Medical Microbiology: CNS Infections and Diagnostic Tools

This article discusses the global incidence and prevalence of CNS infections caused by bacteria, viruses, parasites, and prions. It covers bacterial, viral, and fungal meningitis, their signs and symptoms, and CSF lumbar puncture analysis. The article also talks about the role of diagnostic tools in detecting the pathogens responsible for these infections.

Running head: MEDICAL MICROBIOLOGY
MEDICAL MICROBIOLOGY
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Introduction:
According to Scheld et al. (2014), central nervous system infections can be defined as
infections that affect the brain and the spinal region of the human body. A wide range of
microorganisms affect the normal functioning of the central nervous system and cause
infections. These microorganisms include, bacteria, viruses and parasites. Additionally, a
special class of microorganism known as the prion has been reported to damage the normal
functioning of the brain. It should be noted in this regard that infection within the central
nervous system can either lead to meningitis, encephalitis or meningoencephalitis which
could either be acute or chronic (Teasdale & Jennet, 1974)
Global Incidence and Prevalence of CNS Infection:
According to He et al. (2016), CNS infections are classified on the basis of their
anatomic localization. Encephalitis, Meningitis, formation of brain abscess and myelitis has
been reported to be the most common forms of CNS infection. Bacterial Meningitis has been
considered as the most fatal CNS infection that leads to approximately 500 deaths every year
in US. The mortality rate associated with the disease is 6% to 26% (He et al., 2016).
As mentioned by Jones and Winograd (2018), the causative agents Haemophilus
influenza, Streptococcus pneumonae and Neisseris meningitides remain the highest
contributor of bacterial Meningitis in the global population. According to Jones and
Winograd (2018), it has been mentioned that fungal meningitis caused by Cryptococcus
species is equivalent to 70.1% within the paediatric and the adult patients account. Further,
Coccidioides sp, Candida sp. And Histoplasma species contribute to approximately 16.4%,
7.6% and 6.0% of the fungal Meningitis within USA.

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Bacterial Diseases:
Bacterial meningitis has been reported to be a severe form of meningitis that elicits
serious effect on the normal functioning of the brain. It leads to drastic consequences such as
hearing impairment, brain damage, learning impairment and limb amputation (Masri et al.,
2018). It is usually caused by the bacteria Neisseria meningitides (Stone & Hawkins, 2007).
The causative agent for Meningitis varies across different age groups (Hacochen et al., 2013):
Age-group Causative Agent
New born Streptococci, E.coli and Listeria
monocytogenes
Infants Neisseria meningitis, Streptococcus
pneumonia, Haemophilus influenzae
Children N.meningitidis, S. pneumoniae
Adults S.pneumoniae, N.meningitidis and
Mycobacteria
Bacterial meningitis has been reported to be contagious and spreads through the
exchange of respiratory fluids and throats secretions (Hase et al., 2014). The incidence of
bacterial meningitis has been reported to be 0.6-4 per 100,000 individuals in the adults across
developed countries (Jones & Winograd, 2018). It should further be noted that the prevalence
rate is estimated to be ten times higher in different parts of the world. The most common
causative agents of bacterial encephalitis that cause 85% of the infections has been recorded
to be S.pneumoniae and N.meningitis (Abbas et al., 2016). Infection caused by Haemophilus
influenza type b and seven serotypes of streptococcus pneumoniae has reduced significantly
in paediatrics after the introduction of conjugate vaccines (Heydeman & Klein, 2000).
Signs and Symptoms:
The signs and symptoms for bacterial meningitis include the following (Kumar, 2005) :
 Nausea and vomiting tendency
 Pertinent fever

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 Pain in muscular joint
 Pertinent headache and stiffness of neck
 Manifestation of rashes
 Feeling of numbness and coldness in hand or feet and mottled skin
The signs and symptoms for bacterial encephalitis include similar symptoms as that of
bacterial meningitis. However, severe cases are marked by speech and hearing impairment,
double vision. Hallucinations and personality changes. Other symptoms also include,
memory loss, seizures, partial paralysis of the limbs and impaired intellectual ability
(Hosseininasab et al.,2011).
CSF Lumbar Puncture Analysis:
Cerebrospinal Fluid Analysis can be defined as a series of laboratory tests that is
performed on a sample of cerebrospinal fluid. The CSF is produced by the Choroid plexus
region of the brain and the fluid is reabsorbed to the bloodstream. The fluid is regenerated at
brief intervals and circulates the nutrients around the brain and spinal column (Seehusen et
al., 2003). Also, the fluid is responsible for the protection of the brain and the spinal column.
The CSF lumbar puncture is performed by the collection of the CSF sample through spinal
tapping. The analysis of the sample facilitates analysis of fluid pressure, protein and glucose
level, RBC and WBC content, bacterial and viral profile and detection of invasive antigen
(Seehusen et al., 2003). The sample is collected from the lower back area through a needle. It
is extremely important for the patient to lay completely motionless so as to avoid incorrect
placement of the needle. The patient is generally made to sit with a curled spine so as to make
space in between the bones present at the lower back. The procedure takes place in a span of
thirty minutes and the procedure is directed by fluoroscopy that helps the physician in placing
the needle between the two vertebrae (Bonadio, 2014). It should be noted in this context that

