High risk of contamination makes seafood dangerous; people should avoid it for own health if not animal welfare

Health and fitness advisers often emphasise on seafood for muscles, high protein, weight loss, etc. Few of them have studied the immense health risks that come with eating seafood.

Mali Ston is an Adriatic Sea coastal town in Croatia, known all over the world for its unique farmed oysters, of which 5 million are sold every year. For centuries, rows of oyster-filled underwater farm beds have spread through the bay. Tourists pour into the town during its annual oyster tasting feast. In 2019, they have had to cancel it because the Institute for Marine and Coastal Research in Dubrovnik has detected norovirus in the oysters. The virus has been caused by the sewage from the town pouring in all these years into the bay. Norovirus is a dangerous virus, causing over 20 million illnesses and hundreds of deaths annually. Symptoms, which include chronic vomiting and diarrhoea, can become very severe very quickly, requiring the need for emergency treatment.

Representational image. Reuters

Flame-grilled carp, seasoned with sauces and known as masgoof, is Iraq's national delicacy. Iraq produces 29,000 tonnes of carp each year, grown in farms along the Euphrates river. In 2018, millions of carp died overnight in the fish farms. Samples of the dead fish, the water and the sediment, sent to laboratories, confirmed that the fish died of a virus caused by low temperatures, overstocking of fish farms and polluted river water. Warnings have been issued by the government not to eat carp.

Seafood is responsible for a large proportion of food-borne illnesses. These are caused by a variety of bacteria, viruses, and parasites. Chemicals, metals, marine toxins, and infectious agents have been found in seafood as well. The illnesses caused by these agents range from mild gastroenteritis to life-threatening conditions.

Seafood includes molluscs (eg, oysters, clams, and mussels), finfish (eg, salmon and tuna), marine mammals (eg, seal and whale), fish eggs (roe), and crustaceans (eg, shrimp, crab, and lobster). Some seafood commodities are inherently more risky than others, depending on the environment from which they come, their mode of feeding and how they are prepared and served. All seafood are susceptible to surface, or tissue contamination. Bivalve molluscs feed by filtering large volumes of seawater. During this process, they can accumulate and concentrate pathogenic microorganisms. Contamination of seafood by pathogens can occur when areas are contaminated with human sewage. Additionally, seafood may become contaminated during handling, processing, or preparation. Unlike meat and poultry, that are usually fully cooked, seafood is often consumed raw or prepared in ways that do not kill the organism.

Seafood has been implicated in so many outbreaks of illnesses that data is collected by official agencies in every country. The Food and Veterinary Office of the European Union has initiated a Rapid Alert System for food. The source of danger and the country of origin are reported. Between 1992 and November 1997, the 71 seafood alerts from this system represented 42.5 percent of all food alerts. The seafood products implicated mussels, tuna fish products, oysters, squid, raw sole, shrimp, octopus, shellfish, crawfish, scallops, cuttlefish, anchovy, Nile perch, bivalve molluscs, king prawn, salmon, mullet fillets, canned fish and clams. These alerts have doubled and tripled since.

Thirty-three different countries had exported seafood/fish on which an alert was reported. The highest alerts were received on fish sent from India. So you can imagine the state of seafood being sold within India.

Thirty-four people died from poisoning by shellfish and fish in Japan in the 1,475 outbreaks of poisoning (33,253 cases) reported between 1987 and 1996.

In Canada, 29 different species of fish and shellfish, and/or seafood products were implicated in seafood-borne illnesses. The top six in number of outbreaks were mussels, clams, tuna, barracuda and marlin. These six represented 56 percent of the outbreaks. The others were whelk, mahimahi, mackerel, swordfish, crab meat, salmon, oysters, clams and dips, haddock, halibut, sole fillets, sharks, scallops, pollock, chicken haddie, shrimp, quahogs, kippers and parrotfish/doctorfish. Ten countries that had exported these fish to Canada were implicated. India was one of them.

In the United States, from 1973 to 2006, over 500 outbreaks involving thousands of people, have taken place. Forty-nine percent were due to infectious agents generally associated with faecal pollution, and 46 percent were from agents associated with processing and preparation.

