19~chapter 22 pathogens

8/13/2019 19~Chapter 22 Pathogens

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Examples of Four Major Types of Pathogens

Copyright 2010 Pearson Education, Inc.


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Bacteria

Single-celled organisms

Three major types: cocci, bacilli, and spirilla

Bacterial toxins cause disease.

Antibiotics are used to kill bacterial infections

UNLESS the bacteria become resistant to theantibiotics.

AntibioticsResistance


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Other Pathogens Fungiare hundreds of species of uni- and

multicellular plant organisms that cause diseasessuch as candidiasis, athletes foot, and

ringworm.

Protozoans are single-celled organisms thatcause diseases such as trichomoniasisand

giardiasis.

Parasitic worms are the largest of the pathogens;they include pin worms and tape worms.

Prionsare self-replicating, protein-based agents.

Prions are responsible for Mad Cow disease


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Viruses

A Virus is an OBLIGATE PARASITE.

It contains a Nucleic acid and a Protein coat

Many scientists dont consider Viruses

ALIVE as they cannot reproduce UNLESS

inside another living host!!

SEE NEXT SLIDE this is how viruses

replicate inside host.


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Colds and Influenza

Colds are endemic, that is, always present.

You can catch a cold from the airborne droplets of

anothers sneeze or contact.

You cannot catch a cold from a chill.

Five to 20 percent of Americans get the flu each

year.

Three major varieties exist of the flu virus, each

having many different strains.

Those who should be vaccinated include seniors,

pregnant women, those with heart and lung diseases,

and those with certain other diseases.


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Is It a Cold or the Flu?

Copyright 2010 Pearson Education, Inc.


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Streptococcal Infections and Meningitis (Some examples)

Streptococcal infections (Bacterial Infections of

coccus-shaped bacteria, specific to STrep)

Group A streptococci (GAS), or strep throat

Necrotizing fasciitis, or flesh-eating

strep

Group B streptococci can cause illness in

newborns and immunocompromised adults

Meningitis

An infection of membranes that surround the

brain and spinal cord


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Five Modes of Transmission

Waterborne transmission

- drinking water or swimming (usually via ingestion)

- fecal-oral route

- fecal contamination of drinking water from municipal wastewater sources or

animal feedlots

Example: Giardia

Foodborne transmission

ingestion of infectious agents in food

poor sanitation, hygiene (fecal-oral route)

insufficiently cooked fish and shellfish

in US there are 76 million cases/yr with 325,000 hospitalizations and

5000 deaths

Person to person transmission

requires direct physical contact between hosts

sexually-transmitted diseases

respiratory infections (coughing, sneezing)

Example: HIV, syphilis,


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Airborne Transmission

inhalation of pathogens in aerosols

aerosols created at wastewater treatment plants

Examples: legionellosis, fungal infections

Modes of Transmission (cont.)

Vector-borne transmission

transmission by the e of an animal host

Examples: malaria, sleeping sickness, yellow fever, Lyme disease

Can you identify the vector in each of these diseases?


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Bacterial Pathogens

High minimal infective dose

104-109

Bacterial pathogens do not remain infectious in the

environment very long

typical half-life less than 24 hours

Outbreaks can be prevented with proper sanitation and

chlorination of drinking water, proper food handling and

preparation


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Enteric bacteria -- Salmonella

Found in particularly high numbers in the intestines of birds and reptiles

Over 2000 serotypes can cause disease in humans

serotypes differentiated by O-antigen, a cell wall antigen

Serotypes Typhimurium, Enteriditis, Typhi, and Paratyphi cause human disease

Genome ~ 50% homologous with E. coli

Salmonellosis caused primarily by serotypes Typhimuriumand Enteriditis

fever, abdominal cramps, and diarrhea (sometimes bloody), 5-7 days

disease due to cell lysis in stomach and release of endotoxin (LPS)

may lead to septicemia or Reiters syndrome (e.g., chronic arthritis)

minimal infective dose: 104107

40,000 confirmed and 1.4 million estimated cases in US/yr, ~ 500 fatalities

2% develop chronic arthritis

Usually a foodborne disease (food poisoning), but may also be waterborne


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Typhoid fever (Read about this one)

infection of intestines and blood caused by serotype Typhi

fever, headache, constipation, malaise, chills, myalgia for 3-4 weeks

Rare in industrialized nations (400 cases per year in the U.S. most from

international travel). ~16 million cases and 600,000 deaths occur

worldwide each year

In 5% of cases, victims become carriers, and shed S. typhifor at least a

year in feces


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Waterborne Protozoan Parasites

Phylum Zoomastigina, Order Diplomonadida, Family Hexamitidae

i.e. a flagellate

Trophozoites(active, feeding stage)

14 m long

teardrop shaped

4 pairs of flagella

ventral sucking disk

two nuclei

Giardia lamb lia (G. intestinalis, G. duodenalis)

Very primitive

no mitochondria, nucleoli, peroxisomes anaerobic!

rRNA more like prokaryotes in size

replicates by binary fission

Giardia has 5 chromosomes, with 4-10 copies of each in each nucleus


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Giardia lamblialive in theduodenum, jejunum andupper ileum of humans.They attach to the surfaceof epithelial cells using theiradhesive disc.Giardiadivide by binary fission and

can swim rapidly using multipleflagella. In severe infections nearlyevery intestinal cell is covered byparasites.

In the colon as fecesbegin to dehydrate,begin to encyst. The cystsare then passed into theenvironment.

Giardia

When swallowed by the host,

cysts pass through the stomachand excyst in the duodenum.

Many animals especially beaversare reservoirs of infection.

Waterborne transmissionis a common route ofinfection

Dividing

Cyst formation

Excysting

Consumption ofcontaminated wateror fecal-oraltransmission arecommon routesof infection


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Consumption ofcontaminated wateror fecal-oraltransmission arecommon routesof infection

Many animals especially cattleare reservoirs of infection.

Excystationof oocysts

Oocyst is expelledfrom cell surface

Attachment ofsporozoites toepithelial cells

Type II meront(schizont)

Gametocytes

merozoite

Type I meront(schizont)

Four second generationmerozoites formed.

Merozoites releasedfrom type II meront

attach and form eithermicro or macrogametocytes.

A micro and macrogametejoin to form a zygote, whichdifferentiates into a newoocyst.

Sporozoite is enveloped bymicrovilli and matures intotype I meront. Asexualreproduction results in theformation of eight merozoites

which can reinfect or moveinto sexual reproduction.

Oocyst can sporulatein the intestines andreinfect the host.


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Emerging Waterborne Pathogens

Helicobacter pylori Binds to epithelium in stomach and duodenum

produces urease that locally lowers pH, disrupting mucous layer and causing

peptic and gastric ulcers

90% of duodenal and 80% of gastric ulcers caused by H. pyloriinfection, not

spicy food, acid, or stress ~2/3 of the worlds population is infected

Most likely a waterborne disease

In 1996, the FDA approved the use of antibiotics to treat (and cure!) peptic

ulcers

19~chapter 22 pathogens

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