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BMS1042 > Week 7: Communicable Diseases > Flashcards

Week 7: Communicable Diseases Flashcards

1
Q

What is a communicable disease?

A
  • Caused by infectious agents and can be passed from one person or animal to another
  • Examples include malaria, influenza and chicken pox
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2
Q

• Infectious agents include:

A
  • Bacteria
  • Viruses
  • Parasites
  • Fungi or their toxic products.
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3
Q

• Transmission can occur:

A
  • directly - through contact with bodily discharge
  • indirectly - by sharing a drinking glass
  • vectors - such as mosquitoes
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4
Q

How common are communicable diseases?

A

• Common – most people have a communicable disease in their lifetime e.g. cold,
stomach bug
• Prevalence of short lived and mild communicable diseases is difficult to determine

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5
Q

What is an infection?

A

The invasion and multiplication of microorganisms such as bacteria, viruses, and
parasites that are not normally present within the body. May cause no symptoms and
be subclinical, or it may cause symptoms and be clinically apparent. May remain
localized, or may spread through the blood or lymphatic vessels to become systemic.

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6
Q

What is infection caused by?

A

Infectious agents which include viruses, microogranisms, nematodes, fungi and macroparasites

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7
Q

What is a chronic disease?

A

Long duration, of the order of weeks or months

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8
Q

What is an acute disease?

A

Short duration, of the order of several days

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9
Q

Primary pathogen vs opportunistic pathogen?

and Why are they contagious?

A

Primary pathogen – the presence of this pathogen causes the disease and their intrinsic virulence
Opportunistic pathogen – requires a depressed immune response e.g. TB
Contagious because–>Easy transmission by an ill persons secretions e.g. influenza.

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10
Q

Chronic infections stage

A 
⚫ Duration of infection
⚫ Incubation period
⚫ Symptomatic period
⚫ Infectious period
⚫ Carrier state
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11
Q

Transmission of chronic infections depends on

A

How infectious a disease is
How many contacts an infectious person makes each day
How long they are infectious
—- People infected with chronic diseases are infectious for a long
time
Very common
Geographical distribution determined by the means of
transmission
Very diverse

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12
Q

Examples of chronic infections

A 
Hepatitis B
 Hepatitis C
Tuberculosis
 Syphilis
 Creutzfeldt-Jakob disease
 HIV infection
Malaria
Chickenpox/herpes zoster
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13
Q

Food and water borne diseases

A

Typhoid fever, Cholera, Salmonella, Norovirus, Hepatitis A

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14
Q

Faecal-oral route diseases

A

Poliomyelitis

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15
Q

Polio

A
  • Highly infectious disease caused by a virus (destroy nerve cells in the spinal cord)
  • Spreads through person-to-person contact
  • Mainly affects children under 5 years of age
  • 1 in 200 infections leads to irreversible paralysis
  • 5% to 10% die when their breathing muscles become immobilized
  • No cure for polio
  • Prevention vaccine - Salk (1954), Sabin (1957)
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16
Q

Blood borne diseases

A

HIV infection, Hepatitis B and Hepatitis C

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17
Q

Human immunodeficiency virus (HIV)
transmission
prevention

A
  • Disable the body’s immune system until it can no longer fight infection
  • Once the person is immunocompromised:
  • they exhibit flu like symptoms
  • become vulnerable to pneumonias, fungal infections and intestinal disorders
  • Transmission: sexual, mother to child and blood routes
  • Prevention is by:
  • Safe sex
  • Disposable of sharps or safe injecting rooms
  • Transfusion
  • Manageable with anti-retrovirals
  • No vaccine
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18
Q

Hepatitis

A
  • Means inflammation of the liver
  • Caused by virus risk factors include heavy alcohol use & toxins
  • Hepatitis can be prevented, diagnosed, treated and even cured
  • Hep A, Hep B, Hep C – 3 different viruses
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19
Q

