Case diagnosis and characterisation of suspected paralytic shellfish poisoning in Alaska

In Alaska shellfish harvested for recreational uses are not routinely tested for toxins such as PSP. Between 1973 and 1996, 200 incidents of PSP were recorded although this number is expected to be higher as not everyone with PSP will seek medical attention, this is due to no symptoms or the issue of no accessible diagnostic kit. Saxitoxins (STX) contain congeners which results in a ‘cocktail’ of derivatives that vary in toxicity. These include STX, neosaxitoxin and gonyautoxins. These toxins block sodium pore channels preventing sodium entering cells. STX and neosaxitoxin are thought to be the most potent toxins, although biotransformation from low affinity to high affinity isoforms can occur.

This study tested for STX in urine by using a recently developed method of mass spectrometry. This method is developed for clinical use currently and directly detects STX without the need to oxidise or conjugate the substance, unlike previous research. This study described its patients clinically more than previous research. By the additional information provided in the tables, it is easy to see each individual’s progression through the experiment including symptoms and the timings of these symptoms. This further understanding has proved useful as it is easy to generalise and neglect human individuality and previous health conditions can allow us to see if this will effect reaction to PSP toxins.

Clinical specimens from 11 patients with suspected PSP were sent for clinical analysis of STX. Where possible unconsumed portions of shellfish were analysed for PSP toxins and associated with mouse bioassay for analysis. Nine patients had presumed PSP based on reported symptoms. The remaining two patients showed no symptoms, so PSP was not presumed despite consuming non-commercially harvested shellfish. Results showed seven patients reported paraesthesia and/or dizziness and/or chest pain, these symptoms were reported as early as 15 minutes to 28 hours after consumption. The remaining two patients died (both patients previously reported symptoms), initially presumed a result of PSP however was later attributed to other health issues. There is speculation if death was brought on by infection of PSP toxins, although it is not confirmed within the paper.

Patient D consumed 80-90 (individual) mussels and Patient G consumed 20-40, both showing symptoms one hour after consumption. Symptoms included paraesthesia, general weakness and dysphagia, with patient G also reporting dyspnea. Patients E and F both ate 3-4 mussels and showed no symptoms. By looking at the results of D and G compared to E and F it may be conclusive that higher consumption of contaminated species can increase the risk of illness. However, patient G consumed much less than D, but both had the same amount of STX/100g (5037µm/100g of shellfish) and the level of urinary STX was much higher in patient G (364µgSTX/g Cr) than patient D (47.8µgSTX/g Cr). This suggests the presence of dysphagia and dyspnea combined may be strong indicators of exposure to STX.

The historical method of mouse bioassay can be combined with the new laboratory method of screening for STX to confirm diagnostic of STX-PSP, it may be a possible in the future to develop a method to fully replace mouse bioassay. Another step forward would be a self-diagnostic kit as recreational consumption of shellfish is popular, yet unmonitored and the irregular timing of symptoms can be deadly. Further research needs to include other components of PSP toxins such as neosaxitoxins or gonyautotoxins to understand their roles in PSP. It would also be beneficial to understand how bioaccumulation of isoforms would affect urinary STX concentrations. 

Paper referenced:
Knaack, J. S., Porter, K. A., Jacob, J. T., Sullivan, K., Forester, M., Wang, R. Y., ... & Thomas, J. (2016). Case diagnosis and characterization of suspected paralytic shellfish poisoning in Alaska. Harmful algae, 57, 45-50. http://www.sciencedirect.com/science/article/pii/S1568988316300646