Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Seafood toxins are becoming increasingly important as etiologic agents of foodborne diseases around the world. This is partly because of greater awareness of the potential problems of the paralytic shellfish poisoning PSP , neurotoxic shellfish poisoning NSP , diarrheic shellfish poisoning DSP and more recently, a new type of seafood toxicity, called amnesic shellfish poisoning ASP. View on SAGE.
|Published (Last):||13 May 2006|
|PDF File Size:||13.20 Mb|
|ePub File Size:||16.7 Mb|
|Price:||Free* [*Free Regsitration Required]|
The conditions for an algal bloom are not yet fully elucidated but the phenomenon is probably influenced by climatic and hydrographic circumstances Van Egmond and Speijers, The explosive growths sometimes appear during changes in weather conditions but important contributing causes may be variations in upwellings, temperature, transparency, turbulence or salinity of the water, the concentration of dissolved nutrients, wind or surface illumination Bower et al.
There are no reasons to assume that shellfish intoxication can be predicted by the properties of the regional area. In general, red tides often occur when heating or freshwater runoff creates a stratified surface layer above colder, nutrient-rich waters.
Fast-growing algae quickly strip away nutrients in the upper layer, leaving nitrogen and phosphorus only below the interface of the layers, called the pycnocline. Non-motile algae cannot easily get to this layer whereas motile algae, such as the dinoflagellates, can thrive. Many swim at speeds in excess of 10 metres a day, and some undergo daily vertical migration; they reside in surface water like sunbathers and then swim down to the pycnocline to take up nutrients at night.
As a result, blooms can suddenly appear in surface waters that are devoid of nutrients and seem incapable of supporting such prolific growth Anderson, It is even possible that algal species which are normally not toxic may be rendered toxic when exposed to atypical nutrient regimes e.
Changed patterns of land use, such as deforestation, can also cause shifts in phytoplankton species composition by increasing the concentrations of humic substances in land runoff. Acid precipitation can further increase the mobility of humic substances and trace metals in soils Hallegraeff, Some species produce basically harmless water discolorations. On the other hand, some species can bloom so densely, under exceptional conditions in sheltered bays, that they indiscriminately kill fish and invertebrates due to oxygen depletion.
Other algal species can be harmful to fish and invertebrates especially in intensive aquaculture systems by damaging or clogging their gills.
Furthermore, there are micro-algal species about 75 which have the capacity to produce potent toxins called phycotoxins that can find their way through levels of the food chain e. Some algal species already produce toxins at low abundances of some hundreds of cells per litre, while other algal species must occur in some millions of cells per litre in order to cause any harm.
Most of the harmful species have a restricted distribution pattern but some harmful species have a worldwide distribution Hallegraeff et al. It is not clear why some micro-algal species produce toxins. These toxins are secondary metabolites with no explicit role in the internal economy of the organisms that produce them and with very specific activities in mammals.
They are probably used by their producers as a way to compete for space, fight predation or as a defence against the overgrowth of other organisms Botana et al. During the past two decades, the frequency, intensity and geographic distribution of harmful algal blooms has increased, along with the number of toxic compounds found in the marine food chain.
Figures 1. The transportation of dinoflagellate resting cysts, especially from paralytic shellfish poisoning toxin producers McMinn et al. The resting cyst or hypnozygote is the immobile form of some dinoflagellates.
These cysts sink to the bottom of the sea and accumulate at the borderline of water and sediment where they over-winter. When favourable growth conditions return, the cysts may germinate and reinoculate the water with swimming cells that can subsequently bloom.
In this way the survival of certain dinoflagellates from one season to the other season is assured Mons et al. Incomplete elimination of harmful organisms is caused by the incomplete discharge of water and sediments in the ballast tank during reballasting Zhang and Dickman, However, mid-water exchange within regional seas for example the North Sea, Irish Sea or English Channel is less efficient than within oceanic waters.
Mid-water exchange in regional seas may reduce the risk from polluted European harbour waters but may result in the transportation of potentially harmful phytoplankton species from the regional seas Macdonald and Davidson, The most important marine phycotoxins are shellfish toxins and ciguatoxins. Until now, five groups of shellfish toxins have been distinguished, namely:. These PSP toxins are accumulated by shellfish grazing on algae producing these toxins.
Symptoms of human PSP intoxication vary from a slight tingling or numbness to complete respiratory paralysis. In fatal cases, respiratory paralysis occurs within 2 to 12 hours of consumption of the PSP contaminated food.
The PSP toxins are a group of 21 closely related tetrahydropurines see Figure 2. The PSP toxins are produced mainly by dinoflagellates belonging to the genus Alexandrium, which may occur both in the tropical and moderate climate zones.
