Investigations on blood coagulation in the green iguana (Iguana iguana)

Coagulation testing in green iguanas (Iguana iguana) with development of prothrombin time assays using reptile and avian thromboplastin

BACKGROUND

Captive reptiles often present with clinical signs suggestive of a clotting disorder or severe illness that can induce or exacerbate a coagulopathy. However, coagulopathies in reptiles are difficult to characterize due to lack of species-appropriate reagents to perform coagulation tests. The objective of this study was to develop screening tests to evaluate the extrinsic and common pathways of coagulation in green iguanas (Iguana iguana).

KEY FINDINGS

Reptile and avian thromboplastin, extracted from reptile and avian brains, respectively, were used to initiate coagulation in prothrombin time (PT) assays and commercially available reagents were used to determine Russell's viper venom time, thrombin time, and fibrinogen using the Clauss method. Coagulation assays were performed on citrate-anticoagulated plasma from 18 healthy green iguanas. Results were summarized as median (minimum-maximum): PT (reptile thromboplastin), 34.8 seconds (27.1-42.1 s), PT (avian thromboplastin), 78.5 seconds (51.6-114.23 s), Russell's viper venom time, 56.15 seconds (18.4-79.7 s), thrombin time, 10 seconds (7.0-36.5 s), and fibrinogen, 258 mg/dl (89-563.0) (2.58 [0.89-5.63 g/L]).

SIGNIFICANCE

Commercial reagents can be used to evaluate the common pathway and fibrinogen; however, avian- or reptile-sourced thromboplastin is preferred for a reliable coagulation trigger to perform the PT assay and evaluate the extrinsic pathway.

Effects of brodifacoum and diphacinone exposure on four species of reptiles: tissue residue levels and survivorship

BACKGROUND

Anticoagulant rodenticides are used worldwide to control pest rodent species. However, the risks posed to non-target reptiles have not been well characterized. In this study, 46 giant ameivas (Ameiva ameiva), 39 boa constrictors (Boa constrictor), 33 wood turtles (Rhinoclemmys pulcherrima), and 47 green iguanas (Iguana iguana) were orally dosed with one of two levels of either diphacinone or brodifacoum anticoagulant in propylene glycol solutions. Dosages were derived using daily food intake (DFI) equations, converting DFI to an equivalent anticoagulant bait amount and gavaging the solution volume needed to deliver the quantity of anticoagulant in that amount of bait. Animals were dosed on days 0 and 7 and monitored for a further 7 days for signs of anticoagulant intoxication and differences in behaviors and postures. At necropsy on day 14, animals were examined for thoracic and abdominal bleeding, and both tissue and organ samples were taken for histology. Liver and whole-body anticoagulant residues were assessed.

RESULTS

No turtles or boas died due to anticoagulant exposure. However, anticoagulant intoxication was suspected in one iguana dosed with brodifacoum. A few treated ameivas died but exhibited no hemorrhaging. Liver residue levels were higher than whole-body remainder residue levels for all species. Unlike the other species, turtles had higher diphacinone residue levels than brodifacoum.

CONCLUSION

Turtles and boas exhibited a relative insensitivity to diphacinone and brodifacoum, while the lizards appeared to be somewhat more sensitive to these compounds. This study provides data for future assessments of the risks to these species associated with anticoagulant use. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Basic Shock Physiology and Critical Care

Veterinarians practicing emergency medicine and/or working with exotic animals must be well versed in the pathophysiology of shock because many exotic pets present with an acute crisis or an acute manifestation of a chronic process causing poor organ perfusion. This article discusses the pathophysiology of shock and the systemic inflammatory response syndrome, which may lead to organ dysfunction, organ failure, sepsis, and death. The physiology of perfusion, perfusion measurements, categories of shock, and altered function of the immune system, gastrointestinal barrier, and coagulation system are discussed. Veterinarians providing emergency care to patients with shock must also be aware of comorbidities.

Comparative aspects of blood coagulation

Blood coagulation is a basic physiological defense mechanism that occurs in all vertebrates to prevent blood loss following vascular injury. In all species the basic mechanism of clot formation is similar; when endothelium is damaged a complex sequence of enzymatic reactions occurs that is localized to the site of trauma and involves both activated cells and plasma proteins. The reaction sequence is initiated by the expression of tissue factor on the surface of activated cells and results in the generation of thrombin, the most important enzyme in blood clot formation. Thrombin converts soluble fibrinogen, via soluble fibrin monomers, into the insoluble fibrin that forms the matrix of a blood clot as well as exerting positive-feedback regulation that effectively promotes additional thrombin generation that facilitates the rapid development of a thrombus. Both spontaneous and trauma-induced haemorrhagic episodes can develop in all mammals with inherited or acquired abnormalities in one or more of the coagulant proteins. Experimental studies with plasma from a wide range of species have led to the conclusion that there are extensive differences in the rates of thrombin generation and fibrin formation among species. However, current evidence suggests that at least some of these quantitative differences are likely due to the use of non-species specific laboratory reagents. Although the individual proteins involved in the procoagulant pathways exhibit similar functions in all animals, differences in amino acid sequence cause incomplete homology and varying degrees of immunological cross-reactivity for the same protein across species.