Exam 3: Chapter 13 Prions and Parasites

What are prions?

• “Proteinaceous infectious particles”

• Misfolded, infectious proteins from animal tissues

• Not living organisms of viruses

• Infectious prions can damage normally folded proteins until illness occurs

• Control achieved through containment, prevention, and regulations

Prions are resistant to…

• Protease

• Dry-heat > 15 min at 600 C (1,112 F)

• All known food processing methods

Global Burden of Prions

• Difficult to predict

  • Challenging for global food supply

• Exceptional resistance

  • Challenging to find solutions

Prion Diseases: Transmissible Spongiform Encephalopathy

• Transfer from animal to animal

• Sponge-like appearance in brain

• Neurodegenerative brain disease

Prion Diseases: Animals

• Bovine Spongiform Encephalopathy (BSE)

  • Cattle (“mad cow disease”)

• Scrapie

  • Sheep and goats

• Chronic wasting disease (deer, elk, moose)

Prion Diseases: Humans

• Classic and variant Creutzfeldt-Jakob disease

  • Variant is associated with BSE

• Kuru

  • Associated with cannibalism

Prion Diseases: BSE

• Mad Cow Disease → Bovine Spongiform Encephalopathy (BSE)

• Outbreak in the UK in 1986

  • Feeding calves food that was infected with the prion (possibly scrapie)

  • US has had 6 cases in the last 15 years

What are parasites?

• Microorganisms that obtains energy from another living host

  • Goal is to obtain energy, not kill

• Parasite life cycle may involve development in a both intermediate and final/definitive hosts

Parasitic life cycles: Intermediate hosts

• Animals that harbor immature larval forms or non-infective/non-living stages (development occurs)

Parasitic life cycles: Transport hosts

• Animals that serve for transportation, not development, of worm or protozoa

Parasitic life cycles: Definitive hosts

• Animals that harbor mature adult worms or protozoa that are infective and use the host as their main source of energy.

Global burden of parasites

• Possibly higher numbers that estimated

• Why should the US care?

  • Global food supply and importation

  • Minimally processed foods

  • Larger aging population

  • Weathering patterns

Foods associated with parasites

• Water

• Raw/fresh fruits and veggies

• Organic foods

• Undercooked meat, poultry, and fish

• Wild game

• Pickled meats

Factors associated with parasites

• Improper practices

• Poor hygiene

• Immunosuppression

• Global food supple

Characteristics of protozoan parasites

• Invasive

• Shed through feces (cysts or oocysts)

• Compatible with multiple hosts

  • Must be a living host

Protozoan parasite symptoms

• Range of symptoms

  • Asymptomatic, mild or moderate diarrhea

  • Serious symptoms for elderly or immmunocompromised

Toxoplasma gondii Characteristics

• 3rd leading cause of death in US related to foodborne illness

• Most common human parasite (in the US)

  • Developed countries: 10-40% population infected

    • Average higher in France

  • Underdeveloped countries - one of top parasites

Toxoplasma gonii: Animal transmission

• Zoonotics

  • Oocysts shed through feces of infected cats

• Cats are definitive hosts

  • Ingestion of cycts/oocysts

  • Cells invade small intestine

  • Sexual/reproducive phase only happens in cats

  • Shed oocysts in feces which form infective, thick-walled spore

Toxoplasma gondii: Human transmission

• Congenital

  • Mother to child

• Occassional transmission through blood or transplant organs

• Human infection (inermediate host) - not immediately inefective

  • Tachyzoites replicate inside specialized vacuoles (created upon entry) to multiply (asexually)

  • Host cell dies and ruptures → spreads throughout bloodstream

  • Immune system pressures tachyzoites → bradyzoites (slower replicators)

Toxoplasma gondii symptoms and onset

• Onset time → 5-25 days (highly variable)

• Symptoms → Flu-like aches, ocular disease, miscarriage/stillbirth, birth defects, complications for immunocompromised

Toxoplasma gondii associated foods and prevention

• Association with undercooked meat/game or contamination of fruits/vegetables with unsanitary water, unpasteurized goat milk

• Prevented by hand washing, safe food handling.

Cryptosporidium parvum characteristics

• Obligate intracellular parasite of most mammals

• Est 700,000 cases per year in the US

• Fecal-oral route

Cryptosporidium parvum risk factors and onset

• Risk factors: Childcare, community pools, international travelers, livestock workers, infected wells

• Immediately infective → they dont have to go through another stage in the life cycle

• Onset 2-10 days

Cryptosporidium parvum symptoms

• Watery diarrhea (3 L/day), cramps, low fever, self limiting

  • Lasts 1-2 days. Relapse is possible

• Severe cases can last 4-7 weeks or lifelong (fatal)

  • Diarrhea 10-20 L/day

Cyclospora cayetanensis Characteristics

• Reside in mole intestines (could be considered transport host)

• Oocytes not immediately infective

  • Must invade and grow in humans (only known true host)

• Seasonal

Cyclospora cayetanensis causes

• Water

  • Runoff

  • Dilution of pesticides

  • Contaminated drinking and irrigation water

• Soil

Cyclospora caetanensis onset and symptoms

• Onset time: approx. 1 week

• Cycling (periods of remission) watery diarrhea (sometimes “explosive,” non-bloody)

  • Dehydration and anorexia

  • Nausea, cramping, low-grade fever, flu-like symptoms

  • Inflammation in infected small intestines

• Immunocompromised

  • Continuous weeks-long diarrhea and weight loss

  • 37% AIDS/Stage 3 HIV patients

Giardia lamblia characteristics

• Discovered by Leeuwenhoek

• More than 40 Giardia spp.

  • Mammals, reptiles, birds, insects, and more

  • Zoonotic (humans ingest cysts shed from infected animals)

• Most common intestinal infection in developed world (>2,800,000,000)

  • Very serious in developing countries

• Waterborne, flagellated, binucleated

• Improperly sanitized irrigation water, stagnant water

Giardia lambia life cycle and infectious dose

• Two-stage life cycle

  • Trophozoites – teardrop-shaped

  • Cyst – infectious form

    • Infectious dose: 10-100 cysts

Giardia lambia: How does it infect?

• cyst ingested → excystation in the small intestine → trophozoites multiply → some encyst → cysts shed in feces → ingested by the next host

Giardia lambia onset and symptoms

• Onset: 1-14 days; lasts 1-3 weeks

• Diarrhea, malaise, nausea, excessive gas with vomiting, foul-smelling greasy stools, bloating, loss of appetite

• Severe: violent vomiting and weight loss

Controlling foodborne parasites

• Animal husbandry/inspection

• Sanitation and hygienic practices (clean water, workers, environment)

• Processing – marination, pickling, smoking, fermentation, cooking/heat

• Freezing (parasitic worms)

• Targeting life cycles