There are two types of meningitis—an inflammation of the meninges which are the tissues covering the brain and spinal cord. Bacterial meningitis, such as meningiococcal meningitis, is a bacterial infection. Aseptic meningitis is caused by viral, fungal, or other infection. Aseptic meningitis also may have a noninfectious cause such as an underlying illness. Some types of aseptic meningitis respond to antibiotic treatment, but viral meningitis does not. Aseptic meningitis causes between 25,000 and 50,000 hospital admissions per year in the United States alone.
The symptoms of meningitis vary, but severe headache, neck stiffness, and an aversion of light are common. Accurate diagnosis of the cause of meningitis, through examination of the cerebrospinal fluid, is important because treatment for bacterial meningitis needs to begin as soon as possible. Viral meningitis is rarely fatal, but may occasionally cause permanent disability.
More than 80% of cases of aseptic meningitis are caused by viruses. Many different viruses are implicated, including: enteroviruses, mumps, herpes, HIV, and viruses borne by mosquitoes and ticks, otherwise known as arboviruses. The enteroviruses account for around 90% of cases of viral meningitis. These viruses live in the human intestine. They rarely cause meningitis, but are a common cause of colds, sore throats, stomach upsets, and diarrhea. Until the introduction of the MMR (measles, mumps, and rubella) vaccine, the mumps virus was the most common cause of viral meningitis among children under five years of age.
Although viral meningitis is usually considered to be a mild illness, it often requires physician care or hospitalization for treatment. Some symptoms of viral meningitis are caused by pressure on the brain from inflamed meninges (membranes that envelop the nervous system) and include a severe headache and stiffness of the neck. A high fever and photophobia—an aversion to light—are also common side effects of enterovirus-associated meningitis. Patients may have a strong desire to be in a quiet, dark room.
Many people with viral meningitis experience non-specific symptoms such as vomiting, cough, diarrhea, loss of appetite, and rash. Many such cases are mistaken as influenza (flu). Where symptoms are severe, bacterial meningitis might be suspected and immediate hospital admission is appropriate. Occasionally, the virus affects the brain itself causing encephalitis, an inflammation that can lead to lasting brain damage.
The symptoms of viral meningitis have a rapid onset, usually within three to ten days after exposure. Other causes of aseptic meningitis may produce disease following a slower course. In the early stages, it can be hard to distinguish aseptic and bacterial meningitis. One clue is that the person with aseptic meningitis usually remains alert. Confusion and disorientation may occur with bacterial meningitis, along with neurological abnormalities such as deafness or visual disturbances—such symptoms are uncommon in viral meningitis.
It is more difficult to identify the symptoms of viral meningitis in infants. Fever, fretfulness and irritability, difficulty in waking up, or refusal to eat may be noted.
Anyone with possible meningitis symptoms should seek prompt medical attention. Though viral meningitis is generally less severe, early symptoms of viral and bacterial meningitis may be difficult to distinguish without medical testing. Bacterial meningitis requires antibiotic treatment and can cause permanent disability or death if left to untreated. Diagnosis involves an examination of the cerebrospinal fluid (CSF), the watery fluid that bathes and protects the brain and spinal cord. A sample of CSF is removed from around the spinal cord in a procedure called lumbar puncture. Bacteria can usually be cultured from this in cases of bacterial meningitis.
Most people make a full recovery from viral meningitis, with no lasting effects. Sometimes recovery is slow, with patients experiencing headache, tiredness, fatigue, depression, and loss of concentration for many months.
Transmission of meningitis depends upon the underlying viral cause. Enteroviruses, the most common cause, are spread through direct contact with the saliva, mucus, or nasal mucous of an infected person. Exposure to their coughs and sneezes, shaking hands, or touching some-thing they have handled can cause infection if one then touches their nose or mouth. However, this kind of person-to-person transmission is unusual.
Enteroviruses are also shed into the feces of people who are infected. Children who are not yet toilet-trained may spread the virus in this way. Adults changing the diaper of an infected infant may therefore be at risk. The infectious period lasts from about three days after a person has been infected until ten days after they develop the symptoms of viral meningitis.
