For the most part, wild hedgehogs are quite able to look after themselves,
except when they encounter humans in some form or another.  There are some
maladies that do affect wild hedgehogs -- usually as the result of stress or
injury.

One particular problem to note, occurs primarily in autumn babies.  That is
that they do not pack on enough weigh to be able to survive hiberating.
Hedgehogs need to weight at least 500-600 grams in order to have a reasonable
chance of surviving hibernation.  If you have autumn babies in your garden
that are too small to hibernate successfully, you may need to bring them
indoors for a while, and fatten them up.

Here is a reminder from Peter Captijn that as friendly as wild hedgehogs are, 
they are still wild animals and certain realities apply:

    When a wild hedgehog has to be kept in house or with other 
    hedgehogs, it's a good idea to get rid of the fleas and ticks [9.4]
    before you infect your clean house. Most people use cat spray, but
    ticks tend to live through that. Bathing in vermin killing stuff 
    will be the solution. It can be done (preferably once) in a little 
    warm water so the hedgehog can't drown. Never use sprays or 
    whatever on piglets/hoglets, and never spray something in the 
    eyes, you can blind the hedgehog.  Please remind: a healthy wild 
    hedgehog has vermin, always!  This is natural.

Also from Peter are some pointers on various other health problems:

    Rabies: from various sources - European hedgehogs don't get
    rabies.  Whether that means they just die very quick, or that
    they are immune, I don't know.

[Editor's note: hedgehogs `can' get rabies, but due to the way they live, it
is exceptionally rare, at least as compared to other, more aggressive or
easily bitten animals]

    About lungworms, Fritzsche writes about German scientific study
    regarding lungworms by hedgehogs.  Lungworms are capsulated
    in the lungs and die.  If the hedgehog isn't healthy, this
    apparently doesn't work [fast enough?], and the hedgehog dies.  
    I do have hedgehogs running free in the garden, and I hear and 
    see [them] (in that order) eat snails and slugs, every day, and 
    quite a lot of them.  I won't hesitate to offer a hedgehog a 
    snail, but I can't estimate the involved risk (if any).

In my other readings and researches I've learned that the level of vermin
(fleas, ticks, mites, etc.) on wild hedgehogs often has a lot to do with
their living conditions, or more specifically how stressful they are.
Hedgehogs living well out in the country, with a plentiful supply of food and
water, relatively little or no pollution, or problems from human
encroachment, will have little, or not detectable vermin.  Those which are
under much more stress will have considerably higher levels of hitchhikers.

Injuries can provide an opportunity for various vermin to infest a hedgehog.
If you are helping a visiting friend out, check for ticks and even maggot
infestations where wounds or injuries might have happened.  Maggots might
need to be removed from the wound with a pair of tweezers, and the wound
thoroughly cleaned with an antiseptic solution.

Ticks should be treated with something designed to kill them.  Don't try to
simply remove them, or their mouth parts will be left attached, causing
infection and more serious problems.

I would suggest the book _The_Natural_Hedgehog_ to anyone who is planning to
try and help out hedgehogs in need.  Also, don't try to treat anything more
than minor problems without the help of a qualified veterinarian.

If all else fails, or you aren't sure what to do, get in touch with one of
the organizations listed in section [11.4] -- they will be happy to assist
you in helping a little friend.