Overview of Polio

Polio (poliomyelitis), also known as "polio" Polio is caused by the acute infectious diseases. Clinical fever, upper respiratory tract symptoms, physical pain, a few cases of flaccid paralysis in limbs characterized.
China in the Ming and Qing two generations have similar records of the disease, referred to as the "children frightened paralysis." Preventive vaccines commonly used in recent years, the incidence rate has dropped significantly.
[Pathogen]
Polio virus (polioviruses) are small RNA virus Branch, an intestinal virus. A diameter of 20 to 30 nm, single unit containing the RNA, no envelope. Under the electron microscope showed Park granular shape. Exist in a large number of patients with spinal cord and brain, in the nasopharynx, intestinal mucosa and lymph nodes can be found, according to their antigenic differences can be divided into I, II, III three serotypes, between occasional cross-immunity. The virus can be used human embryonic kidney, human embryonic swelling, and Hela monkey kidney cells, and other training.
Polio virus cold, low-temperature (-70 ° C) retain vitality as long as eight years, in the water, faeces and milk to survive a few months, at 4 ℃ refrigerator holds few weeks, but very sensitive to drying, it is not appropriate freeze-drying method used preservation. For heat. 60 ° C for 30 minutes will enable the inactivated, boiled and ultraviolet radiation can quickly be killed. Can tolerance general concentration of chemical disinfectants, such as the 70% ethanol and 5% coal phenol liquid soap. But potassium permanganate, hydrogen peroxide, bleaching powder and other sensitive, which can be rapidly inactivated.
The polio virus has now adopted a new naming method. Identification should include virus type, the State (or city), the number and the strains isolated life (such as P1 China / 112/88)
[Epidemiological]
(A) The source of infection of human poliovirus is the only source of infection, the patient can be at the end of the incubation period of detoxification from nasopharyngeal secretions and feces of detoxification period since the onset ago on the 10th to disease after four weeks, a few up to 4 On. Because asymptomatic infections can be 50 to 500 times the symptoms are, therefore asymptomatic virus is the most important source of infection.
(B) The main mode of transmission through fecal - mouth transmission, and daily life is the main mode of transmission of contact, contaminated hands, food, supplies, clothing, toys can spread the disease. A few cases can be spread through air droplets.
(C) susceptibility to four months following few ill babies, 1 to 5-year-old children with a maximum incidence. In recent years, children generally use vaccines, it has increased the incidence of age trends. The body of polio virus infection, first appeared in the specificity of serum IgM, two weeks after IgG and IgA. And in the protective antibodies can be maintained for life. After the disease is the same type of virus lasting immunity, the second incidence are rare.
(D) popular features of this disease throughout the world, was particularly prevalent in temperate. Dissemination of pop, summer and autumn the highest incidence of tropical and subtropical and morbidity in the season there was no significant difference. Pop in the past mainly virus type I, III at least. Large-scale use vaccines, reducing virus type I, II III relative increase. The original three to five years the law has been a popular disappear.
[Principle and pathological changes in the incidence]
Oral polio virus enters the human body, which penetrated the throat and intestinal lymphoid tissue, including tonsils, lymph nodes ileum set neck deep lymphatic and mesenteric lymph nodes, and in which breeding, so when the body produce specific antibody, local infection under control, a hidden infection; virus antibodies are entering the lower blood circulation, cause viremia. The virus arrived in systemic blood flow through the reticular endothelial system, in which the further proliferation, and then re-enter the blood circulation, leading to the second viremia, blood circulation for all days of specific antibodies to the virus and in, the disease developed to this end, this stage of the clinical equivalent of the prodromal period; if the body lacks immunity, with the blood virus penetrated the central nervous system by the blood-brain barrier and the spread along the nerve fibers, cause no symptoms of paralysis if serious damage to motor neurons , the lead muscle paralysis caused paralysis of symptoms.
According to the human body after infection with the virus virulence strong or weak immunity level of performance to be hidden infection (asymptomatic type), frustrated type (light), no type of paralysis and paralysis of different clinical types. In addition, the cold, fatigue, partial injury, tonsil removal, injecting stimulation, immune deficiency, pregnancy, genetic factors, and the incidence of paralysis, have a certain impact on development. The first 19 pairs of chromosomes carrying the polio susceptibility gene, the decision is particularly important genetic HL-A3 and HL-A7 and the increased incidence of paralysis.
Diseases involving the central nervous system, and the main damage to the spinal cord, brain stem times, in addition to spinal cord front-most notable, can still spread to the whole spinal cord gray matter, horn and dorsal root ganglia. To cervical lesions and damaged lumbar than drama, especially lumbar damage caused paraplegia. The brain lesions can be involved, in the brain and the medulla oblongata, the cerebellum and brainstem, reticular structure, vestibular nucleus, and cerebellar vermis process can also damage the cerebellum, cerebral cortex lesions slight movement. Festival sympathetic ganglion and around occasional lesions.
Pathological changes including nerve cell damage and inflammatory response in two ways. Nerve cell damage manifested as cytoplasm of Nissl bodies and the dissolution chromatin until necrotic cells completely disappeared. Focal inflammatory response, including vascular and inflammatory cell infiltration around to lymphocyte predominance, with neutrophils, resulting in temporary loss of function. Convalescence, inflammation receding, the large number of nerve cells and necrosis formation empty glial fibrillary hyperplasia. Unencumbered by the damaged nerve atrophy of muscle fibers, in the normal muscle fibers showed Island fractal distribution.
Other focal lesions have myocarditis, interstitial pneumonia, liver and other organs and turbidity congestive swelling, such as swelling of lymph node hyperplasia.