Tuesday, September 15, 2009

Bearded Dragon Health: Parasites and Adenovirus


Bearded dragons have a number of parasites and commensals, one of the most common is pinworms or Oxyurids. These nematodes are debatable parasites, since they cause no real pathology unless they super infect a captive animal that is over exposed to the eggs. Most veterinarians consider them to be pests, but mostly commensals rather than parasites. They appear as small, short, white, tapered worms approximately 5-8mm long, though rarely some may be over 10mm. These worms reside in the colon and cloaca, rarely venturing outside to be seen by the owner. They lay eggs ranging in size around 95 microns long with a roughly triangular shape and recognizably sculptured, brown shell.
The life cycle is fairly straight forward. The worms reside in the colon where they lay eggs. Eggs are passed in the feces. In the environment they mature rapidly into infectious eggs and are ingested where they hatch in the bowel and attach to the colon to mature into adult worms.

The treatment of choice is fenbendazole, though in recent years this has proven to be largely ineffective in treating mammal nematodes due to resistance, and may be ineffective in treating reptile nematodes as well. Working with several breeders, I have noticed a significant decline in the effectiveness of fenbendazole (sold commercially as panacur). One population I have worked with has shown little or no response to fenbendazole treatment, showing that resistance has occurred in at least one population to the point of virtual immunity.
Currently there is no real treatment that is decisively effective. Ivermectins have been used with some success in reptiles, but the margin of safety is so narrow that it is too risky for most people to try. Ivermectins are another class of drug that has treated nematodes very successfully in mammals, but reptiles are extremely sensitive to it and can easily overdose and die. For that reason, it is generally considered better to live with the pinworms than to give ivermectins.


Two species of coccidia are known to infect bearded dragons. The first was described by Cannon in the 1960's and is named Isospora amphiboluri. The second was described by Walden in 2009 and is named Eimeria pogonae.

Isospora amphiboluri
Isospora amphiboluri has been associated with mortality and poor doing in bearded dragons and the infections can be severe. The life cycle appears to be a direct one within the intestine and it moves through the intestine as infection progresses. The prepatent period can be up to 25 days. The prepatent period is the time between infection and detectable numbers of oocysts appearing in the feces. The best way to diagnose the presence of this parasite is with modified Sheather's solution fecal floatation. The parasite infects the host by fecal oral contact and reproduces and amplifies within the host. A single oocyst can give rise to thousands of oocysts that are shed in the feces. Sporulation largely takes place in the colon or cloaca, so oocysts are infectious when first deposited.
Eimeria pogonae
Eimeria pogonae is less well understood, and may be a gall bladder infecting species, but the site of infection is as yet undetermined, though it is shed in the feces and can be detected with modifed Sheather's solution fecal floatation. Presumably the life cycle is roughly similar to I. amphiboluri and other members of the Isospora and Eimeria genera and consists of an amplification phase followed by sexual phase and the formation of new infectious oocysts. Oocysts are largely passed sporulated and infectious.
To date there has been no established disease state associated with E. pogonae, and it may actually be better classified as a commensal.

Coccidia Life Cycle
The life cycle of the coccidia in the genera Isospora and Eimeria are similar. In gut limited species that do not form tissue cysts in other tissues of the body (like Toxoplasma for example), the life cycle begins with the ingestion of the oocyst, usually from fecal oral contact.
  • Ingestion
  • The oocyst passes unharmed through the stomach and into the intestine.
  • Excystation - bile acids and enzymes trigger the oocyst wall to split at its seams and fall away exposing the sporocysts (2 sporocysts each containing 4 sporozites in Isospora and 4 sporocysts each containing 2 sporozites in Eimeria).
  • The sporocysts then split along tiny seams or, in those species with a Steida body, the Steida body swells and then literally pops out followed by the sub Steidal body (in those species in which a sub Steidal body is present).
  • The freed sporozoites then look for host cells and penetrate the cells using organelles in their anterior end (specifically rhopteries, dense granules and micronemes). The sporozoite uses the host cell's own membrane to make a protective bubble around itself called a parasitiphorous vacuole as it pushes into the host cell's cytoplasm and takes over machinery causing the host cell to feed the parasite.
  • The sporozoite then becomes a meront (sometimes called a schizont - pronounced skizont). The meront undergoes merogony (schizogony), which is asexual reproduction, and forms numerous merozoites.
  • Merozoites burst from the host cell and infect more host cells. The merozoites repeat the same process as the sporozoite and a new round of merogony begins in each new infected cell, continuing the amplification phase of the infection.
  • The number of rounds of merogony is species dependent, but most Isospora average around 3, though some species of Isospora and Eimeria can go through 5 or more.
  • The last round of merogony results in infected cells where the merozoites differentiate into female or male and form gamonts.
  • Female gamonts (macrogamonts) are a single cell. Male gamonts (microgamonts) form many cells analogous to sperm and called microgametes. These burst out of the host cell and fertilize the macrogamonts to form zygotes.
  • Zygotes mature into oocysts which are released into the lumen of the gut and defecated into the environment. The oocysts of some species form new sporocysts and sporozoites (a process called sporulation) quickly and are infectious when they first are deposited. However, some species must take some time to sporulate and are not infectious for a certain period of time ranging from hours to days.
Coccidia Treatment
Treatment for coccidia has classically been sulfadimethoxine (commercially called Albon). Studies by Walden (2009) have shown that sulfadimethoxine was effective in treating coccidia, but even after 21 consecutive days of treatment, some animals were still positive. Studies conducted by Walden also evaluated the probiotic Pediococcus and oregano oil (both of which have had some success in controlling coccidia in poultry) and found that these treatments had no significant effect. Ponazuril (commercially marketed as Marquis) compounded as a 90mg/ml solution and given at 30-45mg/kg was very effective in treating coccidia.

