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The Hitchcocks hitchcws at phoenix.net
Sun Mar 16 20:36:14 EST 1997

Claire - these are interesting questions, so I'm crossposting this to
bionet.parasitology on the chance some reader there may be interested in
answering some.  ..teresa.........

Claire wrote:
> I'm currently trying to get rid of a scabies infestation and I could
> do with some more information about it.  I'm not a medic but I do
> have a well-informed lay-person's knowledge of genetics, evolution etc.
> (and a sufficiently scientific background to be able to formulate
> experiments and assess the "evidence" for something).
> What I'd like to know
> *********************
> 1.  Is it true that there are known to be strains of the scabies mite
> resistant to malathion &/or other treatments?
> (Because I was travelling I've seen two different doctors over the last
> few weeks about this and they said contradictory things about that.  But
> I seem to remember reading recently that head lice were developing
> resistance to malathion, so it wouldn't surprise me if it _were_ true
> for scabies as well.)
> 2.  Is anything conclusive known about how long you have to be
> touching skin for the scabies mite to transfer from person to person?
> If I shake hands with someone (touching for a few seconds), can they
> get it from that much contact?  Or does it take longer than that for
> a mite to get going?
> (Note that a common belief, apparently shared by the manufacturers
> of the treatments, is that either (a) "prolonged" or "intimate" skin
> contact, or (b) sharing bedding, are necessary to transmit the mite.
> Frankly, this is certainly false, or I never would have caught the thing
> in the first place.)
> 3.  What's the minimum temperature for washing clothes, that will
> definitely kill the mite?
> 4.  How long can the mite survive away from the human body?  (for
> instance, on clothes that can only have a cool wash, or on upholstery
> etc. that can't be washed and would have to be "quarantined".)
> 5.  Why is it believed that the mite can't live on the faces or
> scalp of adults?  Is it possible that the resistant strains (if there
> are such things) are becoming so partly by changing their habitat?
> (All treatment instructions agree that it isn't necessary to treat
> the face or scalp except in babies.  So the evolutionary pressure is
> for them to learn to live there it seems to me.)
> 6.  Is there any chance that the mite can live in ears, nose, anus
> or vagina and survive the treatment in that way?  If not, what is it
> about those environments that prevents it from doing so?
> 7.  Is the mite mobile away from the human body, or does it basically
> just sit there waiting for another host to come along?  For instance,
> could it crawl through sheets and onto the mattress, and then back again
> after we change the sheets?  Could it crawl through socks and onto shoe
> linings, and then back again later?
> 8.  Is anything known about the relative vulnerability of the mite at
> different points on its life cycle?  (For instance, if eggs are more
> likely to survive than larvae or adults, it would presumably make sense
> to re-treat _after_ any surviving eggs have hatched and _before_ the
> larvae become adult and lay some more.)
> 9.  Itching increased over the week following the second treatment with
> Derbac (active ingredient: malathion).  Is it possible that this is due
> to reaction to the treatment?  or would that result (gradual increase
> over days) _always_ be because the mites are still there?  I realise
> that reactions to the treatment are possible, but I would expect such a
> reaction to flare up shortly after treatment and then _decrease_ gradually
> in the following.  But maybe that's not the case.
> 10.  Is malathion noticeably toxic to humans?  What about permethrin
> or benzyl benzoate - how do they compare?  I know that Quellada used
> to be made with lindane which is now considered a Bad Thing.
> 11.  Any more useful advice...  including other sources of information
> on the net.
> That's what I actually want to know... some history follows in case
> it's useful.
> Thanks in advance for answers.
> Background history from a few years ago:
> ****************************************
> About 8 years ago, went to doctor A with unidentified itching, which
> I suspected was parasitic.  He said it was midge bites and nothing
> to worry about.  It continued to get worse and worse for some weeks.
> Then some friends whom I'd visited during that time were diagnosed
> with scabies.  With that as a clue, I looked up scabies in my local
> college's medical library and was sure that was what I had.  I found
> one "track mark" and also recognised the pattern of worst itching at
