The abundance of a parasitic worm (anisakid worm) in raw or undercooked seafood has increased by 283 times between 1962 to 2017, according to researchers from the University of Washington.
The study, which was published on March 19, 2020, found that there is a significant increase in the abundance of a parasitic worm that can be transmitted to humans when consuming raw or undercooked seafood.
What are anisakid worms and how do they affect humans?
According to the study, the adult anisakid worm is a parasitic worm whose eggs are consumed by hosts such as fish (like sardines, cuttlefish, cod fish, salmon and anchovies).
These worms, when accidentally consumed by humans, can affect the intestines and cause symptoms similar to that of food poisoning, such as nausea, vomiting and diarrhea.
While the worm dies after a few days and the symptoms disappear, the disease, referred to as anisakiasis or anisakidosis, is rarely diagnosed as people assume it is a case of food poisoning.
Some consumers of seafood, such as raw fish in sushi or sashimi, might discover their infection by the parasitic worm when they find live worms in mucus, vomit or faeces, and in some cases, nausea, vomiting and diarrhea persisted for months, according to the study.
Increase in parasitic anisakid worms in the last 40 years
A 283‐fold increase in abundance of parasitic anisakid worms was observed in studies published between 1978 and 2015.
The study estimated that on average, the parasitic anisakid worms increased in abundance from one anisakid per 100 hosts (e.g. fish) in 1978 to more than one anisakid worm in every host examined in 2015.
This result has an impact on fisheries and their economic profitability as fish or seafood raised for human consumption could be affected by rising rates of parasitic anisakid worm infections.
Reasons for the increase in abundance of worms
The study mentions two possible reasons for the increase in the abundance of parasitic worms.
One reason could be that increased agriculture and deforestation has led to nutrients running off from land into the ocean, which then increases plankton blooms, which the hosts of the worms eat.
This increase in hosts for the worms could explain the increase in parasitic anisakid worms.
Another potential reason is that marine mammals, such as seals, sea lions, whales and dolphins, which can be hosts to the parasitic worms, have been protected in certain parts of the world.
For example, many countries have adhered to the ban on commercial whaling imposed by the International Whaling Commission in 1982.
This protection of marine mammals has seen an increase in marine mammal populations in the same time period as this study.
This means that the increase in parasitic worms could also be a sign that the ecosystem is improving.
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