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Introduction
Echinophthiridae are anopluran parasites of seals and a few other aquatic/marine
species that are physically unusual, even bizarre, in appearance. All
echinophthirids bear densely clustered long setae and scale-like setae on their
cuticles (Figure 1).
Because of their host selection, on seals, sea lions, and otters, echinophthirids
may face restrictions of habitat on their hosts due to:
•Limited access to skin for feeding
oAlmost all the body hairy except the flippers
oExtremely dense under coat makes penetration to skin difficult
•Lice often exposed to temperatures <5oCelsius
All species inevitably spend a considerable proportion of their lives immersed in
water, and on large seals, e.g. Elephant seals, this may be for up to 8 months at a
time.
Clearly the lice cannot breath under water. But lice can survive for long periods
without breathing, e.g. Pediculus immersed in fresh water can survive long
periods, but they suffer osmotic influx of water within 24 hours. In sea water
endosmosis is not a problem but, how to Echinophthiridae manage to get the right
amount of oxygen to stay alive?
Survival in water
All Anoplura are adapted to moderate tolerance of immersion in water. After all
most mammals have experienced periods when their coat remains soaked for
hours or days at a time. All lice have spiracles that inhibit water ingress.
However, in the Echinophthiridae this is taken to more extreme lengths than in
other groups because their host pelage does not trap air, and they are constantly
immersed for long periods
Ferris suggested that seal lice may take breaths of air at the same time as their hosts
when they surface –but, since most lice are on flippers when at sea and the flippers
of most seals only leave the water while resting, this seems unlikely.
Murray suggested they may take up oxygen from the surrounding water by
diffusion through the thinner cuticle on the ventral side of the thorax.
But, he also observed that lice burrowed into the host epidermis and remained in
the burrow where there would be little exposure to flow of oxygenated water. More
likely the thin cuticle facilitates uptake of heat from the host skin, which can occur
as blood flow increases in the flippers when seals surface from a dive.
How much oxygen do these lice need anyway? They don’t move about under
water, they don’t lay eggs or mate, and nymphs usually do not survive the
swimming period. But they do feed even when immersed –presumably because
the spiracle structure effectively prevents blockage, so they do not become
immobilised in the same way as terrestrial lice whose spiracles become “blocked”
when immersed or if the atrium is filled with fluid. Blocked lice appear to die
because they run out of energy through starvation rather than from lack of oxygen.
Too much oxygen?
Murray showed that Lepidophthirus macrorhini survived for weeks unfed at 5-10o
C but on flippers, whether in water or out they all died in 10 days at temperatures
between 15oand 25oC. This suggests they need to keep cool, and he also found
that oxygen metabolism increased 5-10 fold between 10oand 30oC.
Lice on flippers feed at intervals under water . Seal blood contains more
haemoglobin, more oxygen-efficient haemoglobin, and more erythrocytes than
other mammals. Thus each blood meal has a high oxygen content.
In some cases the ingested blood may be too oxygen rich and has been shown to be
quite toxic, for arthropods which is why most terrestrial insects limit spiracle
opening and mainly use them for expiration of carbon dioxide.
•Thompson found a negative correlation between louse numbers and total
erythrocyte count, haematocrit, and haemoglobin concentration for
Echinophthirius horridus on harbour seals
•Murray found that lice on flippers of restrained seals lived only a few days in
warm water –probably because the increased blood supply was over-rich in
oxygen.
I postulate that intermittent feeds by echinophthirids provide more than
enough oxygen for the lice to sustain themselves, and there is no requirement
to obtain oxygen by other means.
Literature cited
Crovetto A, R Franjolab, R Silvac. Primer registro en Chile de Antarctophthirus microchir
(Anoplura) en lobo marino común (Otaria flavescens). Arch Med Vet 2008; 40: 305-308.
Murray MD, Nicholls DG. Studies of the ectoparasites of seals and penguins. 1. 1. The ecology
of the louse Lepidophthirus macrorhini Enderlein on the southern elephant seal, Mirounga
leonina (L). Aust J Zool. 1965; 13: 437-454.
Thompson PM. Corpe HM, Reid RJ. Prevalence and intensity of the ectoparasite
Echinophthirius horridus on harbour seals (Phoca vitulina): effects of host age and inter-annual
variability in host food availability. Parasitology 1998; 117: 393-403.
Webb JE. Spiracle stucture as a guide to the phylogentic relationships of the Anoplura (biting
and sucking lice), with notes on the affiinities of the mammalian hosts. Proc Zool Soc, Lond.
1946; 116: 49-119
Acknowledgments
Thanks to everyone from whom I have shamelessly borrowed images, including A
Crovetto, Birgit Mehlhorn, Vince Smith, JE Webb and anyone else not specifically
attributed
Ian F Burgess
Medical Entomology Centre, Insect R&D Limited, Stow-cum-Quy, Cambridge, UK
How do Echinophthiriidae on seals survive months of immersion?
–A hypothesis for debate
A
B
C
Figure 1.
Antarctophthirus microchir (A);
Echinophthirius horridus (B);
Antarctophthirus trichechi (C)
to show the numerous
cuticular setae and scales
Figure 2
Figure 3
Figure 2. Diagrammatic representation of the
abdominal spiracle atrium and distal trachea of
Antarctophthirus microchir, showing protruding
atrium and robust triangular closure plate.
Figure 3. SEM of the opening of
the spiracle atrium of
Antarctophthirus microchir
Protruding atrium
Triangular closure plate
Figure 4. Section of
Antarctophthirus ogmorhini
showing thick cuticular
integument on the dorsal
surface and thin cuticle on the
ventral surface (arrowed)