Some of the pathogens responsible for seafood infections are:

Vibrio bacteria, which cause outbreaks of gastroenteritis. Symptoms include watery diarrhoea, abdominal cramps, nausea, and vomiting. Vibrio vulnificus is particularly virulent, especially among patients with liver disease and iron storage disorders, who are at increased risk of invasive disease. Infections can lead to sepsis and severe wound infections. The fatality rate is about 50 percent for bloodstream infections and 25 percent for wound infections. In January 2007, vibriosis became a nationally notifiable disease in the US.

Salmonella bacteria, which cause acute gastroenteritis, with symptoms including diarrhoea, abdominal cramps and fever. Seafood-associated outbreaks have been caused by fish, shrimp, oysters and clams.

Shigella bacteria in fish comes from sewage in the water. Clinical manifestations range from watery and loose stools to more severe symptoms, including fever, abdominal pain and bloody diarrhoea. Complications include seizures in young children, toxic megacolon, Reiter's syndrome and hemolytic-uremic syndrome.

Clostridium botulinum infection is characterised by an acute paralysis. Early signs and symptoms of botulism often include twitching, slurred speech, and difficulty in swallowing, progressing to descending weakness and paralysis. Foods identified in outbreak investigations have included fermented or salted seafood, especially salmon and whale.

Other toxin-forming bacteria: Staphylococcus aureus, Clostridium perfringens and Bacillus cereus can form enterotoxins that cause acute gastrointestinal illness.

Norovirus infection is characterised by diarrhoea, vomiting, nausea, abdominal cramps, headache, myalgias and low-grade fever. Seafood, harvested from sewage-contaminated waters, has caused large outbreaks of norovirus gastroenteritis.

Hepatitis A virus is the most serious viral infection associated with seafood consumption. It is an acute illness associated with fever, malaise, jaundice, anorexia and nausea. Symptoms may last from several weeks to several months. However, deaths can occur too. Outbreaks of hepatitis A virus (HAV) infections associated with oysters and clams have been known since the 1960s. The largest reported outbreak occurred in China in 1988; almost 3,00,000 persons were infected after consuming clams harvested from a sewage-contaminated area.

Helminths are large, worm-like parasites that infect most marine animals. Clinical manifestations, associated with helminthic infections range from no symptoms to mild and chronic gastrointestinal symptoms, allergic reactions, and sometimes intestinal perforation. Infections are likely underdiagnosed and underreported due in part to a lack of routine diagnostic tests.

Some other common seafood-related diseases and infections around the world include diarrhoetic shellfish poisoning, paralytic shellfish poisoning, scombroid histamine poisoning, Vibrio cholerae, Listeria monocytogenes, Staphylococcus and Bacillus cereus. Many outbreaks likely go unrecognised and are not investigated.

Contamination through sewage is a very common practice around the world and especially in India. Overboard sewage discharge into seafood harvest areas, illegal harvesting from sewage-contaminated waters and sewage runoff from land after heavy rains or flooding are the many ways in which this happens.

Right from the production phase to packaging, transport and consumption, seafood is likely to be contaminated with bacteria, viruses and fungal infections. Intensive fish farming, which involves massive crowding of fish into pens, has substantially enhanced the incidence of seafood diseases in India and abroad.

At the processing and packaging stage, seafood is often exposed to unhygienic handling by workers, bad storage conditions, irregular temperatures and the addition of preservative compounds. With a heavily globalised food trade, the long journey seafood travels before reaching our plates, drastically increases the chances of it becoming dangerously contaminated.

At the consumption stage, seafood is often prepared in ways that do not kill organisms or even many times eaten undercooked or raw — making it a particularly dangerous food.

It is important that you understand the consequences of seafood consumption. If not for reasons of sustainability and animal welfare, look at seafood in terms of your own immediate health. People with underlying medical conditions such as liver disease, diabetes or immuno-suppressing conditions, are at higher risk of acquiring severe infection and should be especially careful.

As the waters grow warmer, seafood will get more and more dangerous to eat.