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bs127: aids > Lectures 23-28 > Flashcards

Lectures 23-28 Flashcards

1
Q

Epidemiology of infectious diseases refers to what?

A

Transmission,

Contact Patterns,

Rate of spread and recovery,

Immunity (how long lasting),

Control of disease and population structure.

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2
Q

What is the difference between micro and macroparasites?

Macro = endo/ectoparasites
Micro = virus/bacteria/fungi

A

Micro - small, difficult to count. Multiply in the host.

Macro - large, can be counted. Multiply externally to the host.

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3
Q

Tell me about the three types of 1 to 1 contact.

A

Direct - contact between infected/colonized individual and host. (Shaking hands and kissing).

Indirect - infectious agent on surface survives and transfers onto another person. (Not washing hands between patients).

Droplet - Contact but transmission through the air. (Sneezing or coughing).

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4
Q

Tell me about the 3 types of Non-contact.

A

Airborne - Transmission through aerosols that contain organsims in nuclei or dust. (Spread via ventilation systems).

Vehicle - A single contaminated source spreads infection to several hosts. (Infected batch of food which leads to food-borne outbreak).

Vector-borne - Transmission by insect or animal vectors. (Mosquitos and malaria).

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5
Q

What are DALY’s?

A

Disability adjusted life years. The number of healthy years of life lost due to premature death and disability.

DALY = Years lived w/out disability + Years of life lost.

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6
Q

Tell me about the transmission cycle. Using fleas, humans, cats and mammals.

A

Fleas become infected after feeding on mammal host.

New mammals become infected, which in turn causes humans to be infected.

Cats etc become infected by flee bites or consumption of infected rodents.

Cats spread infection to humans through scratches and bites.

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7
Q

Summary of The Plague:

A

Caused by Yersinia pestis,

Endemic in nature, constantly present,

Transmitted by fleas via small mammals, rodents,

Causes 3 types of disease; bubonic, pneumonic and septicaemic.

High mortality w/out treatment, high survival w/.

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8
Q

Examples of arthropod vector-borne protozoan microparasites:

A

Trypanosoma cruzi = Chagas disease.

Trypanosoma brucei = African sleeping sickness.

Plasmodium spp = Malaria.

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9
Q

Chagas Disease:

A

Vector-borne by kissing bugs and infected blood.

Congenital: mother to foetus (vertical transmission).

Scratching or rubbing bite from bug leads to cell penetration. Cell is disrupted and breaks, colonisation of muscle or neural tissue. Gets into blood stream.

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10
Q

Acute vs Chronic Chagas Disease:

A

Acute: Pseudocysts form (replication sites). Rupturing leads to release of inflammatory mediators. Localised cell damage.

Chronic: Type III hypersensitivity and myocarditis and kidney disease.

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11
Q

Epidemiology definitions:

A

Infection - presence of parasite/pathogen in the host.

Disease - clinical state of host.

Vertical transmission - passage of infection from mother to offspring.

Endemic - native to.

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12
Q

Macroparasites:

A

Chronic recurring infections.

High morbidity, low mortality.

Endemic in nature.

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13
Q

Schistosoma mansoni causing schistosomiasis using snails:

A

Pathogen in excrement. Eggs hatch releasing miracidia.

Miracidia penetrate snails. Sporocysts present in snails.

Cercariae released by snail into water.

Penetrate skin. Cercariae lose tails and become schistosomulae.

Circulation and migrate to portal blood in liver and mature into adults.

Paired adult worms migrate to rectum, laying eggs.

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14
Q

What is an epidemic?

A

An increase in incidence of disease in excess of that expected.

Incidence = number of new cases per unit of time.

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15
Q

Sequence of host stages:

A

Susuceptible -> Infected -> Recovered

Need to think of individuals in groups and infections passing through those groups.

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16
Q

What is R0?

A

The basic case reproduction number, not a rate.

The average number of new cases arising from one infectious case introduced into a population of wholly susceptible individuals.

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17
Q

What is Pc?

A

The % of the population likely to get a disease in a fully susceptible population.

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18
Q

How to estimate R0 for a pathogen?

A

R0 = p x c x D

p: probability that contact results in transmission.

c: frequency of host contacts between infectious and susceptible individuals.

p x c: effective contact rate.

D: the average amount of time the host is infectious.

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19
Q

What is Re?

A

Effective R (Re) is the restrained growth rate.

R0 is defined for a virgin population where all individuals are susceptible.

Re is the true reproductive rate = R0 x fraction of susceptible individuals (S).

