Session 7 Flashcards
(30 cards)
What are the consequences of transmission?
- endemic disease = usual background rate
- outbreak = two or more cases linked in time and place
- epidemic = rate greater than usually background rate
- pandemic = very high rate across many regions
How can diseases be transferred?
- vectors e.g mosquitoes
- environmental
- food/water
- animal
What’s the basic reproduction number?
The average number of cases one case generates over the course of its infectious period, in an otherwise uninfected, non immune population.
If R0 > 1, increase in cases
If R0 = 1, stable number of cases
If R0<0, decrease in cases
What are the reasons for outbreaks?
- new strain of pathogen e.g virulence factor, mutated or more resistant to antibiotics
- new hosts e.g. newborns haven’t been exposed to antigen so have no resistant antibodies. So, when the antigen comes back = get infected.
- new practise e.g Hep E outbreak due to changes in farming practise. Outbreaks associated also with tattoos and needles.
What is infectious dose?
Infectious dose
- number of micro organisms required to cause infection
- varies by micro organism, presentation of micro organism, immunity of potential host
Why are people more likely to get ill in the winter?
Winter = people gather together inside = more susceptible to illness
What intervention can be done for the pathogens and vectors?
- reduce/eradicate pathogen: antibacterials, decontamination, sterilisation
- reduce/eradicate a vector: eliminate breeding sites
What interventions can be done for patients?
- improved health: nutrition, medical treatment
- immunity: passive e.g maternal antibody, intravenous immunoglobulin or active e.g vaccination
What interventions can be done for practise?
- avoid pathogen/vector: geographic, don’t go there or protective clothing e.g long sleeves and trousers against bites and protective clothes in hospitals e.g gloves, masks etc.
- behavioural e.g safe sex, safe disposal of sharps, food and drink preparation
What interventions can be done for place?
environmental engineering
- safe water
- safe air
- good quality housing
- well designed healthcare facilities
What are the consequences of control?
Good
- decreased number of incidence and more likely to eliminate disease
Bad
- decreased exposure = decreased immune stimulus = decreased antibody = increased susceptibility to outbreak
- later average age of exposure = increased severity e.g polio and chicken pox
What are some presenting features of HIV?
- oral candidiasis: fungal mouth infection = sign of immunosuppressed
- kaposi’s sarcoma = red blotchy skin
- pneumonia
What group is most susceptible to HIV?
MSM
What is the general structure of a virus?
1) genome - DNA/RNA
2) capsid - protein shell, protects genome
3) lipid envelop - present or absent
4) replication strategy
What is HIV?
- Human immunodeficiency virus
- A retrovirus
- SsRNA -> DNA -> ssRNA
- infects cell with CD4 surface receptors
- replicates inside T helper cell, destroying it and causing inflammation
How does HIV infect a cell?
1) binds a CD4 molecule to a receptor on T helper cells surface
2) virus penetrates the cell
3) single strands of viral RNA become dsDNA by the reverse transcriptase enzyme
4) viral dna is combined with the cells own DNA and sets of viral protein are synthesised and come together
5) immature virus pushes out of cell, taking somme of cell membrane before breaking free of the infected cell
6) viral particle matures and becomes a working virus
How is HIV transmitted?
1) sexual contact
2) transfusions
3) contaminated needles
4) perinatal: through placenta, during delivery or ingestion of breast milk
What are the main symptoms of acute HIV infection?
- fever
- weight loss
- mouth sores/thrush
- enlarged lymph nodes
- skin rash
- nausea/vomiting
- splenomegaly and hepatomegaly
- oesophageal sores
What conditions are associated with severe HIV?
- meningitis
- heart disease/stroke
- genital ulcers
- HPV and cervical cancer
- osteoporosis
What factors affect HIV transmission?
- type of exposure: type of sexual act and transfusion vs needlestick vs mucus membrane (easier for virus to pass)
- viral level up blood
- condom use
- breaks in skin or mucosa:other STI/ sexual assault
What diagnostic tests are done for HIV?
blood test serology
- HIV antigen (Ag) and antibody (Ab)
- may get false positive
Blood tests PCR
- detects HIV nucleic acid
- slow results
Rapid tests
- detect antibody
- blood test/saliva
- if negative, accurate but may get a false positive
What are the aims of HIV treatment?
Reduce general inflammation Reduce risk of transmission Good quality o life Normalise lifespan Reconstitute CD4 count
Why are 3 ARV drugs given to treat HIV?
3 drugs = harder for virus to mutate and become resistant to all 3.
Which ARVs are given to treat HIV?
- nucleoside reverse transcriptase inhibitor x2
And either
- non nucleoside reverse transcriptase inhibitor
- protease inhibitor
- integrate inhibitor
