Exotis ISSN 2398-2985

Reptiles

Renal disease

Synonym(s): Kidney disease

Contributor(s): Vicky Strong, Bruce Maclean

Introduction

  • Cause: various including infectious, degenerative, dietary, neoplastic, toxic, nutritional, inherited, anomalous. Note: the vast majority of reptiles which present with renal disease have chronic changes for which the underlying etiology cannot be determined.
  • Signs: often non-specific, and include lethargy, anorexia, weight loss and dehydration.
  • Diagnosis: clinical signs, complete blood count, plasma biochemistry, urinalysis, imaging.
  • Treatment: identification +/- elimination of underlying cause, fluid therapy, antibiotic therapy (if indicated), supportive care, +/- allopurinol.
  • Prognosis: depends upon cause and stage of diagnosis. Many animals are diagnosed at late stage with advanced chronic renal damage and so prognosis can be poor.
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Pathogenesis

Etiology

  • Chronic dehydration.
  • Pathogen-related renal damage.
  • Inflammatory renal damage.
  • Toxin-related renal damage (myolysis products, ingested toxins).
  • Neoplasia .

Predisposing factors

General

  • Poor husbandry, eg inadequate humidity, improper temperature settings (eg too hot, no gradient) leading to dehydration Chelonia husbandry Lizard husbandry Snake husbandry.
  • Improper diet Nutritional requirements, eg excess protein (meat feeding of herbivorous species), hypovitaminosis A Hypovitaminosis A.
  • Stress, eg caused by overcrowding.
  • Poor hygiene (can result in ascending infections and therefore bacterial pyelonephritis).
  • Underlying illness, especially if requiring drug administration.
  • Genetic predisposition.

Specific

  • Inappropriate humidity: many basking lights can be dangerously dehydrating if the animal needs to bask extensively to reach POTZ.
  • Offering water in inappropriate form (some species/individuals will not drink from standing water). Some individuals will also reject water in certain plastic containers.

Pathophysiology

Chronic renal disease and gout

  • The vast majority of reptiles that present with renal disease have chronic changes for which the underlying etiology cannot be determined.
  • These changes include:
    • Glomerular +/- tubular degeneration and/or necrosis.
    • Interstitial and glomerular fibrosis.
    • Dystrophic calcification.
    • Gout crystal deposition.
  • Pathogenesis is typically multifactorial, stemming from an underlying chronic history of inadequate husbandry, improper diet +/- chronic dehydration.
  • Gout can be the cause or a consequence of renal disease. Uric acid is the end-product of reptile protein metabolism. It can therefore build up due to:
    • Protein metabolism or catabolism, and therefore uric acid production, exceeding uric acid excretion, eg due to an inappropriately high protein, meat based diet in herbivores/omnivores.
    • Severe dehydration.
    • Renal failure.
  • When uric acid levels are chronically high, uric acid crystals become deposited within the tubular epithelium, and begin to accumulate. Over time, the crystals break through the basement membrane into the deeper tissues and are accompanied by an inflammatory response (forming gout tophi). The result is progressive renal damage and dysfunction.
  • Gout crystal deposition can also occur within numerous other organs throughout the body (visceral gout).

Specific etiologies associated with renal disease

Infectious causes
  • Parasitic:
    • Protozoa, eg coccidia, microsporidia, entamoeba, spironucleus (hexamita), myxosporidia.
    • Metazoa, eg trematodes, strongyloids.
  • Bacterial, eg:
    • Ascending infections from the lower urinary tract.
    • Bacterial sepsis, secondary to immunosuppression (caused by, eg overcrowding, stress, improper diet or husbandry).
    • Hematologic spread of bacteria from, eg bite or thermal injury.
    • Most commonly gram-negative bacteria, eg Pseudomonas spp, Aeromonas spp (Myocobacterial infections have also been reported but are uncommon).
  • Viral:
    • Viral infections, specifically affecting the kidneys, are uncommon in reptiles.
    • Inclusion body disease, which mostly affects boas and vipers but also pythons, can affect the epithelial cells of many organs including the kidneys.
Toxins
  • Nephrotoxic drugs, eg aminoglycosides (gentamicin Gentamicin, amikacin Amikacin), and some sulfonamide-containing antibiotics:
    • Risk increased if high doses are used or if the animal is dehydrated.
    • Reptiles have a renal portal system, which receives blood from the lower third of the body and shunts it via the kidneys to the heart, bypassing the liver. There is some belief that this system might make reptiles particularly prone to nephrotoxicity if drugs are delivered by injection into the caudal third of the body. The true clinical significance of this, however, is not known. Note that the renal portal system perfuses the tubules, not the glomeruli; drugs excreted by glomerular filtration should be unaffected.
    • Cause renal tubular damage and/or gout crystal formation.
  • Heavy metals, eg lead (foreign body ingestion).
Nutritional
Neoplasia
  • The main renal tumors reported in reptiles are adenocarcinoma, adenoma, nephroblastoma.
Vascular
  • Any disease process which causes a reduction in renal perfusion, or thromboemboli can cause renal damage and therefore failure.
Deposition disorders
  • The deposition of various substances within the kidney can be associated with renal injury or damage. In some instances, the deposition itself might be the primary inciting cause, in others it might be an effect, but nonetheless play a role in the ongoing pathogenesis.
  • Nephrocalcinosis:
    • Metastatic mineralization; due to disturbance in calcium metabolism.
    • Dystrophic mineralization; occurs secondary to cellular/tissue injury.
  • Amyloidosis.
  • Cholesterol.
  • Gout (see earlier) Gout.
  • Pigmentation, eg lipofuscin, hemosiderin, bile.
Anomalies or inherited disorders
  • Agenesis/hypoplasia.
  • Renal cysts.

Timecourse

  • Incubation very variable depending on cause; usually unknown. May be chronic damage over years, or rapid toxic effect.

Epidemiology

  • Environmental issues will accumulate effect over time - older/longer resident individuals will tend to be affected first.
  • Toxins may have acute and/or chronic effects.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Reavill D R & Schmidt R E (2010) Urinary tract diseases of reptiles. J Exotic Pet Med 19 (4), 280-289 VetMedResource.
  • Miller H A (1998) Urinary diseases of reptiles: pathophysiology and diagnosis. Semin Avian Exotic Pet Med 17 (2), 93-103 JExoticPetMed.

Other sources of information

  • Wright K (2013) Diagnosing and Managing Renal Disease in Reptiles. In: Proc Assoc Reptilian and Amphibian Veterinarians. pp 127-132.
  • Hernandez-Divers S J & Innis C J (2006) Renal Disease in Reptiles: Diagnosis and Clinical Management. In: Reptile Medicine and Surgery. 2nd edn. Ed: Mader D. Saunders Elsevier, USA. pp 878-892.
  • Johnson J D (2004) Urogenital System. In: BSAVA Manual of Reptiles. 2nd edn. Eds: Girling S J & Raiti P. pp 261-272.


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