Waterborne Pathogens: Viruses February 16 th -18 th, 2010

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

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

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

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

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

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 January 4; 97(1): 73–78.

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)

Polio in the United States 20 th century: seasonal epidemics Last wild-type case: 1979

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

The Sabin vaccine Live attenuated virus vaccine Tested in the Soviet Union Easy to administer Spreads immunity

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

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

Polio: an ideal target Person-to-person transmission No animal reservoirs, insect vectors Limited survival in the environment No persistent carrier state Effective vaccine

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

Polio in the world today Total casesYear-to-date 2008Total in 2007 Globally in endemic countries: in non- endemic countries: 80107

Geographic distribution of polio CountryYear-to-date 2008 Total in 2007 Pakistan6732 India Afghanistan2017 Nigeria Chad2122 Angola258 Niger1311

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

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)

Control of waterborne viruses Vaccination to prevent infection Poliovirus Hepatitis A Rotavirus