From Nancy Wight's post I find two segments that don't quite say the same
thing.
First:
"A sample of the mother's breast milk obtained 16 days after delivery tested
positive for WNV-specific IgM.
The infant remained afebrile and healthy, although a serum sample from the
infant at age 25 days tested positive for WNV-specific IgM.  Virus culture
is pending."

and later:
"A new mother in Michigan contracted West Nile virus from a blood
transfusion shortly after giving birth. Laboratory analysis showed evidence
of West Nile virus in her breast milk. She breastfed her infant, and three
weeks later, her baby's blood tested positive for West Nile virus."

I am not questioning that the WNV antibodies in the baby, were a consequence
of the mother's milk, which contained antibodies after her infection with
WNV fromt the blood transfusion.  I am wondering, though, whether it is the
baby who is producing them.

In the first quote, all it says it that IgM specific to WNV was found in the
mother's milk and in the infant's serum, and that the virus itself has not
been shown to be there, yet.  In the second, it says 'evidence of WNV' and
that the baby's blood tested positive for WNV, not for antibodies to WNV.
Which is it?

Also, I was taught here that IgG's are the immunoglobulins passed on by the
GRAVID mother to the fetus via blood, and that IgM's are passed to the baby
via MILK.  According to what I learned, the IgM could be maternal, in
response to the infection stemming from the blood transfusion, and like many
other immunoglobulins, they are secreted in milk to protect the baby from
new infections sustained by the mother.  One of the reasons postulated for
the relative permeability of the newborn gut is to be able to absorb IgM's
from mother, as they are such large molecules that they can't cross the
epithelium of the gut later on.  After gut closure, it is my understanding
that IgM acts locally but not systemically in the baby.  By then the baby is
making its own IgM too.

So, has the virus itself been identified in the mother's milk or in the
baby's serum?  Or are we to assume that the baby has been exposed to virus
and that the baby's IgM is made by the baby, and not passively received as
part of the package in mother's milk?

In any case, I agree that CDC is to be applauded for advising continued
breastfeeding.

Rachel Myr
Kristiansand, Norway

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