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20
Q

When does an epidemic occur?

A

WHen the number of secondary cases is on average >1.

21
Q

Why do epidemics end?

A

The pool of susceptible individuals is depleted, due to infection.

Re declines to <1.

Re cannot return to >1 until new susceptibles are generated.

22
Q

How do epidemics continue?

A

Susceptibles are born or migrate into the population.

No immunity.

Pathogen mutates and re-infects.

Immunity wanes.

23
Q

How do epidemics recur in small populations?

A

Slow birth rate due to small population size.

24
Q

What can patterns in epidemic data tell us?

A

Prevalence and incidence.

Origin of the outbreak.

Mode of spread through the population.

Incubation period and time of exposure.

Clues to identify the infectious agent.

25
Q

Incubation vs Latency:

A

Incubation is the period between infection and clinical onset of the disease.

Latency period is the time from infection to infectiousness.

26
Q

What is point epidemic?

A

single common exposure and incubation period.

Does not spread by host-to-host transmission.

27
Q

Continuous common source exposure:

A

Prolonged exposure to source over time.

Cases not all within single incubation period.

Curve decay may be sharp or gradual.

28
Q

Propagated progressive source epidemic:

A

Spread between hosts.

Larger curves until susceptibles are depleted/intervention made.

Tends to be in smaller populations.

Larger populations, the graph would merge together.

29
Q

When is an epidemic not an epidemic?

A

When waves of infection are waiting for new susceptibles to infect.

The host-parasite relationship dampens to an equilibrium.

30
Q

Endemic equilibrium:

A

Re = 1, not growing.

Re>1 means epidemic.

31
Q

What determines the persistence of an infection?

A

Critical community size.

Rate of contact for transmission.

Duration of infectious period.

Survival of host.

32
Q

What is the CCS?

A

Critical community size.

The minimum host population size required for the pathogen to persist.

33
Q

Reservoirs and Carriers:

A

Reservoir host = refers to population or species.

Carrier = refers to an individual.

Clinically normal but infectious.

34
Q

Measurements of macroparasite infections:

A

Infection intensity/mean burden.

Prevalence determined by mean burden and degree of parasite aggregation.

35
Q

What is the aim of intervention?

A

Control,

Elimination,

Eradication,

Extinction.

36
Q

Further maths equations:

A

S* = 1/R0 (Endemic Equilibrium)

S = 1 - Pc

(Pc = immune proportion).

1 - Pc = 1/R0.

Pc = 1 - 1/ R0.

37
Q

Vaccination demography equations:

A

A = average age of infection.

L = life expectancy.

R0 = 1 + L/A

38
Q

measles and smallpox:

A

Similarities:
No reservoir
Safe, cheap and vaccine availabe.
High morbidity and high compliance.

Differences:
Measles transmitted more readily
R0 much higher
Highly infectious but not as virulent.

39
Q

What is involved in infectiveness curtailment?

A

Surveillance

Tracing

Isolation

40
Q

Anthroponotic meaning?

A

Human - arthropod- human interaction.

41
Q

Zoonotic meaning?

A

Animal- arthropod-human interaction.

42
Q

How do you stop vectors?

A

Vectorial Capacity (C).

R0 = C x d.

C = (V/N)(ah)^2 p^2 / -lnp

a^2 = vector biting rate per day.

h^2 = the proportion of bloodmeals taken on the host.

p = daily vector survival rate.

n = latent period of agent inside vector.

43
Q

Examples of vector control?

A

Human and non-human bait traps

Urban breeding site source reduction.

Rural drainage of breeding sites.

44
Q

Non-human bait traps.

A

Tsetse control.

Controlled by case detection and treatment but only reaches 75% of population.

Reactive intervention rather than proactive.

45
Q

Human protection.

A

Anopheles gambiae.

Insecticide treated nets.

May provide herd immunity and protects against other vectors.

Increases vector mortality rate excito-repellancy
increased zoophagy.

46
Q

Climate may affect how long the average vector may be infectious.

A

Dv = p^EIP / (-lnp)

47
Q

COVID:

A

Infection - Sars Cov 2

1/6 species

Disease is COVID-19.

Wuhan, China December 019’.

Reservoir host, infection due to spillover event.

Zoonosis.

48
Q

What is a waning immunity?

A

A reduction in the hosts immune response

A specificity of immune response that does not respond to a mutated/different strain.

49
Q

What will a vaccine do?

A

Prevent disease - lowers morbidity and mortality.

Prevent infection transmission.

bs127: aids (3 decks)

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