Poisonings in the Captive Reptile

Chapter 27 Poisonings in the Captive Reptile









EMERGENCY MANAGEMENT OF THE POISONED REPTILE


Emergency situations in reptiles are not always obvious for veterinarians and certainly not for average reptile owners. Many veterinarians are not familiar enough with the anatomy, physiology, and vital signs of captive reptile species. In addition, like other wild animals, exotic reptiles do much to mask outward signs of disease. However, the basic tenets of emergency medicine remain the same regardless of species.


Emergency care begins with a sound history. How long has the reptile been in the home, what is its origin, are cage mates involved, what type of cage setup is employed, heat and light sources (how long a photo period and how warm is the cage setting?) are all pertinent questions. How often is the animal fed and watered, what type of diet is used, how often is the environment cleaned and with what cleaners? This pattern of questioning can help the clinician more closely focus on the cause of the problem.


Next a thorough physical examination is performed. Heart rate, respiration, hydration status, neurological condition, and mentation are all critical cues to both diagnosis and prognosis. However, physical examination and clinical signs are only part of obtaining a successful diagnosis. Laboratory parameters will also help determine what treatment modalities are necessary. Still the maxims—treat the patient not the poison and treat the patient not the lab—are more than empty slogans and bear remembering.


Reptiles injured or seriously ill nearly always benefit from administration of fluids. Various methods of fluid administration are touted, but actually intravenous fluid therapy is not practical for most reptiles. Many reptiles (particularly desert species) can tolerate dramatic degrees of dehydration. Lizards, snakes, and turtle relatives all show sunken eyes and changes in skin if dehydrated. Intraosseous catheters are a legitimate alternative to intravenous types. Enteral, intracoelomic, and subcutaneous fluids are also available to support the poisoned reptile.


Reptiles are ectothermic and dependent on environmental temper-ature for their warmth. Reptilian species have their own preferred body temperature and optimum thermal zone. For most temperate species, a range of 72° F to 75° F to 82° F to 85° F is fairly safe. Debilitated reptiles can be so weak that they cannot move away from heat sources and may end up overheating or even being burned. Use only safe heat sources, such as heating small rooms, overhead heat lights, and under-tank heating pads. Cage thermometers must be diligently monitored to ensure animals are kept within a safe thermal range. Rigorous, persistent nursing care can often help save severely poisoned reptiles.



COMMON TOXICANTS





Antimicrobial toxicity


Selection of antibiotics should be made judiciously. Selection depends on experience of the clinician, empirical considerations, the type of infection present based on culture and sensitivity and Gram stains, and, last but not least, the size, age, species, and condition of the reptilian patient. There is no antibiotic that can be relied upon to be effective for all situations. In addition, antibiotics are no substitute for good wound management, nursing care, nutrition, or husbandry.



GENTAMYCIN.


Gentamycin is an aminoglycoside antibiotic. Other aminoglycosides include amikacin, tobramycin, neomycin, streptomycin, and kanamycin. Gentamycin is bactericidal and is a broad spectrum antibiotic (except against streptococci and anaerobic bacteria).4 Its mechanism of action involves inhibition of bacterial protein synthesis by binding to 30S ribosomes. Gentamycin is indicated for acute serious infections, such as those caused by gram-negative bacteria. Amikacin is more consistently active against resistant strains of bacteria.


Nephrotoxicity of gentamycin in reptiles is well documented.58 Patients must have adequate fluid and electrolyte balance during therapy. Ototoxicity in reptiles has also been reported. Recommended dosage for gentamycin varies from 1.5 to 2.5 mg/kg given no sooner than every third day.




CHLORAMPHENICOL.


Chloramphenicol is an antibacterial agent with a broad spectrum of activity against gram-positive bacteria, gram-negative bacteria, and Rickettsia. Its mechanism of action is by inhibition of bacterial protein synthesis by binding with ribosomes.


The major toxicity of chloramphenicol is hematological.9 In all vertebrates studied, it produces direct, dose-dependent bone marrow depression resulting in reductions in red blood cells, white blood cells, and platelets. This manifestation is aggravated by inappropriate doses, extended treatments, and repeated use of the drug. Treatment of chloramphenicol intoxication is supportive and may require blood transfusions. The drug has also been reported to be appetite suppressive. Like gentamycin, chloramphenicol is being used less frequently as safer antibiotics appear. The recommended dosage for chloramphenicol is 50 mg/kg administered once daily or every other day.



ENROFLOXACIN.


