Then we need to figure out well what type of bacteria, virus, fungi, or parasite is this? And it
turns out that different types of organisms affect different people during the course of the
lifespan. So let's look first at the bacteria. In neonates, we see certain types of bacteria that
can cause meningitis, encephalitis, or even cerebritis. The most common, as you see here,
is group B strep followed by E. coli, listeria, Strep pneumoniae, and klebsiella. So those are the
things we're going to think about and test for in young neonates. As we age in young children
and young adults, we see a different organization of organisms and types of organisms,
bacteria, that cause CNS infections. Strep pneumoniae, Neisseria meningitides, and H. flu are
the most common that really we've seen less H. flu since the development of a vaccine for
that agent. We don't see as much group B strep or listeria except in certain populations. In
older adults, we think of Strep pneumoniae, listeria actually comes back and increases in its
frequency like we saw in neonates, and group B strep rounds off the top 3. And then there
are other rare causes of the bacterial infection in the brain or spinal cord and that includes
legionella, bartonella, brucellosis or brucella, neurosyphilis, and TB. What about with viruses?
Well, different types of viruses have different predilection for different areas of the brain.
Certain viruses like to infect the meninges, others like the subarachnoid space, and still others
affect the brain parenchymal compartment and causes cerebritis. We call that tropism, and
that's an organism's propensity, predilection to affect a certain area of the nervous system.
In the meninges causing meningitis, we see enteroviruses and adenoviruses and before the
development of vaccines, we saw a lot of measles, mumps, and rubella. And those are things
that we may see more of if vaccines are not utilized to prevent those agents in organisms.
In the subarachnoid space with encephalitis, we see commonly arboviruses which includes
West Nile and you can see some other less common arboviruses there as well as herpes simplex
virus, an important cause of encephalitis that we'll focus more on in a subsequent lecture.
For cerebritis, we also see arboviruses and HSV, so some similarities between that
subarachnoid space and brain parenchymal compartment. And then there are some other
viruses to know about. Varicella zoster likes to cause a vasculopathy and often an encephalitis.
Cytomegalovirus likes to cause a ventriculitis or an ependymitis. Epstein-Barr virus is something
we see in patients with primary CNS lymphoma. HHV-6 is seen in immunocompromised patients
and HIV can cause many types of infections including those in the brain. So some important
things to think about when it comes to each of our types of infection in the nervous system.
And then there's some other things we should think about, fungal infections and a cryptococcal
meningitis is something that we'll focus on when we think about fungal infections in the brain,
but we can also see histo, coccidio, and blastomycosis infections. There are certain parasites
that have a predilection for the brain, toxoplasmosis really likes the basal ganglia so we
commonly see large basal ganglia lesions in patients with toxoplasmosis and that's usually
occurs in immunocompromised patients. Neurocysticercosis is endemic in certain areas of the
world and we can see that in certain populations with enhancing lesions often scattered
throughout the brain and is an important thing to consider in patients presenting with epilepsy.
We can see tick-borne infections in the nervous system. Rocky Mountain Spotted Fever, Lyme,
and ehrlichiosis are things that we often include on differential diagnoses in a patient who may
have had a tick exposure. And then there are some non-infectious causes of meningeal
irritation in a meningitis type of picture or an encephalitic presentation in an encephalitis type
of picture. And some of those are non-steroidal anti-inflammatories, intravenous,
immunoglobulin, IVIG, methotrexate, we can see paraneoplastic or cancer associated immune
attacks on these areas and other potential non-infectious or aseptic causes of a CNS process.