Parasites

Foodborne Parasites

Two Major Groups of Foodborne Parasites

  • Protozoa
  • Helminths
    • Example: Roundworms

Characteristics of Foodborne Parasites

  • Intracellular Pathogens: Parasites that reside within the cells of the host.
  • Size: Considerably larger in size than most bacteria.
  • Proliferation: Do not proliferate in foods, meaning they do not reproduce while stored or processed.
  • Culturing: Classified as non-culturable, which means they cannot be grown on standard laboratory media.
  • Life Cycle Requirement: Require one or more animal hosts for a complete life cycle.

Pathogenic Protozoa

  • Species Count: Over 45,000 species of protozoa exist.
  • First Detection: Protozoa were first detected between 1674 and 1716.
  • Medical Importance: Among these, certain species are critical due to their impact on human health.
  • Characteristics: Protozoa are single-celled organisms.
  • Transmission: They are predominantly foodborne and waterborne.
  • Major Examples:
    • Cryptosporidium parvum
    • Cyclospora cayetanensis
    • Toxoplasma gondii
    • Giardia intestinalis

Cryptosporidium

  • General Information: Cryptosporidium is recognized as a leading cause of waterborne outbreaks.
  • Historical Outbreak: Responsible for the largest waterborne outbreak in the United States, occurring in Milwaukee in 1993.
    • Illness Caused: Cryptosporidiosis.
    • Global Impact: Approximately 51% of reported global protozoan waterborne diarrheal outbreaks are associated with Cryptosporidium.
    • Common Transmission: More commonly linked with recreational swimming in pools, especially during the summer months.
    • Infectious Nature: Highly infectious enteric pathogen primarily causing diarrhea.
Epidemiological Data
  • Outbreak Analysis: An epidemic curve related to a contaminated swimming pool in Utah in 2007 showed:
    • Median Duration of Illness: 9 to 10 days, ranging from 3 to 28 days.
    • Infectious Dose: Generally less than 100 oocysts.
    • Hygienic Practices: The risk increases if sick individuals swim in pools without following proper hygiene practices.
Transmission and Life Cycle
  • Transmission: Cryptosporidiosis is transmitted through ingestion of
    • Oocysts: Specifically for C. parvum and C. hominis.
      • C. parvum is zoonotic, originating from infected cattle, deer, and other ruminants.
      • C. hominis is exclusively infective to humans and has been identified as a relatively new species.
Life Cycle Dynamics
  • Infection Process:
    • Host Interaction: Infects epithelial cells and disrupts intestinal barrier functions.
    • Fecal Shedding: Capable of producing about 10^{10} oocysts in feces.
Clinical Manifestations
  • Infectious Dose: Ranges from 1 to 30 oocysts.
  • Incubation Period: Between 5 to 12 days post-infection.
  • Routes of Infection
    • Fecal-Oral Route: Via drinking or swimming in contaminated water, or through contact with animals.
    • Additional Sources: Food items, flies, and insects.
Symptoms of Infection
  • Primary Symptoms: Watery diarrhea, which can be as much as 1-17 liters per day, lasting from 4 to 30 days, with an average duration of 10 days.
  • Associated Symptoms: Include vomiting, fever, and abdominal discomfort.
Food Transmission and Contamination
  • Association with Food Products: Cryptosporidiosis has been linked to various food items.
  • Nature of Contamination: Reports have identified Cryptosporidium oocysts in fresh produce globally, as well as ready-to-eat foods like:
    • Prepared salmon
    • Noodle salads
    • Fruit salads
    • Sandwiches.
Inactivation Methods
  • Effective Treatments:
    • Ozone Treatment
    • Heat Sanitation: Bringing water to a full rolling boil for at least 1 minute, as recommended by the CDC.
    • Other Possible Solutions: Physical removal from water using flocculation, membrane filtration, or treating contaminated water with Ultraviolet light (UV).
Notable Outbreaks**

  • Milwaukee Outbreak: (March 23 - April 30, 1993)

    • Cases: 403,000 cases of gastroenteritis marking it as the largest outbreak in the U.S.
    • Attack Rate: 52%.
    • Duration of Illness: Ranged from 1 to 55 days, averaged 12 days.
    • Hospitalizations: 4,000 people required hospitalization, with 100 fatalities linked.
    • Cause: A failure in the water treatment plant.

  • Other Incidents:

    • Central Maine: 1994 involved apple cider at an agricultural fair resulting in over 160 cases.
      • Secondary attack rate: 15%
      • Found oocysts in cider press and cow feces at concentrations of 375-750 oocysts/ml.
    • New York State: 1996 linked to cider with 31 cases resulting from tree-picked apples washed and brushed.
    • Ohio: 2003 involved 144 cases in the context of agricultural fairs linked to apple cider.
    • Illinois: 2015 outbreak included 30 to 70 individuals due to apple cider contamination with both Cryptosporidium and pathogenic E. coli.