Viral meningitis is far more common than bacterial meningitis. It is found mainly among babies, children, and adolescents. There are an estimated 300,000 cases per year in the United States, with 25,000–50,000 hospital admissions. Because many mild cases are not reported to the physician, the true number of cases is unknown. Moreover, as the main purpose of hospital investigations is to rule out bacterial meningitis, the specific virus involved in an aseptic case is often not detected.
There are seasonal variations in viral meningitis, depending upon the virus involved. Viruses borne by arthropods, such as mosquitoes and ticks, cause disease most often in late summer and early fall. Enteroviruses follow a similar seasonal pattern. Mumps virus tends to cause meningitis most often in late winter and early spring while herpes meningitis does not have a seasonal pattern.
There is no general anti-viral treatment for viral meningitis, although the anti-viral drug aciclovir might be used if the cause is found to be herpes simplex. Accurate diagnosis is needed to be sure the cause really is viral. Bacterial meningitis and some types of aseptic meningitis respond to antibiotic therapy. Sometimes antibiotics will be started straight away if someone is admitted to hospital with any form of meningitis, but these will be discontinued if the cause is found to be viral. Bed rest, fluids, and medication to relieve pain and fever are the best approach to alleviating the symptoms associated with viral meningitis.
It is difficult to prescribe a specific way of preventing viral meningitis, because there are so many different causes of the disease. The MMR vaccine will prevent meningitis caused by the measles and mumps virus. Since the majority of cases are caused by enteroviruses, which are spread by infected saliva and other bodily secretions, good personal hygiene stems transmission. Regular and thorough handwashing can stop enteroviruses from spreading. Potentially contaminated surfaces should be cleaned down with soap and water or diluted bleach. These precautions are especially important in institutions such as child care centers, schools, public bathing facilities, and dormitories.
WORDS TO KNOW
ARBOVIRUS: An arbovirus is a virus that is typically spread by blood-sucking insects, most commonly mosquitoes. Over 100 types of arboviruses cause disease in humans. Yellow fever and dengue are two examples.
ARTHROPOD: A member of the largest single animal phylum, consisting of organisms with segmented bodies, jointed legs or wings, and exoskeletons.
ENTEROVIRUS: Enteroviruses are a group of viruses that contain ribonucleic acid as their genetic material. They are members of the picornavirus family. The various types of enteroviruses that infect humans are referred to as serotypes, in recognition of their different antigenic patterns. The different immune response is important, as infection with one type of enterovirus does not necessarily confer protection to infection by a different type of enterovirus. There are 64 different enterovirus serotypes. The serotypes include polio viruses, coxsackie A and B viruses, echoviruses and a large number of what are referred to as non-polio enteroviruses.
MENINGITIS: Meningitis is an inflammation of the meninges—the three layers of protective membranes that line the spinal cord and the brain. Meningitis can occur when there is an infection near the brain or spinal cord, such as a respiratory infection in the sinuses, the mastoids, or the cavities around the ear. Disease organisms can also travel to the meninges through the bloodstream. The first signs may be a severe headache and neck stiffness followed by fever, vomiting, a rash, and, then, convulsions leading to loss of consciousness. Meningitis generally involves two types: nonbacterial meningitis, which is often called aseptic meningitis, and bacterial meningitis, which is referred to as purulent meningitis.
Viral meningitis is a serious condition. Though viral meningitis may alleviate without treatment, all people who suspect that they have meningitis should seek medical care. Viral meningitis rarely has serious long-term health consequences in otherwise healthy individuals. Bacterial meningitis, however, can be life-threatening. Since early symptoms of viral and bacterial meningitis are similar, prompt and accurate diagnosis is necessary to distinguish between the two forms of meningitis.
In August 2006, an outbreak of viral meningitis was reported from the region of Khabarovsk, on the Russian Far East border, affecting over 800 children. It is thought they contracted the infection through either swimming in the river Amur or from drinking its waters. There have been ongoing summer outbreaks of viral meningitis in this area for some time, arising usually from fecal contamination of the Amur's waters. Swimming is therefore prohibited in the summer months. During the 2006 outbreaks, public health doctors tried to stem the outbreak by asking parents to keep their children away from social activities, as the meningitis could be spread by infected air droplets.
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