Invasive disease linked to raw freshwater fish
An emerging foodborne hazard has been detected in several countries in Southeast Asia, prompting FAO to publish a risk profile document. As only little is known and the list of uncertainties and identified data gaps is extensive, a proper risk assessment is not yet possible without sufficient and validated data-sets.
It started in 2015, when at least 146 people got sick by eating raw freshwater fish in Singapore. Some experienced severe consequences, as some had to lose their arms and legs. The illness was later linked to a bacterium called Streptococcus agalactiae, also referred to as Group B Streptococcus (GBS) and the specific strain responsible for the outbreak was sequence type 283 (ST283).
“Many microbiologists were surprised as invasive GBS disease has not been known to be foodborne previously,” said Dr Timothy Barkham, an expert in Singapore. “Another surprising point was that this foodborne GBS ST283 affected healthy adults. GBS is normally very uncommon in healthy adults.”
Outside of Singapore, invasive GBS ST283 disease is found in China, Hongkong SAR, Lao People’s Democratic Republic, Thailand and Viet Nam. However, it does not mean this is happening only in the listed countries, as other countries in the region have not yet been studied. On the other hand, researchers looked into the countries beyond the region, including Africa, Europe and North and South America to conduct numerous typing studies but only few cases have been reported. While it may mean that the disease hot spot is in Southeast Asia, it may also mean that identifying GBS ST283 is simply a challenge for many low- and middle-income countries, as it requires advanced methodology for sequencing typing. It is possible that GBS ST283 cases have been extremely under-reported.
What countries can do
It is ideal for food safety competent authorities to have full risk assessment results to consider risk management options, but with all the uncertainties and the lack of data, only limited practical recommendations can be provided. In general, it is a good idea to promote good aquaculture practices (GAPs). Also planning of a general and targeted food safety campaign aimed at consumers, local populations or villagers to inform them of the potential risks of consumption of raw freshwater fish works as an effective preventative measure, especially in the locations where consumption of raw freshwater fish may be common. Specifically, below are the few consideration points experts have suggested to communicate:
- visual inspection: discarding visibly abnormal/diseased fish is expected to reduce risk, but we should not rely on visual inspections alone, as healthy-looking fish are no guarantee of safety;
- heat-treatment: proper heating / cooking is the only known effective risk mitigation measure; and
- non heat-treatments: there is no evidence that traditional fish preparation methods without heat treatment are effective. Freezing is not an effective control measure.
Dr Masami Takeuchi, a Food Safety Officer at FAO said: “While it is important to continue strengthening the various aspects of national food control systems, it is important for the competent authorities to be aware of the issue first.” As the issue is relatively new, having an overview of what is currently known on this foodborne disease is possible by reading the FAO risk profile. Discussing among all stakeholders in food safety, public health and fisheries/aquaculture to exchange information and share views is also a good first step, she suggested.
Download the 4-page factsheet:
Download the full publication:
For more information:
- FAO Food safety and quality
- FAO Fisheries & aquaculture
- FAO Regional Office for Asia and the Pacific
Photo: ©Warren Andrew Turner