Shellfish grazing on these algae can accumulate the toxins but the shellfish itself is rather resistant to the harmful effects of these toxins. During the last 20 years, there seems to have been an increase in intoxications caused by PSP. However, as yet it is unclear whether the increase is real, whether it could be a consequence of improved identification, detection and medical registration, or whether it is due to expanded shellfish culture and consumption.
A few dozen countries have regulations for PSP toxins. Most regulations are set for PSP toxins as a group. Diarrhoeic Shellfish Poisoning DSP in humans is caused by the ingestion of contaminated bivalves such as mussels, scallops, oysters or clams.
The fat soluble DSP toxins accumulate in the fatty tissue of the bivalves. DSP symptoms are diarrhoea, nausea, vomiting and abdominal pain starting 30 minutes to a few hours after ingestion and complete recovery occurs within three days.
DSP toxins can be divided into different groups depending on chemical structure. The first group, acidic toxins, includes okadaic acid OA and its derivatives named dynophysistoxins DTXs. The second group, neutral toxins, consists of polyether-lactones of the pectenotoxin group PTXs. The third group includes a sulphated polyether and its derivatives the yessotoxins YTXs see Figures 3. DSP toxins are produced usually by dinoflagellates that belong to the genera Dinophysis spp.
DSP toxin production may vary considerably among dinoflagellate species and among regional and seasonal morphotypes in one species. The number of dinoflagellate cells per litre of water needed to contaminate shellfish is also variable. The most affected areas seem to be Europe and Japan. DSP incidences, or at least the presence of DSP toxins, appear to be increasing and DSP toxins producing algae and toxic bivalves are frequently reported from new areas.
At this time, ASP caused three deaths and cases of acute human poisoning following the consumption of blue mussels. The symptoms included abdominal cramps, vomiting, disorientation and memory loss amnesia. The causative toxin the excitatory amino acid domoic acid or DA was produced by the diatom species Pseudo-nitzschiapungens f. In September , the unexplained deaths of pelicans and cormorants in Monterey Bay, California were attributed to an outbreak of DA poisoning produced by a related diatom Pseudo-nitzschia australis.
This diatom was consumed by anchovies that in turn were eaten by the birds. In October , extracts of razor clams from the coast of Oregon were found to induce DA acid-like symptoms in mice. These incidents prompted the regulatory authorities in the United States to conduct a massive survey of many marine species for the presence of DA. The toxin was found widely from California to Washington, and was also found unexpectedly in crabs, the first time this toxin was demonstrated in a crustacean.
Since these incidents, global awareness of DA and its producing sources has been raised Wright and Quilliam, Neurologic or neurotoxic shellfish poisoning NSP is caused by polyether brevetoxins produced by the unarmoured dinoflagellateGymnodinium breve also called Ptychodiscus breve, since called Karenia brevis.
The brevetoxins are toxic to fish, marine mammals, birds and humans, but not to shellfish. An unusual feature of Gymnodinium breve is the formation by wave action of toxic aerosols which can lead to asthma-like symptoms in humans. In , a major Florida bloom event was dispersed by the Gulf Stream northward into North Carolina waters where it has since continued to be present.
In early , more than human shellfish poisonings were reported from New Zealand caused by an organism similar to G. In November , at least eight people in the Netherlands became ill after eating mussels Mytilus edulis cultivated at Killary Harbour, Ireland. The known organisms producing DSP toxins were not observed in water samples collected at that time.
In addition, a slowly progressing paralysis was observed in the mouse assay using the mussel extracts. These neurotoxic symptoms were quite different from typical DSP toxicity Satake et al. It was then that azaspiracid formerly called Killary Toxin-3 or KT3 was identified and the new toxic syndrome was called azaspiracid poisoning AZP. Ciguatera fish poisoning CFP has been known for centuries. Endemic areas are mainly the tropical and subtropical Pacific and Indian Ocean insular regions and the tropical Caribbean, but continental reef areas are also affected Legrand, The causative toxins, the ciguatoxins, accumulate through the food chain, from small herbivorous fish grazing on the coral reefs into organs of bigger carnivorous fish that feed on them Angibaud and Rambaud, ; Lehane, In the past, the ciguatera food poisoning in humans was highly localized to coastal, often island communities of indigenous peoples.
However, with the increases in seafood trade, increased worldwide seafood consumption and international tourism, the target populations have become international. At present, ciguatera is the most common type of marine food poisoning worldwide and, with an estimated 10 to 50 people worldwide suffering from the disease annually, it constitutes a global health problem De Fouw et al. It is this lack of warning signal that has contributed to the dread of ciguatera poisoning De Fouw et al.
¿Qué son las biotoxinas?