Enrofloxacin is a fluoroquinolone antibacterial drug. It is bactericidal with a broad spectrum of activity. Its mechanism of action involves inhibition of deoxyribonucleic acid (DNA) gyrase, thus inhibiting both DNA and ribonucleic acid (RNA) synthesis.4 Sensitive bacteria include Staphylococcus, Escherichia coli, Proteus, Klebsiella, and Pasteurella. Pseudomonas is moderately susceptible, but requires higher doses. In most species studied, enrofloxacin is metabolized to ciprofloxacin. Damage to cartilage has been seen in growing animals treated with fluoroquinolones. Doses of enrofloxacin range from 2.5 to 5 mg/kg. There are other choices of antibiotics for use in reptiles, based on Gram staining, culture and sensitivity, and age of the animal.




Antifungal toxicity


A variety of fungal infections have been documented in reptiles. Ranging from dermatophytes to systemic mycotic infections, these conditions are treated with a variety of antifungal medications. Often caused by the small size of the reptilian patient, the mechanism of action of these drugs, and idiosyncrasies of reptilian physiology, treatment with antifungals can lead to serious intoxications.



AMPHOTERICIN B.


Amphotericin B is a macrolide class antibiotic unrelated to erythromycin. This antifungal inhibits ergosterol synthesis.13 Ergosterol is a component of the cell membrane unique to fungal organisms. Amphotericin is a potent nephrotoxin.14 It produces signs of renal toxicity in 80% of patients that receive it. Its action causes renal vasoconstriction, reduces glomerular filtration rate, and has direct toxic effects on the membranes of the renal tubule cells. Through these mechanisms, amphotericin B causes acute tubular necrosis. Hypokalemia develops in almost 35% of human patients treated with amphotericin, which is sufficient to warrant potassium supplementation.


Clinical signs mimic acute renal failure: anorexia, lethargy, weight loss, and other signs. Elevated blood urea nitrogen (BUN) and creatinine with decreased potassium and sodium are commonly seen.15


Treatment includes discontinuing the drug, aggressive fluid therapy to prevent further kidney damage, and diminishing renal effects with sodium chloride-containing fluids. Treatment with mannitol may help increase the elimination of amphotericin B.


Prognosis after amphotericin B toxicity depends upon the severity of the renal damage. Amphotericin B is still listed as a treatment for aspergillosis in reptiles (1 mg/kg intracoelomically once daily for 2 to 4 weeks).16 There may be safer drugs available. A less toxic, new formulation of amphotericin B is available for humans and may soon be available for veterinary use. Amphotericin B should not be used in animals that already have renal disease.




IMIDAZOLES (KETOCONAZOLE) AND TRIAZOLES (FLUCONAZOLE AND ITRACONAZOLE).


These antifungal drugs inhibit fungal replication by interfering with ergosterol synthesis. Ketoconazole also has direct effects upon the fungal membrane. The liver metabolizes these fungistatic drugs. Itraconazole is more potent than ketoconazole and is better tolerated by patients.


Clinical signs of intoxication include anorexia, lethargy, weight loss, and diarrhea. Elevated liver enzymes may be present in intoxicated animals. Dosages recommended for reptiles include 2 to 5 mg/kg orally daily for 5 days for fluconazole, 25 mg/kg given orally daily for 3 weeks for ketoconazole, and 23.5 mg/kg orally once daily for itraconazole.18 There seems to be little problem with miconazole preparation applied topically.19


There is no specific antidote for toxicity by these antifungals. Treatment involves stopping the drug, decontaminating any topical material remaining, and supportive therapy (fluids, warmth). For ketoconazole, treatment includes countering the hepatotoxicity. Mild intoxications usually improve with simple cessation of the drug.


The safest, most effective drugs must be selected for use in fungal infections in reptiles and must reflect the severity of the infection, the size of the animal, and the condition of the animal before treatment. Doses must be meticulously checked, particularly for topicals and dips to be used on reptiles. Finally, reptiles must never be left alone in any bath or medicated dip.



Organophosphates and carbamates


Organophosphates are the most commonly used insecticide worldwide. In the United States alone, 250 million pounds of organophosphates are used annually at a cost of $2.4 billion to produce.20 They are found in agriculture, in the home, and on or around various domestic animals. Some organophosphates are meant to stay on surfaces to which they are applied, and others are absorbed and become systemic in animals. They are the active ingredients in a long list of products. For animal use as insecticides, they are formulated as dips, sprays, topical medications, systemic parasitic agents, and flea collars. This group of insecticides includes chlorpyrifos (Dursban), dichlorvos, diazinon, cythioate (Proban), fenthion (ProSpot), malathion, ronnel, parathion, metrifonate, and vapona. Their cousins, the carbamates, include aldicarb, carbaryl (Sevin), bendiocarb, methiocarb, propoxur, and carbofuran. As newer, safer insecticides are marketed, these two groups are involved in fewer accidental poisonings, but still account for a large number of intoxications.


