Lethal methemoglobinemia in the invasive brown treesnake after acetaminophen ingestion

Tom Mathies,Richard E Mauldin

doi:10.1038/s41598-019-56216-1

Abstract

The invasive brown treesnake (Boiga irregularis) has extirpated much of Guam’s native birdlife and poses significant threats to other parts of the western Pacific. Acetaminophen (APAP) is a proven lethal oral toxicant in reptiles but the physiological mechanism is unknown. The effects of a lethal APAP oral dose on methemoglobin (MetHb, non-oxygen carrying form) levels and other blood parameters were examined in brown treesnakes. Co-oximetry was used to measure MetHb (%) and other hemoglobin species. Assessment of red blood cell integrity, white blood cell differential counts, and plasma biochemical analyses were conducted to evaluate tissue damage, stress, and liver function. Changes in oxygen carrying capacity were noted in APAP-treated snakes indicated by a 50–60% increase in methemoglobin levels and a 40% decrease in oxyhemoglobin (oxygen-carrying form) levels compared to controls. APAP-treated snakes had decreased lymphocyte and increased monocyte counts while also having increased levels of blood analytes associate with impaired liver function and muscle damage. The proximate cause of death in APAP-treated snakes was likely acute methemoglobinemia and respiratory failure due to severe hypoxia with no observed signs of distress or pain. An orally-ingested lethal dose of APAP appears to be a humane method for lethal control of this species.

Highlights

The invasive brown treesnake (Boiga irregularis) has extirpated much of Guam’s native birdlife and poses significant threats to other parts of the western Pacific
We examined red blood cells for abnormalities, evaluated white blood cell differential counts as indices of stress, and characterized plasma chemistry for changes in analyte levels associated with liver and muscle damage
Mean O2Hb for APAP and C groups was similar at 2.4 h post dose but declined linearly in the APAP group to a minimum at 12 h post-dose (Fig. 1A)

Summary

Introduction

The invasive brown treesnake (Boiga irregularis) has extirpated much of Guam’s native birdlife and poses significant threats to other parts of the western Pacific. The effects of a lethal APAP oral dose on methemoglobin (MetHb, non-oxygen carrying form) levels and other blood parameters were examined in brown treesnakes. Changes in oxygen carrying capacity were noted in APAP-treated snakes indicated by a 50–60% increase in methemoglobin levels and a 40% decrease in oxyhemoglobin (oxygen-carrying form) levels compared to controls. APAP-treated snakes had decreased lymphocyte and increased monocyte counts while having increased levels of blood analytes associate with impaired liver function and muscle damage. An orally-ingested lethal dose of APAP appears to be a humane method for lethal control of this species. It was previously determined that an orally-delivered 80 mg dose of APAP was lethally toxic to brown treesnakes (n = 29, 47–300 g body mass) resulted in 100% mortality within 24 h High blood MetHB concentrations (methemoglobinemia) can be lethal because MetHb cannot bind or release oxygen[8], resulting in death by anaemic hypoxia[9]

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Discussion

Conclusion