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Yolk sac retention / infection


Introduction

  • Cause: premature emergence from eggshell for yolk sac retention and exposure to bacteria and/or fungi, often from suboptimal conditions for infection to develop.
  • Signs: exterior yolk sac observed. Homogenous in color and texture, and yellow if healthy neonate but prematurely emerged. If not homogenous and yellow this is an indication of infection. If there is a closed umbilicus but palpable firm swelling in the coelom, this is an indication of an infected yolk sac. Skin changes: discolored, roughened. Dehydration. General malaise, lethargy, anorexia.
  • Diagnosis: based on observation and clinical signs. Visualization of yolk sac with a change in color and appearance if infected. Malodorous smell. Swabs for bacterial and fungal culture and sensitivity.
  • Treatment: if healthy individual and normal appearance to yolk sac (bright yellow and homogenous), environmental management (place in dark container lined with damp paper towels). Surgical intervention in most cases if infected.
  • Prognosis: good if premature and healthy individual. Favorable if omphalectomized with supportive care. Poor if coelomic swelling and closed umbilicus as many neonates are septic.

Presenting signs

  • Observation of an exteriorized yolk sac:
    • Homogenous in color and texture, and yellow if healthy neonate but prematurely emerged.
    • If not homogenous and yellow this is an indication of infection.
  • Palpable firm swelling in the coelom and a closed umbilicus. In a snake, coelomic mass palpable approximately 50-65% of its snout-vent length.
  • Non-specific signs:
    • General malaise.
    • Lethargy.
    • Anorexia.
  • Failure to complete the postnatal shed successfully (neonatal snake).
  • Failure to eat within 30 days (neonatal snake).
  • Behavior changes of the neonate, eg neonate seen within enclosure instead of hiding as a result of not being attended to by the parents; this can be seen in some viviparous lizards, such as prehensile-tailed skinks.

Acute presentation

  • Exteriorized yolk sac.
  • Moribund.

Age predisposition

  • Neonatal, very recently emerged from egg (oviparous reptiles) or recently from birth (viviparous reptiles).

Gender predisposition

  • No predilection.

Breed/Species predisposition

  • No predilection.

Public health considerations

  • Standard basic hygiene and PPE (gloves) when handling reptiles with exposed and infected yolk sacs.

Cost considerations

  • Minimal costs if healthy individual with a normal appearance to yolk sac (bright yellow and homogenous), environmental management often successful.
  • Substantial costs if infected; costs for stabilization, surgery, culture and sensitivity testing and post-operative management.

Special risks

  • Anesthetic risks Anesthesia overview:
    • Neonate.
    • Often septic.
    • Other underlying factors, eg localized or systemic infection if neonate has swallowed or inhaled contaminated fluid when emerging from the egg.

Pathogenesis

Etiology

  • Premature emergence from eggshell (oviparous reptiles).
  • Premature birth (viviparous reptiles).

Predisposing factors

General

  • Human intervention – checking eggs too often and provoked neonate to emerge from the eggshell too early.
  • Contaminated incubation media and an exposed yolk sac increases the risk of infection.
  • Suboptimal maternal nutrition and health as this would increase the risk of neonate immunocompromise.

Specific

  • Hybridization attempts with different subspecies increases susceptibility for yolk sac problems. Seen more commonly in certain species:
    • Prehensile-tailed skinks.
    • Galapagos tortoises.
    • Intergeneric hybrids such as jungle corn snakes.

Pathophysiology

  • The reptilian egg at oviposition comprises of the eggshell, the albumen (whites) and the yolk.
  • As incubation progresses, development of the embryo and extraembryonic membranes occurs within the egg.
  • The extraembryonic membranes include the amnion, the allantois and the chorion. The amnion surrounds the embryo. Contraction of smooth muscles in the amnion during hatching causes retraction and is responsible for the internalization of the yolk.
  • The yolk and yolk sac attach to the developing embryo at the umbilicus and continue as the vitelline duct (omphalomesenteric duct). This allows the direct transfer of nutrients from the yolk for the developing embryo’s intestines and is the primary energy source for the embryo and hatchling.
  • Yolk size decreases as the incubation period progresses and the embryo size increases.
  • Normally, the yolk sac is internalized into the coelomic cavity of the hatchling, immediately before hatching. Once the yolk is internalized the body wall closes around the navel.
  • The process of hatching and emergence from the shell takes 24-48 h. Premature emergence such as manual pipping (owners breaking eggshell and/or removing hatchling from egg) can lead to a hatchling not having completely internalized its yolk sac.
  • An exposed yolk sac places the hatchling at risk of infection, yolk sac rupture and/or strangulation.
  • Yolk sac infection may also occur even if the yolk was internalized prior to full emergence from the shell.
  • An infection may cause closure of the vitelline duct preventing the neonate receiving nutrition.
  • This may progress to generalized coelomitis and toxic metabolite production.

Timecourse

  • Recently emerged from egg.
  • Recently born.

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.
  • Keller K A (2017) Reptile perinatology. Vet Clin North Am Exotic Anim Pract 20 (1), 439-454 PubMed.
  • Pezaro N, Doody J S, Green B et al (2013) Hatching and residual yolk internalization in lizards: evolution, function and fate of the amnion. Evol Dev 15 (2), 87-95 PubMed.
  • Nechaeva M V, Makarenko I G, Tsitrin E B et al (2005) Physiological and morphological characteristics of the rhythmic contractions of the amnion in veiled chameleon (Chamaeleo calyptratus) embryogenesis. Comp Biochem Physiol A Mol Integr Physiol 140 (1), 19-28 PubMed.

Other sources of information

  • Wright K & Raiti P (2019) Breeding and Neonatal Care. In: BSAVA Manual of Reptiles. 3rd edn. Eds: Girling S J & Raiti P. BSAVA, UK. pp 70-88.