Meningococcemia pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Ammu Susheela, M.D. [3]

Overview

Meningococcal infection is caused by Neisseria meningitidis and they spread through respiratory and throat secretions. Once it get absorbed by endocytosis into the body, it get seeded in skin , meninges and other organs and cause a variety of clinical manifestation from meningitis to septicemic shock. The meningococcal lipopolysachride is an important factor in the infection and host factors like Toll like receptor (TLR) and inflammatory cytokines play an important role in the pathogenesis of the disease.

Pathophysiology

Host Pathogen Interaction

Colonisation

• Meningococcal disease is caused by the bacterium Neisseria meningitidis, also called meningococcus.
• About 10% of people have this type of bacteria in the back of their nose and throat with no signs or symptoms of disease; this is the carrier state. But sometimes Neisseria meningitidis bacteria can invade the body causing certain illnesses, which are known as meningococcal disease.
• Neisseria meningitidis bacteria are spread through the exchange of respiratory and throat secretions.
• The bacteria are not spread by casual contact or by simply breathing the air where a person with meningococcal disease has been.
• Sometimes Neisseria meningitidis bacteria spread to people who have had close or lengthy contact with a patient with meningococcal disease. People in the same household, roommates, or anyone with direct contact with a patient's oral secretions, such assaliva, would be considered at increased risk of getting the infection.
• The bacteria attach to and multiply on the mucosal cells of the nasopharynx.
• Adhesive factors like pilli helps to get it attached itself to nonciliated epithelial cells.

Invasion

• IgA protease, factors that inhibit ciliary activity and polysaccharide capsule enable it to avoid host defence mechanisms.
• Newborn, individuals deficient in terminal components of complement pathway and properdin deficiency have recurrent infections.
• Mutations in mannose binding lecithin gene have increased risk of infections

• Shock is due to lipooligosaccharide which is a potent toxin. This toxin initiates release of inflammatory cytokines, reactive oxygen radicals, prostaglandins, arachidonic acid, complement activated products, platelet aggregating factor, and perhaps nitric oxide.
• In a small proportion (less than 1%) of colonized persons, the organism penetrates the mucosal cells and enters the bloodstream.
• The bacteria spread by way of theblood to many organs. In about 50% of bacteremic persons, the organism crosses the blood–brain barrier into the cerebrospinal fluid and causes purulent meningitis. An antecedent upper respiratory infection may be a contributing factor.
• The meningococci after getting attached, gets endocytosed by parasite directed endocytosis across epithelium.
• The alteration in the gene expression induce a specific structural change which causes endocytosis.
• Meningococci once it enters the circulation survives and multiplies in it causing systemic circulation.

Activation of Host Immune Response

• Major damage is induced by host immune mechanisms.
• N. meningitidis has blebs of endotoxin rich vesicles which are released into the blood stream which activitates host immune response.
• Endotoxin binding protein binds and alters the conformation of endotoxin enabling it to bind it to macrophages.
• CD14 in the endothelial cells act as receptors for endotoxin and activates macrophages which trigers an intense inflammatory response through the release of tumor necrosis factor alpha, interleukin 1beta, IL-6, IL-8, IL-10, GM-CSF and interferon gamma.
• The more number of cytokines involved greater the severity of the disease.
• Endotoxin and the complements activate the neutrophils which release inflammatory proteins through respiratory burst and degrade the tissue.

Microvascular Injury in Meningococcal Sepsis

Increased Vascular Permeability and the Capillary Leak Syndrome

• The inflammatory process induced by meningococcal pathogen alters vascular permeability.
• Proteinuria, hypovolemia and nephrotic syndrome are results of this event.
• Pulmonary edema and respiratory failure are consequence of increased vascular permeability.

Pathological Vasoconstriction and Vasodilation

• Due to hypovolemia, intense compensatory vasoconstriction occurs which manifest as cold, pale, ischemic limbs.
• Sevre patholgical vasoconstriction causes thromobosis within the microvasculature and gangrene.
• Some patients develop vasodilation after resuscitation, yet maintain severe hypotension, acidosis and organ impairment known as warm shock.