Hepatitis A vs Hepatitis B vs Hepatitis C

A

• Hepatitis A – short-term infection acute & vaccine preventable
• Hepatitis B & C chronic infections (life-long)
• Hepatitis B - vaccine preventable
• Hepatitis C – no vaccine however current treatments are 99% effective at
curing the condition with 8-12 weeks of treatment

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20
Q

Hepatitis B

transmission

A

• Can survive outside the body for at least 7 days
• Transmission: mother to child (perinatal transmission), needles or medical equipment, percutaneous or mucosal exposure to infected blood and various body fluid, saliva, menstrual, vaginal, seminal fluids and sexual transmission
Estimated 257 million people are living with hepatitis B virus infection
• Root cause of liver cancer (accounts for 60%)
• Prevented by currently available safe and effective vaccine

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21
Q

HBV-HIV co-infection

A
  • Approx 1% of persons living with HBV infection (2.7 million people) are also infected with HIV
  • Conversely, the global prevalence of HBV infection in HIV-infected persons is 7.4%
  • WHO since 2015 recommends Tenofovir treatment for everyone diagnosed with HIV infection (regardless of disease stage)
  • Tenofovir recommended in first intention against HIV infection, is also active against HBV
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22
Q

Hepatitis case studies

A

Willowbrook States School Hepatitis Study
Mentally retarded children housed at the Willowbrook State School in Staten Island, New York, were intentionally given hepatitis in an attempt to track the development of the viral infection. The study began in 1956 and lasted for 14 years.

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23
Q

Prion diseases

A 
Bovine spongiform encephalopathy (BSE-mad cow disease)
Conformation of a brain protein
Transmission
Cannibalism: Kuru
Infected meat
Blood?
Untreatable
Prevent exposure
Dementia
24
Q

Vector borne Diseases

A

• Human illnesses caused by parasites, viruses and bacteria that are
transmitted by mosquitoes, sandflies, triatomine bugs, blackflies,
ticks, tsetse flies, mites, snails and lice.
• Main vectors include:
• Mosquitoes (Aedes) – Zika, yellow fever, dengue fever
• Mosquitoes (Anopheles)- Malaria
• Ticks – Lyme disease
• Fleas – Plague, Rickettsosis
• Lice - Typhus
• Preventable through informed protective measures
• Disproportionately affect the poorest populations
• Global travel & trade, unplanned urbanization and environmental
challenges such as climate change can impact on pathogen
transmission

25
Q

Malaria

A 
⚫ Parasite
⚫ Complicated life cycle
⚫ Anopheles mosquitoes (found particularly in tropical regions)
⚫ Prevent by stopping mosquito bites
⚫ Bed nets
⚫ Treatable
⚫ Relapses
26
Q

Airborne Diseases

A

Caused by pathogenic microbes discharged from an infected person
via coughing, sneezing, laughing and close personal contact or
aerosolization of the microbe.
Discharged microbes remain suspended in the air on dust particles,
respiratory and water droplets.
Tuberculosis, Measles, Chickenpox and Influenza

27
Q

Tuberculosis (TB)

A

• Mycobacterium tuberculosis
• Requires close contact for extended period of time
• People with weakened immune system at risk
• Vaccine – BCG (bacille Calmette-Guerin)
• Chronic infection
• Most cases are asymptomatic but
approx. 10% of latent cases will
develop into disease
• Of those active cases many are fatal
• Countries with high HIV rates also have high TB rates due to reduced immunity

28
Q

Controlling infection

A

Treat active TB disease
• Initial phase
• 4 drugs per day for first 56 days (224 doses)
• Continuation phase
• 2 drugs per day for 126 days (252 doses) AND
• 2 drugs bi-weekly for 18 weeks (36 doses)
• Treat latent TB disease
• Variety of options ranging from 120 to 270 doses for a non-observed patient
• Prevents progression to active disease but has side effects (e.g. orange tears/sweat,
flu-like symptoms etc.)
• Only 12-76 doses required if the patient is in a Directly Observed Therapy (DOTs)
program → electronic medicine could help by monitoring compliance

29
Q

Measles

A

Highly infectious, droplet spread
• Incubation period 10–14 days
• Symptoms include rash, fever, cough, runny nose,
inflammation of the eye
• Complications
• Ear, brain and lung infections, which can lead to brain damage and death
• 1/1,000 develop encephalitis; of these 1/10 die, 4/10 have permanent brain damage
• Vaccine preventable (MMR @12m & MMRV @18m)

30
Q

Is there any difference between immunisation and vaccination?

