What causes polio?

What we often call polio is medically known as poliomyelitis. It is an acute infectious disease that can endanger children's lives. So what exactly causes polio?

The pathogen of poliomyelitis is a filterable virus whose diameter is 8 to 17 μm under an electron microscope. It is called polio virus. This virus is divided into three different types: I, II, and III. Type I is the most common, followed by type III, and type II is rare.

In addition to poliovirus, certain other viruses, such as individual enteroviruses, including coxsackie virus and echo virus, can also cause damage to the central nervous system and cause paralytic poliomyelitis, which is clinically difficult to distinguish from paralysis caused by poliovirus.

The polio virus is very resilient and cold-resistant. It can survive for several months in frozen conditions and is also highly resistant to dryness. The virus can survive for several days at room temperature; for weeks to months in sewage; for more than a hundred days in water and milk; and for 3 to 6 weeks or longer in feces. Ultraviolet radiation, boiling, or the use of chlorine-containing lime (bleaching powder) and potassium permanganate can quickly kill it.

The source of infection is patients with paralytic and non-paralytic forms of the disease. Latently infected people and healthy virus carriers can also spread the disease. The virus is mainly excreted from feces and nasopharyngeal secretions. Its main transmission routes are directly through the digestive tract through contaminated food, dirty hands and various utensils, or through the respiratory tract through air droplets.

The disease occurs throughout the world, especially in poor countries. In our country, due to effective prevention, current cases are mainly sporadic. The disease is most common in summer and autumn from June to September.