Reference: Michael R. Walden, MS, DVM, PhD; Characterizing the Epidemiology of Isopora amphiboluri in Captive Bearded Dragons (Pogona vitticeps). PDF available at http://etd.lsu.edu/docs/available/etd-05292009-214931/
You can also check out my amazon.com reading list if you are interested in herpetoculture, herpetology or herp medicine by clicking the "Selected Herpetology References" link below.
Selected Herpetology References - New Category (1)

Parasite Fecal Floatation Pictures

Oxyurid ovum with coccidia oocyst of Isospora amphiboluri.  Bar = 100 microns. 200x.  Used with permission.
Oxyurid ovum with coccidia oocyst of Isospora amphiboluri. Bar = 100 microns. 200x. Used with permission.
Isospora amphiboluri oocyst.  Bar = 20 microns. 600x.  Used with permission.
Isospora amphiboluri oocyst. Bar = 20 microns. 600x. Used with permission.
Eimeria pogonae oocyst.  Bar = 20 microns. 600x  Used with permission
Eimeria pogonae oocyst. Bar = 20 microns. 600x Used with permission

Adenoviruses are a widespread group of viruses that infect many species including amphibians, reptiles and mammals. In recent years a poorly characterized adenovirus has been observed killing bearded dragons.
The adenovirus kills dragons by caused necrosis (death) of numerous cells, particularly the enterocytes (gut lining cells) and hepatocytes (liver cells). Recently Louisiana State University developed a PCR test to test for adenovirus in bearded dragons. The test was conducted by the Dr. Alma Roy of the diagnostic lab along with Dr. Shawn Zimmerman and Dr. Michael Walden. The standard test to date had been electron microscopy of the feces to see the viruses, and it had been assumed that the EM was sufficiently diagnostic. The study places doubt on that.
What does adnovirus do?
  1. Adenovirus causes interference with cellular machinery and ultimately ruptures and kills the host cell.
  2. Its cellular specificity is not understood, but it is known to use enterocytes, hepatocytes and renal cells as hosts.
  3. Fatality usually results from hepatitis in severe cases or starvation in milder, more protracted cases.
  4. Gross lesions are not present externally, making diagnosis difficult for the clinician.
  5. Some animals have pale livers resembling glycogeniasis, lipidiasis or lipidosis grossly.
  6. At least 2 outbreaks have been reported in the U.S. recently.
EM has certain pitfalls.
Threshold – is around 1,000,000 (106) particles per gram of unprocessed feces.
Time consuming – very time consuming.Preparation of samples – hours.
Grid preparation – hours.
Staining and sample to grid – minutes.
Grid examination – hours.

PCR in a nutshell
 Disadvantages of PCR
Currently not as widely available as EM

Advantages of PCR
Quicker than EM
More sensitive than EM
Probably as specific in reality as EM
Chance for false negatives is lower than EM
Chance for false positives is higher than EM – Huh?

Chance for false positives is higher than EM. Why is that an advantage?
Production situations would rather have false positives than false negatives when introducing new stock.
False negatives introduced into a true negative population can cause severe economic consequences.
In most cases culling 100 new introductions to maintain a negative breeding population is more cost effective in the long run than having a costly outbreak in a population of several thousand.

Comparison of Results Between EM and PCR
5 of 132 samples were positive for Adenovirus (3.79%).
8 of 132 samples were positive for Parvoviral like particles consistent with Dependovirus (6.06%).
117 of 132 samples were positive for Adenovirus (88.64).
So PCR is far better for detecting adenovirus in bearded dragons. So if you think you have adenovirus in your population, contact LSU.

Unfortunately there is no treatment and positive animals should be culled from the population.

Association of Reptilian & Amphibian Veterinarians - proceedings from 2007 in New Orleans.

Adenovirus EM

Electron microscopy colorized photo showing Adenovirus (red) and associated dependovirus (yellow).
Electron microscopy colorized photo showing Adenovirus (red) and associated dependovirus (yellow). Copyright Dr. Michael Walden, 2009, all rights reserved.

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