Gastrointestinal parasites are more common in pet reptile species than owners and veterinarians often expect. However, interpretation of faecal parasitology in captive reptiles and knowing when to treat can be tricky, depending on the environment and diet of the patient. For example, carnivorous species such as pythons may ingest rodent parasites such as Syphacia muris, the rat pinworm, when ingesting prey. The eggs then pass in the python’s faeces, but are not pathogenic, and as such are referred to as pseudoparasites. A small burden of Isospora amphiboluri in an adult bearded dragon may not be of clinical concern even though it is a pathogen, but when we consider that the patient lives in an enclosed vivarium which is a far smaller territory than its wild counterparts, we need to consider that the patient will continue to shed and re-ingest the parasite, allowing for the burden to become much larger over time.
Previous survey studies have shown that endoparasite burdens are common in captive chelonians and lizards, and less common in terrapins, and that snakes are more likely to be affected by protozoal parasites than nematodes or helminths (Hatt, 2010). A study of 100 pet reptiles with no clinical signs showed that 52 percent of all animals had at least one species of endoparasite. A certain degree of parasitism is normal in wild reptiles; however, in captivity reptiles are more likely to be exposed to poor husbandry, stress and overcrowding, which makes imbalances more likely to occur (Rivera, 2013). Any newly introduced reptile or reptile patient that is anorexic, hyporexic, thin or lethargic should have a faecal parasite examination as part of a diagnostic work-up.
A number of coprological methods are available to assess a faecal sample for a parasitic burden. A combination of a direct smear and flotation (Figure 1) has been shown as superior for identifying flagellates, coccidial oocysts and nematode eggs (Wolf et al., 2014). Direct smears are important for identifying flagellates and eggs that do not float well. The addition of a drop of Lugol’s iodine can aid in highlighting protozoal cysts (Wolf et al., 2014). Flotation can be performed with a zinc chloride or sodium chloride solution with or without centrifuging (Rom et al., 2018). If a clinician is not comfortable identifying parasites in-house, then a number of commercial exotic laboratories in the United Kingdom offer this service. Veterinarians will encounter a number of different endoparasites in their reptile patients; however, the most common ones are discussed here.
Pinworms (Figure 2) belong to the order Oxyurida and are a common parasite of tortoises and lizards (Arabkhazaeli et al., 2018). They are generally considered non-pathogenic in herbivorous reptiles in low numbers and have been hypothesised to actually play a role in digestive function (Rivera, 2013). They have a direct lifecycle, are spread via the faecal-oral route and tend to be host-specific (Wellehan and Walden, 2019). Treatment is controversial; generally, oxyurids do not require treatment, unless the patient has a severe burden or is anorexic, is losing weight or has evidence of diarrhoea (Hatt, 2010). Fenbendazole is often used to treat pinworm burdens; however, it has been shown to cause a heteropaenia with transient hypoglycaemia, hyperuricaemia and hyperphosphataemia in tortoises treated orally (Neiffer et al., 2005) and so benefits of treatment should be weighed with potential side effects.
Coccidia is a subclass of intracellular parasites and contains members that are commonly seen in companion reptiles. Most commonly reported are Isospora, Eimeria and Cryptosporidium, which have direct lifecycles, passing oocysts in the faeces with infection occurring via the faecal-oral route (Wellehan and Walden, 2019). Oocysts need to sporulate prior to becoming infectious and following ingestion the sporozoites leave the oocyst and enter the endothelial lining of the gastrointestinal tract. Sexual and asexual generations are produced and gametes go on to produce zygotes which then become walled, completing the lifecycle by becoming an oocyst (Wellehan and Walden, 2019).
Isospora amphiboluri (Figure 3) is of particular significance in juvenile bearded dragons (Pogona vitticeps), causing anorexia, stunting of growth, coelomic pain from gaseous intestinal distension, diarrhoea and subsequent dehydration (Rivera, 2013). Clinical signs are usually related to malabsorption (Hatt, 2010). Inversely, infections in adult bearded dragons are usually asymptomatic. Diagnosis is through a direct faecal smear or faecal flotation. Treatment is with toltrazuril (Hatt, 2010), although in the author’s experience treatment can cause anorexia in some patients, so treatment of asymptomatic animals should be undertaken with caution.
Cryptosporidium is of particular concern in snakes and geckos. Identification of the organism to species level is important in carnivorous patients with Cryptosporidium identified on faecal exam, as prey items may carry their own species of Cryptosporidium that is non-pathogenic. Oocysts can last for months in the environment in cool and moist environments (Rivera, 2013). Clinical signs in snakes include regurgitation, anorexia, weight loss and mid-body swelling in snakes, usually caused by hypertrophic gastritis (Hatt, 2010). Juvenile geckos show signs of wasting, commonly referred to as “stick tail” and anorexia. Diagnosis is via polymerase chain reaction (PCR) of faeces or a stomach wash (Wellehan and Walden, 2019), histopathology of gastric biopsies or modified Ziehl Neelsen stain of faeces (Arabkhazaeli et al., 2018). No treatment has been reported as successful, and at present the best practice is prevention and quarantine of incoming reptiles.
Flagellates and ciliates are commonly encountered but not always pathogenic. Both groups have a direct lifecycle and infection is by the faecal-oral route. Giardia is encountered; however, its clinical significance is unknown (Wellehan and Walden, 2019). Hexamita parva is a parasitic flagellate that can cause tubulointerstitial nephritis in tortoises, with infection suspected to ascend from the cloaca to the kidneys (Wellehan and Walden, 2019). The ciliates Balantidium spp. and Nyctotherus spp. are non-pathogenic, commonly found in tortoises and thought to be an important part of the flora of the gastrointestinal tract (Hatt, 2010). Diagnosis of flagellates and ciliates is through direct smear of fresh faecal samples, but renal biopsy is often required for definitive diagnosis of Hexamita (Wellehan and Walden, 2019).
When performing coproscopy it is important to also be aware of material within slide preparations that may look similar to parasitic burdens and may result in false diagnoses. Uric acid crystals can mimic the appearance of coccidia (Figure 4), but coccidia will be uniform in size, whereas uric acid crystals will vary in size and sometimes shape. Small fragments of fibres, either ingested or contaminating the sample during collection, can resemble larval or adult worms (Figure 5A). Increasing the power of the microscope and viewing the cranial and caudal ends of the suspected organism can help to identify mouthparts and posterior anatomy (Figure 5B).
Coproscopy is a useful, cheap and simple-to-perform diagnostic test for reptile patients. It is useful for screening new reptiles coming into collections, for routine health examinations and for investigating anorexia, weight loss and faecal changes in companion reptiles. It can also be an excellent way to engage new reptile keepers as clients. Direct faecal smears and faecal flotations can be performed in-house, providing useful diagnostics during consultation and allowing for prompt treatment.