Summary Basics Of Infectious Diseases (NEM-20806)

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