This article is from the Fleas, Ticks, and Your Pet FAQ, by tittle@zmall.com (Cindy Tittle Moore) with numerous contributions by others.
Very young animals can die from overinfestation of fleas. They are
small enough that they can become dangerously anemic within hours, and
are young enough that they will be poisoned by dipping chemicals.
Consult your vet immediately if you have a less than 8-10 week old
kitten or puppy with a bad case of the fleas. Do not attempt to "dip"
them, you can easily kill them this way.
Symptoms of anemia: if flea-infested baby animals become lethargic,
weak, and pale, you may have *only hours* before they die. A good test
for anemia is to take your finger, lift the upper lip, and press
gently but firmly into the upper gum. The gum will turn white for a
moment and then return almost immediately to a pink color. If the gum
stays white for more than a couple of seconds, anemia is indicated.
Take them to the vet *now*.
If they do not yet appear anemic, use a flea comb on them. You should
take steps to prevent infestation by keeping the mother clear of
fleas, and regularly (at least every other day) changing and
laundering the bedding. While you should not dip them in chemicals,
giving them a plain soap-and-water bath can help remove the fleas from
their body: wash the bedding at the same time and then use the flea
comb regularly to keep fleas from taking hold again. The mildly
insecticidal shampoo Mycodex (tm) can be used on kittens, but requires
flea combing afterwards anyway because of its mildness.
From Orca Starbuck:
Most flea shampoos, sprays, and powders are not cleared for use on
pregnant, nursing or young animals. In addition, the act of
bathing, spraying, or powdering a pregnant or young animal can
frighten or chill the animal. So most vets are hesitant to
recommend ANY course of action if you have pregnant, flea-infested
animals. However:
Low concentration pyrethrin products (or allethrin, like mycodex)
ARE considered safe. In "Feline Husbandry" pyrethrin is the only
flea poison included in a list of chemicals and drugs that are
known to be safe during pregnancy. Methoprene is also considered
safe, although its use is new enough that it doesn't appear in many
of the texts.
Zodiac pyrethrin + methoprene spray for cats is considered safe for
pregnant and nursing cats and kittens that are at least 24 hours
old! The same is true for the similar spray for dogs. Likewise, the
Zodiac premise sprays are safe for use where pregnant and nursing
animals and young animals are housed, as long as the spray is
allowed to dry before the animals are introduced back into the
area.
Since spray can often be upsetting to the mother cat, a paper towel
which has been sprayed with Zodiac spray for cats until it is about
1/2 saturated is better. Rub the towel all over the queen (except
for her face and nipples) and comb out with a flea comb, and repeat
the treatment a week later.
If there are still problems with fleas once the kittens are born,
it is quite safe to do the same treatment on the kittens about once
a week, starting at a week of age.
 
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