Meningitis is an inflammation of the meninges, the protective membranes surrounding the brain and spinal cord. While it can be a severe condition, meningitis is not directly passed down genetically. It is primarily caused by infections from various microorganisms, though an individual’s genetic makeup can influence their susceptibility.
Common Causes of Meningitis
Meningitis is most frequently triggered by infectious agents such as viruses, bacteria, and fungi. Viral meningitis is the most common type and is often milder, with many cases resolving without specific treatment. Enteroviruses are a frequent cause of viral meningitis, typically entering the body through the mouth or nose and spreading through direct contact or contaminated surfaces. Other viruses, including herpes simplex virus, HIV, and the West Nile virus, can also lead to viral meningitis.
Bacterial meningitis is less common but can be life-threatening and requires immediate medical attention. Several types of bacteria are responsible, with Streptococcus pneumoniae being a leading cause in infants, young children, and adults in the United States. Neisseria meningitidis is another bacterium that causes outbreaks, particularly in close-quarter environments like college dormitories. These bacteria often start as respiratory infections before traveling through the bloodstream to the brain and spinal cord, or they can directly invade the meninges through conditions like ear or sinus infections.
Fungal meningitis is the least common type and typically affects individuals with weakened immune systems, such as those with HIV or cancer. Fungi like Cryptococcus neoformans, found in soil and bird droppings, can be inhaled and lead to this infection. Unlike bacterial or viral forms, fungal meningitis is not usually spread from person to person. Although treatable with antifungal medications, fungal meningitis can sometimes recur.
Genetic Influences on Susceptibility
An individual’s genetic makeup can influence their susceptibility to meningitis when exposed to an infectious agent. These genetic factors do not directly cause the disease but affect the immune system’s ability to fight infections. Variations in genes related to immune function can make some people more prone to severe or recurrent infections, including those that lead to meningitis.
One area of genetic influence involves the complement system, a part of the innate immune response that helps destroy pathogens. Deficiencies in specific components of the complement system, such as C5, C6, C7, C8, C9, or properdin, can increase an individual’s risk of recurrent or severe infections, particularly with Neisseria meningitidis. For example, properdin deficiency leads to a higher risk of fulminant meningococcal disease. These deficiencies compromise the body’s ability to form the membrane attack complex (MAC), a structure that helps kill bacteria.
Primary immunodeficiencies (PIDs) are another group of inherited conditions that can increase susceptibility to meningitis. These disorders arise from defects in various components of the immune system, leading to recurrent or unusual infections. Patients with congenital deficiencies in antibody production or early complement components, such as C1 through C3, may be at higher risk for bacterial meningitis caused by organisms like Streptococcus pneumoniae or Haemophilus influenzae. While most people with bacterial meningitis do not have an underlying immunodeficiency, the occurrence of meningitis, especially in infants or young children, can sometimes be the first indication of a congenital immune system disorder.