waterborne pathogens: viruses february 16 th -18 th, 2010
TRANSCRIPT
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Waterborne Pathogens: Viruses
February 16th-18th, 2010
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Viral pathogens in water
• Enteric diseases• We don’t always know the distribution of
causes of diarrheal disease, but many diarrheal disease outbreaks of unidentified cause are probably viruses
• Diseases contracted by ingestion of contaminated water
• Viral diseases in developed and developing countries impose a heavy disease burden on children
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Categories of waterborne disease
• Diseases contracted by ingestion of contaminated water
• Also fecal-oral transmission without water as an intermediate– norovirus– rotavirus– hepatitis A– poliovirus
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Norovirus
• Family Calciviridae• Genus norovirus and saprovirus• Self-limiting diarrheal disease• Diagnosis by PCR• Food and waterborne• Also spreads in crowded conditions• Cruise ships• Institutional settings
– Schools, nursing homes, psychiatric units
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Rotavirus
• Family Reoviridae• Genus rotavirus• Humans are only reservoir• Fecal-oral• Can spread via fomites• Largest burden of disease for young children• Infection is nearly universal in first few years of life• Is now vaccine preventable
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Hepatitis A
• Family Picornaviridae• Genus hepatovirus• Diarrheal disease• Liver disease• Humans are only reservoir• Fecal-oral• Infection is nearly universal in first few years of life;
many people are immune by adulthood• Vaccine preventable
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The Poliovirus
• Family Picornaviridae, genus enterovirus
• 3 serotypes
• Fecal-oral spread
• Paralysis: mostly Type 1 infection
Belnap et al., Proc Natl Acad Sci U S A. 2000 January 4;
97(1): 73–78.
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Poliovirus
• Polio is an enteric infection with central nervous system complications
• Often asymptomatic
• Destruction of motor neurons
– skeletal muscles (spinal poliomyelitis)
– respiratory muscles (bulbar poliomyelitis)
– both (bulbo-spinal poliomyelitis)
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Polio in the United States• 20th century: seasonal epidemics• Last wild-type case: 1979
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The Salk vaccine
• Inactivated virus vaccine• Tested in one of the largest clinical
trials ever done at the time: over 1 million U.S. schoolchildren
• Only vaccine used in current U.S. immunization program
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The Sabin vaccine
• Live attenuated virus vaccine
• Tested in the Soviet Union
• Easy to administer
• Spreads immunity
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The role of sanitation
• In areas of poor sanitation, infection rates are high
• Many infected very early in life
• As improved sanitation reduces exposure, control by vaccination is crucial
• Improved sanitation reduces both primary exposure and secondary spread of vaccine strains
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Objective: Eradication
• Only one other human infectious disease ever successfully eradicated
• WHO campaign to end polio
• Original objective: year 2000
• Large areas of the world are polio free
• Virus is still endemic in some countries
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Polio: an ideal target• Person-to-person transmission• No animal reservoirs, insect vectors• Limited survival in the environment• No persistent carrier state• Effective vaccine
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Steps in eradication
• Interrupt natural transmission
– National Immunization Days
– Mop-up campaigns
• Confirm global eradication
– No transmission for 3 years
• Phase out the oral polio vaccine
• Laboratory containment of polioviruses
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Polio in the world today
Total cases Year-to-date 2008Total in
2007
Globally 1308 1315
- in endemic countries: 1228 1208
- in non-endemic
countries:80 107
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Geographic distribution of polio
Country Year-to-date2008
Total in2007
Pakistan 67 32
India 449 874
Afghanistan
20 17
Nigeria 692 285
Chad 21 22
Angola 25 8
Niger 13 11
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Eradication: the last push
• Endemic countries: from 125 in 1988 to four today
• Spread in endemic areas still aided by poor sanitation
• Natural disasters
• Civil and political unrest
• Cultural factors
• The last few places are the hardest
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Control of waterborne viruses
• Drinking water:
• Prevention of water contamination– ADEQUATE SANITATION
• Barrier methods– Treatment trains– Too small for filtration– Disinfection (more resistant to disinfectants than
bacteria)
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Control of waterborne viruses
• Vaccination to prevent infection
• Poliovirus
• Hepatitis A
• Rotavirus