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Public health risks from fish and fish products
Craig Burton
Scottish Food Enforcement Officers
Perth
April 08
Potential hazards
• Potential public health risks can arise from– Toxins– Parasites– Xenobiotes (Man-made substances)
Definitions
• Toxin– A poisonous substance produced by an organism
• Parasite– An organism that lives on or in another and derives
nutrition from the host with a detrimental effect on the host.
• Xenobiote– A substance that is not of biological origin found in the
ecosystem or body
Fish toxins
• 3 main toxins and several minor ones– Ciguatera– Tetrodotoxin– Scombroid poisoning
– Clupeoid fish poisoning– Gempylid poisoning– Hallucinatory fish poisoning– Ichthyohaemotoxic poisoning– Ichthyohepatotoxic poisoning– Ichthyootoxic poisoning– Elasmobranch poisoning
Ciguatera
• Most serious toxin world-wide and commonest• Mainly tropics and sub-tropics
– Between 35o N and 35o S• Mainly reef fish species – 400 species implicated
– Barracuda– Grouper– Snapper– Sea Bass– Coral Trout– Rock Cod– Jacks / Tevally– Parrot Fish– Moray Eel
Ciguatera
• No external indication of toxicity• Heat stable• Possible 5 toxins involved
– Ciguatoxin– Maitotoxin– Scaritoxin– Palytoxin– Okadic acid
• Cause – dinoflagellates (Gambierdiscus toxicus)
Ciguatera
• Symptoms:– Various, 2 – 12 hours after ingestion
– Gastro-intestinal (nausea, vomiting, cramps, diarrhoea)
– Cadiovascular (hypotension, tachycardia, bradycardia)
– Neurological (headache, joint pain, delirium, paralysis, coma)
– Sensation (itch, burning, numbness, tingling, dysaesthesia)
– Skin lesions
• Can be fatal (0.1 - 10%)
Ciguatera
• Can be treated– Treat symptoms and provide support
• Best tactic – Avoidance – Be cautious of large reef fish – especially
predators– Do not eat fish liver, gonads or intestines– Caution if evidence of algal blooms– Sale of some fish species banned in some
areas / seasons
Tetrodotoxin
• Most famous fish toxin• Japanese ‘Fugu’• Toxin found in
– Puffer Fish– Ocean Sunfish– Porcupine Fish
• Occurs in– Ovaries– Liver– Intestines
Tetrodotoxin
• Heat stable• Slightly water soluble• Neurotoxin
– 65 mg lethal– Has medical uses as a pain killer
• Symptoms: 5 – 40 minutes (to 3 hours)
– General (weak, pale, dizzy, unco-ordinated, salivation, sweating)
– Neurological (numbness, paraesthesia, muscle twitching, paralysis)
– Gastro-intestinal (nausea, vomiting, diarrhoea, pain)
– Cardiovascular (chest pain, irregular pulse, hypotension)
Tetrodotoxin
• Treatment– Respiratory support and general care– Can improve rapidly– Full resolution
• Can be fatal (up to 60% if untreated and can kill in 17 mins)
Scombroid toxin
• Fish spoilage problem• Associated with
– Tuna (all species)– Mackerels (all species)
– Herring– Sardine– Anchovy– Bluefish– Amberjack– Kingfish
Scombroid toxin
• Cause– Fish treated incorrectly after capture or during
storage– Left in the sun– Kept at room temperature for hours
• What happens– Bacteria (Proteus, Clostridium, Salmonella, Klebsicila, Escherichia)
convert Histidine in the muscles to Suarine (histamine-like)
Scombroid toxin
• External Indication– Fish taste sharp, bitter or peppery
• Laboratory confirmation– Histamine > 100 µM (mg) per 100 g fish
muscle(Codex Std < 20 mg 100g-1)
Scombroid toxin
• Symptoms: 20 – 60 mins– General (dry mouth, thirst, burning throat, cannot swallow,
headache, metallic taste, weakness, pain, fever)
– Gastro-intestinal (nausea, vomiting, diarrhoea, cramps)
– Cardiovascular (palpitations, tachycardia, hypotension, ST depression)
– Skin (general redness, itching, urticaria)
– Respiration (bronchospasm, distress, cyanosis)
Scombroid toxin
• Often mistaken for fish allergy• Treat with anti-histamines (steroids)• Rarely fatal• Usually resolves 12 – 16 h, but can last days
Rarer toxins
• Clupeoid fish poisoning– Anchovy– Herring– Sardine
– Rapid onset (minutes)– Often fatal– Liver failure (if survive)
– Possibly related to Ciguatera poisoning• Gempylid poisoning
– Escolars and pelagic mackerels
– Diarrhoea
Rarer toxins
• Hallucinatory fish poisoning– Mullet– Goatfish– Drummers– Rockcod– Surgeon fish
– Rare and localised– Heat stable– Rapid onset - < 2 h– Symptoms
– Impaired consciousness– Hallucination– Bizarre dreams– Paranoia
– Resolves < 24 h
Rarer toxins
• Ichthyohaemotoxic poisoning– Drinking fish blood, especially freshwater eels
– Heat labile, protein-bound– Symptoms
– Gastro-intestinal (nausea, vomiting, pain)– Neurological (numbness, weakness, paralysis)
– Can be fatal• Ichthyohepatotoxic poisoning
– Eating fish livers (tuna, mackerel, bass, grouper, snapper, sandfish)– Like vitamin A overdose
• Ichthyootoxic poisoning– Eating fish eggs / roe (eg Barbel roe, but can affect caviar by bacterial
spoilage)– Rare– Symptoms
