Infections in the brain and spinal cord can cause dangerous inflammation. This inflammation may lead to a wide range of symptoms, such as fever, headache, or confusion, and in severe cases, it can result in brain damage, stroke, seizures, or death.
Infection of the meninges, the membranes surrounding the brain and spinal cord, is called meningitis, while inflammation of the brain alone is referred to as encephalitis.
Myelitis is an infection of the spinal cord. When both the brain and spinal cord are inflamed, the condition is called encephalomyelitis.
What causes meningitis and encephalitis?
Meningitis and encephalitis are commonly caused by viruses or bacteria.
The body’s immune system can contain and overcome an infection. However, if the infection enters the bloodstream and then reaches the cerebrospinal fluid that surrounds the brain and spinal cord, it can affect the nerves and travel to the brain and surrounding membranes, causing inflammation. This inflammation can damage or destroy neurons and lead to cerebral bleeding.
Meningitis
Meningitis is commonly caused by a bacterial or viral infection. It can also result from a fungal infection, a reaction to certain medications or medical treatments, an inflammatory disease such as lupus, certain types of cancer, or a traumatic injury to the head or spine.
Bacterial meningitis
A rare but potentially life-threatening disease.
It can be caused by several types of bacteria that initially produce an upper respiratory tract infection and then travel through the bloodstream to the brain. The disease can also occur when certain bacteria directly invade the meninges and may block cerebral blood vessels, causing a stroke and permanent brain damage.
Pneumococcal meningitis
It is the most common form of meningitis and the most severe type of bacterial meningitis.
The disease is caused by the bacterium Streptococcus pneumoniae, which also causes pneumonia, blood poisoning (septicemia), and sinus and ear infections. Children under the age of 2 and adults with weakened immune systems are particularly at risk. Individuals with pneumococcal meningitis often experience neurological damage ranging from hearing loss to severe brain injury.
Meningococcal meningitis
Caused by the bacterium Neisseria meningitidis, it is common in children aged 2 to 18 years.
High-risk groups include infants under 1 year of age, individuals with suppressed immune systems, travelers to foreign countries where the disease is endemic, and college students (particularly freshmen) living in dormitories. Between 10 and 15 percent of cases are fatal, with another 10 to 15 percent resulting in brain damage and other serious complications.
Haemophilus meningitis
It was once the most common form of bacterial meningitis.
Fortunately, the Haemophilus influenzae type b vaccine has greatly reduced the number of cases. Those at highest risk of contracting the disease are children in daycare centers and those without access to the vaccine.
Other forms of bacterial meningitis
These include meningitis caused by Listeria monocytogenes, which can cross the placental barrier and result in stillbirth or neonatal death; meningitis caused by Escherichia coli, more common in the elderly and newborns and transmissible to an infant through the birth canal; and meningitis caused by Mycobacterium tuberculosis, a rare condition that occurs when the bacterium responsible for tuberculosis infects the meninges.
Viral or aseptic meningitis
It is the most common form of meningitis. This typically mild and non-fatal disease is generally caused by enteroviruses, common viruses that enter the body through the mouth and travel to the brain and surrounding tissues where they replicate.
Enteroviruses are present in mucus, saliva, and feces and can be transmitted through direct contact with an infected person or with a contaminated object or surface. Other viruses that cause meningitis include varicella zoster (the virus that causes chickenpox and may later reappear as herpes), influenza, mumps, HIV, and herpes simplex virus type 2 (genital herpes).
Encephalitis
Encephalitis can be caused by a bacterial infection and, more frequently, by viral infections. Several thousand cases of encephalitis are reported annually, but the actual number may be much higher since symptoms may be mild or absent in most patients.
Caused by a direct viral infection of the spinal cord and brain. The infection may be focal (localized to a single area) or diffuse (affecting multiple different areas).
Secondary or post-infectious encephalitis
It may result from complications of a current viral infection. Secondary encephalitis due to a prior viral infection or immunization is known as acute disseminated encephalitis. This condition often occurs 2 to 3 weeks after the initial infection.
Most cases of encephalitis are caused by enteroviruses, herpes simplex virus types 1 and 2, the bite of a rabid animal (rabies virus), or arboviruses, which are transmitted from infected animals to humans through the bite of an infected tick, mosquito, or other blood-sucking insect. Lyme disease, a bacterial infection spread by tick bites, can also cause encephalitis.
Herpes simplex encephalitis (HSE)
It accounts for approximately 10 percent of all encephalitis cases, with an incidence of about 2 cases per million people per year. More than half of untreated cases are fatal. Around 30 percent of cases result from an initial herpes simplex virus infection; the majority are caused by reactivation of a previous infection.
HSE due to herpes simplex virus type 1 (which causes sores or blisters around the mouth or eyes) can affect any age group but is more commonly seen in individuals under 20 or over 40 years old. The virus is transmitted through contact with an infected person.
Symptoms include headache and fever lasting up to 5 days, followed by personality and behavioral changes, seizures, partial paralysis, hallucinations, and altered levels of consciousness. Brain damage is typically observed, which can be severe in adults and children beyond the neonatal period, particularly in the frontal and temporal lobes.
Type 2 virus (genital herpes) is most commonly transmitted through sexual contact. An infected mother can transmit the disease to her child at birth through contact with genital secretions, although this is rare. In newborns, symptoms such as lethargy, irritability, tremors, seizures, and poor feeding typically develop between 4 and 11 days after birth.
Powassan encephalitis
It is the only well-documented tick-borne arbovirus.
Symptoms appear 7 to 10 days after the bite and may include headache, fever, nausea, confusion, partial paralysis, and coma. Permanent neurological damage occurs in approximately half of the cases, and death in about 10 to 15 percent of cases.
- Equine encephalitis
It affects both horses and humans.
In humans, symptoms appear 4 to 10 days after transmission and include fever, flu-like muscle aches, and progressively worsening headache, followed by coma and death in severe cases.
Approximately half of the infected patients die from the disorder.
Western equine encephalitis is found in agricultural regions of the western and central plains states. Symptoms begin 5 to 10 days after infection. Children, particularly those under 12 months of age, are more severely affected than adults and may experience permanent neurological damage. Death occurs in approximately 3 percent of cases.
Venezuelan equine encephalitis is very rare in this country. Children are at higher risk for severe complications, while adults typically experience flu-like symptoms. The epidemic in South and Central America has killed thousands of people and left others with severe permanent neurological damage.
- LaCrosse encephalitis
Most cases occur in children under 16 years of age.
Symptoms such as vomiting, headache, fever, and lethargy appear 5 to 10 days after infection. Severe complications include seizures, coma, and permanent neurological damage. Approximately 100 cases of LaCrosse encephalitis are reported annually.
- St. Louis encephalitis
It is more prevalent in the temperate regions of the United States but can occur anywhere in the country.
The disease is generally milder in children than in adults, with the elderly at greater risk of severe illness and death.
Symptoms typically appear 7 to 10 days after infection and include headache and fever. In more severe cases, confusion and disorientation, tremors, seizures (especially in very young patients), and coma may occur.
- West Nile encephalitis
The disease is generally transmitted through the bite of an infected mosquito but can also occur following transplantation of an infected organ or through transfusions of infected blood or blood products.
Symptoms resemble those of the flu and include fever, headache, and joint pain. Some patients may experience a skin rash and swollen lymph nodes, while others may be asymptomatic. The elderly and adults with weakened immune systems are at higher risk.
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