Development of a polymerase chain reaction test for Entamoeba invadens

MANAGEMENT OF ENTAMOEBA INVADENS IN THE HERPETOLOGICAL COLLECTION AT THE SINGAPORE ZOO

Amebiasis caused by Entamoeba invadens is an important disease in reptile collections, causing severe morbidity and mortality. Surveillance of the parasite at the Singapore Zoo was carried out over a 4-yr period by PCR testing on reptiles that presented with lethargy and enteritis for disease investigation. Asymptomatic reptiles sharing the same enclosures as positive individuals were also tested as part of outbreak investigation. Animals in the collection that tested positive for the parasite were treated with metronidazole at various doses, with the addition of paromomycin for two cases, until a negative PCR test result was obtained at the end of the treatment course. A total of 97 samples from 49 individuals across 19 species of reptiles were obtained, of which 24 samples (24.7%) from 19 animals were positive for E. invadens. Of these positive samples, 11 samples were for disease investigation, eight samples for outbreak surveillance, and five samples for treatment monitoring. Treatment was initiated for 10 animals, four of which were showing clinical signs of disease. The parasite was cleared in nine of these 10 animals (90%), with eight animals receiving metronidazole as a sole therapeutic agent. A total of nine animals died of the disease, four of which (44.4%) presented dead or died within 24 h of presentation. Necrotizing enteritis was a consistent postmortem finding resulting in gastrointestinal perforation in two cases, and coelomic adhesions and hepatic trophozoites were each seen in five animals. The results suggest that the management of Entamoeba epizootics in the collection requires prompt outbreak investigation. Diagnosis of the disease with advanced diagnostic tools like PCR, endoscopy, and ultrasonography and treatment with metronidazole in both symptomatic and asymptomatic animals may reduce mortalities during an outbreak.

Beyond Sea Turtles: Fusarium keratoplasticum in Eggshells of Podocnemis unifilis, a Threatened Amazonian Freshwater Turtle

The endangered yellow-spotted river turtle (Podocnemis unifilis) has experienced a dramatic population decline in the Ecuadorian Amazonia, mainly due to overexploitation of its eggs. To reverse this trend, the Wildlife Conservation Society has developed a head-start program in Yasuní National Park since 2008, but the potential risk that microbes associated with its eggs might represent for hatching success has not been evaluated yet. Members of the Fusarium solani species complex (FSSC) are involved in egg failure in sea turtles under natural and hatchery conditions, but their role in infecting the eggs of P. unifilis is unknown. In this study, we collected eggshells of P. unifilis and obtained 50 fungal and bacterial isolates. Some potentially pathogenic fungi of the genera Fusarium, Penicillium and Rhizopus were identified based on molecular data. Most importantly, the sea turtle pathogenic species F. keratoplasticum not only was present, but it was the most frequently found. Conversely, we have also isolated other microorganisms, such as Pseudomonas or Phoma-like species, producing a wide spectrum of antifungal compounds that may have a protective role against fungal diseases. Our survey provides useful information on potential pathogens found in P. unifilis eggshells, upon which the success of conservation programs may depend.

A RETROSPECTIVE ANALYSIS OF AMOEBIASIS IN REPTILES IN A ZOOLOGICAL INSTITUTION

Amoebiasis is a significant protozoal disease of reptiles causing nonspecific clinical signs including diarrhea, anorexia, and lethargy. It frequently results in acute death. Investigation of the pathophysiology of amoebiasis in reptiles has been hampered by the inability to accurately identify amoeba to the species level using conventional techniques. This study reviewed reptile medical records from the Wildlife Conservation Society's archives from 1998 to 2017. Amoebae were identified histologically in 54 cases in 31 different species. Of these, amoebiasis was the cause of death in 32 (18 chelonians, 7 lizards, and 7 snakes), a significant co-morbidity in 14 (six chelonians, two lizards, and six snakes), and seen incidentally in eight cases (one chelonian, six lizards, and one snake). Relocation from one enclosure to another was also evaluated and 65% of cases had been moved within 180 days of death (median 46 days). Frozen tissue samples from 19 of these cases were tested via an Entamoeba (genus-specific) polymerase chain reaction (PCR) assay. PCR products were sequenced and Entamoeba species were identified. Six individuals were positive for Entamoeba invadens (three chelonians, two snakes, one lizard), two for Entamoeba ranarum (both snakes), and one for Entamoeba terrapinae (chelonian); the other 10 cases were negative via PCR. Entamoeba ranarum has typically been considered a disease of amphibians with only one report of disease in a snake. Entamoeba terrapinae has only been reported without associated disease in chelonians. These results suggest that amoebiasis is a complicated and nuanced disease of reptiles, and warrants additional study.

