Foodborne Parasites in the Food Supply Web

Occurrence and Control

Alvin A Gajadhar

• Publisher: Woodhead Publishing
• Year: 2015
• ISBN:
  9781782423508
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Foodborne Parasites in the Food Supply Web: Occurrence and Control provides an overview of the occurrence, transmission, and control of parasites in the food chain, including an introduction to the topic from the perspectives of various issues surrounding foodborne parasites. The text then explores the different types of foodborne parasites, the dynamics of parasite transmission in different food sources, and the prevention and control of foodborne parasites in the food chain.

• Provides an overview of the occurrence, transmission, and control of parasites in the food chain
• Explores the different types of foodborne parasites and the dynamics of parasite transmission in different food sources
• Highlights prevention and control methods to ensure the safety of the food chain

Part One

Perspectives

1

Introduction to foodborne parasites

A.A. Gajadhar Canadian Food Inspection Agency, Saskatoon, SK, Canada

Abstract

Parasites transmitted by food are increasingly recognized as a global threat to food safety and trade. Phylogenetically and biologically, parasites represent one of the most diverse groups of pathogens. Unlike bacteria and viruses, they are typically endowed with structural and functional attributes that facilitate their survival, replication, and transmission in the food web. These characteristics, in addition to the globalization of the food supply, the increasing trend of consuming fresh, ready-to-eat food, the general lack of knowledge of parasites, and the paucity of practical diagnostic and effective control methods have all led to the understanding that foodborne parasites are among the most neglected global pathogens affecting humans. Basic information to inform readers about foodborne parasites is an essential introductory step to understanding the occurrence and control of these parasites and their importance to consumers, the industry, and its regulators.

Keywords

Food safety

Foodborne

Parasites

Pathogens

Neglected diseases

Socio-economic impact.

1.1 Introduction

A safe food supply is essential to the survival of humankind. As people have multiplied and technology has advanced, the food supply has evolved from a base of local consumer production to large-scale integrated production and distribution practices. Consumers, particularly those in urban regions, are largely unaware of the origin and processing of their food. Similarly, most producers are unaware of the variety of potential public health hazards that are transmissible by food. Both consumers and producers rely on government regulations and oversight for guidance and protection. Although information regarding foodborne hazards is widely available from many sources, especially regarding hazards such as bacteria and chemical residues, there is limited information on foodborne parasites. This is becoming an urgent matter as the food supply web is now global and expertise in parasitology in developed countries has waned. This complacency has been driven primarily by improved hygiene standards and the increasingly effective control of zoonotic parasites in food animals in those regions. This chapter introduces the diversity and unique characteristics of foodborne parasites, the food vehicles by which they are transmitted, and their significance to consumers. A ranking of these foodborne parasites by various socioeconomic factors and information relevant to their control are presented.

The world’s population currently exceeds 7 billion consumers living in regions where foodborne parasites are endemic or where there is risk of infection from imported food. Yet, relatively little is known about parasites, and their identity and characteristics are often confused with those of bacteria and viruses. Parasites are eukaryotic organisms that are classified within diverse taxa ranging from single-cell protozoa to complex hermaphroditic helminths. Foodborne parasites that are prevalent globally or regionally include the flagellated protozoon Giardia, the coccidian protozoa Cryptosporidium and Toxoplasma, the roundworms (nematodes) Trichinella and Anisakis, the tapeworms (cestodes) Taenia and Echinococcus, and the flukes (trematodes) Opisthorchis, Clonorchis, and Fasciola. The diversity of their structural and life-cycle characteristics that are employed in astounding strategies for survival, transmission, host adaptation, and replication makes parasites difficult to control but also fascinating to study.

1.2 Parasites transmitted by food

Human parasitic infections originate from many sources and are acquired by various modes of transmission. Oral transmission via food and water represents the most common route of infection. Because food is produced globally in a wide range of microenvironments, and because it originates from a variety of aquatic or terrestrial animals and plants, there is a diverse range of strategies for parasite survival, replication, and transmission. A list of various food products and examples of the parasites they transmit is provided in Table 1.1. Although many waterborne parasites such as Giardia and Entamoeba have simple, direct life cycles, foodborne parasites often have life cycles that involve multiple stages and various host species that exploit both the exogenous and endogenous environments and food habits of consumers. Generally, meatborne parasites replicate and attain infectivity in protective structures such as cysts within muscle, established during the animal’s development (Table 1.1). Examples include Toxoplasma gondii, Sarcocystis hominis, and Trichinella spiralis. Other parasites such as Giardia and Cryptosporidium can infect consumers by contaminating surfaces of ready-to-eat fruits and vegetables.

