Sunday, January 12, 2014

Pentastomid infections in Australian Snakes

Armillifer armillatus taken from a Python sebae
Species in this genus are known to infect humans. 
Photo credit: José Grau de Puerto Montt at en.wikipedia
Parasites are an important but often overlooked part of food webs and biodiversity. One estimate places 40% of the known species as parasitic. The number of amphibians species and amphibian parasites is about 1:1, for reptiles it is about 1 reptiles species for 2 parasites,  and for birds it is about 3.5 parasites for each species. Of course the actual number of parasites species per species is probably much greater.

In a forthcoming article Kelehear and colleagues examine the diversity of pentastomids in Australian snakes. Pentasomids are endoparasites of the respiratory system of vertebrates, maturing primarily in carnivorous reptiles. Adult and larval pentastomids can cause severe pathology resulting in the death of their intermediate and definitive hosts. The study of pentastomids is a neglected field, impaired by risk of zoonoses, difficulties in species identification, and life cycle complexities.

Pentastomids are long-lived endoparasites of the respiratory system of vertebrates, and are arguably the oldest metazoan parasites known to science. Prehistoric larvae resembling extant primary larvae appeared in the fossil record approximately 100 million years prior to the vertebrates they now parasitize. Larval pentastomids enter their definitive host when it consumes an infected intermediate host. These larvae tunnel out of the digestive system and through their definitive host to the lungs, generating lesions and scars along their migration path. In intermediate or accidental hosts these larvae can establish widespread visceral infections. In humans, pentastomiasis may be transmitted via food or water contaminated with their eggs, or via consumption of undercooked snake flesh. Adult pentastomids feed primarily on blood from host capillary beds in the lungs and can cause severe pathology resulting in death. Adult pentastomids reach large body sizes (up to 15 cm), physically occluding respiratory passages and inducing suffocation. The two pairs of hooks they use for attaching to lung tissue can cause perforations and haemorrhaging, and degrading molted cuticles shed into the lung lumen by growing pentastomids may induce putrid pneumonia.

Kelehear et al.  surveyed wild snakes in tropical Australia to determine which host species possess these parasites, and then attempted to identify the pentastomids using a combination of morphological and molecular techniques.  Pentastomid infections occurred 59% of the 81 snakes surveyed. They ubiquity of pentastomid infections in the snakes sampled alarmingly high considering the often-adverse consequences of infection and the recognized zoonotic potential of these parasites. The pentastomids identified were in the genera Raillietiella and Waddycephalus and infected a range of host taxa, encompassing seven snake species from three snake families. All seven snake species represent new host records for pentastomids of the genera Raillietiella and/or Waddycephalus. The arboreal colubrid Dendrelaphis punctulatus and the terrestrial elapid Demansia vestigiata had particularly high infection prevalences (79% and 100% infected, respectively). Raillietiella orientalis infected 38% of the snakes surveyed, especially frog-eating species, implying a frog intermediate host for this parasite. R. orientalis was previously known only from Asian snakes and has invaded Australia via an unknown pathway. Their molecular data indicated that five species of Waddycephalus infect 28% of snakes in the surveyed area. And their morphological data indicate that features of pentastomid anatomy previously utilized to identify species of the genus Waddycephalus are unreliable for distinguishing species, highlighting the need for additional taxonomic work on this genus. This open -access article is on-line in early view.

Citation
Kelehear, C. Spratt, DM, O’Meally D, Shine, R. 2014. Pentastomids of wild snakes in the Australian tropics. International Journal for Parasitology: Parasites and Wildlife. : 2213-2244, doi.org/10.1016/j.ijppaw.2013.12.003

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