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Emerging Pathogens and You. Maria Gallo, Ph.D. HHMI/ICORE, June 16, 2008. 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.

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Emerging pathogens and you
Emerging Pathogens and You

Maria Gallo, Ph.D.

HHMI/ICORE, June 16, 2008

Common disease organisms
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

Contributing factors cont
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

Vibrio cholerae
Vibrio cholerae

Dr. John Snow

1853, Soho, England

Dr. Robert Koch

1884, Berlin, Germany

Filippo Pacini, Ph.D.

1854, Florence, Italy

Vibrio cholerae1


toxins lead to watery diarrhea

symptoms within hours


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

Vibrio cholerae

Salmonella enterica
Salmonella enterica

Daniel Elmer Salmón, DVM,

1885, Washington,D.C.

Dr. Theobald Smith, 1885, Washington, D.C.


  • 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


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
Escherichia coli

Dr. Theodor Escherich,

1885, Munich, Germany

Escherichia coli1
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
Annual Cost of Pathogenic E. coli

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


SARS: Severe Acute Respiratory Syndrome

Plant disease bacteria 10 15 crop loss
Plant Disease Bacteria: 10-15% Crop Loss

  • Spots: fruits, leaves or stems

    • decrease photosynthesis

    • disfigure fruit

Xanthomonas Spot on tomato fruit

Courtesy Clemson University Cooperative Extension

Plant disease bacteria
Plant Disease Bacteria

  • Softrots

    • enzymes produced by the bacteria cause tissue to become soft and liquid

    • post-harvest loss

Erwinia species on potato

Courtesy UC Davis IPM Program

Plant disease bacteria1
Plant Disease Bacteria

  • Wilts

    • clog conductive tissue so that water and minerals cannot get from roots to leaves

Bacterial wilt on a tomato plant

Courtesy Carlos A. Lopes, EMBRAPA, Brazil

Plant disease fungi
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 fungi1
Plant Disease Fungi

  • Toxic Fungus: Aspergillusflavus

    • corn, peanut, and others

    • aflatoxin

      • potent carcinogen

Plant disease fungi2
Plant Disease Fungi

  • Rusts: most destructive

    • famines, economic depression

    • cereals: harms growth and seed

Puccina species

Courtesy Clemson University Cooperative Extension

Plant disease fungi3
Plant Disease Fungi

  • Blights: e.g. Southern corn leaf blight

    • 1970: destroyed 15% of US corn crop, billions $$$ lost

Cochliobolus species

Courtesy Clemson University Cooperative Extension

Plant disease fungi4
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

Plant disease fungi5
Plant Disease Fungi

Claviceps purpurea on Millet head

  • Blights: Ergot of grains

    • Salem witch trials (rye ergot)

      • forms hallucinogenic drugs in bread

        • crazy behavior, “bewitched” (stoned)

    • Black plague

      • can be poisonous


Plant disease viruses
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 viruses1
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

Plant disease viruses2
Plant Disease Viruses

  • Tomato Spotted Wilt Virus (TSWV)

    • thrips vectored, wide host range

    • huge threat to peanut production

TSWV on Tomato fruit

TSWV on a Peanut Leaf

Courtesy SWEAT

Courtesy Clemson University IPM Program