emerging pathogens and you maria gallo, ph.d. hhmi/icore, june 16, 2008
TRANSCRIPT
Common Disease Organisms
– bacteria, fungi, viruses– can be host specific or have a
broad host range (more difficult to control)
– > 250 known water-, soil-, and foodborne human diseases
Contributing Factors
• Changes in Human Demographics and Behavior
– Increasing numbers of people susceptible to infections with specific potential pathogens
– Rural urbanization allows infections to arise in isolated rural areas
– Decay of basic sanitation practices
Contributing Factors, Cont.
• Breakdown of Public Health Measures– Pathogens reemerge when classic
measures breakdown
• Microbial Adaptation– Microbes change in virulence and toxin
production
• Changes in Agricultural Practices– Increased river and stream pollution by
agricultural waste and runoff
Dr. John Snow1853, Soho, England
Vibrio cholerae
Filippo Pacini, Ph.D.1854, Florence, Italy
Dr. Robert Koch1884, Berlin, Germany
Vibrio cholerae• Symptoms
– toxins lead to watery diarrhea– symptoms within hours
• Transmission– contaminated water, food (fish, shellfish), swimming– feces of asymptomatic and sick human carriers – no person-to-person transmission
• Infectious Dose (in healthy adults)– 108-1011 cells– antacids = more susceptible to infection
• Survival Outside Human Hosts– biofilms; zooplankton, shellfish– viable non-culturable state
Daniel Elmer Salmón, DVM, 1885, Washington,D.C.
Salmonella enterica
Dr. Theobald Smith, 1885, Washington,
D.C.
Salmonella • WHO: 1,400,000 instances of salmonellosis in the US• Salmonella cost per year US $3,000,000,000• 2,300 serotypes
– wide host range (humans, cattle, chickens (eggs),horses, rodents, cats, dogs, birds, reptiles, etc.)
• Multi-drug resistant S.e.Typhimurium DT104• Most common diseases caused by Salmonella:
– gastroenteritis (self-limiting, 2-5 days)– enteric/typhoid fever (incubation 1-10/7-14 days,
lasts 2-3 wks)– septicemia (incubation12-36 hrs, may lead to
chronic infection)– symptoms and disease manifestation differ in
hosts
Salmonella
Most “commonly-used” bioterrorism agent
1939 - Japanese Imperial Army contaminated rivers on the Manchurian border
1972 - “Order of the Rising Sun” obtains S. Typhi to contaminate water supplies in the Midwest
1984 - Rajneesh Cult. Successfully contaminates restaurants in Dalles, OR in an attempt to thwart local elections
Escherichia coli
• Normal flora of human GI• Uropathogenic E. coli. 90% of all UTI• Enterovirulent E. coli serotypes
– Enteroinvasive E. coli (EIEC) – Enterohemorrhagic E. coli (EHEC=VTEC)
O157:H7. Bloody diarrhea. Hemolytic Uremic Syndrome (HUS)
– Enterotoxigenic E. coli (ETEC). Travelers diarrhea (cholera-like)
– Enteropathogenic E. coli (EPEC). Diarrhea in newborn nurseries.
– Enteroaggregative E. coli (EAggEC). Acute and chronic diarrhea in children
Annual Cost of Pathogenic E. coli
O157:H7 cases
Non O157:H7
STEC cases
O157:H7 costs
Non O157:H7
costs
No medical care 35, 632 17, 816 N/A N/A
Physician visit 24, 983 12, 492 $ 6, 900, 000 $ 3, 400, 000
Hospitalized, survived
1790 895 $ 32, 900, 000 $ 16, 500, 000
Deaths 52 26 $ 1, 500, 000 $800, 000
Chronic illness, HUS 46 23 $ 36, 500, 000 $18, 500, 000
Total 60, 615 30, 308 $659, 000, 000
(includes lost productivity)
$ 329, 700, 000
(includes lost productivity)
Source: Economic Research Service, USDA, Oct. 20, 2000.
SARS: Severe Acute Respiratory Syndrome
• Agent: SARS coronavirus
• Global epidemic: Between November 2002 and July 2003, 8,096 known infected cases and 774 deaths
• Positive-strand, enveloped RNA viruses
• Pathogens of mammals and birds: cause enteric or respiratory tract infections
• http://www.cdc.gov/niosh/topics/SARS
Plant Disease Bacteria: 10-15% Crop Loss
• Spots: fruits, leaves or stems– decrease
photosynthesis– disfigure fruit
Courtesy Clemson University Cooperative Extension
Xanthomonas Spot on tomato fruit
Plant Disease Bacteria• Softrots
– enzymes produced by the bacteria cause tissue to become soft and liquid
– post-harvest loss
Courtesy UC Davis IPM Program
Erwinia species on potato
Plant Disease Bacteria
• Wilts– clog conductive
tissue so that water and minerals cannot get from roots to leaves
Courtesy Carlos A. Lopes, EMBRAPA, Brazil
Bacterial wilt on a tomato plant
Plant Disease Fungi• Can have devastating losses
– produce toxin, secrete a slime, attack seedlings at germination, dead spots
• Microscopic or larger (molds, mushrooms, yeast)
• 100,000 known species– most live on dead organic matter
which they help decompose– >8,000 cause plant disease
Plant Disease Fungi
• Toxic Fungus: Aspergillus flavus– corn, peanut, and others– aflatoxin
•potent carcinogen
Plant Disease Fungi
• Rusts: most destructive– famines,
economic depression
– cereals: harms growth and seed
Courtesy Clemson University Cooperative Extension
Puccina species
Plant Disease Fungi• Blights: e.g. Southern corn
leaf blight– 1970: destroyed 15% of US
corn crop, billions $$$ lost
Courtesy Clemson University Cooperative Extension
Cochliobolus species
Plant Disease Fungi• Blights: e.g. Late blight of potato
– 1846: great potato famine in Ireland•entire crop wiped out in 1
week•>1 million deaths• initiated emigration to the US
– 4 to 8 million people in 10 years
Courtesy Univ. of Minn. BlightCast
Courtesy Univ. of Minn. BlightCast
Phytophthora infestans
Plant Disease Fungi• Blights: Ergot of grains
– Salem witch trials (rye ergot)•forms hallucinogenic drugs in bread
–crazy behavior, “bewitched” (stoned)
– Black plague•can be poisonous
Claviceps purpurea on Millet head
Courtesy CGIAR-ICRISAT
Plant Disease Viruses
• Smallest infectious agents– electron microscope to see
them– not cells, but RNA or DNA
wrapped in a coat of protein•few genes, few proteins produced–replication–coat protein–movement
Plant Disease Viruses
• Parasitic– only reproduce in living cells
•weakens the host• Many are vectored (delivered) by
insects– aphids, thrips, leafhoppers,
whiteflies•probing mouth parts