An introduction to infectious diseases
Communicable infectious disease: can be transmitted directly or indirectly from one host to another
Non-communicable infectious disease: caused by an opportunistic pathogen from an individuals
own microflora
Three questions on ID outbreak investigations
- First steps to determine if the situation is an outbreak of an ID
Identify cases person, place, time
- Next three critical questions of an outbreak investigation
Identify the pathogen
Identify the source
Identify the transmission cycle
- Specific purpose and examples of measures to control outbreak
Isolate
Cure
Break transmission cycle
Outbreak control
- Prevention of exposure containment of the source(quarantine) and break transmission cycle
- Prevention of infection protection of susceptible group with vaccination, safe water,
sanitation, afstand houden, geen handen geven, in ellenboog hoesten
- Prevention of disease prophylactic treatment of high risk group
Host types
- Definitive host: host in which pathogen reach maturity and reproduces
- Intermediate host: host in which pathogen undergoes essential developmental transition
- Transportation host: host in which pathogen undergoes no essential developmental transition
- Reservoir: long-term natural host of pathogen that does not cause a disease in this host
Two types of epidemics
- Common source epidemics: infectious disease without human to human transmission
- Propagated epidemics: due to human to human transmission
Latent period: time interval from initial exposure until start of transmission to other
host
Incubation period: time interval from initial infection until onset of clinical disease
Infectious period: period during which a person is infectious and enabling transmission
,Basic reproductive rate (R0)
- Number of secondary infections by a case of an infection during its entire transmission lifetime
when a population is totally susceptible (transmission success)
- R0=c x l x D
c= number of contacts of infected case with susceptible individuals
l= probability of transmission of causal agent during a contact (Infectiousness)
D= duration of infectious period
- Effective reproduction rate(R)= R0 x % of susceptible individuals in a population
- Herd immunity threshold= (R0-1)/R0, percentage of susceptible population that needs to be
protected by vaccination to stop an epidemic outbreak
Prevalence: total number of cases at given time point (how many have the disease)
Incidence: number of new cases (how fast it spreads)
Disability adjusted life years(DALY)= years of healthy life lost due to poor health(YLD) + years of life
lost due to premature death (YLL)
- YLD= l x DW x L
l= number of cases
L= average duration of the case until remission or death
DW= disability weight (0 or 1)
- YLL= N x L
N= number of deaths
L= standard life expectancy at age of death in years
Changes in human demographics (enhanced transmission)
- Population growth
- Urbanization
- Migration
- Human mobility
- International travel
Poverty and social inequality( enhance transmission and persistence of sources)
- Poverty
- Sanitation and hygiene
- Contaminated food and water supplies
- Food security
- Inadequate governance
- Lack of public health service
Economic development and changes in land use(open up new sources)
- Deforestation
- Introduced species/pathogens
- Biodiversity loss
- Hydrological changes
- Climate change
, Bacteria
Prokaryotes
- Plasma membrane
- Nucleoid
- Cell wall
- Capsule
- Fimbriae or pilli(attachment, secretion)
- Flagella(movement)
- Ribosomes, macromolecules, organic compounds and ions
Cell wall
- Gram positive bacteria: have a thick peptidoglycan later and no outer lipid membrane
- Gram negative bacteria: thin peptidoglycan later and outer lipid membrane, and
lipopolysaccharides on outside
Old microbial diseases are (re) emerging
- Cholera (vibrio cholerae)
Diarrheal disease
Rapid disease progression
Food/waterborne disease
Cholera toxin: activate chloride channel raises luminal osmotic pressure water into
gut diarrhoea
- Black death, bubonic plague, great plague (yersinia pestis)
Spread by fleas
Lymphatic system, later in blood
Toxins
Vector disease
- Leprosy (mycobacterium leprae)
Chronic
Affects skin, nerves and mucous membranes
Contact disease, splash borne
Incubation/treatment years
Multi-drug therapy
- Tuberculosis (mycobacterium tuberculosis)
Asymptomatic, mostly latent TB infection
Airborne
Treatment 6-20 months
Pathogenicity: the ability to cause disease
Virulence: the degree of pathogenicity, or aggressiveness
Evolution of virulence: trade-off hypothesis
- Infectivity: ability to establish infection point
- Invasiveness: ability to spread
- Pathogenic potential: ability to damage
