Bệnh bại liệt

Cúm là gì?

Bệnh bại liệt (bại liệt) là do nhiễm trùng đường tiêu hóa (ruột) với một trong 3 loại vi rút bại liệt (serotype 1, 2 hoặc 3). Poliovirus là RNA enterovirus từ Picornaviridae gia đình.

Once an individual is infected, the poliovirus replicates in the gut and enters the bloodstream via lymphoid tissue where it can then cause symptoms in the central nervous system.

Cần để ý những gì

Approximately 70% of polio infections are asymptomatic or present as a non-specific febrile illness. In symptomatic cases an individual may experience fever, headache, gastrointestinal disturbance (nausea and vomiting) or malaise. In severe infections muscle pain and stiffness of the neck and back can occur.

Paralysis typically presents asymmetrically and can be life threatening when the respiratory and swallowing muscles are affected. The extent of paralysis is usually seen within 3-4 days of symptom onset and any existing paralysis present after 60 days is likely to be permanent. It is estimated that flaccid paralysis occurs in less than 1 percent of all polio cases.

A recurrence of muscle weakness in the years after an initial polio infection is known as post-polio syndrome. It is attributed to a progressive loss or dysfunction of motor neurons as opposed to a persistent or reactivated infection.

Bệnh lây truyền qua đường nào

Wild polio is transmitted through contact with the faeces or saliva of an infected person and is most often associated with conditions of poor sanitation.

The incubation period of polio is 3-35 days, with a person infectious during the 7-10 days prior to the onset of symptoms. Following acute infection, a person can continue to excrete the polio virus for up to 6 weeks in their faeces, or 2 weeks in saliva.

Dịch tễ học

Polio infection predominantly occurs in children with the greatest burden of disease affecting those less than 5 years of age (80-90% of cases).

Global vaccination programs and high rates of immunisation have shown great success with the near eradication of wild polio worldwide. A total of 350,000 infections were reported in 1988 across 125 countries and in 2021 this was reduced down to 6 reported cases across countries including Pakistan and Afghanistan. The COVID-19 pandemic has greatly impacted these vaccination programs and since 2022 a resurgence of case across many countries (including the United States and the UK) have been reported, largely in pockets of unimmunised communities.

Phòng ngừa

Vaccination remains the most effective measure in disease prevention with protection available in Australia through the administration of a course of inactivated vaccines. Polio vaccination is funded on the National Immunisation Program (NIP) as a combination vaccine for children at:

• 6 weeks, 4 months and 6 months – Infanrix® hexa/Vaxelis®
• 4 years – Infanrix® IPV/Quadracel®

Individuals who missed a dose or who have an incomplete vaccine history should be offered immunisation to ensure that they are protected. Catch up vaccines are funded for some individuals.

Completing a primary course of vaccination generally provides life-long protection and booster doses are not routinely indicated for the broader population. However, they may be indicated for travellers visiting countries with known cases of polio.

Các biện pháp phòng ngừa

The oral live-attenuated polio vaccine is no longer available in Australia due to the potential low risk (1 case per 2.4 million doses) of Vaccine Associated Paralytic Poliomyelitis (VAPP), also known as Vaccine Derived Poliovirus (VDPV). Following receipt of the oral polio vaccine some of the vaccine virus may be shed in a person’s faeces for up to 6 weeks. In areas of low vaccine coverage this has the potential to cause disease in an unvaccinated individual.

Tài liệu

• Australian Immunisation Handbook: Poliomyelitis
• CDC: Vaccines and Preventable Diseases – Vaccine Derived Poliovirus
• The Blue Book: Guidelines for the control of infectious diseases
• Bộ Y tế và Chăm sóc Người cao tuổi của Chính phủ Úc: Những thay đổi đối với lịch trình của Chương trình Tiêm chủng Quốc gia từ ngày 1 tháng 7 năm 2023