Bronte Wells
Poliomyelitis, or polio, is a highly infectious disease caused by the poliovirus, which affects the nervous system and can lead to paralysis and even death. The disease is transmitted through person-to-person contact, mainly via the faecal-oral route, and multiplies in the intestine. While polio has been largely eradicated globally due to vaccination efforts, it still persists in certain regions, and the risk of re-emergence remains. This raises the question of whether polio is a virus or a result of pollution.
| Characteristics | Values |
|---|---|
| Nature | Polio is a highly infectious disease caused by a virus |
| Affects | Humans are the only known reservoir for the polio virus |
| Transmission | Person-to-person spread through the faecal-oral route, contaminated water or food, nasal and oral secretions |
| Incubation Period | 7-10 days, but can range from 4-35 days |
| Symptoms | Fever, fatigue, headache, vomiting, stiffness in the neck, pain in the limbs, paralysis, and in some cases, death |
| Treatment | No specific treatment, can be prevented by the polio vaccine |
| Global Status | Cases have decreased by over 99% since 1988, but failure to eradicate polio from the remaining areas could result in a global resurgence of the disease |
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What You'll Learn
Polio is a virus
Poliomyelitis, or polio, is a highly infectious disease caused by a virus. It is transmitted by person-to-person spread, mainly through the faecal-oral route, and less frequently by a common vehicle such as contaminated water or food. The virus multiplies in the intestine and can invade the nervous system, causing paralysis. In most people with a normal immune system, a poliovirus infection is asymptomatic. However, in about 25% of cases, the infection produces minor symptoms such as a sore throat and low fever. These symptoms are temporary, and a full recovery occurs within one to two weeks.
Polio occurs naturally only in humans. It was first recognised as a distinct condition by English physician Michael Underwood in 1789, and the virus that causes it was first identified in 1909 by Austrian immunologist Karl Landsteiner. Major outbreaks started to occur in the late 19th century in Europe and the United States, and in the 20th century, it became one of the most worrying childhood diseases.
There are three distinct serotypes of wild poliovirus: types 1, 2, and 3. Type 1 has historically been the predominant cause of poliomyelitis worldwide and continues to be transmitted in endemic areas. While transmission of types 2 and 3 has been successfully interrupted globally, with the last reported cases in 1999 and 2012 respectively, type 1 remains endemic in Afghanistan and Pakistan.
The disease can be prevented by the polio vaccine, with multiple doses required for lifelong protection. There are two broad types of polio vaccine: the injected polio vaccine (IPV) uses an inactivated poliovirus, while the oral polio vaccine (OPV) contains a weakened live virus. Through the use of both types of vaccines, the incidence of wild polio has decreased from an estimated 350,000 cases in 1988 to 30 confirmed cases in 2022, confined to just three countries.
The global effort to eradicate polio has been declared a Public Health Initiative of International Concern, and the World Health Organization (WHO) is working with affected countries to implement eradication strategies, focusing on immunisation and disease surveillance. The key to success is ensuring that strategic approaches are fully implemented and resourced, as failure to do so leads to the ongoing transmission of the virus.
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It is highly infectious
Poliomyelitis, or polio, is a highly infectious disease caused by a virus. It is transmitted by person-to-person spread, mainly through the faecal-oral route, and less frequently by a common vehicle, such as contaminated water or food. Poliovirus only infects humans, entering the body through the mouth and multiplying in the intestine. It can then invade the nervous system, causing paralysis or even death.
Polio is a highly contagious virus, and an infected person can spread it to others immediately before and up to six weeks after symptoms appear. The incubation period is usually 7–10 days but can range from 4–35 days. The virus is shed by infected people, usually children, through their faeces, and can spread quickly, especially in areas with poor hygiene and sanitation systems.
The disease mainly affects children under five years of age, and in rare cases, it can lead to irreversible paralysis, with one in 200 infections resulting in paralysis, usually in the legs. Among those paralysed, 5–10% die when their breathing muscles become immobilized. However, most people who get infected with poliovirus will not have any visible symptoms. About 25% experience mild or flu-like symptoms that may include a sore throat and low fever.
Polio is a dangerous disease, and there is no cure. However, it can be prevented through safe and effective vaccination. The polio vaccine, given multiple times, can protect a child for life. The global effort to eradicate polio has been ongoing, and wild poliovirus cases have decreased by over 99% since 1988. However, failure to stop polio in the remaining areas, such as Afghanistan and Pakistan, could result in a global resurgence of the disease. Therefore, it is crucial to ensure polio is eradicated completely through strategic approaches and widespread vaccination.
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Humans are the only known reservoir
Poliomyelitis, or polio, is a highly infectious disease caused by the poliovirus. Humans are the only known reservoir for the poliovirus, which spreads through person-to-person contact, mainly via the faecal-oral route. The virus can also be transmitted through oral-oral contact or contaminated food and water.
Polio has existed for thousands of years, with depictions of the disease found in ancient art. The disease was first recognised as distinct by English physician Michael Underwood in 1789, and the poliovirus was identified in 1909 by Austrian immunologist Karl Landsteiner. Major outbreaks began in the late 19th century in Europe and the United States, and in the 20th century, polio became one of the most concerning childhood diseases.
