Poliomyelitis & A Little COVID-19

Poliomyelitis is a disease that has been described as early as 1403 to 1365 BC, when it was depicted in ancient Egyptian paintings and carvings. It is caused by the poliovirus, a human enterovirus that belongs to the Picornaviridae family of viruses. Humans are the only natural host, meaning that eradication can be achieved (Nomoto, 2007). Poliomyelitis is mainly a disease of childhood, with children under the age of 5 years being most affected. In rare instances it can have long-term consequences, making it vital to prevent the disease before the development of irreversible pathology.

The poliovirus is transmitted through the faecal-oral route. The virus is ingested and multiplies within the alimentary tract, primarily in the tonsils and Peyer’s patches. It then enters the bloodstream causing a viremia. The circulating virus then enters the central nervous system (CNS) by one of two methods: 1) it permeates through the blood-brain barrier or 2) it is transmitted along peripheral nerves. Once in the CNS, it replicates in neurons (especially motor neurons) and may cause paralytic polio if there is neuronal destruction from lytic viral replication (Nomoto, 2007).

Nomoto, 2007

After infection with the poliovirus, there is an incubation period that lasts 2 - 35 days (7 - 14 days in the majority of cases). During the first 3 - 5 days of the incubation period the infected individual begins shedding the virus, thus becoming infectious before being symptomatic (if they ever do develop symptoms). 90 - 95% of cases remain asymptomatic but continuously shed the virus, making detection and containment difficult. There are 3 other presentations of poliomyelitis, albeit rarer, that may occur in patients infected with the poliovirus. The first is that of abortive poliomyelitis. This occurs in 4 - 8% of cases and is a mild viremic form of the disease. Patients present with symptoms such as gastroenteritis, influenza-like illness, and mild respiratory tract infections, which typically subside within a week. The next presentation is that of septic meningitis, which is seen in only 1% of cases. These patients present with a prodrome similar to abortive poliomyelitis but later develop painful muscle spasms of the neck, back and lower limbs. These spasms usually subside within 10 days and there is usually complete recovery. The last presentation is the most feared - paralytic poliomyelitis. This occurs in less than 1% of cases and presents as excruciating muscle pain in the back and lower limbs. In children, the presentation is usually biphasic, with a prodrome of 7 - 10 days followed by a symptom-free period and then asymmetric paralysis of the limbs (acute flaccid paralysis). There are 3 forms of paralytic poliomyelitis. 1) spinal - which is most common and presents with motor weakness/paralysis, 2) bulbar - the most deadly, as the brainstem is affected thus leading to respiratory depression and failure, 3) bulbospinal - a mix of 1 and 2. Patients who do not recover motor function within 12 months remain paralysed for life. There is also the possibility of post-polio syndrome, which can occur 25 - 30 years after the initial infection. These patients develop irreversible muscle atrophy due to ongoing motor neuron degeneration or due to viral persistence in the brain and spinal cord (Mehndiratta and Pande, 2014).

The diagnosis of poliomyelitis is done by lumbar puncture, viral culture (stool, throat swab, or cerebrospinal fluid), reverse-transcriptase polymerase chain reaction of blood or cerebrospinal fluid, or by serological testing for poliovirus subtypes (MSD manual, 2020). Once a diagnosis is made, there is no cure and only supportive treatment can be offered. This is the reason why prevention of the disease is vital. In 1988, the Forty-first World Health Assembly was held and adopted a resolution to eradicate poliomyelitis worldwide - the Global Polio Eradication Initiative (GPEI). Since the initiative was launched there has been a 99% fall in the number of poliomyelitis cases, with 350,000 cases reported in 1988 and only 33 reported in 2018. In 1994, the World Health Organisation (WHO) certified America polio-free. In 2000, the Wesstern Pacific Region was declared polio-free, followed by the European Region in 2002, India in 2011, and the South-East Asia Region in 2014 (WHO, 2020).