Intravascular Thrombosis

• Most severe complication of meningococcemia is widespread purpura fulminans, thrombosis and hemorrhagic necrosis in large areas of the skin and infraction of limbs resulting in gangrene.
• Procoagulation pathways are upregulated in sepsis causing intravascular generation of thrombin.

Myocardial Dysfunction in Meningococcemia

• Acute myocardial failure may manifest as hypotension, tachycardia and shock.
• Pro inflammatory mediators can have a negative ionotropic effect depressing the myocardial function.
• Tumor necrosis factor alpha, interleukin 1beta and nitric oxide have a negative ionotropic effect.
• Electrolyte imbalance also plays a vital role in cardiac dysfunction.

Gross Pathology

[(http://phil.cdc.gov/phil/quicksearch.asp)]

[(http://phil.cdc.gov/phil/quicksearch.asp)]

The above pictures shows the hands and feet affected by gangrene in meningococcemia.

Other Impaired Organ Perfusion

Renal Impairment

• Impaired renal perfusion causes elevated urea and creatinine levels.
• Vasomotor nephropathy and acute tubularr necrosis occurs in severe cases.

Pulmonary Impairment

• Neutrophil adhesion, coagulation activation and platelet activation causes microvacular obstruction resulting in pulmonary function impairment.
• It may manifest as tachypnea in early stages.
• Pulmonary edema and respiratory failure are the late complications of the sepsis.

Gastrointestinal Impairment

• Impaired blood flow causes dysfunction of gastrointestinal tract.
• Prolonged ileus can cuase ischemic ulceration and perforation.

Central Nervous System Involvement

• Direct invasion of meninges by bacteria causes meningitis.
• Organ underperfusion causes signs and symptoms of shock.
• Raised intracranial tension may cause cerebral hernation.
• Direct bacterial activity, indirect inflammatory mediator activity and cerebral edema causes neurological damage.

Molecular Pathophysiology of Meningococcemia

• The toll like receptor system (TLR) protects the body from invasive pathogens and also causes destruction of host in fulminent infections.
• The cell wall of Neisseria meningitidis has molecules that activate the TLR system in a dose dependent manner. This causes the release inflammatory mediators which can cause organ dysfunction and meningococcemia.
• The lipopolysacchrides in the outer membrane is another factor that illicits immune response.
• Peptidoglycan, bacterial lipoprotein and genetic polymorphism are factors that help contribute to broaden the inflammatory response.
• There is a close association between the load of meningococci, (alive or dead in CSF), plasma and magnitude of inflammatory response to the patient.

[(http://www.cdc.gov/meningococcal/)]

Neisseria meningitidis IgA1 Protease

• Neisseria secretes IgA1 protease which splits IgA1 at the hinge region.

Systemic Infection

Meningococci after entering the systemic circulaion get seeded to different parts of the body mainly meninges and skin. Sites like eyes, joints, pericardiucan also be seeded by the organism. When the breeding bacteria reaches a threshold it produces systemic symptoms like musche ache, fever and malaise. The TLR4 and TLR2 from the preoptic area of anterior hypothalamus are expressed which produces the fever causing cytokines like interleukin 1 and interleukin 6 and tumor necrosis factor alpha. They activate the cycloxygenase system which produces prostaglandin E2 and activates the hypothalamic prostaglandin E2 and the hypothalamic thermoregulation center raises the body temperature, increases muscle work and alter skin perfusion.

Proliferation Markers

• Meningococcal lipopolysachride in plasma
• Meningococcal lipopolysacchride in CSF.
• Meningococcal DNA copies.

Patients who were diagnosed to have massive disseminated intravascular coagulation or disseminated septic shock had almost 1000 fold higher amount of LPS in plasma and CSF and copies of DNA of meningococcus than those with only meningitis with the same incubation period.

Meningitis

• Meningococcal meningitis presents as headache, fever, nuchal rigidity. Kernig sign will be present.
• A hemorrhagic skin rash is usually found which is less than 10 mm in diameter.
• As the organism grows in the blood stream, it transverse blood brain barrier and invade subarachnoid space.
• There they multiply and produce the signs and symptoms of meningitis.
• Approximately 50 % of the patients will have a positive blood cultures.

Scavengor Receptor System

The endothelial cells and Kupffer cells forms a complex receptor system that helps to remove the whole bacteria, lipopolysacchrides (LPS) and DNA molecules.