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Food Safety Focus (107th Issue, June 2015) – Food Incident Highlight
Bacteria and Parasites in Raw Crabs
Last month, six persons were reported to have food poisoning following consumption of marinated raw crabs. The Centre for Food Safety (CFS) reminds the public that consuming raw or undercooked crabs increases the risk of developing foodborne illnesses.
Different pathogens may be present in crabs living in various environments. For instance, Paragonimus westermani , a parasite also known as lung fluke, may be present in freshwater crabs. Vibrio cholerae (VC), a bacterium indigenous to fresh and brackish water environments in tropical, subtropical and temperate areas worldwide, may infect crabs living in those environments. Vibrio parahaemolyticus (VP), another kind of bacterium, may be present in crabs living in estuaries and coastal waters.
When a person consumes raw or undercooked crabs infected with lung fluke, the parasite may migrate from the intestines to the lung causing paragonimiasis. The initial signs and symptoms may be diarrhoea and abdominal pain. This may be followed several days later by fever, chest pain, fatigue, and sometimes coughing up blood. Sometimes the fluke can travel to the brain where it can cause symptoms of meningitis. Onset of symptoms of lung fluke infection usually occurs many weeks after exposure and the disease may last for many years. In South Korea, nationwide survey data showed that paragonimiasis had been prevalent in 1960s, lowered in the 1990s, but raised again in 2000s.
Cholera is transmitted through ingestion of food or water contaminated with VC, especially via faeces of infected persons. Cholera is an acute intestinal infection. Its incubation period ranges from a few hours to five days. Symptoms include severe diarrhoea and vomiting, which may lead to dehydration. The common symptoms of VP infection include diarrhoea, vomiting, mild fever and abdominal pain usually within one to two days upon consumption of contaminated food. The illness usually lasts a few days. Severe disease is rare and occurs more commonly in children, the elderly and persons with weakened immune systems.