Parasites of sea turtles - School of Veterinary Science

Transcription

Parasites of sea turtles - School of Veterinary Science
Parasites of sea turtles: Variety of parasites and impact on
turtles.
David Blair
School of Marine and Tropical Biology,
James Cook University, Townsville
Outline of talk;
• Survey of the parasite groups (especially trematodes) and their
transmission to turtles.
• What is known about the effects on the hosts?
Green, hawksbill and
loggerhead turtles.
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Most parasites are acquired by their host via the food chain.
• Green turtles, as juveniles in the open ocean, have a mixed diet
which includes a range of invertebrates etc. As sub-adults they
return to near-shore habitats and become herbivorous (seagrasses
and algae).
• Hawksbills feed on sponges, algae, seagrasses and
invertebrates.
• Loggerheads feed on a wide range of benthic invertebrates.
• Sea turtles have lots of parasites, mostly trematodes, but some
nematodes and a few protists.
• Taxonomy of turtle parasites still in poor shape. Huge numbers
of trematode species have been named, but many of these will
prove to be synonyms.
Trematode families known from sea turtles.
Juvenile Green
Hawksbill
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Pronocephalidae
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Spirorchiidae
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Rhytidodidae
Calycodidae
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Plagiorchiidae
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Hemiuridae
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Paramphistomidae
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Gorgoderidae
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Pachypsolidae
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Brachycoeliidae
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Aspidogastrea
Loggerhead
Adult Green
Microscaphidiidae
Trematode
Family
Parasite fauna of
green turtles is best
known.
Few researchers have
noted whether
parasites from green
turtles were from
adult or juvenile
animals.
My own poorly
documented
observation has been
that a much wider
range of trematodes
occurs in juvenile
greens: ontogenetic
shift in diet leads to a
change in parasite
fauna.
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Some trematodes
of sea turtles
Left: a pronocephalid and
right, a microscaphidiid.
Members of these families are
termed “monostomes” because of
the lack of a ventral sucker.
Most of these trematodes live in
the gut or its associated organs.
Most cause little overt pathology…
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… but spirorchiid
trematodes are real
villains. These live in
the circulatory system.
Their eggs accumulate
throughout organs all
over the body.
Above: from Werneck et al 2006;
appearance of serosal surface of gut of
green turtle infected with blood flukes.
Right: A common spirorchiid –
Learedius learedi.
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Spirochiids are very important parasites of turtles. All sea
turtles around here have spirorchiids in them, and these
commonly debilitate or kill the turtles.
Spirorchiid
eggs in turtle
brain
Packet of eggs on edge
of spinal cord
Above: these spirorchiid
eggs were thought to be
schistosome eggs when they
were found in the faeces of
aborigines in northern
Australia. Probably, hunters
had caught a turtle and had
eaten the gut lining,
containing many eggs.
These eggs could not pose a
threat to humans.
Blair & Miller 1992
Below: spirorchiid eggs come in a
range of shapes and sizes.
Work et al 2005
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Adult flukes in heart – Mark Flint.
Blocked aorta in turtle – Mark Flint.
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Fluke eggs in brain and salt glands – Mark Flint.
Spirorchiid eggs are very common in fibropapilloma
lesions, but are probably not a direct cause of them.
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What do we know
about the life-cycles
of any of these
trematodes?
Nothing!
Spirorchiids are
likely to have forktailed cercariae and
penetrate the skin of
the host directly.
The “monostomes”
are likely to have
metacercariae sitting
on seagrasses and
algae.
Nematodes. The few species in sea turtles are most likely to be
encountered in loggerheads. Sulcascaris sulcata (below) has a
larval stage in bivalve molluscs such as scallops.
Lester et al image of Sulcascaris sulcata
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