– Gastro-intestinal (nausea, vomiting, diarrhoea)– Neurological (tinnitus, respiratory distress, coma)– General (dry mouth)
– Resolves in days
Rarer toxins
• Elasmobranch poisoning– Associated with eating sharks and rays
– Often from liver and gonads (but also in muscle)– Heat stable– Water soluble– Symptoms
– Gastro-intestinal (nausea, vomiting, diarrhoea, pain)– Neurological (numbness, tingling, weakness, visual,
paralysis, delirium, coma)– Cardiovascular (tachycardia, thready pulse)– Skin (itchy, peel off)– General (headache, pain, prostration)
– Can be fatal– Recovery 5 - 20 days
Parasites
• Affect freshwater and marine fish• 76 recognised pathogenic species• 3 main groups:
– Nematodes (Round worms)– Trematodes (Flukes)– Cestodes (Tape worms)
• Also– Acanthocephala
Parasites
• Problems mainly associated with raw or lightly processed fish
• Typical ‘risk’ dishes– Raw fish (eg Sashimi, Sushi)– Cold-smoked fish– Lightly salted (cured) fish (eg Gravfisk)– Pickled fish (eg Roll-mop herring)– Marinated fish– Undercooked fish
Parasites
• Penetrate human gut if ingested– Inflammation– Ulceration– Granuloma formation– Can migrate to other organs (serious)
• Infection rare in UK(but 40 – 50 million people (5-7%) affected world-wide,
mainly Asia)
• Can be of short duration (days) or can be chronic (decades)
Nematodes (Round worms)
• Main condition– Anisakiasis (eosinophilic phlegmonous enteritis, eosinophilic
granuloma)
• Main causal agents– Herring Worm (Anisakis simplex)
– Cod Worm (Pseudoterranova decipiens)– Eustrongylides spp– Gnathostoma sprinigerum (FW - Thailand)– Angiostrongylus cantonensis (FW)
• Worms mainly found in fish gut, but move to muscle tissue after death
Nematodes
• Symptoms (within hours)– Abdominal pain– Nausea– Vomiting– May cough up larvae– After 1-2 weeks, mimics Crohn’s disease (IBS)
– Other (more serious) if migration to other organs
– Brain– Heart– Lungs
Nematodes
• Common fish hosts– Herring– Cod– Pollock– Haddock– Alaskan pollock– Mackerel– Anchovy– Tuna– Salmon– Squid
Trematodes (Flukes)
• Fish are intermediate host• Several genera can infect humans
– Heterophyes spp– Microphallus spp– Nanophyetus spp– Opisthorchis spp – Chlonorchis spp– Metagonimus spp– Paragonimus spp (crustacea)
Trematodes
• Symptoms– Depends on main site of infection of fluke
– Liver flukes – Chlonorchis spp– Opisthorchis spp
– Abdominal pain– Nausea– Diarrhoea / Constipation– Eosinophilia
– Cholangitis– Cholelithiasis– Pancreatitis– Cholangiocarcinoma– Heptamegaly– Malnutrition
Trematodes
• Symptoms– Intestinal flukes
– Heterophyes spp– Metagonimus spp
– Abdominal pain– Diarrhoea
– Heart (muscle and valves)– Brain
Trematodes
• Symptoms– Lung flukes
– Paragonimus spp– Abdominal pain– Diarrhoea– Fever– Cough– Urticaria– Hepatospleanomegaly– Lung abnormality– Eosinophilia
– Cough– Expectoration– Haemoptysis– Brain– Other organs
Trematodes
• Symptoms– Other “fish flu”
– Nanophyetus spp– Abdominal discomfort– Diarrhoea– Nausea– Fatigue– Weight loss– Eosinophilia
Trematodes
• Common fish hosts– Mullet (Mugil spp)– Sea Bass (Dicentrarchus spp)– Herring– Salmonids– Tilapia– FW fish (carps)
Cestodes (Tape worms)
• Fish are intermediate host• Main concern 2 genera
– Diplogonoporus spp – Diphyllobothrium spp
– Diphyllobothrium latum– Broad tapeworm– Human optimum host– Grows to 10 m– Long lived (decades)
Cestodes
• Symptoms– Can be none (asymptomatic)– Abdominal discomfort– Diarrhoea– Vomiting– Weight loss– Vitamin B12 deficiency– Pernicious anaemia– Intestinal obstruction
Cestodes
• Common fish hosts– Pike– Perch– Burbot– Salmonids– Drums (Serranids)– Blue Whiting– Anchovy– Sardine– Turbot
Prevention of parasite infection
• Freeze fish– EU requirement (853/2004)
– Freeze to -20oC for 24 h– Other advice (FDA)
– Blast freeze to -35oC for 15 h– Freeze to -23oC for 168 h – Freeze or store at -20oC for minimum of 7 d
• Cook fish to > 60oC throughout depth• Candling and removal (minimise risk)
• Belly flap removal (minimise risk)
• Gut at sea or as kill (and cure) can reduce risk
Xenobiotes
• Several non-biological substances of health concern can occur in fish and fish products– From the environment
– Hydrocarbons– Persistent Organic Pollutants (Dioxins,
Polychlorinated biphenols [PCB], Organophosphates, Organochlorides)
– Polycyclic Aromatic Hydrocarbons (PAH)– Heavy metals (Pb, Hg (CH3-Hg), Cd etc)– Radionucleotides– Synthetic hormones (freshwater)
Xenobiotes
– From direct intervention– Veterinary medicine residues (aquaculture)
– Polycyclic Aromatic Hydrocarbons (PAH) (processing)
– Colourants (processing)
Xenobiotes
• Some have permitted maximum levels set in legislation
– International (Codex Alimetarius)
– European (1881/2006, 2377/90, 94/36/EC)
– UK (Contaminants in Food Regs 2007)
• UK fisheries and aquaculture monitored• Imports should be certificated
(EU approved residue monitoring plan in export country)
