NeuroLearn NeuroHelp Bacteria @ Acute meningitis
Background Histopathology & Immunohistochemistry
BACKGROUND AND CLINICAL INFORMATION:
Head
Definition: Neonatal period is defined as the first 30 days of
life.
Clinical features:
Early onset (less than 48 hr old): obstetric complications are common; transmission
is usually mother to infant; infants are usually mature and usually present
as sepsis clinically with only one third with CNS dysfunction; common agents
include Group B streptococci (especially group III) and E. coli but
nosocomial pathogens are rare; mortality is about 35%.
Late onset (later than 7 days after birth) group: obstetric complications are rare but babies are
often premature; transmission is from mother or other adults to infants;
fever is more prominent; CNS manifestation is more striking and seizures is
present in about half the cases; common agents include Group B strepptococci
and nosocomial pathogens but E. coli is uncommon; mortality is about 15%.
Incidence and risk factors: 0.5% of all life birth.
Risk factors:
Low birth weight:
Infants below 2,500 grams have a three times increased risk.
Metabolic:
Risk factors specific for E. coli sepsis include galactosemia, excess free
iron (administer to prevent iron deficiency anemia in some situations) and
excess vitamin E (adminstered to prevent retinopathy in premature babies).
Other risk factors:
premature rupture of membrane, resuscitation at birth and babys born to
mothers with a temperature greater than 37.8 øC postpartum.
Pathogenesis:
lack of transplacentally acquired antibodies against potential meningeal
pathogens, absence of alveolar macrophages at birth, a small PMN pool with
chemothactic deficiencies compared with adults, and inefficient synthesis of
antibodies during the neonatal stages all add to the increased susceptibility of
neonates to meningitis.
Amniotic fluid
is inhibitory to the growth of E. coli and certain other organisms because of
the presence of lysozyme, transferrin, and certain immunoglobulins. The amniotic
fluid is no longer a hostile environment for E. coli if it contains meconium or
vernix. In contrast, Group B Streptococcus can grow in "normal"
amniotic fluid. Macrophages in the amniotic fluid are derived from the maternal
circulation.
Infectious agents:
almost half of the cases are caused by streptococci (especially group B),
followed by Staphylococcus (S. epidermis, S. aureus, and S. pneumoniae),
Klebsiella-Enterobacter species and then Escherichia coli (most commonly type
K1).
Common pathogens and route of
infection:
Group B Streptococcus:
early onset disease acquired in the birth canal; late onset disease-
contamination.
Staphylococcus epidermidis: comtaminated intravascular cannulae.
Staphylococcus aureus:
usually a primary focus of infection is evident, with heel punctures and
intravenous cannula entry sites as most common foci.
Escherichia coli:
multiple pathways including acquisition through the birth canal and
contaminated nursary personals.
HISTOPATHOLOGY AND IMMUNOHISTOCHEMISTRY:
Head
Arachnoiditis
around the base of the brain may be particularly prominent, alternatively, the
exudate may be distributed over the cerebral cortex surface.
Vasculitis
is an invariable component of neonatal meningitis. Perivascular inflammatory
infiltration in the adventitia with the intima spared is common in arteries;
phlebitis with thrombosis and complete occlusion is common in veins; this may
lead to thrombotic hemorrhagic infarction.
Pathogenesis:
One of the explanation for the increase in severity of neonatal meningitis
is the relatively paucity and functional immaturity of arachnoid villi in the
newborn. Thus, the egress of bacteria is slower, which can lead to bacterial
accumulation in the CSF. The inflammatiory exudate in the ventricular CSF drains
into and "Plugs" the arachnoid villi, producing dysfunction of this
exit valve and transiently increasing intracranial pressure. Choroid plexitis,
ventriculitis, and glial tufts and bridges formation within the ventricles will
lead to obstructive hydrocephalus.
Rhombencephalitis
often associate with meningitis due to Listeria in both pediatric and adult
cases [Uldry
PA et al., J Neurol 1993 24:235-42]