First report of mixed Entamoeba polecki (ST 1) and E. suis infection in piglets shedding abnormalfeces by histopathological and molecular surveys

Of the three species of Entamoeba found in swine, namely E. histolytica, E. polecki and E. suis, E. histolytica can also infect humans, producing colitis or abscesses of liver and leading to death. However, the pathogenicity of other species of Entamoeba has not been fully characterized. Here, we conducted histopathology and molecular surveys on a pig farm where piglets had blackish feces or muddy diarrhea. Histopathological examination of two piglets showed necrosis of the mucous surface at the ileum, cecum, or colon, infiltration of neutrophils, and formation of ulcers. Based on morphological characteristics, E. polecki and E. suis trophozoites were mainly detected at lamina propria and surface of the lesion, respectively, and Lawsonia intracellularis, a bacterial pathogen, was also detected. Molecular analysis using the small subunit ribosomal RNA gene on other piglets and a sow revealed infection with both E. polecki and E. suis. These findings corroborate our previous reports that the two Entamoeba spp. are pathogenic in pigs as aggravations of symptoms with L. intracellularis. This is the first report about mixed infection with E. polecki and E. suis.

Entamoeba mitosomes play an important role in encystation by association with cholesteryl sulfate synthesis

Hydrogenosomes and mitosomes are mitochondrion-related organelles (MROs) that have highly reduced and divergent functions in anaerobic/microaerophilic eukaryotes. Entamoeba histolytica, a microaerophilic, parasitic amoebozoan species, which causes intestinal and extraintestinal amoebiasis in humans, possesses mitosomes, the existence and biological functions of which have been a longstanding enigma in the evolution of mitochondria. We previously demonstrated that sulfate activation, which is not generally compartmentalized to mitochondria, is a major function of E. histolytica mitosomes. However, because the final metabolites of sulfate activation remain unknown, the overall scheme of this metabolism and the role of mitosomes in Entamoeba have not been elucidated. In this study we purified and identified cholesteryl sulfate (CS) as a final metabolite of sulfate activation. We then identified the gene encoding the cholesteryl sulfotransferase responsible for synthesizing CS. Addition of CS to culture media increased the number of cysts, the dormant form that differentiates from proliferative trophozoites. Conversely, chlorate, a selective inhibitor of the first enzyme in the sulfate-activation pathway, inhibited cyst formation in a dose-dependent manner. These results indicate that CS plays an important role in differentiation, an essential process for the transmission of Entamoeba between hosts. Furthermore, we show that Mastigamoeba balamuthi, an anaerobic, free-living amoebozoan species, which is a close relative of E. histolytica, also has the sulfate-activation pathway in MROs but does not possess the capacity for CS production. Hence, we propose that a unique function of MROs in Entamoeba contributes to its adaptation to its parasitic life cycle.

Molecular epidemiology and genetic diversity of Entamoeba species in a chelonian collection

Veterinary medicine has focused recently on reptiles, due to the existence of captive collections in zoos and an increase in the acquisition of reptiles as pets. The protozoan parasite, Entamoeba can cause amoebiasis in various animal species and humans. Although amoebiasis disease is remarkably rare in most species of chelonians and crocodiles, these species may serve as Entamoeba species carriers that transmit parasites to susceptible reptile species, such as snakes and lizards, which can become sick and die. In this study, we identified the Entamoeba species in a population of healthy (disease-free) chelonians, and evaluated their diversity through the amplification and sequencing of a small subunit rDNA region. Using this procedure, three Entamoeba species were identified: Entamoeba invadens in 4.76 % of chelonians, Entamoeba moshkovskii in 3.96 % and Entamoeba terrapinae in 50 %. We did not detect mixed Entamoeba infections. Comparative analysis of the amplified region allowed us to determine the intra-species variations. The E. invadens and E. moshkovskii strains isolated in this study did not exhibit marked differences with respect to the sequences reported in GenBank. The analysis of the E. terrapinae isolates revealed three different subgroups (A, B and C). Although subgroups A and C were very similar, subgroup B showed a relatively marked difference with respect to subgroups A and C (Fst = 0.984 and Fst = 1.000, respectively; 10-14 % nucleotide variation, as determined by blast) and with respect to the sequences reported in GenBank. These results suggested that E. terrapinae subgroup B may be either in a process of speciation or belong to a different lineage. However, additional research is necessary to support this statement conclusively.

Increased sampling reveals novel lineages of Entamoeba: consequences of genetic diversity and host specificity for taxonomy and molecular detection

To expand the representation for phylogenetic analysis, ten additional complete Entamoeba small-subunit rRNA gene sequences were obtained from humans, non-human primates, cattle and a tortoise. For some novel sequences no corresponding morphological data were available, and we suggest that these organisms should be referred to as ribosomal lineages (RL) rather than being assigned species names at present. To investigate genetic diversity and host specificity of selected Entamoeba species, a total of 91 new partial small subunit rRNA gene sequences were obtained, including 49 from Entamoeba coli, 18 from Entamoeba polecki, and 17 from Entamoeba hartmanni. We propose a new nomenclature for significant variants within established Entamoeba species. Based on current data we propose that the uninucleated-cyst-producing Entamoeba infecting humans is called Entamoeba polecki and divided into four subtypes (ST1-ST4) and that Entamoeba coli is divided into two subtypes (ST1-ST2). New hosts for several species were detected and, while host specificity and genetic diversity of several species remain to be clarified, it is clear that previous reliance on cultivated material has given us a misleading and incomplete picture of variation within the genus Entamoeba.