All living organisms, including fish, can have parasites. They are as common in fish as insects are in fruits and vegetables. There are two types of parasites that can infect people through food or water: parasitic worms and protozoa. Parasitic worms include roundworms (nematodes), tapeworms (cestodes) and flukes (trematodes). These worms vary in size from barely visible to several feet in length. Protozoa are single-cell animals, and cannot be seen without a microscope.
Just as there are risks to eating raw or undercooked meat, there are also risks with eating raw, undercooked, pickled, and lightly or cold-smoked seafood dishes. Parasites do not present a health concern in thoroughly cooked fish.
Parasites become a concern when consumers eat raw or lightly preserved fish such as sashimi, sushi, ceviche, and gravlax. When preparing these products, use commercially frozen fish. Alternatively, freeze the fish to an internal temperature of -4°F for at least 7 days to kill any parasites that may be present. Home freezers range from 0°F to 10°F and may not be cold enough to kill parasites.
Parasites (in the larval stage) consumed in uncooked, or undercooked, unfrozen seafood can present a human health hazard. Among parasites, the nematodes or roundworms (Anisakis spp., Pseudoterranova spp., Eustrongylides spp. and Gnathostoma spp.), cestodes or tapeworms (Diphyllobothrium spp.) and trematodes or flukes (Chlonorchis sinensis, Opisthorchis spp., Heterophyes spp., Metagonimus spp., Nanophyetes salminicola and Paragonimus spp.) are of most concern in seafood. Some products that have been implicated in human infection are: ceviche (fish and spices marinated in lime juice); lomi lomi (salmon marinated in lemon juice, onion and tomato); poisson cru (fish marinated in citrus juice, onion, tomato and coconut milk); herring roe; sashimi (slices of raw fish); sushi (pieces of raw fish with rice and other ingredients); green herring (lightly brined herring); drunken crabs (crabs marinated in wine and pepper); cold-smoked fish (lox); and, undercooked grilled fish.
The process of cooking (145°F for 15 seconds) raw fish sufficiently to kill bacterial pathogens is also sufficient to kill parasites.
The effectiveness of freezing to kill parasites depends on several factors, including the temperature of the freezing process, the length of time needed to freeze the fish tissue, the length of time the fish is held frozen, the fat content of the fish, and the type of parasite present. The temperature of the freezing process, the length of time the fish is held frozen, and the type of parasite appear to be the most important factors. For example, tapeworms are more susceptible to freezing than are roundworms. Flukes appear to be more resistant than roundworms.
Freezing and storing at -4°F (-20°C) or below for 7 days (total time), or freezing at -31°F (-35°C) or below until solid and storing at -31°F (-35°C) or below for 15 hours, or freezing at -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours is sufficient to kill parasites. FDA’s Food Code recommends these freezing conditions to retailers who provide fish intended for raw consumption.
Trimming away the belly flaps of fish or candling and physically removing parasites are methods for reducing the numbers of parasites. However, they do not completely eliminate the hazard, nor do they minimize it to an acceptable level.
The health risk from parasites is far less than the risk from bacterial pathogens and mishandling of seafood.
Additional Links for More Information:
A California Sea Grant publication “Fish Parasites and Human Health, Epidemiology of Human Helminthic Infections” by J. Sakanari, et al. includes the life cycles of common parasites in freshwater and marine fishes, transmission, and prevention.
The US Food and Drug Administration’s “BAM” (Bacteriological Analytical Manual) has a chapter on Parasitic Animals in Foods which discusses techniques for examining foods for the presence of parasites. An in-depth discussion of the candling method with finfish and molluscs is described.
The US Food and Drug Administration’s “Bad Bug Book” (Foodborne Pathogenic Microorganisms and Natural Toxins Handbook) includes basic facts on foodborne pathogenic microorganisms and natural toxins. The material is collected from the Food and Drug Administration, the Centers for Disease Control & Prevention, the USDA Food Safety Inspection Service, and the National Institutes of Health.
The US Food and Drug Administration’s “Fish and Fisheries Products Hazards and Controls Guidance” describes the potential hazard of parasites and methods of its control in commercially processed seafood.
