MIC 252 23. Factors favouring Global Eradication of an Infectious Disease

1. 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

2. 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

3. 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

4. Eradication

5. Eradication

6. Eradication

7. 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

8. 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

9. 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

10. 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

11. Eradication Countries where yellow fever is endemic

12. 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

13. 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

14. 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!!!)

15. Eradication

16. 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

17. 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