A

• Vaccination and immunisation are often used interchangeably, however they are slightly different….
• Vaccination is the physical injection of the inactivated or weakened pathogen
• Immunisation is the process that occurs AFTER vaccination i.e. antibodies
are produced in response to this pathogen and protect you from future infections

31
Q

Vaccines

A
  • Vaccines only developed for some bacterial/viral – no parasitic disease (possible malaria vaccine.)
  • Aims to interrupt transmission of disease
32
Q

What is endemic?

A
  • Endemic = relatively stable pattern of occurrence in a given geographical area – with high prevalence and incidence.
  • e.g. Malaria in low-income tropical countries
33
Q

Can endemic disease become epidemic?

A

• IF conditions change: host, agent or environment … THEN endemic disease MAY become epidemic.
• e.g. Smallpox during WWI
• HIV endemic in many areas, emerging epidemics in previously
unexposed areas.
• Climate affects mosquitos à malaria/dengue fever.

34
Q

EPIDEMIC DISEASE

A

Epidemic: “the occurrence in a community or region of cases of an illness clearly in excess of that expected.” (Benenson, 1990)
• Specify time period, geographical region and population.
• Identification – looks at usual frequency of disease in the area in the same season/year.
• Very small number of cases not previously recognised in an area may – over time – be epidemic.
• Dynamics of an epidemic: characteristics of agent, pattern of transmission & susceptibility of human hosts.

35
Q

TYPES OF OUTBREAKS

A

Point-source epidemic: susceptible individuals exposed ~simultaneously to one source of infection
Contagious/propagated epidemic: disease passed from person to person.

36
Q

Communicable disease VS Contagious disease

A
  • Communicable disease – caused by transmission of a specific pathogenic agent to a susceptible host.
  • Contagious disease: human spread without vector/vehicle.
  • Malaria = communicable (mosquito), not contagious.
  • Measles, syphilis = communicable and contagious.
37
Q

Control of disease =

A

change one or more components in the chain of infection

38
Q

Pathogenicity

A

: ability to cause disease

39
Q

Virulence

A

: severity of disease.

40
Q

Infective dose

A

: amount required to cause infection (in

susceptible individuals).

41
Q

Reservoir

A

: natural habitat (humans, animals, environment)

42
Q

Source of infection

A

: person/object.
• Remember carriers – infected but no clinical sign of disease. (HIV/AIDS
during asymptomatic period.)

43
Q

modes of transmission :Direct

A

: Immediate transfer of the infectious agent from an infected
host or reservoir to an appropriate entry point.
• e.g. Touching, kissing, sneezing, blood transfusion.

44
Q

modes of transmission: Indirect:

A
  • Indirect: Vehicle-borne, vector-borne or airborne.
  • Vehicle: contaminated food, clothes, bedding, cooking utensils, etc.
  • Vector: agent carried by insect or animal.
  • Airborne: dust particles, e.g. fungal spores.
  • Method of transmission will influence control methods
45
Q

HOST

A

Person/animal where infectious agent grows and multiplies under natural conditions
• Points of entry: skin, mucous membranes, respiratory / GI tracts
• Reaction varies from no symptoms à severe illness
• Incubation period (time from entry à first sign of disease) also varies – from hours (food poisoning) to years (AIDS)
• Immunisation can protect individuals from disease
• e.g. Modified agent, inactivated organisms/toxin
• Passive immunisation: antibodies given as post-exposure prophylaxis (e.g. rabies)

46
Q

Environment

A

The environment plays a critical role in the development of communicable diseases
• Includes:
• General sanitation
• Temperature
• Air Pollution
• Water quality
• Socioeconomic factors (e.g. poverty, population
density & overcrowding) also important

47
Q

Explain using examples the difference between pathogens of high and low virulence

A
  • Virulence = a microorganism’s degree of pathogenicity i.e. ability to cause disease.
  • Those with higher virulence cause diseases of greater severity than those of low virulence e.g. some strains of influenza virus will cause a more severe form of influenza than other strains.
  • HOWEVER, pathogens of low virulence may infect a greater proportion of the population than one of high virulence because infected individuals are not necessarily restricted to bed – hence greater the spread!
48
Q

Explain the difference between reservoirs and sources of infections, using examples of each.

