Molecular characterization of Trichuris spp. from captive animals based on mitochondrial markers
Graphical abstract
Introduction
Parasitic infections may represent a major threat for animals housed in zoological gardens, where overcrowding in confined environments may significantly facilitate transmission, with special regard to parasites with direct life-cycles [1,2]. In addition, as parasites commonly found in such sites are known to be responsible for zoonoses, they could represent a potential public health issue [3]. Among monoxenous parasites, nematodes of the genus Trichuris Roederer, 1761 (Nematoda: Trichuridae) are commonly reported in mammals living in captivity [4,5]. Whipworms are soil-transmitted helminths distributed worldwide, naturally parasitizing a broad range of mammalian hosts including ruminants, marsupials, rodents, and primates [6,7]. Humans are commonly infected as well, mainly by the species Trichuris trichiura and, occasionally, by zoonotic species such as Trichuris vulpis and Trichuris suis [[8], [9], [10]].
Reports from captive animals are mainly based on the detection of eggs in fecal samples or adults recovered after deworming or during necropsies [[11], [12], [13]]. These infections can be fatal, as recently described for the hamadryas baboon (Papio hamadryas) and the dromedaries (Camelus dromedarius) hosted in the Seoul's zoo, emphasizing the importance of the management of parasitic infections in confined environments [14,15].
Once captive animals are found infected by whipworms, a specific identification would be advisable, in order to infer intra- and interspecific transmission pathways and to estimate the related zoonotic potential. Trichuris species identification may be particularly difficult and complex. Given the strong convergence of adaptive traits, morphology is usually not sufficient for a correct assignment of species, considering that diagnostic features occur mainly in adult males [16]. Another criterion probably erroneously considered of strong taxonomic value is host affiliation. In this context, the molecular characterization is desirable, for a correct identification of the parasite and for a detailed epidemiological picture of the infection [17].
The taxonomic status of Trichuris infecting humans, i.e. T. trichiura, is largely debated. Recent studies have revealed the existence of more than one taxon able to infect humans and other primates, including captive individuals, thus suggesting the status of T. trichiura as a complex of species, counting different cryptic units [10,16,[18], [19], [20], [21], [22]].
Moreover, three new species have been described in primates other than T. trichiura: Trichuris rhinopiptheroxella [23] described from the golden snub-nosed monkey (Rhinopithecus roxellana); Trichuris colobae [24] from the mantled guereza (Colobus guereza); and Trichuris ursinus [25] from the chacma baboon (Papio ursinus).
Similarly, several species of the genus Trichuris (Trichuris ovis, Trichuris globulosa, Trichuris discolor and Trichuris skrjabini) have been reported in ruminants hosted in zoological gardens [14,17,26]. T. ovis and T. globulosa are considered as valid species, although morphological features are mostly overlapping and very few subtle traits are available to differentiate them, such as spicule sheath and spines [27,28].
The aim of the present study was to characterise Trichuris spp. detected in animals hosted at the Bioparco Zoological Garden of Rome and to infer possible routes of transmission and potential zoonotic risk. Species characterization was carried out using molecular sequencing of two diagnostic mitochondrial markers, the cytochrome c oxidase I (cox1) and the cytochrome b (cytb), useful for taxonomy and molecular systematics [17,29,30].
Section snippets
Isolation of material
Adult specimens belonging to Trichuris spp. were collected during necropsies carried out at the Istituto Zooprofilattico Sperimentale del Lazio e della Toscana “M. Aleandri” aimed to determine the cause of death of animals hosted at the Bioparco Zoological Garden of Rome. Whipworms (n = 49) were found in four animal species: 10 specimens from a ring-tailed lemur (Lemur catta), 11 from a camel (Camelus bactrianus), 15 from a screw horn antelope (Addax nasomaculatus) and 13 from two Patagonian
Results
Molecular analyses gave 19 readable Trichuris sequences at cox1 amplification (5 for camel, 4 for screw horn antelope, 7 for lemur, 3 for Patagonian maras) and 18 at cytb (7 for camel, 4 for lemur, 3 for both Patagonian maras and screw horn antelope). Reliable sequences were submitted to GenBank under the accession numbers indicated in Table 1.
Molecular characterization of Trichuris spp. found in the four animals species here analysed suggested the presence of five different putative taxonomic
Discussion
The use of molecular techniques to identify parasitic species is of great importance, in particular in taxonomic groups with a complex systematics and with stable evolution characterised by morphological convergence, as in the genus Trichuris [25,44]. In the present study, genetic distances and phylogenetic evidences obtained on whipworms infecting ring-tailed lemur, camel, screw horn antelope and Patagonian maras hosted in the Zoological Garden of Rome suggest a separation for most of the
Conclusions
The data presented in this paper, as well as in other previous studies, support a strong affiliation of Trichuris species in relation to hosts as each animal showed different and specific Trichuris taxa. However, cross-infection and/or hybridization events may occur, as supposed for Trichuris infecting the ring-tailed lemur and the Japanese macaque, both hosted in the same zoological garden. Multiple species environments and conditions resembling natural settings may favor the spread of
Funding
Two Starting Grants (2016), from Sapienza University of Rome and from the Italian Society for Parasitology SOIPA, partially supported this work.
Declaration of Competing Interest
The authors declare no competing interests.
Acknowledgments
The authors wish to thank Carlo Taccari for graphical support.
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