Toxic blooms and their effects according to CDC report

Toksyczne zakwity

The U.S. Centers for Disease Control and Prevention (CDC) has just released a report of submissions to the One Health Harmful Algal Bloom System (OHHABS). It is a system for recording cases in which toxic water blooms have caused medical or veterinary problems. In addition, the detection of algal toxins during water quality monitoring is reported, even without health effects. Reports are submitted by the relevant state departments. The system is not mandatory, so its data is not comprehensive, and the CDC stipulates that it is not necessarily representative of the entire country. Nevertheless, some conclusions can be drawn from them.

Toxic blooms – basic information from the report

As is usually the case with a large amount of information from different sources – verification is necessary – so the report published in July this year is based on data from 2021. They come from sixteen states. The overwhelming majority involve inland waters, most of them standing, including dam reservoirs. Therefore, as a rule, they involve cyanobacteria (more than1/3 of all cases are toxic blooms caused by the genus Aphanizomenon).

Unfortunately, reports from Texas, which is most affected by blooms caused by Prymnesium parvum, were not reported to the system, and this species does not appear in the report at all. From here, it should be remembered that in the United States a major problem, especially for aquaculture, are toxic ocean blooms caused by fur-borers or diatoms of the genus Pseudo-nitzschia (cf.“Why do seals become aggressive?“).

Most of the environmental analysis for bloom toxicity was performed as part of routine monitoring. Some were undertaken at the request of concerned users or after human or pet poisonings were found. Few cases involved reports of dead fish or suspicious odor. Interestingly, in as many as 10% of the toxin findings, there was no visible bloom. Microcystins were spotted in 89% and anatoxin-A in 17%, the second size shown in the report. Sometimes several toxins were detected in a single bloom.

Poisoning in humans and animals – similarities and differences

What is striking about the report is the differences in approach to human and animal poisoning. No fatalities were found in the first category, while as many as 92% of animal poisonings proved lethal. This may be due to the fact that in the case of humans, all suspicions are reported, including relatively mild ones, manifested by a rash or loss of appetite, which in the case of animals, even pets, may have been ignored. The high percentage of animal mortality is influenced by a case of mass poisoning of at least two thousand bats in Washington state.

In humans, 8% of cases resulted in admission to a hospital emergency department. Humans generally react with disgust to a bloom, so it’s harder to get fatally poisoned. At least as far as acute cases are concerned, meanwhile, the report does not take into account morbidity resulting from long-term intoxication or poisoning by cyanobacterial, dinoflagellate or diatomic toxins accumulated in seafood.

For humans, about half of the reports are for people under the age of 18, who may be less immune and more likely to come into contact with water, even with symptoms of a bloom. The vast majority of poisonings caused by toxic blooms resulted from direct contact with water, although in some cases the vector was air. The most common symptoms, meaning aboutone-third of cases, were diarrhea and vomiting. As a rule, they appeared about twelve hours after contact with the bloom and passed after a day. In humans, a total of 117 poisonings of various types have been reported. Most often they occurred at the beginning of the holiday season – in June. From October to April, only isolated incidents were recorded.

For animals, the most numerous illnesses caused by toxic blooms were recorded in August and September, which is in proportion to the frequency of the blooms. There is definitely less data here. Leaving aside the description of the mass poisoning of bats, these mainly involve dogs as the animals most often receiving veterinary care. Cattle were also poisoned, but the details are not known. In wildlife, basically the only recorded symptom is dark urine in fish. Symptoms of dog poisoning most often included vomiting and weakness. They appeared faster than in humans, but passed at a similar time, ie. On average, a day after poisoning.

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