> night.  I treated myself with something - I _think_ it was benzyl
> benzoate (which had been prescribed for the friends) although the name
> Quellada seems familiar too and it might have been that.  (Unfortunately
> I can't think of where I may have written it down at the time.)
> This successfully eradicated the apparent infestation, although eczema
> had built up over the weeks of scabies and the eczema persisted for
> some months.
> Because of the symptoms, and because the treatment worked, I've never
> doubted since then that it _was_ scabies I'd had.
> Recent history:
> ***************
> A month ago my partner (who is one of the friends who had it before,
> although we weren't partners then) recognised the symptoms on himself,
> and a couple of days later I started itching as well.  Because of our
> earlier experience we were sure of what it was.
> 1st treatment & 2nd treatment
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> We treated ourselves with stuff from the chemist.
> Because we were in different towns at the time and went to different
> chemists, we ended up with different stuff:  I had "Lyclear" (active
> ingredient, permethrin) and he had "Derbac M" (active ingredient,
> malathion).  (This is in the UK, I don't know if they have different
> brand names elsewhere.)
> For both of us, the itching decreased over the first couple of days,
> then gradually built up again, so we deduced that a few eggs, or perhaps
> mites, had probably survived.  So a week later we both treated ourselves
> again, exactly simultaneously, this time both with Derbac.  We also
> washed all our clothes, the sofa cover and the sheets, changed bedding,
> and covered the mattress with plastic sheeting in case that had any
> mites or eggs on it.
> Again, the itching decreased, and after about four or five days we
> thought the treatment may have worked.  However, on about the 9th day
> after that second treatment, I again noticed itching.  This built up
> for some days, and 16 days after the second treatment, I was sufficiently
> sure it hadn't worked that I went to the doctor.
> What one doctor said
> ********************
> Doctor B said:
> - scabies is difficult to diagnose, but he always believes people
> who've had it before if they say they've got it again
> - we probably have a resistant strain;  that's much more likely than
> that we've caught it back off our clothes or bedding
> - treat again with Derbac, and if that doesn't work, go back to the
> doctor after two weeks for a "second line of treatment".  (I asked
> what that would be but he didn't know off hand, he said he'd have to
> look it up.)
> 3rd treatment
> ~~~~~~~~~~~~~
> So we treated it again with Derbac.  Unlike the first two times, I had
> little noticeable decrease in itching.  It's now 10 days since that third
> treatment, and I'm sure I've still got the mites living on me.
> On the other hand, my partner had fewer symptoms before that third
> treatment, and now _seems_ to be clear.  (We've not had physical contact
> since a few days before that third treatment, first because of travel and
> then as a deliberate attempt to avoid one of us re-infesting the other.)
> Although the two weeks weren't up, I decided to go back to the doctor's
> early.
> What my own doctor said
> ***********************
> Doctor C said:
> - we probably caught it back off our clothes, or someone else
> - it won't be a resistant strain, and Derbac is just as good as
> anything to treat it
> - we should re-treat with Derbac again when the two weeks are up, and
> again two weeks later if necessary;  but we can treat it now if we
> really want to (i.e. with a smaller gap between treatments)
> Discrepancies
> *************
> a) Clearly the two doctors disagree.  One says it's probably a resistant
> strain, the other says it isn't.  One reckons I need an alternative
> treatment, the other says keep using Derbac.
> b) Also, the Lyclear instructions say
> "Scabies cannot be caught from bed linen or clothing."
> (which I don't believe)
> whereas the Derbac instructions say
> "No special sterilisation of clothing is necessary, ordinary laundering
> or dry cleaning with hot-iron pressing is sufficient."
> c) The Lyclear instructions also say "The scabies mite is transmitted by
> direct and prolonged skin contact (for example holding hands).  It is
> commonly passed between family members and parents sharing the same bed,
> or any other intimate personal contact."
> However, that doesn't explain how we got it in the first place, either
> this time or eight years ago, since those situations did not apply.
> It also doesn't go with Doctor C's idea that we've caught it back from
> our environment in some way.
> So there you have it!  Comments welcome!  Thanks.

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