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MIC 252 23. Factors favouring Global Eradication of an Infectious Disease. Learning Outcomes Compare public health measures for controlling infectious diseases caused by various reservoirs (domestic and wild animals, insects, humans)

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slide1

MIC 252

23. Factors favouring Global Eradication of an Infectious Disease

  • Learning Outcomes
  • Compare public health measures for controlling infectious diseases caused by various reservoirs (domestic and wild animals, insects, humans)
  • Describe public health measures (immunization, quarantine, etc) used to halt the spread of an epidemic
slide2

Public Health Measures: Goals

  • Maximum control of disease and improvement of health  goals of every effective public health programme
  • Smallpox  eradicated three decades ago
  • Polio next
  • Attempts to eradicate malaria and yellow fever  failed
slide3

Eradication

  • Eradication can be defined in various ways:
    • extinction of the disease pathogen
    • elimination of the occurrence of a given disease, even in absence of all preventive measures
    • control of an infection to the point at which transmission ceased within a specified area
    • reduction of the worldwide incidence of a disease to zero as a result of deliberate efforts  obviating the necessity for further control measures
slide7

Eradication

  • Intervention targets:
    • Vector Control (e.g., Malaria)
      • Insecticide spraying  Elimination of malaria in an area does not require the elimination of all Anopheles mosquitoes
      • Socio-economic improvements (e.g., houses with screened windows, air conditioning) combined with vector reduction efforts and effective treatment have led to the elimination of malaria in USA and Europe
        • Vector control for the prevention of malaria includes:
        • Insecticide-treated bed nets
        • Indoor and outdoor residual spraying (e.g., with DDT)
      • Genetic control  Sterile male release  aims to develop mosquitoes that are refractory to the parasite
slide8

Eradication

  • Intervention targets:
    • Vector Control (e.g., Malaria)
      • Biological control  include toxins from the bacterium Bacillus thuringiensis var. israelensis (Bti)
        • Other potential biological control agents, such as fungi (e.g., Laegenidium giganteum) or mermithid nematodes (e.g., Romanomermis culicivorax)
        • Mosquito fish (Gambusia affinis) are effective in controlling mosquitoes in larger bodies of water
      • Chemical control  Oils may be applied to the water surface, suffocating the larvae and pupae
      • Most oils in use today are rapidly biodegraded
      • Insect growth regulators such as methroprene  specific to mosquitoes
slide9

Eradication

  • Intervention targets:
    • Vector Control (e.g., Malaria)
      • Source reduction  above methods PLUS larval habitats may be destroyed by filling depressions that collect water, by draining swamps, or by ditching marshy areas to remove standing water
      • Container-breeding mosquitoes are particularly susceptible to source reduction as people can be educated to remove or cover standing water in cans, cups, and rain barrels around houses
      • Mosquitoes that breed in irrigation water can be controlled through careful water management
slide10

Eradication

  • Intervention targets:
    • Control of Animal Reservoirs (wild and domestic) (e.g., Yellow Fever)
      • Vector-borne transmission via bite of infected mosquito (Aedes or Haemagogus)
      • BUT non-human and human primates are main reservoirs of infection AND there is human-to-vector-to-human (anthroponotic) transmission
      • To complicate things more there are 3 transmission cycles:  sylvatic, intermediate, urban
slide11

Eradication

Countries where yellow fever is endemic

slide12

Eradication

  • Intervention targets:
    • Control of Animal Reservoirs (wild and domestic) (e.g., Yellow Fever)
      • Control through Drugs and Vaccines  vertebrate host and/or reservoir may also be the target for control measures
      • E.g., Vaccination of foxes against rabies in Europe and Canada is an effective means to reduce the threat of rabies
      • In addition, reduction of host reservoirs, such as rodents, birds and monkeys from areas of human habitation
      • Port control and quarantine measures
      • Personal Protection
      • Repellents
      • Vaccines
    • Early Diagnosis and Treatment = surveillance
slide13

Eradication

  • Public Health Measures to curb spread of Epidemic (e.g., SARS)
    • 12 March 2003  150 suspected cases in seven countries
    • By end of the outbreak  27 countries had reported 8,096 suspected cases + 5 incidents of transmission on commercial aircraft
    • WHO issued travel advisories in an attempt to slow the international spread of the disease
    • Case isolation was also effective in the control of onward transmission
    • Timeline and response measures
      • March 31  Hong Kong authorities impose general quarantine to prevent spread from island  residents of severely affected apartment complex had to remain indoors for 10 days
      • 12 February  12 people staying in Metropole Hotel in Hong Kong was infected via a physician  USA, Singapore, Vietnam, Canada, Ireland
slide14

Eradication

  • Timeline/ Control measures
    • February 28  Vietnam and Singapore index cases contained and spread halted
    • March 5  Canadian index case died at home (superspreader)
    • March 7  her son became ill and was admitted to hospital where he infected many staff and patients  died on March 13, one day after global alert issue
    • 12 March  Global alert
    • 15 March  Public awareness – report suspected symptoms and to avoid contact with people and areas where SARS had been detected; international travel restrictions
    • 26 March  Ontario, Canada issues provincial emergency and starts quarantine procedure (LATE!!!)
slide16

Eradication

  • Timeline/ Control measures
    • 28 March  quarantine situation in China
    • 20 April  “nationwide war on SARS”  mayor of Beijing and Minister of Health fired
    • Larger quarantine measures imposed in China  no public gatherings, travel from cities, closure of government offices, universities, schools
    • June 2003  disease contained in China
  • Containment in terms of quarantine and international collaboration in terms of identification of the causative agent and vaccine design played pivotal roles in the control of the epidemic
slide17

Eradication

    • Control measures
      • Vaccination
      • Vaccination is the most effective measure for reducing the overall impact of an established epidemic
      • December 2004- China starts testing a vaccine against SARS  staggering as it normally takes up to 14 years to get to human trials
      • Role of passive immunization?
  • Other factors: antivirals
  • All in combination stopped the spread of epidemic and pandemic