Cyclospora cayetanensis

  • Emerging Concern: Recognized as an emerging human parasitic cause of diarrhea.
  • Discovery: First reported in 1986.
  • Morphological Characteristics: Produces a Cryptosporidium-like oocyst measuring about 7.5 - 10 µm in diameter.
Distribution and Occurrence
  • Geographical Predominance: Identified primarily in Central America (notably Guatemala) and South America (Peru), with noted occurrences also in the Caribbean, Southeast Asia, and Eastern Europe.
  • Travel Related Cases: Most U.S. cases are associated with foreign travelers.
  • Seasonal Trends: Most common during the rainy months from April to August.
Cyclospora Disease Manifestation (Cyclosporiasis)
  • Susceptible Populations:
    • General population, including children and immunocompromised individuals.
  • Infectious Dose: Likely low, with a median attack rate of 93% noted in outbreaks linked to raspberries.
  • Incubation Period: Median of 7 days.
  • Symptoms: Include gastroenteritis, watery diarrhea, fatigue, nausea, vomiting, abdominal cramps, and weight loss, lasting from a few days to several weeks.
Transmission Pathways
  • Primary Transmission Mode: Waterborne routes.
  • Food Sources: Fresh produce, particularly known vectors include:
    • Raspberries
    • Basil
    • Cilantro
Life Cycle of Cyclospora cayetanensis
  • Infection Process: Involves oocysts entering food chains and becoming infective through environmental sporulation steps.
Outbreak Reports

  • Outbreaks Associated with Food: Include raspberries, basil, parsley, snow peas, and various leafy greens which have been implicated in 19 reported outbreaks.

  • Contamination Sources:

    • Oocysts shed by humans, contamination can occur preharvest (via soil, irrigation water, animals) and postharvest (through human handling, equipment, transport containers).

  • Specific Incidents: 1990 in Chicago linked Cyclosporiasis with fresh fruits and vegetables.

  • Noteworthy Outbreaks:

    • May-June 1996: Raspberries associated with 1465 cases across 20 states, with links to raspberries from Guatemala due to contaminated irrigation sources.
    • 1997 outbreaks linked to mesclun lettuce and basil also traced back to suspected water contamination sources.
    • Multiple infections associated with salad greens and herbs continued from 2012 to 2015 with various states reporting cases.
Sources of Contamination
  • General Causes:
    • Fecal contamination during growing processes or through irrigation water.
    • Inadequate cleaning or sanitizing of equipment that comes in contact with fruits and vegetables is crucial in contamination pathways.

Toxoplasma gondii

  • Historical Background: Originally identified in Africa as a rodent parasite over 100 years ago.
  • Pervasiveness: It is an omnipresent parasite that infects:
    • Humans
    • Domestic and wild animals
    • Livestock.
  • Prevalence: Approximately 30-50% of the U.S. population possesses antibodies to T. gondii.
  • Medical Significance: Toxoplasmosis ranks as the fourth leading cause of hospitalizations due to foodborne illness and the second leading cause of mortality
Transmission Mechanisms
  • Main Routes:
    • Transplacentally (from mother to fetus)
    • From house cats
    • Through consumption of contaminated water and undercooked meat, particularly pork.
  • Environmental Considerations: Oocysts, which are excreted unsporulated by cats (the definitive hosts), will sporulate and become infective approximately 24 hours later.
Life Cycle Dynamics
  • Primary Infection Pathways: Humans can ingest oocysts or tissue cysts from contaminated meat. Infection can also occur when the organism crosses the placental barrier, causing congenital infections.
  • Consequences of Congenital Infections: Neonatal infections can vary in symptomatology; most are asymptomatic but some can lead to significant health complications including death or disability.
Manifestations of Toxoplasma gondii Infection
  • Symptoms in Immunocompetent Individuals:
    • Fever
    • Muscle aches
    • Headaches.
  • Congenital Infections: May result in impaired vision, mental retardation, and developmental delays due to damage to the brain, eyes, and other organs.
Infection Sources in the U.S.
  • Primary Sources:
    • Ingestion of undercooked meats including wild boar, other wild animals (black bears, polar bears), pork, sheep, goats, free-range birds, and organically-raised chickens.
      • Reference: A CDC report in 2000 noted that 15-20% of 12 to 49-year-olds were found seropositive for Toxoplasma.
    • Survivability Notes: Healthy individuals can manage to keep the infection at manageable levels without serious health implications.

Preventive Measures for Parasitic Infection

  • Basic Hygiene Practices:
    • Thoroughly wash hands with soap and water post-toilet use and prior to food handling or consumption.
    • Avoid swimming in public waters if experiencing diarrhea.
    • Refrain from swallowing recreational water.
    • Avoid drinking untreated water from natural sources (e.g. shallow wells, lakes, rivers).
    • Water Treatment Protocol: Ensure water is boiled to a rolling state for at least 1 minute to eliminate pathogens.