Examination of Sarcocystis spp. of giant snakes from Australia and Southeast Asia confirms presence of a known pathogen – Sarcocystis nesbitti

Abstract

We examined Sarcocystis spp. in giant snakes from the Indo-Australian Archipelago and Australia using a combination of morphological (size of sporocyst) and molecular analyses. We amplified by PCR nuclear 18S rDNA from single sporocysts in order to detect mixed infections and unequivocally assign the retrieved sequences to the corresponding parasite stage. Sarcocystis infection was generally high across the study area, with 78 (68%) of 115 examined pythons being infected by one or more Sarcocystis spp. Among 18 randomly chosen, sporocyst-positive samples (11 from Southeast Asia, 7 from Northern Australia) the only Sarcocystis species detected in Southeast Asian snakes was S. singaporensis (in reticulated pythons), which was absent from all Australian samples. We distinguished three different Sarcocystis spp. in the Australian sample set; two were excreted by scrub pythons and one by the spotted python. The sequence of the latter is an undescribed species phylogenetically related to S. lacertae. Of the two Sarcocystis species found in scrub pythons, one showed an 18S rRNA gene sequence similar to S. zamani, which is described from Australia for the first time. The second sequence was identical/similar to that of S. nesbitti, a known human pathogen that was held responsible for outbreaks of disease among tourists in Malaysia. The potential presence of S. nesbitti in Australia challenges the current hypothesis of a snake-primate life cycle, and would have implications for human health in the region. Further molecular and biological characterizations are required to confirm species identity and determine whether or not the Australian isolate has the same zoonotic potential as its Malaysian counterpart. Finally, the absence of S. nesbitti in samples from reticulated pythons (which were reported to be definitive hosts), coupled with our phylogenetic analyses, suggest that alternative snake hosts may be responsible for transmitting this parasite in Malaysia.

Description of Sarcocystis scandentiborneensis sp. nov. from treeshrews (Tupaia minor, T. tana) in northern Borneo with annotations on the utility of COI and 18S rDNA sequences for species delineation

“…tupaia possesses a smooth type 1 wall ( Xiang et al, 2010 ), the ultrastructure of the present species clearly reveals a thick striated wall with VP that share structural elements with the tightly packed protrusions of wall type 12. Because our phylogenetic results indicate a sister taxon relationship with three previously described Sarcocystis species that undergo a snake-rodent life cycle ( Slapeta et al, 2003 ; Hu et al, 2012 , 2014 , 2015 ; Wassermann et al, 2017 ), morphological comparison with those species is implicit: S . singaporensis , S .…”

“…Values for posterior probability are indicated behind nodes. Note that the new species is part of a monophyletic subclade previously tagged S1 ( Wassermann et al, 2017 ), which includes taxa known to prefer snakes as definitive and rodents as intermediate hosts. Sequences E357-13 and E364-13 are available at GenBank under MN733816 and MN733817, respectively.…”

“…pantherophisi ), which in 18S rRNA trees is an indicator-species of the S2 lineage of Sarcocystis spp. with snake-rodent life cycle ( Wassermann et al, 2017 ). Interestingly, the Toxoplasmatinae formed a monophyletic clade that separated the Sarcocystis spp.…”

Biocontrol of rats in an urban environment in Southeast Asia using Sarcocystis singaporensis

“…Furthermore, according to a recent survey on reticulated pythons from the Australasian archipelago, it also appears unlikely that the reticulated python is a host of S . nesbitti …”

“…Although the reticulated python, the definitive host, is native to Laos, it may be rare in Luang Prabang since only one specimen was spotted for sale on a local market during a survey on local wildlife in September 2005 . In the wild, up to 100% of adult rats and on average 60% of adult reticulated pythons can be infected naturally. The potential absence of S. singaporensis meant that the rat populations in Luang Prabang were likely to have been immunologically naïve towards the parasite.…”