Infections from Eating Raw or Undercooked Seafood

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<ul><li><p>Clinical Microbiology Newsletter 36:3,2014 | 2014 Elsevier 17</p><p>Introduction</p><p>Several years ago, when I coauthored an article inthis newsletter on infections in nail salons (1), oneof my colleagues sent me an email that she wouldnever get a pedicure again. I still get pedicures, soit was certainly not my intention to close downnail salons. However, it turned out that there arecertain precautions that people and salons cantake that will help prevent infection. I do not eatsushi or sashimi, but my sister and many of mybest friends do. I decided to write this articlebecause I wanted to explore the potential conse-quences of eating raw or undercooked seafood. Ihave learned a lot as a result of my research thatmay be comforting or scary depending on yourperspective.</p><p>Epidemiology of Food-Borne IllnessesCaused by Seafood</p><p>Food-borne diseases cause approximately 76 mil-lion illnesses in the United States each year, andseafood is implicated in 10 to19% of these episodes(2). The actual causative agent can be tracked in44% of seafood-related outbreaks, with virusesaccounting for approximately one-half of theevents. There are about 325,000 hospitalizationsand 5,000 deaths annually.</p><p>Sushi and Sashimi</p><p>There are certain basic things that should beconsidered at the outset. The first is the difference</p><p>between sushi and sashimi. Sushi is actually sweet-ened, vinegared rice combined with other ingre-dients, including sliced raw fish. Sashimi is thesliced raw fish itself. A second key point is that thetype of fish involved, whether marine or fresh-water, will ultimately determine the type(s) ofmicroorganism(s) that may cause infection. Thethird thing is that there is a difference betweenmolluscs (oysters, mussels, cockles, and clams)and crustaceans (crabs, shrimp, and prawns) andthe diseases they cause. Molluscs are more trou-blesome, because they are filter feeders; thismeans that they filter and concentrate environ-mental microorganisms in high numbers in theirtissues. These microorganisms may be viablewhen the molluscs are eaten raw (2).</p><p>Diseases from Shellfish</p><p>As stated above, viruses (particularly norovirus)cause 50% of seafood-related illnesses.</p><p>Norovirus</p><p>Norovirus is a calicivirus that was first discoveredin 1972 in feces collected after an outbreak of gas-troenteritis in 1968 in Norwalk, Ohio (3). Thevirus was originally referred to as the Norwalkvirus or Norwalk-like virus (4). An electron pho-tomicrograph of norovirus is shown in Fig. 1; itis a single-stranded RNA virus with an icosahe-dral capsid composed of a single major protein.Norovirus is the leading cause of gastroenteritisassociated with the consumption of raw shell-</p><p>Vol. 36, No. 3February 1,</p><p>I N T H I S I S S U E</p><p>17 Infections fromEating Raw orUndercooked Seafood</p><p>22 CutaneousLeishmaniasis in aCentral AmericanRefugee</p><p>Corresponding Author:Alice Schauer Weissfeld, Ph.D.,D(ABMM), F(AAM), Microbi-ology Specialists Incorporated,8911 Interchange Dr., Houston,TX 77054. Tel.: 713-663-6888.Fax: 713-663-7722.</p><p>ClinicalMicrobiologyN E W S L E T T E R</p><p>CMN</p><p>Stay Current...</p><p>Stay Informed.</p><p>Infections from Eating Raw or UndercookedSeafoodAlice Schauer Weissfeld, Ph.D., D(ABMM), F(AAM), Microbiology Specialists Incorporated, Houston, Texas</p><p>Abstract</p><p>The bacterial, viral, and parasitic diseases that may be contracted from eating raw or undercooked seafoodare reviewed. Diseases frommarine, as well as, freshwater fish are discussed. The Food and Drug Admin-istrations sanitation program for shellfish and their guidelines for preparation of raw fish in restaurantsare also described.</p><p>CMN</p><p></p></li><li><p>18 Clinical Microbiology Newsletter 36:3,2014 | 2014 Elsevier</p><p>fish. Oysters are frequently implicated, but outbreaks have also beenassociated with consumption of mussels, cockles, and clams.