SH public health

Influenza is an acute viral respiratory infection caused by influenza A, B, C viruses. Describe its typical incubation period, and its general symptoms.

• incubation: 1-4 days; infectious from 1 day before symptoms and 5-7 days after symptoms onset.

• symptoms (sudden onset):

  • high fever, chills

  • dry cough, sore throat, runny stuffy nose

  • myalgia, headache, fatigue

How is influenza transmitted?

• transmission route:

  • resp droplets (coughing, sneezing)

  • direct contact (touching contaminated surface then face)

  • aerosols in enclosed spaces

Influenza virus virulence factors

• HA (hemagglutinin) binds host resp epithelial cells

• NA (neuraminidase) helps to release new viral particles

• proteins to suppress host immune responses

• genetic mutations (antigenic shift/drift) to evade immune defense

Information card

Compare influenza A, B, C.

• Influenza A:

  • can cause pandemics, high public health impact

  • undergoes antigenic drift and shift

  • cause moderate to severe symptoms

• Influenza B

  • can cause seaonal epidemics

  • antigenic drift only, mild to moderate symptoms

• Influenza C

  • sporadic, rare epidemics

  • limited genetic drift, mild symptoms, usually low impact

How to distinguish influenza from common cold?

• influenza has more severe symptoms & starts suddenly; it also lasts longer

  • fever, chills, myalgia (body aches) possible

  • can lead to pneumonia

• a common cold is much milder

Which population is most affected by influenza?

• children: high transmission rate

• elderly (>65)

• pregnant women

• immunocompromised

• chronic illness: asthma, diabetes, etc.

Should advise vaccinations

Describe the socio-economic impact of the influenza virus

• large direct medical cost + indirect economic impact

• lost work days & earnings, loss of lives

Influenza viruses can undergo antigenic drift (Flu A & B) and shift (Flu A only).

What causes these genetic mutations when influenza evolves? What are the impact of their evolution?

What causes antigenic drift in influenza evolution? What could be its impact and what subtype of influenza does this occur in?

• antigenic drift causes epidemics

  • caused by mutations in the HA and NA genes of the virus, as viral polymerase makes mistakes during replication

• antigenic shift causes pandemics

  • when 2 influenza viruses infect a cell at the same time → genes are mixed and reshuffled (reassorted)

  • forming a new combination of HA & NA surface proteins

Endemic, epidemic, pandemic - what is the difference?

• endemic: a disease that is constantly present in a particular area or population

  • e.g. Malaria in parts of Africa, chickenpox

• epidemic: a localised outbreak, a sudden increase in disease cases above what is normally expected for an area

  • e.g. Ebola outbreak in West Africa, measles outbreaks

• pandemic: widespread & often global epidemic, across multiple countries / countinents

  • e.g. COVID-19. 1918 Spanish flu

What are the conditions for a pandemic to emerge?

1. new pathogen, the population has little or no immunity

2. able to transmit btw humans, spreads easily & sustainably

   1. resp droplets, aerosols, physical contact, body fluids

   2. less deadly - host is able to stay alive long enough to transmit to others

3. global trade, fast international travel allow the pathogen to spread quickly

4. asymptomatic, with incubation periods etc → delayed detection

Patient presents with myalgia, runny nose, sore throat and fatigue. She has a temperature of 39.

You suspect influenza. How can you investigate? How will you treat.

Investigation

• Rapid influenza antigen tests (fast, but less accurate than molecular tests, potential false negatives)

• molecular tests → test for viral / bacterial DNA, RNA

• nasal / throat swab → PCR

Treatment

• symptomatic relief: rest, hydration, pain relief

• possible antivirals for at-risk groups ( immunocompromised, pregnant, chronic illness, >65yo), seek medical advice

Flu vaccines can give false positives.

How does vaccination work to protect people from secondary exposure?

• vaccines mimic infection & trigger the immune system → B cells produce specific antibodies; memory B cells and T cells are formed

• when the actual pathogen enters the body later, the immune system responds faster & stronger

  • memory B cells rapidly produce high levels of specific antibodies

  • memory T cells destroy infected cells & support other immune cells

Generally what do antibodies and CD8 T cells target, respectively?

• antibodies from B cells → extracellular pathogens

• CD8 T cells → intracellular pathogens

What makes a vaccine good and successful?

• highly effective, provide strong and sustained protection

• safe, minimal side effects

• easy to administer

• low cost, affordable, minimal need for boosters

What are some factors that may affect vaccine efficacy?

• demographic → circulating virus, community proximity, herd immunity

• host → age, cormorbidities, genes

• viral variant → antigen mismatch with vaccines

• immune → quality/amount/function of immune cells

• access

Some pathogens have evolved to reduce their recognition and presentation by the immune system. How can we overcome this?

• adjuvants: substances added to vaccines, that can enhance the body’s immune response to the pathogen antigen

• adjuvants can:

  • stimulate immune system

  • enhance antigen presentation

  • activate immune cells

What does it mean when an infectious disease is sporadic?

occurs infrequently & irregularly

What is the requirement for an infectious agent to cause infection in a new host? What is the infective dose of a pathogen?

• it can survive in the environment

• enough of its kind will reach the new host

• it can establish colonies in the new host & evade immune attacks

Infective dose:

• number of pathogens required in the initial colony

• to cause infection in the new host

How can diseases be transmitted? Describe the routes of transmission.

Direct: spreads immediately from one host to another

1. Horizontal (person-to-person, same species); vertical (parent to offspring), zoonosis (from animals)

2. physical contact, sex, body fluids, droplets

Indirect: disease spread via intermediate object, organism, environment

1. air-borne: suspend in air then inhaled into lungs, e.g. TB, measles

2. contaminated surfaces e.g. RSV, rhinovirus

3. vehicle-born: contaminated water, food, biological products (e.g. cholera, hep A/B/C)

4. vector-borne: transmitted by living organism, typically insects (e.g. malaria, plague from fleas)

How do we prevent an infection from being transmitted?

• reduce & eliminate source of infection

• prevent/reduce disease transmitting vectors

• public health campaign → educate ppl abt high risk behaviours and advise safer practices

3 public health strategies to address drug use: harm reduction, supply reduction, demand reduction

• harm reduction: minimise the negative health and social consequences of drug use, without necessarily eliminating drug use

  • needle exchange programs

  • supervised injection sites

  • drug checking services in music festivals

• supply reduction: reduce the availability of ilicit drugs, by targeting their production, trafficking, distribution

  • police raids

  • arrest traffickers, destroy drug crops, border security

• demand reduction: decrease the desire or need for drugs in the population

  • drug education in schools

  • public awareness campaigns

  • social support