peaking at 4-5 weeks and then decreasing. (jaundice only starts between week 2-3 and lasts until late week 7)
Virus is detectable after 3 or 4 days in both faeces and blood and peaks approximately the same time as onset of jaundice.
The antibody response IgM begins almost immediately and peaks at roughly week 5 before decreasing.
IgG starts after 2 weeks and continues increasing throughout infection - long-term protection

Question 5

Discuss HIV infection in Humans

Answer 5

During Acute infection the Virus concentration increases and the body begins making anti-HIV antibodies
CD4 T cells decrease over months and the Anti-HIV antibody increases - Chronic lymphadenopathy and sub-clinical immune dysfunction.
Aids caused when CD4 levels become too low and Anti-HIV antibody decreases so systemic immune deficiency begins.

Question 6

What i case fatality rate?

Answer 6

Case fatality rate is not the same as infective rate (rewatch)
Case fatality is influenced by other factors such as age and immune system health
Asymptomatic infection

Question 7

Discuss Antigenetic shift/drift of Influenza A.

Answer 7

Influenza A
Different influenza A pandemics were caused by different subtypes and caused different numbers of deaths. E.g. Spanish (H1N1) - killed 40 million people, and Hong Kong (H3N2) - H and N refer to viral surface proteins.
Immune system doesn’t give lifelong immunity with influenza due to angiogenetic drift (new strains)
Descendent strains are still circulating
Antigenic drift - between pandemics (Alteration of H and N structures)
Antigenic shift - launching new pandemics (from animal flu strains if can adapt to be transmitted in humans e.g. H5N1 or H9N2)

Reservoirs - Influenza A
Wild bids of the sea and shore form the natural reservoir. If this spreads to farm animals through farm ducks etc. Can then potentially spread to humans. Bat flu does also exist however it is not thought to be any risk to humans only bird flus.

Antigenic Shift
In birds where it is endemic there is little effect (stable virus)
In animals such as chickens and into pigs the virus evolves causing respiratory infection and disease.
When it can regularly spread from host to host in humans there is a pandemic.
The 1918 pandemic (H1N1) is thought to be a direct jump from birds to humans which may explain the mortality as we had no defences.
There can be shuffling if there is a mix infection. Antigenic Shift.

During 2009 pandemic strain identification could be done during the pandemic.

Antigenic Drift
Over time the human protection against the virus (influenza A) decreases as the antibodies become less and less useful due to mutations. Loss of immunity over time.

Antigenic drift vs. shift. Antigenic drift creates influenza viruses with slightly modified antigens, while antigenic shift generates viruses with entirely new antigens