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

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

Dr. Theodor Escherich,1885, Munich, Germany

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

Disease Viruses

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 Viruses• Tomato Spotted Wilt Virus (TSWV)

– thrips vectored, wide host range– huge threat to peanut production

Courtesy Clemson University IPM ProgramCourtesy SWEAT

TSWV on a Peanut Leaf TSWV on Tomato fruit