Officials have published a document highlighting ways to avoid the risks from foodborne parasites transmitted by pork, freshwater fish and crustaceans.
Foodborne parasitic diseases are often neglected in food safety control systems even though they can cause severe human health problems, according to the Food and Agriculture Organization of the United Nations (FAO).
One challenge is that affected animals might not show signs of disease, making it difficult for farmers and authorities to detect a problem. Also, if there are no production or financial losses associated with the parasite in animals, there is no incentive to control them.
The FAO Regional Office for Asia and the Pacific publication reports different types of parasitic diseases can be transmitted to humans from pork, fish, freshwater crustaceans, vegetables, eggs of tapeworms, and protozoa.
Preventing human exposure to foodborne parasites can be the responsibility of a veterinary or food safety authority in some countries, while in others, there are no controls for parasites.
The document covers parasites transmitted by pigs such as Taenia solium, Trichinella and toxoplasma gondii, as well as those transmitted by raw or undercooked freshwater fish and crustaceans, including Clonorchis sinensis and Opisthorchis viverrini and Paragonimus, and those in vegetables, water and the environment including Fascioliasis.
Parasites from fish
Experts produced factsheets in 2020 on foodborne parasitic infections such as paragonimiasis, taeniasis and cysticercosis, cystic and alveolar echinococcosis, clonorchiasis and opisthorchiasis and fish liver flukes.
Clonorchis sinensis and Opisthorchis viverrini are two species of liver flukes, a type of flatworm shaped like a leaf. Clonorchis sinensis is found in China, some parts of Russia, Japan, the Republic of Korea, northern Vietnam and Taiwan while Opisthorchis viverrini is seen in Cambodia, the Lao People’s Democratic Republic, Vietnam and Thailand.
In heavily infected people, there is a loss of appetite, indigestion and diarrhea, and parasites can block the liver ducts. Untreated infections may last more than 25 years. People can be treated for adult flukes using praziquantel.
Food safety authorities should encourage the proper design and construction of fish farms, such as putting fish ponds away from latrines, livestock and poultry, and promote practices such as ensuring manure is not used to fertilize ponds, and effective snail control, according to the document.
Paragonimus is a kind of lung fluke. Health impacts vary but young parasites can cause abdominal pain, fever and diarrhea. Once they reach the lungs, symptoms can include a chronic productive cough, chest pain, and sometimes fever. If they end up in the brain, chest muscles or under the skin they can produce a variety of signs and symptoms.
Prevention measures include ensuring crabs and crayfish are properly cooked and avoiding cross-contamination of kitchen utensils. Humans can be treated for adult flukes using triclabendazole or praziquantel.
Parasites from plants and meat
Fascioliasis is caused by two species of flatworms called Fasciola hepatica and Fasciola gigantica. It is acquired by eating raw plants such as watercress and other freshwater cultivated or wild plants, or by drinking contaminated water. It is mainly an animal disease but does occasionally affect people.
Young parasites can cause abdominal pain, fever and diarrhea. Once they reach the lungs, symptoms can include a chronic productive cough, chest pain, and sometimes fever. Signs can be similar to those of tuberculosis or lung cancer. Humans can be treated for adult flukes with triclabendazole.
Eating raw aquatic vegetable harvested from or near grazing lands should be avoided. Rinsing them is not enough and freezing is not recommended, according to the FAO. The parasite can be killed by cooking vegetables at 60 degrees C (140 degrees F) for several minutes.
For parasitic diseases from pork, there are steps food safety authorities can take such as pushing good farming practices, conducting meat inspections and promoting awareness of hygiene and the main risk factors.
Recommendations include encouraging the public to adequately cook or freeze food from animal sources before consumption and asking food businesses to use effective filtration and treatment of water for drinking and cooking, or for it to be boiled.
The FAO suggests that the roles and responsibilities of stakeholders need to be clearly defined in legislation and a network with partner agencies could be developed to create awareness in schools to help prevent and control the spread of parasitic diseases.
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