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Оглавление

Entamoeba

BASICS

DEFINITION/OVERVIEW

Entamoeba are characterized into two groupings based on morphology. The two groupings are based on the number of nuclei present. Entamoeba spp. in the group containing four nuclei are considered to be pathogenic and the main concern for reptilian species. Entamoeba spp. in the group containing eight nuclei are considered to be noninvasive. E. invadens is the most common pathogenic species seen in reptiles and has been known to cause significant mortality. Virulence can differ between strains of E. invadens; infectious cysts are 11–20.2 μm with four nuclei and a small central karyosome. Trophozoites are 17.5–50 μm in length (average 36.18 μm), 10–25 μm (average 12 μm) in width and average diameter of 24.1 μm. Trophozoites also possess a single nuclei with a large central karysome that is 5–7.5 μm (average 5.65 μm) in diameter.

ETIOLOGY/PATHOPHYSIOLOGY

E. invadens has a direct life cycle and transmission is through the fecal–oral route.

Cysts are ingested and then undergo excystation in the intestinal tract.

In chelonians, cyst production occurs by cell division and one metacystic form gives rise to eight amoebas.

E. invadens mainly inhabits the small and large intestines but can affect other adjacent organs, including the liver, kidneys, pancreas, and lungs via systemic circulation.

The motile feeding trophozoite can also encyst and then be passed through the host’s GI tract and out in the feces.

Trophozoites undergo encystation in which infective cysts are formed and then excreted in feces.

Cysts can remain infective for 14+ days at temperatures of 8 degrees C and several days at 37 degrees C.

It was first considered that chelonians were only carriers and E. invadens were commensal parasites, but there is sufficient evidence that the parasite can affect and cause mortality in all chelonians, including terrestrial chelonians, freshwater and sea turtles.

The disease process causes severe necrotizing colitis, hepatic and pancreatic necrosis with associated granulomas.

Clinical signs occur approximately 2–10 weeks prior to death.

SIGNALMENT/HISTORY

All ages can be affected. Animals consistently kept in temperatures between 25–33 degrees C.

Carnivorous chelonians appear to be more susceptible versus herbivorous chelonians.

Herbivorous chelonians can be asymptomatic carriers.

CLINICAL PRESENTATION

Anorexia

Diarrhea

Dehydration

Weight loss

Bloody and mucoid stools

Hardening of the large intestinal tract that can be palpated.

Intussusception

Vomiting

Sudden death

RISK FACTORS

Husbandry

Improper husbandry and hygiene, diarrhea, housed with infected animals, decreased immune status, temperatures held between 25 and 33 degrees C.

Invertebrates (i.e., roaches and flies) act as mechanical vectors.

Others

N/A

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

Salmonellosis

GI helminths

DIAGNOSTICS

Microscopic evaluation of fresh fecal material to visualize trophozoites and cysts.

Trophozoites may be seen in fresh fecal but die rapidly within 20–30 minutes once outside the host.

SAF technique can be used for better visualization.

Fecal/cysts can be placed within a petri dish with water and trophozoites will emerge from the dissolved envelope within several hours.

Immunohistochemistry with E. invadens poly clonal antibody is developed for snakes.

Polymerase chain reaction assays can be used to distinguish species of Entamoeba.

PATHOLOGICAL FINDINGS

Gross changes include thickening, edema, erosions, ulcers, and diphtheritic membranes of the large intestine.

Liver abscesses may also be seen.

Histologically, the primary finding is fibrinonecrotic colitis.

TREATMENT

APPROPRIATE HEALTH CARE

N/A

NUTRITIONAL SUPPORT

Nutritional supplementation may be indicated if diarrhea, dehydration is severe.

CLIENT EDUCATION/HUSBANDRY RECOMMENDATIONS

Practice proper hygiene

Wash fruits and vegetables before being fed.

Do not house infected individuals with non‐infected chelonians.

MEDICATIONS

DRUG(S) OF CHOICE

Metronidazole 25 mg/kg PO q24h for 5–7 days

PRECAUTIONS/INTERACTIONS

N/A

FOLLOW‐UP

PATIENT MONITORING

Monitor for weight gain

Take fecal samples

EXPECTED COURSE AND PROGNOSIS

Good

MISCELLANEOUS

COMMENTS

E. invadens in culture, dies at 37 degrees C, so can raise the temperature to 37 degrees C if it is within the animal’s preferred optimum temperature range.

E. histolytica and E. dispar, which are found in humans GI tracts, are morphologically similar to E. invadens but are considered to be non‐pathogenic.

ZOONOTIC POTENTIAL Unknown

SYNONYMS Amebiasis

ABBREVIATIONS

GI = gastrointestinal

SAF = Sodium acetate acetic acid formalin

INTERNET RESOURCES

de Cardenas C. Amebiasis in Reptiles. PetMD, October 1, 2008. www.petmd.com/reptile/conditions/digestive/c_rp_amebiasis• Amebiasis in Snakes. Wag! 2020. https://wagwalking.com/reptile/condition/amebiasis‐in‐snakes

Divers SJ. Parasitic Diseases of Reptiles. MSD Manual Veterinary Manual, June 2020. www.merckvetmanual.com/exotic‐

and‐laboratory‐animals/reptiles/parasitic‐ diseases‐of‐reptiles