The poliovirus is transmitted by infected individuals through droplets or aerosols from the throat and by faecal contamination of hands, utensils, food, and water. The virus enters the body through the mouth and multiplies in the intestine before invading the nervous system. Symptoms of polio include fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs. In more severe cases, the virus can cause paralysis, typically of the legs, and this is often permanent.
The development of vaccines has been critical in the fight against polio. The first injectable vaccine, created by Jonas Salk, was introduced in 1955, followed by an oral polio vaccine (OPV) developed by Albert Sabin in 1962. Both vaccines are still used today, with the oral vaccine being easier to administer and distribute. The oral polio vaccine contains live attenuated (weakened) poliovirus, while the injected polio vaccine (IPV) uses an inactivated poliovirus.
The Global Polio Eradication Initiative (GPEI), launched in 1988, has successfully reduced the global incidence of polio by over 99%. Cases have decreased from an estimated 350,000 in 1988 across 125 endemic countries to just 30 confirmed cases in 2022, confined to three countries. However, failure to eradicate polio completely could result in a global resurgence. Therefore, maintaining high vaccination coverage and implementing strategic approaches are crucial to ensuring the disease's eradication.
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It is transmitted via the faecal-oral route
Poliomyelitis (polio) is a highly contagious viral disease that affects only humans, mainly children under five years of age. It is transmitted via the faecal-oral route, primarily through person-to-person spread. The faecal-oral route involves the ingestion of contaminated food or water, or fingers that have been in contact with faecal matter. It can also be transmitted via droplets expelled from the throat of an infected person.
The faecal-oral transmission of polio occurs when an individual comes into contact with the faeces of an infected person. This can happen when food or water is contaminated with human faeces, or when hands or utensils become contaminated and are then used to handle food or drinks. Poor hygiene and sanitation systems increase the risk of transmission.
The poliovirus is shed in the faeces of infected individuals, and it can spread quickly through these means, especially in areas with inadequate sanitation and hygiene practices. The virus can also be transmitted through oral secretions, such as droplets or aerosols from the throat, which can contaminate food, hands, or utensils. This transmission route is less common but still possible.
The faecal-oral route is a significant contributor to the spread of polio, as the virus can remain infectious in the faeces for up to six weeks, even if the infected person shows no symptoms. This long shedding period increases the likelihood of transmission, especially in communities with poor sanitation practices.
The oral polio vaccine (OPV) has been crucial in reducing the spread of polio via the faecal-oral route. OPV contains weakened polioviruses that stimulate immunity without causing the disease. It has been widely used due to its low cost, ease of administration, and ability to provide excellent immunity in the intestine, which helps prevent infection with wild poliovirus. However, in rare cases, the attenuated virus in OPV can revert to a virulent form, leading to vaccine-derived poliovirus (cVDPV) cases.
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Vaccines are available
Polio is a highly infectious disease that can cause paralysis and even death. It is transmitted by person-to-person spread, mainly via the faecal-oral route, and can also be transmitted through contaminated water or food. While there is no cure for polio, safe and effective vaccines are available to prevent it.
There are two types of polio vaccines: the inactivated polio vaccine (IPV) and the oral polio vaccine (OPV). IPV is administered via injection and offers protection against severe disease caused by poliovirus. Two doses of IPV provide at least 90% protection, while three doses offer at least 99% protection. IPV has been the only polio vaccine administered in the United States since 2000 and is recommended for children as part of their routine childhood immunisation schedule.
On the other hand, OPV is a weakened poliovirus administered by mouth. It produces excellent immunity in the intestine, the primary site of wild poliovirus entry, which helps prevent infection in areas where the virus is endemic. OPV is easier to administer than IPV as it does not require sterile syringes, making it more suitable for mass vaccination campaigns. It also provides longer-lasting immunity than IPV and can induce immunity in unvaccinated individuals through indirect exposure. However, OPV has an inherent risk of inducing vaccine-associated paralytic poliomyelitis (VAPP) in rare cases, occurring in approximately one individual per 2.7 million doses administered.
The choice between IPV and OPV depends on various factors, including the availability of medical equipment and the expertise required for administration. OPV is favoured by many countries and has been crucial in the global initiative to eradicate polio. The World Health Organization (WHO) recommends that all children be fully vaccinated against polio with multiple doses to ensure lifelong protection.
In addition to routine childhood immunisation, polio vaccines are also recommended for adults who are at increased risk of exposure to poliovirus. This includes international travellers, laboratory workers, and healthcare workers. These individuals may receive a single lifetime booster dose of IPV for added protection.
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Frequently asked questions
Polio, or poliomyelitis, is a highly infectious disease caused by the poliovirus. It largely affects children under 5 years of age.
Polio is transmitted by person-to-person spread, mainly through the faecal-oral route. It can also be transmitted via the oral-oral route or by common vehicles such as contaminated water or food.
In most cases, polio is asymptomatic. However, some people may experience mild symptoms such as a sore throat, low fever, headache, fatigue, vomiting, stiffness in the neck, and pain in the limbs. In rare cases, the virus can cause paralysis, usually of the legs, and in some cases, death.
There is currently no cure for polio. However, it can be prevented through vaccination. The polio vaccine, given multiple times, can protect a child for life. There are two types of vaccines available: the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV).
