Use of intravenous lipid emulsion therapy as a novel treatment for brevetoxicosis in sea turtles

Abstract

The southwest coast of Florida experiences annual red tides, a type of harmful algal bloom that results from high concentrations of Karenia brevis. These dinoflagellates release lipophilic neurotoxins, known as brevetoxins, that bind to sodium channels and inhibit their inactivation, resulting in a variety of symptoms that can lead to mass sea turtle strandings. Traditional therapies for brevetoxicosis include standard and supportive care (SSC) and/or dehydration therapy; however, these treatments are slow-acting and often ineffective. Because red tide events occur annually in Florida, our objective was to test intravenous lipid emulsion (ILE) as a rapid treatment for brevetoxicosis in sea turtles and examine potential impacts on toxin clearance rates, symptom reduction, rehabilitation time, and survival rates. Sea turtles exhibiting neurological symptoms related to brevetoxicosis were brought to rehabilitation from 2018–2019. Upon admission, blood samples were collected, followed by immediate administration of 25 mg ILE/kg body mass (Intralipid® 20%) at 1 mL/min using infusion pumps. Blood samples were collected at numerous intervals post-ILE delivery and analyzed for brevetoxins using enzyme-linked immunosorbent assays. In total, nine (four subadults, one adult female, four adult males) loggerheads (Caretta caretta), five (four juvenile, one adult female) Kemp’s ridleys (Lepidochelys kempii), and four juvenile green turtles (Chelonia mydas) were included in this study. We found that plasma brevetoxins declined faster compared to turtles that received only SSC. Additionally, survival rate of these patients was 94% (17/18), which is significantly higher than previous studies that used SSC and/or dehydration therapy (47%; 46/99). Nearly all symptoms were eliminated within 24–48 h, whereas using SSC, symptom elimination could take up to seven days or more. The dosage given here (25 mg/kg) was sufficient for turtles in this study, but the use of a higher dosage (50–100 mg/kg) for those animals experiencing severe symptoms may be considered. These types of fast-acting treatment plans are necessary for rehabilitation facilities that are already resource-limited. Intravenous lipid emulsion therapy has the potential to reduce rehabilitation time, save resources, and increase survival of sea turtles and other marine animals experiencing brevetoxicosis.

Emerging Insights into Brevetoxicosis in Sea Turtles

“…Plasma and whole blood PbTx-3 concentrations in live stranded green turtles appear to be lower than those found in loggerheads and Kemp's ridleys [40]. This difference may, in part, be a result of dietary preference [25,41]. Plasma brevetoxin concentrations in smaller sea turtles, as measured by both mass and carapace length, have been observed to be higher than in larger individuals [40].…”

“…These turtles were provided with fluid therapy, which was expected to dilute plasma brevetoxins. The observed increases in plasma brevetoxin concentrations may be attributed to the continued digestion of contaminated prey and reabsorption of brevetoxins from the gut [40,41]. Clearance rates may also depend on the sea turtle species involved.…”

“…The west coast of Florida is near-annually affected by these blooms, with some blooms lasting over one year [12]. From 2000 to 2020, red tide blooms were present for 7 ± 3 months per year on average, although blooms lasted anywhere from 1 to 17 months [41].…”

“…Furthermore, seizures may occur in severe cases [140]. While moderate symptoms may impair the animals' ability to forage and evade predators, generalized lethargy and partial paralysis may compromise the animals' ability to swim and breathe [41]. This may result in an increase in entanglements and boat strikes, which has been reported in stranded brevetoxin-afflicted sea turtles [42].…”

“…Brevetoxin-afflicted sea turtles may present with a variety of secondary conditions. Frequently reported conditions include bacterial infection, dehydration, hypoglycemia, gastrointestinal ailments, anemia, malnutrition, spirorchiid infection, and metabolic acidosis [41]. Fungal infections, in particular fungal pneumonia, may also be present in affected sea turtles [140].…”