Toxocara pteropodis Baylis, 1936 : life-cycle, epizootiology and zoonotic potential

Abstract

The aim of this study was to establish whether a human epidemic of hepato-enteritis, the "Palm Island mystery disease", could have been a manifestation of nematode visceral larva migrans caused by the flying fox parasite, Toxocara pteropodis. An assessment of the risk of human exposure to such an infection, and of its pathogenicity, required collection of data from field and laboratory studies.The life-cycle was elucidated in Pteropus poliocephalus, the predominant flying fox in the Brisbane region. Adult worms develop in the intestines of suckling juveniles, and infections may become patent in bats as young as 35 days. About 50% of juveniles develop patent infections, and each harbours an average of 1 adult male worm and 2 adult females. These worms are voided spontaneously before the bats leave their summer camps.Each female worm produces about 25,000 eggs per day, most of which are shed into the environment of the summer camp. Eggs become infective from 10 days after voiding; few remain viable longer than 6 weeks. As very little fruit remote from the camps was found contaminated with eggs, adult bats probably become infected in the camps by licking foliage and grooming during wet weather. Eggs ingested by bats hatch in the intestine and the released third-stage larvae penetrate the mucosa to reach the liver via the portal vein. These larvae may remain indefinitely in the liver, where they grow over 3 months from a length of about 420 jim to about 600 pm. In male bats, hepatic larvae gradually accumulate, but in females many leave the livers at the time of parturition and pass through the mammary glands to reach the juvenile intestines in the first 3 weeks after birth. Many developing intestinal larvae, predominantly males, are expelled spontaneously in the faeces of suckling bats. This explains the low average worm burdens in patent infections and their unequal sex representation.Virtually all adult male P_^ poliocephalus harbour larvae in their livers; in adult females the prevalence and intensity of hepatic infection 11 is lower. In the P. alecto and P_^ conspicillatus populations of northern Queensland, the prevalence pattern of T_^ pteropodis appears to be similar whereas in southern P_^ alecto, and in P_^ scapulatus, infection is much less common. T. pteropodis was also found in Pteropus specimens from New Guinea, Indonesia and India. Nematodes from Rousettus sp. from the Philippines, and poorly-preserved type specimens of Toxocara cynonycteridis, from a Rousettus sp. in Burma, were very similar to, if not identical with, T. pteropodis.On detailed examination, T_^ pteropodis had some features distinct from those of other members of the genus. The relatively thick egg-shell may protect against desiccation. The second moult occurs in the egg. Thirdstage larvae grow in the livers of definitive (and some abnormal) hosts.Adult worms have cephalic surface features which may be unique, and do not possess a cervical alar "supporting bar" typical of the genus.Experimental mammals other than bats exhibit v...

Hendra virus infection in a veterinarian

“…During 5 years of fieldwork in north‐eastern Australia for my PhD thesis on Toxocara pteropodis , an intestinal roundworm of flying foxes, 2 which included hundreds of hours observing fruit bats in their natural habitats, not once did I come across a case of natural birth or abortion in fruit bats away from their communal roosts (“camps”), which were always within pockets of dense forest, such as mangrove, eucalyptus or melaleuca swamps. Furthermore, the three coastal fruit bat species exhibited a short, well defined birthing season, generally over 3 weeks from late October through to November.…”