Table 1.1

Food groups and products that can serve as transmission vehicles for parasites capable of infecting consumers

Food		Parasites
Major food groups	Food source	Species/family	Transmission stage
Animals: aquatic	Amphibians (frogs)	Alaria americana Spirometra spp.	Metacercaria Plerocercoid
	Crustaceans (crab, shrimp, etc.)	Anisakidae	Larva (L3)
		Paragonimus spp.	Metacercaria
	Freshwater fish	Alaria Americana Clonorchis sinensis	Metacercaria Metacercaria
		Diphyllobothriidae	Plerocercoid
		Heterophyidae	Metacercaria
		Metrochis spp.	Metacercaria
		Opisthorchis spp.	Metacercaria
	Marine fish	Anisakidae	Larva (L3)
		Diphyllobothriidae	Plerocercoid
		Heterophyidae (brackish water)	Metacercaria
	Shellfish	Cryptosporidium spp.	Oocyst
		Giardia duodenalis	Cyst
		Toxoplasma gondii	Oocyst
Animals: terrestrial	Beef	Sarcocystis hominis	Tissue cyst
		Taenia saginata	Cysticercus
		Toxoplasma gondii	Tissue cyst
	Dairy products	Toxoplasma gondii	Tachyzoite
		Cryptosporidium spp.	Oocyst
	Game meat	Alaria americanum Toxoplasma gondii	Metacercaria Tissue cyst
		Trichinella spp.	Larva (L1)
	Horse	Toxoplasma gondii Trichinella spp.	Tissue cystLarva (L1)
	Pork	Paragonimus spp. Sarcocystis suihominis	Metacercaria Tissue cyst
		Taenia solium	Cysticercus
		Toxoplasma gondii	Tissue cyst
		Trichinella spp.	Larva (L1)
	Reptiles	Alaria Americana Spirometra spp. Trichinella spp.	Metacercaria Plerocercoid Larva (L1)
	Small ruminants	Toxoplasma gondii	Tissue cyst
	Snake	Spirometra spp.	Plerocercoid
Animals: birds	Chicken	Toxoplasma gondii	Tissue cyst
	Water fowl (geese, ducks)	Toxoplasma gondii	Tissue cyst
Plants: aquatic	Fresh produce	Fasciola spp.	Metacercaria
		Fasciolopsis buski	Metacercaria
Plants: terrestrial	Fresh produce (berries, leafy greens, etc.)	Ascaris spp.	Egg
		Balantidium coli	Cyst
		Cryptosporidium spp.	Oocyst
		Cyclospora cayetanensis	Oocyst
		Echinococcus granulosus	Egg
		Echinococcus multilocularis	Egg
		Entamoeba histolytica	Cyst
		Giardia duodenalis	Cyst
		Taenia solium	Egg
		Toxocara spp.	Egg
		Toxoplasma gondii	Oocyst
		Trichuris trichiura	Egg
	Fruit juice	Cryptosporidium spp.	Oocyst
		Trypanosoma cruzi	Trypomastigote

Most foodborne parasites in food animals or the external environment have stages that are capable of survival in a variety of conditions for long periods of time. For example, coccidian protozoa are protected immunologically as they develop within host cells and are located in sites to facilitate replication and exit from the host or to allow for long-term survival in the host. Trichinella spp. larvae also develop within the protective environment afforded by host cells, and most species remain encapsulated as such until consumed by a new host. Many species of cestodes and trematodes are also protected in enclosures such as cysts and eggs in their respective hosts, environments, or food products as they await transmission to consumers. Exogenous stages of many species of parasites can resist a wide range of chemicals and survive for long periods of time under various environmental conditions such as mild heat and extreme cold, drought, and seasonality (Gajadhar and Allen, 2004). Therefore, strategies and measures traditionally used for controlling other foodborne pathogens are often ineffective for parasites. The unique characteristics of their life cycles, and the epi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Woodhead Publishing Series in Food Science, Technology and Nutrition
• Part One: Perspectives
• Part Two: Parasites
• Part Three: Transmission dynamics in food sources
• Part Four: Prevention and Control
• Index