Parasites are organisms that derive nourishment and protection from other living organisms known as hosts. Parasites are of different types and range in size from tiny, single-celled organisms (protozoa) to larger multi-cellular worms (e.g. helminths). They may be transmitted from animals to humans, from humans to humans, or from humans to animals. Several parasites have emerged as significant causes of food and waterborne disease. Parasites live and reproduce within the tissues and organs of infected human and animal hosts, and are often excreted in faeces. They may be transmitted from host to host through consumption of food or water, or by oral contact with infected surfaces.
Cryptosporidium parvum: The protozoan parasite that lives in the intestines of many herd animals, including cows, sheep, goats and deer. C. is a significant cause of water- and foodborne illness worldwide and leads to the disease
Cryptosporidiosis, which is accompanied by watery diarrhoea, stomach cramps, upset stomach and slight fever. C. is passed on via the ingestion of food or water contaminated with C. oocysts (infective stage of the parasite). The oocysts are the environmentally resistant stage of the organism and are shed in the faeces of a host.
It is the protozoan parasite that causes Amebiasis. Food and water borne cases of Amebiasis are very common in developing countries. Symptoms are quite mild and include loose stools and stomach pain and cramps. Amebic dysentery is a severe form of Amebiasis associated with stomach pain, bloody stools and fever.
Giardia intestinalis (Giardia lamblia)
A protozoan parasite that lives in the intestines of infected humans or animals. G. is found in soil, water or surfaces that have been contaminated with faeces of infected hosts. It occurs in every region throughout the world and has become recognized as one of the most common causes of waterborne (and occasionally foodborne) illness. G. is protected by an outer shell and can survive outside the body for long periods of time. G.causes diarrhoeal illness (Giardiasis), typical symptoms being diarrhoea, stomach cramps and nausea.
Examples of Parasites ex: Toxoplasma gondii, Cryptosporidia, Giardia spp., Trichinella spiralis, Taenia solium, Anisakis spp.
Human beings may get infected with parasitic worms through consumption of undercooked meat, freshwater fish and freshwater snails. Examples are tapeworms, Clonorchis sinesis> and Angiostrongylus cantonensis respectively