ISSN 2398-2985      

Cryptosporidiosis

Jreptile

Introduction

  • Cause: infection with Cryptosporidium spp; Cryptosporidia is an apicomplexan coccidian protozoa with a direct life cycle. Phylogenetic analyses have identified two major clades of Cryptosporidium spp - one with tropism for the intestine, the other for the stomach. Two types of oocysts can be formed: thin-walled oocysts which immediately re-infect the host, whilst thick-walled oocysts are excreted in feces allowing persistence in the environment and transmission. Multiple species have been identified in reptiles.
  • Signs: generally associated with the gastrointestinal tract and dependent on whether the infection is with the gastric or enteric form, eg diarrhea, weight loss, vomiting or regurgitation. Body swellings, eg associated with hypertrophic gastritis, can be noted, particularly in snakes. Extra-enteric infections are also possible.
  • Diagnosis: often challenging. Fecal wet mount direct smear or fecal flotation microscopy, often with modified Ziehl-Neelsen staining, although reliable morphological species identification is not possible and false negatives are common due to intermittent fecal shedding of oocysts. IFAT or PCR testing are used for speciation. Gastric washes or biopsies, or intestinal biopsies for histopathology may be required for diagnosis, and in some cases, diagnosis may only be feasible via post-mortem. Differentiation of species affecting reptiles and those from prey animals, ie ‘pass-through’ pseudoparasites, is important but can be challenging.
  • Treatment: no reliable treatment currently available. Euthanasia is recommended for seriously affected clinical cases.
  • Prognosis: guarded in cases showing clinical signs, although asymptomatic carriage appears to be common. Can be devastating within a collection with high levels of morbidity.

Pathogenesis

Etiology

  • Infection with Cryptosporidium spp, C. serpentis and C. varanii (= C. saurophilum) appear to be the main species associated with infection in reptiles, although others have been isolated.
  • C. serpentis is primarily seen in snakes as a gastric form, whereas C. varanii is more commonly seen in lizards and has an enteric form.
  • None of these species have yet been reported to be zoonotic.
  • C. parvum and C. muris have been found in reptile feces, likely from mammalian prey items as pseudoparasites. These do not appear to cause harm to the reptile but might potentially be zoonotic and could be infective to other mammals.

Predisposing factors

General

  • Exposure to and ingestion of cryptosporidial oocysts.

Specific

  • Immunosuppression due to concurrent disease and/or stress such as from overcrowding, poor enclosure hygiene, etc, especially in young stock.
  • Concurrent illness or coinfections, eg with adenovirus, may predispose to developing clinical disease.

Pathophysiology

  • Pathogenicity does not seem to depend on the number of parasites, but more the lowered immunocompetence of the host or presence of concurrent disease.
  • Transmission is via the fecal-oral route, ie ingestion of oocysts through direct contact or contaminated environments.
  • Ingested sporulated oocysts each produce four sporozoites in the gastrointestinal tract which develop into trophozoites in parasitophorous vacuoles within gut epithelial cells. Merozoites are formed and further cycles can continue alongside oocysts formed by sexual reproduction. These can autoinfect or be shed in feces. Shed oocysts are immediately infective and are very resistant within the environment.
  • Clinical signs result from the gastric or enteric inflammation and subsequent maldigestion of food.
  • Coinfections with other agents such as adenoviruses may increase the chance of development of clinical signs.

Timecourse

  • Variable: from days to years before clinical signs become apparent.

Epidemiology

  • Can become prevalent within a group via ingestion of infective oocysts either from direct contact or a contaminated environment (this is compounded by the resistance of oocysts to environmental disinfection).

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

Other sources of information

  • Brown S J L, Naylor A D, Machin R A & Pellett S (2019) Gastrointestinal System. In: BSAVA Manual of Reptiles. 3rd edn. Eds: Girling S J & Raiti P. BSAVA, UK. pp 284-308.
  • De Voe R (2019) Gastroenterology - Oral Cavity, Esophagus, and Stomach. In: Mader’s Reptile and Amphibian Medicine and Surgery. Eds: Divers S J & Stahl S J. Elsevier, USA. pp 752-760.
  • Eatwell K & Hedley J (2019) Parasitology. In: BSAVA Manual of Reptiles. 3rd edn. Eds: Girling S J & Raiti P. pp 411-422.
  • Eatwell K & Richardson J (2019) Gastroenterology - Small Intestine, Exocrine Pancreas and Large Intestine. In: Mader’s Reptile and Amphibian Medicine and Surgery. Eds: Divers S J & Stahl S J. Elsevier, USA. pp 761-774.
  • Eatwell K & Richardson J (2019) Lizard Cryptosporidiosis. In: Mader’s Reptile and Amphibian Medicine and Surgery. Eds: Divers S J & Stahl S J. Elsevier, USA. pp 1320-1321.
  • Schnellbacher R W (2019) Snake Cryptosporidiosis. In: Mader’s Reptile and Amphibian Medicine and Surgery. Eds: Divers S J & Stahl S J. Elsevier, USA. pp 1341-1342.
  • Stacy N, Heard D & Wellehan J (2019) Diagnostic Sampling and Laboratory Tests. In: BSAVA Manual of Reptiles. 3rd edn. Eds: Girling S J & Raiti P. BSAVA, UK. pp 115-133.
  • Wellehan J F X & Walden H D S (2019) Parasitology (including Hemoparasites). In: Mader’s Reptile and Amphibian Medicine and Surgery. Eds: Divers S J & Stahl S J. Elsevier, USA. pp 281-300.
  • Gibbons P M (2014) Therapeutics. In: Current Therapy in Reptile Medicine & Surgery. Eds: Mader D R & Divers S J. Elsevier, USA. pp 57-69.
  • Hnizdo J & Pantchev N (2011) Cryptosporidium spp. In: Medical Care of Turtles & Tortoises. Edition Chimaira, Germany. pp 207-210.

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