Fish and shellfish hygiene

Question 1

Causes of bivalve-associated illness

Answer 1

• Microbiological
  ○ Bacteria
  ○ Viruses
  ○ (Protozoa)
  
  • Biotoxins
    ○ Paralytic shellfish poisoning
    ○ Diarrhetic shellfish poisoning
    ○ Amnesic shellfish poisoning
    ○ Others
  • (Chemical contaminants)
    ○ Little evidence for acute effects
  • Allergies

Question 2

How much can oysters filter

Answer 2

10-24L per hour

Question 3

Bacteria causing bivalve-associated illness

Answer 3

Salmonella

Shigella

Vibrio

Campylobacter

Question 4

Viruses causing bivalve-associated illness (5)

Answer 4

Norovirus
§ Relatively mild gastroenteritis, often including nausea, diarrhoea, vomiting, fever, and abdominal pain
§ Incubation period of 1 to 4 days, duration of about 2 days generally followed by complete recovery
§ The most common cause of infectious intestinal disease in outbreaks and in the community

Sapovirus

Astrovirus

Aichi virus

Hepatitis A virus
§ Extended incubation period of about 4 weeks (range 2-6)
§ Serious debilitating disease with fever, headache, nausea, vomiting, diarrhoea, abdominal pain, and jaundice
§ Self-limiting and rarely causes death, but patients may be incapacitated for several months

Question 5

Protozoa causing bivalve-associated illness

Answer 5

Giardia
(? Cryptosporidium)

Question 6

Pathogenic vibrios

Answer 6

Vibrios and human disease
○ Vibrios are a significant cause of seafood-associated illness worldwide
○ Three main species of interest are V. Cholerae, V. Parahaemolyticus, and V. Vulnificus

Foodborne infections
○ Primarily associated with consumption of raw bivalves
§ May also be associated with consumption of undercooked or re-contaminated bivalves
○ A proportion of cases also associated with consumption of crustacea (shrimps, crab, crayfish) or finfish
○ Relative trend in reported number of vibrio infections occurring annually in the USA, compared with that of other foodborne pathogens

Post-harvest processing
○ Purification - only about 40-50% of pathogenic vibrios removed at 48 hours
○ Other procedures
§ Pasteurisation
§ Freezing
§ Ultra-high pressure

Question 7

Vibrio parahaemolyticus

Answer 7

Widely present in coastal and esturine environments

Causes gastro-enteritis

Ability to produce illness mainly associated with ability to produce certain haemolysins
§ Thermostable Direct Haemolysin (TDH) and TDH-related haemolysin (TRH)
§ E.g. In the USA, only 0.2-3.2% of environmental isolates are TDH +ve

Question 8

Vibrio vulnificus

Answer 8

Causes primary septicaemia or wound infections

Infection via GI tract (raw oysters) or wounds

Death may occur within 2 days of start of symptoms

Predisposition by certain illnesses

Question 9

What is the most common fish associated illness

Answer 9

Scombrotoxin