Infectious diseases of Nervous system

The Central Nervous System

An inflammation of the meninges is called meningitis. An inflammation of the brain itself is called encephalitis. If both the brain and the meninges are affected, the inflammation is called meningoencephalitis.

Bacterial disease of Nervous system Bacterial meningitis Tetanus Botulism

Bacterial meningitis The initial symptoms of meningitis are not especially alarming: a triad of fever, headache, and a stiff neck. Nausea and vomiting often follow. Eventually, meningitis may progress to convulsions and coma. Meningitis can be caused by different types of pathogens, including viruses, bacteria, fungi, and protozoa. Viral meningitis is probably much more common than bacterial meningitis but tends to be a mild disease.

Bacterial Meningitis Historically, only three bacterial species have caused most of the cases of meningitis as well as its related mortality. In adult patients, that is, older than 16 years, about 80% of the cases are now caused by Streptococcus pneumoniae and Neisseria meningitidis and Haemophilus influezae type B. All three of these pathogens possess a capsule that protects them from phagocytosis as they replicate rapidly in the bloodstream, from which they might enter the cerebrospinal fluid . Death from bacterial meningitis often occurs very quickly, probably from shock and inflammation caused by the release of endotoxins of the gram-negative pathogens or the release of cell wall fragments (peptidoglycans and teichoic acids) of gram- positive bacteria.

Haemophilus influenzae meningitis Haemophilils influenzae is an aerobic, gram-negative bacterium that is a common member of the normal throat microbiota. Occasionally, however, it enters the bloodstream and causes several invasive diseases. The carbohydrate capsule of the bacterium is important to its pathogenicity, especially those bacteria with capsular antigens of type b. Strains that lack a capsule are called nontypeable. Medically, the bacterium is often referred to by the Hib.

Haemophilus influenzae meningitis Haemophilus refers to the need the microorganism has for factors in blood for growth (hemo = blood; philus = loving). Hib-caused meningitis occurs mostly in children under age 4, especially at about 6 months, when antibody protection provided by the mother weakens. The incidence is decreasing because of the Hib vaccine, which was introduced in 1988.

Meningococcal meningitis by Neisseria meningitidis Meningococcal meningitis is caused by Neisseria meningitidis (the meningococcus). This is an aerobic, gram-negative bacterium with a polysaccharide capsule that is important to its virulence. Like Hib and the pneumococcus, it is frequently present in the nose and throat of carriers without causing disease. The symptoms of meningococcal meningitis are mostly caused by an endotoxin that is produced very rapidly and is capable of causing death within just a few hours. A case of meningococcal meningitis typically begins with a throat infection, leading to bacteremia and eventually meningitis. It usually occurs in children under 2 years; the maternal immunity weakens at about 6 months and leaves them susceptible.

Botulism Caused by Clostridium botulinum Clinical manifestation: symptoms begin within 18-24 hours after ingestion of toxic foods with visual disturbance, inability to swallow,speech dificulty,signs of paralysis and death occurs as a result of cardiac and respiratory failure. No fever and patient remains fully concious until death. Pathogenesis: Intoxication results from the ingestion of foods in which has grown and produce toxins. In anaerobic condition, such as sealed cans, the organism produce an exotoxin (A-B toxin) which is the most potent toxin. The neurotoxin is highly specific for the synaptic end of the nerve, where it blocks the release of acetylcholine, necessary for transmission of nerve impulses across synapsis. So muscle contraction is blocked. Leads to flaccid paralysis.

The action of botulinum toxin from Clostridium botulinum

Flaccid paralysis

Tetanus The causative agent of tetanus,Clostridium tetani, is an obligately anaerobic, endospore-forming, gram-positive rod, is especially common in soil contaminated with animal fecal wastes. The symptoms of tetanus are caused by an extremely potent neurotoxin, tetanospasmin (A-B toxin) that is released upon death and lysis of the growing bacteria enters the CNS via peripheral nerves or the blood. The bacteria themselves do not spread from the infection site, and there is no inflammation.

In a muscle's normal operation, a nerve impulse initiates contraction of the muscle. At the same time, an opposing muscle receives a signal to relax so as not to oppose the contraction. The tetanus neurotoxin blocks the relaxation pathway so that both opposing sets of muscles contract, resulting in the characteristic muscle spasms.

The action of Tetanus toxin from Clostridium tetani

Effect of Tetanus toxin Neurotoxin Tetanospasmin, becomes bound to to the peripheral motor nerves and travels along this nerve to the CNS. It becomes fixed to the ganglioside in the spinal cord. The toxin prevents the release of glycine, result is that the opposite sets of muscle contract simultaneously and in uncontrollable fashion, giving rise to characteristic tetanic spasm and may be powerful enough to break bones and tear tissues. The muscles of the jaw are affected early in the disease, preventing the mouth from opening, a condition known as lockjaw. In extreme cases, spasms of the back muscles cause the head and heels to bow backward, a condition called opisthotonos. Gradually, other skeletal muscles become affected, including those involved in swallowing. Death results from spasms of the respiratory muscles.

Viral disease of Nervous system- Poliomyelitis Poliomyelitis (polio) is best known as a cause of paralysis. It is an acute infectious disease. It affects the CNS in serious form. Characteristics of Polio virus: A small RNA virus Nonenveloped Survive long periods of time outside the host well developed to the fecal oral mode of transmission. Can survive and replicate in GIT Mode of transmission is ingestion of water contaminated with feces containing the virus

Poliomyelitis Clinical manifestation: 1. Abortive poliomyelitis: Most common form Minor illness-fever,malaise,headache,nausea, vomittitng. Patient recovers in a few days. 2.Nonparalytic poliomyelitis: Pain and stiffness in neck and back Disease lasts for 2-10 days Recovery is rapid and complete 3. paralytic poliomyelitis: Flaccid paralysis resultiing from lower motor nerve damage Maximum recovery occurs within 6 months usually

Prevention-Polio vaccine Two types of vaccine is available- Sabin- 100% effective,easily adminstered oral vaccine Consistes of live attenuated strains Strains infect intestinal tract but unlike virulent strains, they do not cause paralytic disease Rather they produce long lasting immunity Salk- 70-90% effective, adminstered in a series of three intramascular injections. Consists of formalin inactivated strains. It can not prevent intestinal infection by a virulent polio virus, but can prevent polio virus in the blood stream from reaching the spinal cord and causing paralysis.