</p><p>Norovirus is excreted in the feces of infected individuals, where itpersists in the environment. It is transmitted primarily by thefecal-oral route or via contaminated food and water. In fact, con-tamination of fishing waters by human sewage has played a majorrole in seafood-associated outbreaks (5). The infectious dose is low,with </p></li><li><p>reported a diarrheal illness, and the risk of diarrhea was significantlyhigher in individuals who ate raw or cooked oysters. In 1993, theNew York Times published an article regarding findings first reportedat another ICAACmeeting. In this study, researchers reported thatLouisiana hot sauce killed some Vibrio spp. found in raw shellfishwhen tested in the laboratory (10). The lead investigator reportedthat he eats raw oysters, but only with plenty of hot sauce.</p><p>The most common manifestation of V. parahaemolyticus infectionis gastroenteritis (60 to 80%), followed by wound infections (34%)and septicemia (5%). The incubation period is 15 to 19 hours, andgastrointestinal symptoms (abdominal cramps, nausea, vomiting,fever, and diarrhea) last 2 to 3 days before complete recovery inpatients who have no underlying liver disease or any other immuno-suppressive condition. V. parahaemolyticus gastroenteritis is treatedwith hydration and supportive measures.</p><p>Salmonella spp.</p><p>Approximately 7% of all food-borne outbreaks of Salmonella infec-tion are linked to seafood. In fact, between 3% and 54% of seafoodtested is contaminated with Salmonella. Salmonella gastroenteritishas an incubation period of 8 to 72 hours. Symptoms includeacute non-bloody diarrhea, abdominal pain, muscle aches, andfever. As with any limited Salmonella gastrointestinal illness, non-typhoidal Salmonella is usually not treated with antibiotics, whichcan promote a carrier state.</p><p>Other Organisms</p><p>Aeromonas spp., Plesiomonas spp., Listeria monocytogenes, Clostridiumbotulinum, Campylobacter spp., and Streptococcus pyogenes have all beenimplicated in seafood-borne illness but do not occur as frequentlyas the organisms mentioned above and will not be discussed here.</p><p>Parasitic Diseases fromMarine and Freshwater Seafood</p><p>Parasites, discussed below, cause the majority of freshwater andmarine seafood-borne illness. An estimated 50 million people areinfected worldwide (11).</p><p>Anisakiasis</p><p>Anisakiasis is primarily an acute gastrointestinal disease caused byinfection with either the herring worm (Anisakis simplex) or the codworm (Pseudoterrannova decipiens) (12). The highest prevalence ofanisakiasis is in Southeast and East Asia. One thousand cases arereported annually from Japan, but only about 50 cases have beenreported from the U.S. Nearly all marine animals are infected withparasites. Most worms do not cause disease in their natural host orin humans. However, some of these parasites may survive thefood preparation process and cause human infection. The lifecycle of the anisakid nematode is shown in Fig. 3.</p><p>A. simplex accumulates within the host during the fishs lifetime.Anisakids are commonly found in marine mammals, such as dol-phins and sea lions, but are difficult to see within the fish muscu-lature. They excrete eggs, which turn into larvae. After ingestionby the human host, a viable juvenile anisakid may penetrate intoor through the wall of the gastrointestinal tract, causing invasiveanisakiasis.</p><p>These larvae are ingested by crustaceans. Fish then ingest thecrustaceans and become intermediate hosts, with the larvae embed-ded in their flesh. When humans ingest the infected fish, the lar-vae can attach to the gastric mucosa or penetrate the stomach orintestinal wall, leading to acute abdominal pain, nausea, and vom-iting within a few minutes to several hours; abscess formation oreosinophilia granulomatosis (13) may also be present. Severe aller-gic reaction, including angioedema, uticaria, or even systemicanaphylaxis, is also possible (14).</p><p>An antigen capture ELISA with a reported sensitivity and speci-ficity near 100% can be used for serodiagnosis of anisakiasis (15).Diagnosis can also be made by extirpation (total destruction) of theparasite during an upper gastrointestinal tract endoscopic exami-nation. Although many patients expel the worm spontaneously,albendazole has been shown to be an effective treatment.</p><p>Diphyllobothriasis</p><p>The fish tapeworms Diphyllobothrium latum and Diphyllobothriumdendriticum are the common cestodes implicated in seafood-bornedisease episodes.D. latum competes for vitamin B12 in the humanhost, causing pernicious anemia, in which the body cannot makeenough red blood cells. Fifty-two cases were reported in 1980fromWest Coast states in the U.S., and salmon was implicated in82% of them. Infective larvae, also known as plerocercoids, alsoreside in the muscles of trout, pike, and sea bass. The plerocercoidsattach to the mucosa of the small intestine, where they mature intoadult worms. Proglottids can protrude out of the patients anus tohelp make the diagnosis when observed. Niclosamide is used fortreatment.