Communicable infectious disease: can be transmitted directly or indirectly from one host to another
Non-communicable infectious disease: caused by an opportunistic pathogen from an individuals
own microflora
Three questions on ID outbreak investigations
- First steps to determine if the situation is an outbreak of an ID
Identify cases person, place, time
- Next three critical questions of an outbreak investigation
Identify the pathogen
Identify the source
Identify the transmission cycle
- Specific purpose and examples of measures to control outbreak
Isolate
Cure
Break transmission cycle
Outbreak control
- Prevention of exposure containment of the source(quarantine) and break transmission cycle
- Prevention of infection protection of susceptible group with vaccination, safe water,
sanitation, afstand houden, geen handen geven, in ellenboog hoesten
- Prevention of disease prophylactic treatment of high risk group
Host types
- Definitive host: host in which pathogen reach maturity and reproduces
- Intermediate host: host in which pathogen undergoes essential developmental transition
- Transportation host: host in which pathogen undergoes no essential developmental transition
- Reservoir: long-term natural host of pathogen that does not cause a disease in this host
Two types of epidemics
- Common source epidemics: infectious disease without human to human transmission
- Propagated epidemics: due to human to human transmission
Latent period: time interval from initial exposure until start of transmission to other
host
Incubation period: time interval from initial infection until onset of clinical disease
Infectious period: period during which a person is infectious and enabling transmission
,Basic reproductive rate (R0)
- Number of secondary infections by a case of an infection during its entire transmission lifetime
when a population is totally susceptible (transmission success)
- R0=c x l x D
c= number of contacts of infected case with susceptible individuals
l= probability of transmission of causal agent during a contact (Infectiousness)
D= duration of infectious period
- Effective reproduction rate(R)= R0 x % of susceptible individuals in a population
- Herd immunity threshold= (R0-1)/R0, percentage of susceptible population that needs to be
protected by vaccination to stop an epidemic outbreak
Prevalence: total number of cases at given time point (how many have the disease)
Incidence: number of new cases (how fast it spreads)
Disability adjusted life years(DALY)= years of healthy life lost due to poor health(YLD) + years of life
lost due to premature death (YLL)
- YLD= l x DW x L
l= number of cases
L= average duration of the case until remission or death
DW= disability weight (0 or 1)
- YLL= N x L
N= number of deaths
L= standard life expectancy at age of death in years
Changes in human demographics (enhanced transmission)
- Population growth
- Urbanization
- Migration
- Human mobility
- International travel
Poverty and social inequality( enhance transmission and persistence of sources)
- Poverty
- Sanitation and hygiene
- Contaminated food and water supplies
- Food security
- Inadequate governance
- Lack of public health service
Economic development and changes in land use(open up new sources)
- Deforestation
- Introduced species/pathogens
- Biodiversity loss
- Hydrological changes
- Climate change
, Bacteria
Prokaryotes
- Plasma membrane
- Nucleoid
- Cell wall
- Capsule
- Fimbriae or pilli(attachment, secretion)
- Flagella(movement)
- Ribosomes, macromolecules, organic compounds and ions
Cell wall
- Gram positive bacteria: have a thick peptidoglycan later and no outer lipid membrane
- Gram negative bacteria: thin peptidoglycan later and outer lipid membrane, and
lipopolysaccharides on outside
Old microbial diseases are (re) emerging
- Cholera (vibrio cholerae)
Diarrheal disease
Rapid disease progression
Food/waterborne disease
Cholera toxin: activate chloride channel raises luminal osmotic pressure water into
gut diarrhoea
- Black death, bubonic plague, great plague (yersinia pestis)
Spread by fleas
Lymphatic system, later in blood
Toxins
Vector disease
- Leprosy (mycobacterium leprae)
Chronic
Affects skin, nerves and mucous membranes
Contact disease, splash borne
Incubation/treatment years
Multi-drug therapy
- Tuberculosis (mycobacterium tuberculosis)
Asymptomatic, mostly latent TB infection
Airborne
Treatment 6-20 months
Pathogenicity: the ability to cause disease
Virulence: the degree of pathogenicity, or aggressiveness
Evolution of virulence: trade-off hypothesis
- Infectivity: ability to establish infection point
- Invasiveness: ability to spread
- Pathogenic potential: ability to damage