A
  • Source of infection: the individual or object which the infectious agent is actually acquired e.g. contaminated toy
  • Reservoir of infection: a place which provides a pathogen with adequate conditions for survival and multiplication e.g. infected child
49
Q

For each mode of transmission, choose one example of a disease that
is spread by this method and discuss how environmental interventions
can be used to break the transmission.

A
  • Contact transmission
  • Direct contact via touching such as an STI e.g. herpes
  • Intervention: safe sex (condom)
  • Vehicle transmission
  • Can be waterborne or foodborne. e.g. salmonella.
  • Intervention: safe food handling and preparation.
  • Vector-borne transmission
  • Spread by animals (mostly insects) e.g. malaria by mosquitoes
  • Intervention: repellent, mosquito netting, long-sleeved shirts, pants etc
50
Q

ACTIVE SURVEILLANCE

A

• “Specific collection of data from healthcare providers or institutions, both as a
need arises and in the longer term” (313)
• Early warning systems (rapid response)
• Planned (chronic diseases, longer lag time)
• Sentinel health information systems – identifies if prevention or therapy
isn’t working as planned

51
Q

Notifiable diseases

A

– e.g. polio, measles, tetanus, TB, hepatitis.
• Only include conditions where surveillance makes a difference – i.e. leads to prevention.
• Things to consider: incidence/prevalence, severity, mortality, lost productivity, costs, preventability, epidemic potential.
• Data sources – often already collected, can be general / specific.

52
Q

Is there any difference between immunisation and vaccination?

A
  • Vaccination and immunisation are often used interchangeably, however they are slightly different….
  • Vaccination is the physical injection of the inactivated or weakened pathogen
  • Immunisation is the process that occurs AFTER vaccination i.e. antibodies are produced in response to this pathogen and protect you from future infections
53
Q

VACCINES

A
  • Vaccines only developed for some bacterial/viral – no parasitic disease (possible malaria vaccine.)
  • Aims to interrupt transmission of disease
54
Q

Define herd immunity and describe the herd immunity ‘threshold’

A

• Herd immunity refers to protection for whole population by having a high (but not 100%) proportion of the population with acquired immunity to a particular disease.
• The greater proportion of people who are immune, the smaller the probability that a susceptible individual will come into contact with an infectious individual.
• Unvaccinated individuals are indirectly protected by the vaccinated individuals.
• The herd immunity threshold refers to the proportion of immune individuals in a population above which a
disease may no longer persist (often 90-95%, but can vary)

55
Q

INFLUENZA

A

Influenza is spread by airborne droplets and the incubation period is 1-4 days.
• Highly contagious respiratory virus
• Different types of influenza A,B,C and D
• Influenza A and B cause seasonal outbreaks each year
• Influenza A is further divided into different subtypes.
• These subtypes are based off of the combination of two proteins on the viral surface:
• hemagglutinin (HA) and neuraminidase (NA). There are 18 different HA subtypes and
11 different NA subtypes.
• For example, the most common influenza A subtypes that circulate seasonally in humans
are H1N1 and H3N2. In 2017, H3N2 spread to dogs.

56
Q

Explain the difference between antigenic drift and antigenic shift.
Which one is likely to be associated with a pandemic?

A

• Antigenic drift: minor antigenic changes caused by mutations.
• Antigenic shift: major antigenic changes resulting from genetic
reassortment (most probably involving recombination events between human and animal influenza viruses)
—->• Antigenic shift

BMS1042 (9 decks)

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