There have been 2 vaccination programmes that have proved vital in the eradication process. The first is the oral polio vaccine (OPV). The problem with the OPV is that it is a live vaccine and therefore cannot be given to immunocompromised patients. Another issue is that although the individual taking the vaccine is protected, it does not stop viral shedding and the OPV virus can be transmitted to those not vaccinated. This makes it vital that everyone is vaccinated in order for eradication to occur. In very rare cases, the OPV may accumulate changes over time and become similar to the wild-type poliovirus, leading to vaccine-derived poliomyelitis. The OPV has a trivalent form and a bivalent form, the bivalent being created after the poliovirus type-2 was declared eradicated world-wide. The other vaccination option is the inactivated poliovirus vaccine (IPV). Individuals who are administered this IPV do not shed the virus, and are therefore not infectious to the unvaccinated population (CDC, 2020).

COVID-19 continues to have a substantial impact on daily life, including availability and accessibility of healthcare services. On March 24, 2020, the Polio Oversight Board (POB) in charge of GPEI diverted more than 3,700 polio workers to the COVID-19 response teams and halted the GPEI campaign. This is of concern to polio-endemic countries, especially as they move into the tropical rainy seasons when the virus is most transmissible (Reliefweb, 2020). On May 13 of this year there have already been 59 new cases of the wild-type polio and 104 cases of the vaccine-derived polio, before this peak season has even begun (McKenna, 2020). Countries with outbreaks of vaccine-derived polio and wild-type polio are expected to see increases in transmission. The POB has claimed that the surveillance of poliomyelitis will continue, but this will prove difficult due to the mainly asymptomatic nature of the disease (Reliefweb, 2020).

The longer the interruption of the vaccination programme for polio, the more catch-up will be required in the healthcare sector. This will also need to be accomplished on a reduced budget, as a large portion of vaccination funds have been allocated towards the fight against COVID-19, and international donors, such as the Gates’ Foundation, have diverted their funds completely to the coronavirus pandemic (McKenna, 2020). Unless attention is redirected back to essential health services other than COVID-19, there is likely to be a re-emergence of infectious diseases that have taken many years and substantial resources to contain - including poliomyelitis.

References

CDC. 2020. Polio Disease And Poliovirus. [online] Available at: <https://www.cdc.gov/cpr/polioviruscontainment/diseaseandvirus.htm> [Accessed 3 June 2020].

Nomoto, A., 2007. Molecular Aspects Of Poliovirus Pathogenesis. [online] PubMed Central (PMC). Available at: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3859295/> [Accessed 3 June 2020].

McKenna, M., 2020. Polio Is Nearly Wiped Out. Covid-19 Could Halt That Progress. [online] Wired. Available at: <https://www.wired.com/story/polio-is-nearly-wiped-out-covid-19-could-halt-that-progress/> [Accessed 3 June 2020].

Mehndiratta, M., Mehndiratta, P. and Pande, R., 2014. Poliomyelitis. [online] NCBI. Available at: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4212416/> [Accessed 3 June 2020].

MSD Manual Professional Edition. 2020. Poliomyelitis - Infectious Diseases - MSD Manual Professional Edition. [online] Available at: <https://www.msdmanuals.com/professional/infectious-diseases/enteroviruses/poliomyelitis> [Accessed 3 June 2020].

ReliefWeb. 2020. Polio Eradication In The Context Of The Covid-19 Pandemic - Updated Urgent Country And Regional Recommendations (21 May 2020) - World. [online] Available at: <https://reliefweb.int/report/world/polio-eradication-context-covid-19-pandemic-updated-urgent-country-and-regional> [Accessed 3 June 2020].

WHO. 2020. Poliomyelitis. [online] Available at: <https://www.who.int/news-room/fact-sheets/detail/poliomyelitishttps://www.who.int/news-room/fact-sheets/detail/poliomyelitis> [Accessed 3 June 2020].

Who. 2020. Poliomyelitis. [online] Available at: <https://www.who.int/news-room/fact-sheets/detail/poliomyelitis> [Accessed 3 June 2020].