SINGAPORE - A 30-year-old man from California who ate salmon sashimi daily found a 1.6m tapeworm slithering out of his body during a painful visit to the bathroom last August (2017).

The incident gained widespread media attention this week when his emergency department doctor shared details of the case on medical podcast This Won't Hurt A Bit.

Here are seven thing you need to know about these parasites:

1. HOW DO PARASITIC INFECTIONS SPREAD THROUGH FOOD?

Humans are most likely to be infected with parasites like worms when they eat uncooked or undercooked seafood that contains parasite larvae.

These organisms can also be found on raw vegetables that have been contaminated by human or animal faeces.

Food service workers who practise poor hygiene or who work in unsanitary facilities may also be sources of contamination.

The larvae begin growing once they are inside the host.

2. HOW COMMON IS IT?

To date, most cases of parasitic diseases caused by worms have been reported in Japan, but experts have warned that it has become "increasingly recognised in Western countries".

About 2,000 cases of tapeworm infection have been reported in humans, according to a 2017 report by the United States Centres for Disease Control and Prevention.

3. COMMON PARASITES IN SEAFOOD

• Roundworms: They have a long round body, and vary in length from several millimetres to 2m

• Tapeworms: A type of flatworm ranging in size from about 1mm to more than 15m

• Flukes: A flatworm, most of which range from 5mm to several centimetres long

4. SYMPTOMS OF PARASITIC INFECTION

Most people who become infected do not show any symptoms, but some may suffer:

• Stomach cramps, nausea, vomiting and diarrhoea

• Weight loss

• Anaemia

• Damage to major organs such as the liver and the heart

• Damage to the central nervous system

• Vitamin B12 deficiency

5. DISHES THAT COULD CAUSE PARASITIC INFECTIONS

• Ceviche, a Latin American dish with raw fish

• Herring roe

• Sashimi and sushi

• Drunken crabs

• Cold smoked fish

6. HOW CAN I KILL PARASITES?

• By thoroughly cooking seafood

• By freezing seafood at specified temperatures for prescribed periods, depending on the type of parasite. Flukes, for example, are more resistant to freezing than roundworms.

7. TREATMENT FOR PARASITIC INFECTIONS

Two drugs, called praziquantel (Biltricide) and niclosamide (Niclocide), are the main ones used by doctors to kill the parasites.

SOURCES: US FOOD AND DRUG ADMINISTRATION, US CENTERS FOR DISEASE CONTROL AND PREVENTION, BBC, CBS NEWS