The U.S. Food Code 2009 provides the time and temperature for parasite destruction (see Food-Freezing, Chapter 3, Section 402.11)
Viumbe wote walio hai, kutia ndani samaki, wanaweza kuwa na vimelea. Wao ni wa kawaida katika samaki kama wadudu ni katika matunda na mboga. Kuna aina mbili za vimelea vinavyoweza kuambukiza watu kupitia chakula au maji: minyoo wa vimelea na protozoa. Mimea ya vimelea inatia ndani minyoo wa mviringo (nematodes), minyoo wa mviringo (cestodes) na flukes (trematodes). Mdudu huyo ana ukubwa mbalimbali, kuanzia ule usioonekana kabisa hadi urefu wa meta kadhaa. Protozoa ni wanyama wenye chembe moja, na hawawezi kuonekana bila darubini. Kama vile kuna hatari ya kula nyama mbichi au isiyochemshwa, kuna hatari pia ya kula vyakula vya samaki visivyochemshwa, visivyochemshwa, vilivyotiwa chumvi, na vyakula vya samaki vilivyochemshwa kidogo au baridi. Vimelea havisababishi matatizo ya afya katika samaki waliopikwa vizuri. Vimelea huwa jambo la kuogopesha wakati watumiaji wanapokula samaki mbichi au waliohifadhiwa kidogo kama vile sashimi, sushi, ceviche, na gravlax. Unapotayarisha bidhaa hizo, tumia samaki waliofungwa kwa ajili ya biashara. Kwa mfano, unaweza kuhifadhi samaki kwenye joto la ndani la -4 ° F kwa siku 7 ili kuua vimelea vinavyoweza kuwapo. Kwa hivyo, freezers za nyumbani zinaweza kuwa na joto la chini ya 0 ° F hadi 10 ° F, na inaweza kuwa baridi sana kuua vimelea. Vimelea (katika hatua ya mabuu) vinavyotumiwa katika vyakula vya baharini visivyochemshwa, au visivyochemshwa vya kutosha, vinaweza kuwa hatari kwa afya ya binadamu. Miongoni mwa vimelea, nematodes au roundworms (Anisakis spp., Pseudoterranova spp., Eustrongylides spp. Gnathostoma sp. Cestodes au tapeworms (Diphyllobothrium spp.) Mnyama wa aina ya trematodes (Chlorchis sinensis, Opisthorchis spp., Heterophyes spp., Metagonimus spp., Nanophyetes salminicola na Paragonimus spp.) Hii ni kwa sababu ya wasiwasi mkubwa katika chakula cha baharini. "Kama vile ""semi-semi"" (samaki na vikolezo marini katika maji ya limao), ""lomi-lomi"" (samaki marini katika maji ya limao, vitunguu na nyanya), ""poisson cru"" (samaki marini katika maji ya machungwa, vitunguu, nyanya na maziwa ya kokosi), ""sashimi"" (vifungu vya samaki mbichi), ""sushi"" (vipande vya samaki mbichi na mchele na viungo vingine), ""green herring"" (sharing lightly marinated), ""drunken crabs"" (krabs marinated katika mvin na pilipili)." Upasuaji wa samaki mbichi kwa sekunde 15 kwa joto la 145 ° F ni muhimu kwa kuua bakteria na wadudu. Ufanisi wa kufungia ili kuua vimelea hutegemea mambo kadhaa, ikiwa ni pamoja na joto la mchakato wa kufungia, urefu wa muda unaohitajika kufungia tishu ya samaki, urefu wa muda samaki anashikiliwa kufungia, kiasi cha mafuta ya samaki, na aina ya vimelea. Joto la mchakato wa kufungia, muda ambao samaki huhifadhiwa, na aina ya vimelea vinaonekana kuwa mambo muhimu zaidi. Kwa mfano, minyoo wa ukanda huathiriwa zaidi na baridi kali kuliko minyoo wa mviringo. Inaonekana kwamba vimelea hivyo ni sugu kuliko minyoo. Kuhifadhi kwa -30 ° C au chini kwa siku 7 (wakati wote), au kuhifadhi kwa -30 ° C au chini hadi imara na kuhifadhi kwa -30 ° C au chini kwa masaa 15, au kuhifadhi kwa -30 ° C au chini hadi imara na kuhifadhi kwa -30 ° C au chini kwa masaa 24 ni ya kutosha kuua vimelea. Sheria ya Chakula ya FDA inapendekeza hali hizi za kufungia kwa wauzaji wa rejareja ambao hutoa samaki waliokusudiwa kwa matumizi yasiyo ya mbichi. Kuondoa vipande vya tumbo la samaki au kuondoa vimelea ni njia za kupunguza idadi ya vimelea. Hata hivyo, haziondoi kabisa hatari hiyo, wala hazipunguzi hadi kiwango kinachokubalika. Hatari ya afya inayotokana na vimelea ni ndogo sana kuliko hatari inayotokana na vimelea vinavyosababisha magonjwa na kutotumia vyakula vya baharini vizuri. Viungo vya ziada kwa habari zaidi: A California Sea Grant kuchapishwa <unk> Samaki vimelea na Afya ya Binadamu, Epidemiology ya Human Helminthic Maambukizo <unk> na J. Sakanari, et al. Mzunguko wa maisha ya vimelea vya kawaida katika samaki wa maji baridi na baharini, maambukizi, na kuzuia. "Kifungu cha ""Bacteriological Analysis Manual"" cha Shirika la Chakula na Dawa la Marekani (FDA) kinaelezea jinsi ya kuchunguza vyakula kwa ajili ya kuwepo kwa vimelea." Majadiliano ya kina ya njia ya candling na finfish na molluscs ni ilivyoelezwa. "Kifungu cha ""Bad Bug Book"" cha Shirika la Chakula na Dawa la Marekani (FDA) kinaonyesha viini vinavyosababisha magonjwa vinavyosababishwa na chakula na sumu za asili." Vifaa hivyo vimepatikana katika Idara ya Chakula na Dawa, Kituo cha Kudhibiti na Kuzuia Magonjwa, Huduma ya Usimamizi wa Usalama wa Chakula ya USDA, na Taasisi ya Kitaifa ya Afya. "Uongozi wa Ulinzi wa Chakula na Dawa wa Marekani (FDA) unaelezea ""hatari za samaki na bidhaa za uvuvi na udhibiti"" na ""njia za kudhibiti hatari ya vimelea katika samaki na vyakula vya baharini vilivyotengenezwa kibiashara.""" Sheria ya Chakula ya Marekani ya 2009 inatoa muda na joto kwa ajili ya uharibifu wa vimelea (tazama Chakula-Kufungia, Sura ya 3, Sehemu ya 402.11).