</p><p>Flukes</p><p>Heterophyes and Metagonimus are trematodes that are acquired byeating raw, marinated, or improperly cooked fish. Most cases arereported from theMiddle East and Asia. However, one case ofHet-erophyes heterophyes infection was reported in the U.S. in 1986; thepatient had never traveled outside the U.S. but had eaten sushi ina restaurant that served fish flown in from Asia (11).</p><p>Liver Flukes</p><p>Clonorchis sinensis and Opisthorchis viverrini cause human infectionfollowing the ingestion of raw freshwater or brackish-water fish car-rying infective larvae (metacercariae). The larvae migrate to the bileduct, where they develop into adult worms. A heavy infectionmay lead to obstructive jaundice and eventually liver cirrhosisand cholangiocellular carcinoma. Diagnosis is made by seeingcharacteristic eggs in stool. Treatment is with either mebendazole,albendazole, or praziquantel.</p><p>Lung Flukes</p><p>Paragonimiasis is caused by the lung fluke Paragonimus westermanior Paragonimus skrjabini. The disease is endemic in Thailand,Japan, Korea, andChina. Infective larvae (metacercariae) are encystedin freshwater crabs. These larvae penetrate the peritoneal cavity andmigrate across the diaphragm into the lung parenchyma. Theyreach maturity in the lung parenchyma and form solid wormcysts. Typical manifestations include remittent fever, chest pain, and</p><p>Clinical Microbiology Newsletter 36:3,2014 | 2014 Elsevier 19</p></li><li><p>20 Clinical Microbiology Newsletter 36:3,2014 | 2014 Elsevier</p><p>a chronic cough with hemoptysis. Chest X rays show characteris-tic infiltrative, nodular, and cavitating lesions. Confirmation isby detection of the eggs in sputum, stool, or gastric aspirates,although serological tests are also available. Pleural effusions (if pre-sent) must be drained before praziquantel is given.</p><p>FDA National Shellfish Sanitation Program</p><p>The Food and Drug Administration (FDA) is responsible for reg-ulating seafood, as they are with other foods (16). The main pointsin this program are (i) harvest fish from approved areas only and</p><p>process them immediately after capture, (ii) monitor the numberof fecal coliforms in the area, and (iii) candle fish to look for wormsprior to food preparation. Candling involves shining a bright lightthrough the fillet to observe worms not removed by gutting the fish.</p><p>The FDA also sets guidelines for restaurants. These include the fol-lowing: (i) defrost fish fillets at room temperature within 14 hours;(ii) do not store fillets for more than 3 days; (iii) use trays of fishremoved from the refrigerator within 3 hours; (iv) shell shrimpimmediately and preferably before they are completely defrosted;</p><p>Figure 3. Life cycle of A. simplex and P. decipiens, the causal agents of anisakiasis. (Public Health Image no. 3378,CDC, Atlanta, GA.)</p></li><li><p>(v) remove defrosted shrimp from the refrigerator as needed, anddo not keep them at 4C for &gt;48 hours; (vi) use clams within 3 days,including the time required for defrosting; (vii) flash-freeze all fishand shellfish intended for consumption raw, semi-raw (marinated),or partly cooked to -35C or below for 15 hours, or freeze themslowly over time to -30C or below for 7 days.</p><p>Conclusions</p><p>It seems presumptuous to give advice to consumers on whether theyshould or should not eat raw or undercooked seafood. However,a few salient facts are worth summarizing here.</p><p>People with liver disorders or weakened immune systems shouldavoid raw or undercooked seafood. Individuals consuming a sin-gle serving of raw shellfish from an approved harvesting site in theU.S. have an estimated probability of 1 in 100 of becoming infectedwith an enteric virus (2). The risk is even smaller for anisakiasis, withfewer than 10 cases of reported infections each year (17). The attackrate for Vibrio is small, as well, and the infectious dose of V. para-haemolyticus is 105 CFU.While the FDA allows the sale of oysterswith 104 CFU per gram of oyster meat to be sold in the U.S.,transmission has occurred from oyster beds where colony countshave been </p></li></ul>


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