Organophosphates and carbamates interfere with metabolism and breakdown of acetylcholine at synaptic junctions.21 Acetylcholinesterase is the enzyme responsible for breaking down the neurotransmitter at these sites. Acetylcholinesterase is inhibited by organophosphates and carbamates at these cholinergic sites. As a result, acetylcholine accumulates at the synapses, which at first excites and then paralyzes transmission in these synapses, giving it the characteristic “nerve gas” signs associated with organophosphate toxicity.22 This inhibition of the synapse is irreversible with organophosphates and reversible with carbamates. Organophosphates are readily absorbed by all routes: dermal, respiratory, gastrointestinal, and conjunctival. Overdose with organophosphates may happen more readily if given together with imidothiazoles, such as levamisole.


Clinical signs seen in reptiles include salivation, ataxia, muscle fasciculations, inability to right themselves, coma, and respiratory arrest. Death results from massive respiratory secretions, bronchiolar constriction, and effects upon respiratory centers in the medulla leading to the cessation of breathing.


Animals with dermal exposure should be washed with a mild dishwashing detergent and copious amounts of water. Animals should be dried after rinsing to prevent further uptake of the insecticide. The need for fluid therapy to counter dehydration and electrolyte imbalances should be considered. The specific physiological antidote, the muscarinic antagonist atropine, should be given (0.4 mg/kg intramuscular [IM]). This should help with salivation, bronchospasm, and dyspnea. Diazepam may be given as needed for seizures. Use of antihistamines to treat insecticide poisonings is controversial and most likely not that effective. Prognosis is dependent upon dose, duration of exposure, and size of the animal. Therapies both more effective and safer than organophosphates and carbamates exist for treatment of parasites in captive reptiles. These therapeutic regimens are outlined in detail elsewhere in various sources dealing with reptilian parasitology.



Pyrethrins and pyrethroids


Pyrethrin is the oldest used botanical insecticide. It is made from the dried and ground flowers of Chrysanthemum cinerariifolium. Pyrethroids are synthetic derivatives of pyrethrin and are widely available. Pyrethroid insecticides have enhanced stability, potency, and half-life compared with the parent molecule. A variety of dilute pyrethrin- and pyrethroid-containing sprays have been recommended for reptiles.


The mechanism of action of both pyrethrins and pyrethroids is the same. These molecules affect parasites by altering the activity of the sodium ion channels of nerves. These poisons prolong the period of sodium conductance and increase the length of the depolarizing action potential.23 This results in repetitive nerve firing and death. With the right conditions or at higher doses, these compounds can intoxicate host animals. Because of the potential for transcutaneous absorption, pyrethrin and pyrethroid sprays must be thoroughly rinsed from the animal immediately after their application. Rinsing with lukewarm water is usually sufficient.


Like ivermectin, organophosphates, and carbamates, pyrethrins and pyrethroids should never be given concurrently with cholinesterase-inhibiting compounds.


Clinical signs have been reported for pyrethrins and pyrethroids, particularly if sprays used also contain insect growth regulators (e.g., methoprene). Signs can develop in animals within 15 minutes of application. Signs include salivation, ataxia, inability to right themselves, and muscle fasciculations.24 Idiosyncratic reactions to pyrethrins can happen at much lower doses than expected. A small percentage of animals appear to be extremely sensitive to pyrethrins and pyrethroids.


If caught early enough, treatment for pyrethrin and pyrethroid toxicity involves dermal decontamination (bathing in copious amounts of water), isotonic fluids, and diazepam for seizures. Care must be taken to keep pyrethrin and pyrethroid sprays away from the reptile’s eyes and mouth to prevent intoxication. Prognosis depends on the strength of the agent used, the duration of the exposure, and the size of the animal involved. Animals do best that are treated early.


A variety of pyrethrins and pyrethroids have been recommended for use against reptile parasites. If used prudently, they are both safe and effective. Animals are sometimes saturated with the spray. As soon as the parasiticide is applied, it should be rinsed off. Gently running lukewarm tap water should be used to wash off the insecticide. This very brief exposure is enough to kill the parasites. Pyrethrin and pyrethroid sprays should not be left on so as to prevent absorption and systemic toxicity in host animals. In smaller animals that have larger surface-to-volume ratios, most sprays should be diluted to the smallest effective dose to prevent accidental intoxication from transcutaneous absorption.



