global impact

• parasites are 


  protozoa and worms
• parasites cause chronic infections
• pathogens which cause acute infections

  viruses, bacteria, fungi
• parasitism is a type of 


  symbiosis
• what is symbiosis 


  living together
• mutualism 


  benefits both organism
• mutualism example 


  bacteria in colon
• commensalism 


  benefits one and other is neither harmed or benefits
• commensalism example 


  Staphylococcus on skin
• parasitism 


  harms one and benefits other
• parasitism example 


  tuberculosis bacteria in lung
• stages of infectious disease

  • incubation period
  • prodromal period
  • illness
  • convalescence
• incubation period 


  time between infection and occurrence of first symptom
• prodromal period 


  short time of generalised mild symptoms
• illness 


  most severe stage, symptoms evident, host system not fully responded to infection
• convalescence 


  body returning to normal is variable depending on pathogen and damage
• stages of infection

  labels

  A) subclinical disease

  B) chronic disease

  C) death

  
• severity of disease depends on

  • infecting dose
  • age
  • biological sex
  • genetics
  • nutritional status
  • co-infection
• pathogens cause different severity of disease in all infected individuals
• infectious disease stages

  • invasion
  • multiplication
  • spread
  • pathogenesis
• invasion definition 


  entry into host and transmission from one host to another
• invasion pathways

  • inhaled
  • oral transmission
  • intra-uterine
  • sexual transmission
  • direct skin contact
  • direct inoculation such as injections
  • vectors
• protist multiplication 


  influenced by how quickly they multiply
• helminths multiplication 


  influenced by how many infectious stages are acquired as don't multiply in the body
• spread definition 


  ability of organism to move from initial site of infection to infect other areas of the body
• spread depends on

  • movement between systems of the body
  • developmental changes of parasite
  • host immune response to targeting pathogen
• pathogenesis is influenced by

  1. number of pathogenic organisms
  2. virulence of organism
  3. reaction of the host (immunity)
• virulence factors 


  killing host, blockages of organs, toxins, activity of host immune system
• incidence is


  number of new cases of infection occurring in population in defined period of time
• Prevalence 


  total number of infected individuals (number of new and old cases) at a point in time
• Mortality


  total number of deaths from disease in a population in a defined period of time
• in higher income countries there has been a shift in the burden of infectious diseases towards 


  chronic disease, cardiovascular disease, cancers, dementia
• in lower income countries

  infectious disease still has major impact on health
• in higher income countries more money is spend on healthcare and there is improved sanitation facilities
• morbidity is 


  ill heath associated with disease
• DALY is 


  disabilty adjusted life year
• DALY is calculated by

  years of life lost to premature mortality added to the years lost to (lived with) disabilty
• DALY= YLL+YLD
• DALY allows comparisons across health problems to help decide

  health policies and evaluating cost-effectiveness of control programmes
• DALYs limitations 


  no consideration of economic impacts from the disease

  direct cost of treatment

  social stigma associated with disease