Week 11 Flashcards
(105 cards)
Define symbiosis
A interaction between two different organisms living in close physical association
Three types of symbiotic relationships
Mutualistic, commensal or parasitic
Define parasitism
A relationship between two species in which one species benefits and the other species is harmed
What are the stages of infectious disease?
Incubation period
Prodromal period
Illness
Convalescence
What is the incubation period stage of infectious disease?
Time between infection and occurrence of first symptoms of the disease
What is prodromal period stage of infectious disease?
Short time of generalised, mild symptoms - not all infectious diseases have this stage
What is illness stage of infectious disease?
Most severe stage when symptoms are most evident and the host immune system isn’t fully responding yet
What is convalescence stage of infectious disease?
Body gradually returns to normal (variable time depending on pathogen and damage)
What factors cause different biological responses to pathogens?
Infecting dose
Age of host
Biological sex of host
Host genetics
Host nutritional status
Co-infection with other pathogens
What are the four stages of infectious disease when the pathogen has/is infecting?
Invasion
Multiplication
Spread
Pathogenesis
How can pathogens invade organisms?
(Entry into the host and transmission from one host to another)
Inhalation, Oral transmission, Intra-uterine, Sexual transmission, Direct skin contact, Direct inoculation (injections or insect bites)
What 3 main factors influence causation and development of clinical disease?
Number of pathogenic organisms present,
Virulence of the organism (eg direct killing of host cells, blockages within organisms, toxins, inappropriate activity of host immune system)
Reaction of host (degree of resistance)
How is the burden of disease measured, give three ways?
Incidence (number of new cases in a population in a defined time period)
Prevalence (total number of infected individuals in a population at a given point)
Mortality (number of deaths from disease in population in a define time period)
Which pathogens cause acute, chronic or parasitic infections?
Acute = viruses, bacteria, fungi
Chronic = Parasites
Parasites = Protozoa and worms (helminths)
Some pathogens can multiply within the body while others cannot. Give examples?
Protists - Can cause disease following inoculation of only a few infectious stages as they multiply within the body. So disease severity is dependent on how quickly they multiply
Helminths - Cannot multiply within the body and so disease severity is dependent upon the number of infectious stages acquired by host over time
Give the key word: The ability of the organism to move from the initial site of infection to infect other areas of the body
Spread
Also includes movement between body systems
What is the difference of measuring Incidence and Prevalence
Incidence - Number of new cases in a defined period of time
Prevalence - Total number of infected individuals at a point in time
How does economics alter the burden of infection?
Major differences exist between ‘rich’ and ‘poor’ countries with respect to causes of death:
Low income groups - communicable diseases still have major impact on health
Comparison of high and low income countries on the burden of infection: High-income countries
75% of deaths - people aged 70 years+
<1% of deaths among children under 15 years
Predominantly die of chronic, non-communicable diseases: eg cancer, cardiovascular disease, dementia
Comparison of high and low income countries on the burden of infection: Low-income countries?
40% of deaths - children under 15 years
20% deaths - people ages 70 years and older
Predominantly die of communicable diseases: eg lower respiratory infections, malaria, tuberculosis.
Disability adjusted life year (DALY) measures what?
Indication of overall burden of disease
Measures ‘life years’ lost due to premature mortality and equivalent years lost because of morbidity.
How is one DALY calculated?
By adding together ‘years of life lost (YLL) due to premature mortality’ and ‘years of healthy life lost due to disability (YLD)’ for people living with health condition or its consequences.
DALY = YLL + YLD
What does DALY allow for?
Comparisons to be made across range of health problems - quantitative basis for deciding health policies and evaluating cost-effectiveness of control programmes.
Why is studying infectious disease increasing importance?
Pandemics;
Natural/social disasters, poverty, deprivation;
Movement of refugees;
Drug resistant pathogens and vectors;
Rapid and widespread air travel;
Increase in immuno-suppressed people (eg organ transplants);
Lifestyle (eg urbanisation);
Environmental changes including global warming, climate change, deforestation, irrigation, widespread use of antimicrobials.