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the pressure inside the brain is maintained using a manometer (Tamune et al., 2014). After
the collection of the sample, the punctured site a bandage is applied at the punctured site and
the patient is made to lie down for an hour to reduce risks of side-effects such as headaches or
trauma (Seehusen et al., 2003).
CSF findings in bacterial, viral and fungal infections:
The CSF characteristics in case of bacterial, viral and fungal infections can be enlisted
as under (Chadwick, 2002):
Characteristics Bacterial Viral Fungal
Opening
pressure
Glucose
Protein
Rbcs
Wbcs
Difference
Appearance
increased
Low
Elevated
Few
>200
PMNs
Turbid
Normal or
elevated
Normal
Normal
Negligible
<200
Mono
Clear
Normal or
elevated
Low
High
Negligible
<50
Mono
Turbid
Viral Meningitis:
Viral meningitis can be listed as a less severe form of meningitis that causes
inflammation of the tissue that surrounds the brain and the spinal cord (Hosseininasab et al.,
2011). The major causative agent of viral encephalitis has been reported to be Non-polio
eneteroviruses. Other major viral causative agents that cause meningitis are Mumps virus,
Herpes virus, Measles virus, West Nile Virus, Influenza virus and Lymphocytic virus (De
Ory et al., 2013). Meningitis is common in children aged 5 years and below (Hacohen et al.,
2013). Also, individuals who have recently undergone an organ transplantation, bone marrow
transplantation or chemotherapy and possess a weakened immune system are susceptible to

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develop meningitis. The mode of transmission of the viral agent is through coughing or
sneezing.
Viral Encephalitis:
On the other hand, viral encephalitis can be defines as a condition that occurs on
account of inflammation within the brain. It is commonly characterized by the infectious viral
agents that include the category of enteroviruses. The virus typically invades the human body
and multiplies within the brain. On identifying the antigen the body elicits an immune
response that leads to inflammation of the brain. The disease has been associated with
permanent brain damage and has been reported to affect children below 5 years and adults
above 55 years of age. The virus can usually spread through exchange of respiratory fluid or
consumption of contaminated food items and beverage (Stone & Hawkins, 2007). Also, the
viral agent can spread through vectors that include infected insects and recurrent activity of
dormant viral infection. The symptoms of viral meningitis are similar to that of bacterial
meningitis but of lower intensity. The onset of viral meningitis is generally marked by a viral
infection that proceeds to assume the form of acute or chronic viral meningitis.
The signs and symptoms of viral encephalitis include the following (Stone &
Hawkins, 2007):
 Amnesia
 Partial or complete paralysis
 Photophobia
 Elevated temperature
 Stiffness within the neck and back region
 General malaise

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Fungal Meningitis:
Fungal meningitis is caused by the transmission of fungus through the blood to the
spinal cord. The common causative agent of fungal meningitis is Cryptococcus (Abbas et
al.,2016). It is usually common in individuals who are affected with HIV or Cancer that
disrupts the immune system of the body. The disease is spread by the transmission of a
fungus from the brain to the spinal cord (Chen et al., 2014). Fungal meningitis is also
characterized by the intake of medications that include Prednisone which is administered
after organ transplantation as anti-TNF medications (Heydeman & Klein, 2000).
Prevalence aetiology in Paediatric and adult Group:
Bacterial meningitis has been linked to a mortality rate of about 5-10% in the
paediatric group across the globe. The case of recurrent meningitis in children was recorded
to be 39% (Jones & Winograd, 2018). Studies reveal that the incidence of carriage prevalence
significantly increases throughout childhood ranging from 4.5% in infants to 27.3% in
children aged 5 years. Also, population studies has revealed 80.69 cases per 100,000
individuals to be affected with bacterial meningitis who are younger than 2 months in age
(He et al.,2016).
Role of Diagnostic tools in detection of the pathogens:
Diagnosis is generally carried out through clinical examination, neuroimaging and
laboratory testing that includes biochemical tests and assays. Cell culture and direct virus
antigen detection are traditional methods (Chadwick, 2002). Newer methods such as
investigation of CSF for cells, protein and glucose, nucleic acid amplification tests and
polymerase chain PCR have been identified as effective methods to detect a broad spectrum
of antigens (Thomson & Bertram, 2001).

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