Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 29, 2016

Meningoencephalitis is a rare and severe condition affecting the central nervous system that is usually caused by an infection including a viral infection, bacterial infection, parasitic infection or fungal infection. It should be treated promptly, as it can become quite serious very quickly. Whereas meningitis infects the meninges (protective membranes surrounding the brain and spinal cord), meningoencephalitis is an infection of both the meninges and the brain itself.


Definition & Facts

Inflammation of either the brain or spinal cord is extremely dangerous. According to the National Institutes of Health (NIH), less than 10,000 cases are reported in the United States annually. While anyone can get meningoencephalitis, it is most often found in those with weakened immune systems, either as a result of other diseases or as a result of taking immunosuppressive drugs.

Encephalitis, by itself, is poorly understood. Estimates are that as many as 60 percent of cases go undiagnosed due to mild symptoms. However, when it is combined with meningitis, it requires prompt medical attention.

Symptoms & Complaints

Medical professionals point to what is called the triad of an acute case of meningoencephalitis: fever, headache, altered mental state. In addition to these symptoms, the condition can cause nausea, double vision, drowsiness, sensitivity to light, and neck stiffness.

Neck stiffness may be a result of the infection causing increased pressure in the tight fluid space of the spine and/or brain, and is what separates it from a host of other diseases with similar symptoms. Flu-like symptoms may manifest over one to two days. Sometimes a rash is present.

Since meningoencephalitis involves the brain, meningoencephalitis may be characterized by such neurological symptoms as confusion, disorientation, and changes in behavior.

Especially in infants, this condition can cause a bulge in the fontanelle (soft spot on top of the head). If a parent or caregiver suspects an infant two-years in age or less has contracted the disease, it is important to seek immediate medical attention. The condition can rapidly become even more dangerous than in an adult due to a still-developing immune system.


In general, meningoencephalitis can be caused by bacteria, viruses, fungi, parasites, a reaction to certain medications, rheumatic diseases, or even traumatic brain injury. The most frequent causes are bacterial or viral infections.

The bacterial form of this illness usually is caused by either Streptococcus pneumoniae bacteria or (less commonly) Neisseria meningitidis. Lyme disease, which is a bacterial infection (borreliosis), can sometimes precipitate meningoencephalitis. Sometimes bacterial infections can live harmlessly in other parts of the body and migrate to the spine or brain whereupon they cause health problems.

When the problem is bacterial in nature, the offending organism usually invades the upper respiratory tract and then makes its way to the brain via the bloodstream. Less common is for the bacteria to attack the meninges directly. Meningococcal meningitis (which is caused by the Neisseria meningitidis bacteria) is fatal in about 10 percent of cases, and another 10-15 percent are left with brain damage and other serious long-term side effects.

Common viruses can be the causal agent as well, usually entering through the mouth or nose and taking that route to the brain. Since these viruses are present in mucus, saliva, and feces, transmission through direct contact or touching an infected surface is possible. Specific viruses that cause meningoencephalitis are herpes simplex virus (herpes simplex 1 or HSV-1 and herpes simplex 2 or HSV-2]], rabies virus, West Nile virus.

Diagnosis & Tests

If meningoencephalitis is suspected, the first step the doctor will take is to conduct a physical examination and inquire about a patient's medical history and family history. Factors to take into account are recent travel (especially if out of the country), insect or animal bites, contact with ill persons, and a list of medications. If a physician suspects meningoencephalitis, he or she will order up a battery of diagnostic tests in order to assess the presence of an infection and inflammation.

Besides taking blood tests, a battery of neurological examinations should be performed, including those designed to test sensory and nerve function, hearing and speech, coordination and balance, and more. Blood and clinical urine tests can establish if there is an infection in the brain or spinal cord. Cerebrospinal fluid may be drawn directly from the lower back during a procedure called a spinal tap or lumbar puncture

Treatment & Therapy

Immediate, aggressive medical care is called for if meningoencephalitis is diagnosed in order to reduce the risk of severe, permanent brain damage. The first action normally taken to treat this disease if a bacteria infection is suspected is a course of antibiotics that can cross the blood-brain barrier. Infected sinuses might need to be drained.

Often doctors will prescribe corticosteroids to immediately begin reducing brain inflammation. A common choice is prednisone. In the case of a viral infection, antibiotics are not effective. There is no specific treatment in this instance, though a few general rules are usually followed.

The doctor will normally prescribe anticonvulsant medications to prevent seizures. Pain medications and/or sedatives may be appropriate to comfort the patient. Depending upon the level of brain involvement, cognitive rehabilitation might be prescribed after the acute danger has passed, including possible physical therapy and speech therapy. If the illness is caught soon enough, complications may be averted.

Prevention & Prophylaxis

While no preventative measure can guarantee against contracting meningoencephalitis, there are some common sense measures to take. One should stay away from someone with an active case and avoid sharing food, utensils, or glasses. Thorough and frequent hand washing is a good preventative measure.

Where applicable, one should get vaccines against all the bacteria available. Pneumococcal vaccine, meningococcal vaccine can help prevent the infections which cause meningocephalitis.

Since insect bites, especially mosquitoes, are a risk factor, one can protect against the threat by limiting outdoor activities at night. During the day, wearing long sleeves and using insect repellant may help prevent insect bites. Standing pools of water attract mosquitoes and should be avoided or drained where applicable.