Researcher explains the finding of a man who excretes poliomielitis virus for 28 years

According to the researcher Javier Martin, since these viruses lost their original attenuating properties from the vaccine strains, they could potentially cause poliomielitis in susceptible people

A British patient who expels the poliomielitis virus for 28 years was theme of an article published on PLOS Pathogens magazine. According to the studys coordinator, Dr. Javier Martin, who is also head of the Specialized Global Poliomielitis Laboratory at the World Health Organization, the main conclusion is that vaccine-derived polioviruses (VDPV) can replicate for long periods in immunodefficient patients.

Interviewed by the Brazilian Society of Tropical Medicine, Dr. Martin explained the case described in the paper represents the longest excretion period ever reported by a patient, and until nnow, the only known individual to excrete highly evolved VDPVs.

Find the full interview below:

BSTM: How was the discovery of the man who expels the virus 28 years ago?

Javier Martin: The patient was part of a study aimed at assessing the relationship between Enterovirus infection and gut inflammation in immunodeficient individuals. In countries where there are registers of such patients, screening of virus in stool samples from these individuals can be conducted and in fact a number of such studies in some countries have identified some polio excreters although only excreting virus for short periods of time. Search for poliovirus in sewage samples can also be attempted. Indeed, several highly drifted vaccine-derived poliovirus strains with properties similar to those shown by the isolates from the UK patient have recently been isolated from sewage samples in Slovakia, Finland, Estonia and Israel indicating that an unknown number of these chronic excreters might exist elsewhere.

BSTM: How the research was done? What are the results?

Javier Martin: We describe a patient deficient in humoral immunity who has been excreting type 2 vaccine-derived poliovirus for twenty-eight years as estimated by the molecular clock established by comparing the genomic sequences of viruses found in stool samples collected from this patient at different dates. The viruses were isolated in cell cultures. Using a range of in vivo and in vitro assays we show that the viruses were very virulent, antigenically drifted and excreted at high titre suggesting that such chronic excreters pose an obvious risk to the eradication programme.

BSTM: What does this discovery mean for science and society?

Javier Martin: The main conclusion of the study is that vaccine-derived polioviruses (VDPVs) can replicate for very long periods of time in immunodeficient individuals. The case described in our paper represents by far the longest period of excretion described from such a patient and the only identified individual known to be excreting highly evolved VDPVs at present. As these viruses have lost the attenuation properties of the original vaccine strains, they could potentially cause poliomyelitis in susceptible people so it is very important to maintain high levels of vaccine coverage and surveillance activities. Our results in virus neutralization assays with human sera and immunisation-challenge experiments using transgenic mice expressing the human poliovirus receptor indicate that while maintaining high immunisation coverage will likely confer protection against paralytic disease caused by these viruses, significant changes in immunisation strategies might be required to effectively stop their occurrence and potential widespread transmission. Eventually, new stable live-attenuated polio vaccines with no risk of reversion might be required to respond to any poliovirus isolation in the post-eradication era. This is particularly important at this stage of the global polio eradication initiative and will continue for some time after eradication, as we want to minimise the risk of polio coming back. Results from our research will help designing optimal strategies for the polio eradication endgame, which includes improved surveillance methods to quickly detect and characterize poliovirus from clinical and environmental samples and vaccination schemes and antiviral treatments to complete eradication and minimise the risk for a polio comeback.

BSTM: Is Polio still a real threat to the world population?

Javier Martin: Yes it is. As long as poliovirus is circulating anywhere in the world, all countries are at risk of importing polio. It is essential to maintain high levels of immunisation coverage and surveillance for poliovirus until all viruses have been wiped from Earth. Indeed wild poliovirus was detected in sewage samples in Brazil in 2014. Thankfully no cases of paralytic polio were detected. This was probably due to the high levels of anti-polio immunity in the population.

BSTM: Should tropical countries resume vaccination campaigns against polio?

Javier Martin: Immunisation against polio is still part of the routine vaccination program in all countries of the world. No country should have stopped vaccination. However, vaccination coverage is not ideal in several countries leaving them at risk of polio importation. WHO supplies supplementary immunisation activities in countries where there is still poliovirus circulation and in those with higher risk of polio importation.…