Ivermectin


Ivermectin is an antiparasitic from a family of chemicals called avermectins. These are macrocyclic lactones made from the fermentation broth of the fungus Streptomyces avermitilis.25 The macrolide ivermectin is available as an injectable, a spray, and an oral formulation. It has activity against a variety of parasites including nematodes, arthropods, and arachnids.


Avermectins work by potentiating the effects of the inhibitory neurotransmitter, γ-aminobutyric acid (GABA). They stimulate release of GABA by presynaptic sites and increase GABA binding to postsynaptic receptors. This causes neuromuscular blockage. Avermectins also open chloride channels in membranes of the nervous system and further depress neuronal function. These actions cause paralysis and death of susceptible parasites. Ivermectin is absorbed systemically by host tissue. When parasites bite the host they then absorb the ivermectin. Ivermectin is active against intestinal parasites, mites, microfilaria, and developing larva. Concurrent treatment with diazepam, which also works through GABA potentiation, may heighten deleterious effects.


Ivermectin can cause depression, paralysis, coma, and death in chelonians.26 Species susceptible to ivermectin toxicosis may have a blood-brain barrier more permeable than in nonsensitive species. This greater permeability may be due to p-glycoprotein mutation in membranes of the CNS. Another theory postulates the existence of a specific protein receptor only present in the brains of ivermectin-sensitive species. This has not yet been demonstrated. Ivermectin toxicity has also been reported in several species of lizards and snakes.27 Ball pythons (Python regius) in particular may show mild neurological signs when treated. As a result if there is any question regarding safety, it may be more prudent to use ivermectin only as a topical.


There is no known antidote or physiological antagonist for ivermectin. Treatment is supportive and should include decontaminating any topical sprays with soap and water, providing fluid therapy, nutritional support, monitoring electrolytes, and respiratory support. Recovery may take days to weeks. One debilitated tortoise recovered fully after 6 weeks. We have seen two box turtles completely recover in 4 weeks.


Ivermectin, and similarly related compounds, should never be given to chelonians, pregnant animals, or neonatal individuals. Also, for particularly tiny species, other therapies should be investigated. If there is any question, use it only as a topical or find an alternative.



Fenbendazole


Fenbendazole is a benzimidazole type of antiparasitic drug.28 It is safe and effective against many helminth parasites in animals. Fenbendazole inhibits glucose uptake in the parasites. Because of its wide range of activity, its high degree of efficacy, and its broad margin of safety, this anthelmintic is frequently prescribed by veterinarians. Fenbendazole has a good margin of safety and has been reported to be well tolerated, even at six times recommended dose and three times recommended duration. It has been extensively used as an anthelmintic therapy in reptiles at a dosage of 50 to 100 mg/kg PO once (repeated in 2 weeks) or 50 mg/kg PO q 24 hours for 3 to 5 days.30,31


Toxic effects have been reported in birds, rats, cats, and dogs.3236 Recently, evidence of fenbendazole overdose has been reported in individuals of a small snake species given an exceedingly large dose of the drug. Four adult Fea’s vipers (Azemiops feae) died after being administered single doses of fenbendazole ranging from 428 mg/kg to 1064 mg/kg.29 Necropsy findings were suggestive of intestinal changes consistent with fenbendazole toxicity. Fenbendazole is regarded as a safe anthelmintic drug at recommended therapeutic doses.



Chlorhexidine toxicity


Soaking living animals in any solution can be potentially life threatening. Recently, turtles soaked for 1 hour in chlorhexidine scrub were shown to become intoxicated.37 Cutaneous absorption of the solution and possible oral ingestion of these soaks have been postulated as the cause of the problem. Before using any substances as a soak, review the literature for preferred usage, dose, and duration of the soak. Affected animals should be removed from the soak, rinsed, and supported with warmth and fluids. Remember to never leave any reptile unattended in a bath. Animals can drown much faster than anticipated. Also, particular attention must be paid to the depth of fluids reptiles are bathed and soaked in.



Bleach


Various hypochlorite bleach solutions can be found in most households. Typically, these are 3% to 6% hypochlorite solutions in water.38 Bleaches are moderately irritating. If contact with skin is prolonged, the damage is worsened. Bleaches can be very effective in treating cage parasites of reptiles, but should never be applied to live animals. Bleach can cause alkali burns if splashed in the eyes of lizards and turtles. Immediate irrigation of the eye with copious amounts of water minimizes the damage done by the bleach. Skin exposed to bleach should be washed with a mild soap and lukewarm water. Animals should be kept out of recently bleached cages a minimum of 24 hours to prevent respiratory tract irritation. Cages should be allowed to air out, and residual disinfectant removed by wiping with a clean cloth or towel.

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Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on Poisonings in the Captive Reptile
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