Anterior horn lesions of the spinal cord are a manifestation of poliomyelitis. Poliomyelitis is an acute infectious disease caused by poliovirus. Poliomyelitis virus (poliomyelitisvirus) is a genus of enterovirus in the family of small ribonucleic acid viruses. The virus is observed under the electron microscope as a small, rounded sphere with a diameter of 24-30 nm and a circular particle shape. It contains single-stranded ribonucleic acid with a nucleic acid content of 20% to 30%. The viral nucleoshell consists of 32 capsid particles, each containing four structural proteins, namely VP1 to VP4. VP1 has a special affinity for human cell membrane receptors and is associated with the pathogenicity and virulence of the virus. 1, resistance poliovirus is not sensitive to all known antibiotics and chemotherapeutic drugs, can tolerate the general concentration of chemical disinfectants, such as 70% ethanol and 5% coal phenol soap. 0, 3% formaldehyde, 0, 1 mmol / L hydrochloric acid and (0, 3 ~ 0, 5) 10-6 residual chlorine can be rapidly inactivated, but in the presence of organic matter can be protected. It can be completely inactivated by heating to 56℃ for 30min, but can be stored for several years in a frozen environment, for several weeks in a 4℃ refrigerator, and can survive for several days at room temperature. It is sensitive to UV, drying and heat. It can survive for several months in water, feces and milk. Magnesium chloride can enhance the resistance of the virus to temperature, so it is widely used to preserve live attenuated vaccines. 2.Antigenic nature Using serum neutralization test can be divided into I, II, III three serotypes. Each serotype has two type-specific antigens, one is D (dense) antigen, which exists in the mature virus body, and the virus containing D antigen is fully infectious and antigenic; the other is C (coreless) antigen, which exists in the pre-shell of the virus, and the virus containing C antigen is an empty shell particle lacking RNA and is not infectious. The virus can change from D antigenic to C antigenic under the action of neutralizing antibodies and lose the ability to reinfect cells. Heat-inactivated viruses lose VP4 and ribonucleic acid and become C-antigen containing virus particles. The natural D antigen and the heated C antigen can be detected by applying the precipitation reaction and complement binding test. 3. Host range and virulence Humans are the natural and reservoir hosts of poliovirus, and monkeys and orangutans are susceptible animals. The virus binds to specific receptors on the cell surface and is taken up into the cell, replicating in the cytoplasm while releasing inhibitors that inhibit RNA and protein synthesis in the host cell. Natural polioviruses are called wild strains, and strains that have been attenuated in the laboratory are called vaccine strains. Vaccine strains cause paralysis only when injected directly into the central nervous system of monkeys, and are not toxic to human neuronal cells. Vaccine strains, particularly type III viruses, can mutate into virulent intermediate strains when transmitted in the population. The most reliable way to identify wild and vaccine strains is to perform nucleic acid sequence analysis.