Surveillance of Poliovirus Circulation Among Refugees in Italy, 2008–2011
Silvio Tafuri, MD, Department of Biomedical Sciences, University of Bari “Aldo Moro,” Piazza G. Cesare 11, I-70124 Bari, Italy. E-mail: firstname.lastname@example.org
The aim of this study was to evaluate the presence of wild poliovirus or sabin-like poliovirus in 152 stool samples from migrants in the Accommodation Center in Italy and liquid waste from the sewage systems. Two surveys were performed in 2008 and 2011. All stool samples were negative for enterovirus and poliovirus. One of the liquid samples analyzed was positive for Coxsackievirus type B5.
The Global Polio Eradication Initiative was launched in 1988. Ten years ago all seemed to be going well with poliomyelitis eradication. The number of polio cases globally had dropped by 99% from an estimated 350,000 in 1988 to fewer than 500 in 2001.1
However, polio is still endemic in four countries (Afghanistan, India, Nigeria, and Pakistan) and many previously polio-free countries experienced outbreaks following importation of indigenous wild poliovirus (WPV). In 2010, 1,349 WPV cases were reported, with a large outbreak in Tajikistan. This was the first outbreak of polio since the WHO European Region was certified polio-free in 2002.2
In Italy, there is an increased and continuous inflow of refugees from countries where poliomyelitis is still present, and this may represent a risk of the WPV strains being introduced. The Italian region of Puglia (Southern Italy) can be deemed a “border region” because, due to its geographic position, it has to face daily arrivals of refugees. In recent months, following the wars that have arisen in many countries in the region of North Africa, the flow of refugees seeking political asylum in Italy has intensified. The increased and continuous flow of refugees from countries where poliomyelitis is still present may represent a risk of the WPV strains being introduced in Italy.
The aim of this study was to evaluate the presence of WPV or sabin-like poliovirus in stool samples taken from migrants housed in the Accommodation Center in Bari Palese (Puglia, Italy) and liquid waste taken from the sewage systems of the migrant housing units.
Two surveys were carried out in September 2008 and March 2011, respectively, during which stool samples were collected from migrants on a voluntary basis. Following the explanation of the study given by cultural mediators and the signing of informed consent written in the participant's native language, containers to collect stools were distributed from the Accommodation Center to migrants present. The migrants were invited to hand their fecal samples in to the center's outpatient clinic the following morning. A total of 76 stool samples were collected in the survey conducted in 2008, and 76 stool samples were collected in 2011, respectively, of which 11 samples (5 in the 2008 survey and 6 in 2011) belonged to female subjects. The mean age of participants was 20.8 ± 5.5 y for the survey conducted in 2008 and 23.5 ± 6.3 y in 2011. Table 1 shows the subdivision of samples according to the migrant's country of origin; 30% of migrants analyzed came from countries where polio is still endemic (Afghanistan, Nigeria, and Pakistan).
Table 1. Refugees analyzed, per country
Fecal samples were analyzed for the presence of enterovirus by nested-polymerase chain reaction (PCR). RNA was extracted from 200 µL of fecal extract by the use of a commercial kit (High Pure Viral Nucleic Acid, Roche Diagnostics, Milan, Italy). The nested-PCR was carried out using previously published primers (Schwab, Rotbart). The first set of primers produces a product of 195 bp while the second set of primers produces a product of 153 bp. The amplification was performed: one cycle of reverse transcription at 45°C for 30 minutes, one cycle of denaturation at 94°C for 2 minutes, 35 cycles of denaturation at 94°C for 15 seconds, annealing at 55°C for 30 seconds, and elongation at 68°C for 30 seconds followed by one cycle of elongation at 68°C for 5 minutes. The reaction mixtures were then held at 4°C. The second PCR was carried out using the same conditions of the first round PCR. The PCR products were analyzed by 2% agarose gel electrophoresis.3,4
In June 2011, steps were also taken to sample wastewater from the plumbing systems in the migrant housing units. After analyzing the plumbing system structure, four samples were taken at each of the points of articulation in the pipe system. Samples of sewage were treated and concentrated using the two-step phase separation method recommended by the World Health Organization (WHO).5 Typing was performed by micro-neutralization assay on L20B and Buffalo green monkey isolates, using enterovirus serum pools (anti-Coxsackievirus B, anti-Echovirus) and type specific poliovirus antisera. Sewage samples were also investigated with molecular biology methods: reverse transcription-PCR, as previously described.6
All stool samples were negative for enterovirus.
One of the liquid samples analyzed was positive for enterovirus. Standardization made it possible to identify a Coxsackievirus type B5.
The results of our study seem to highlight an absence of wild or sabin-like poliovirus circulation amongst the refugee population living in Puglia. This data substantially agrees with the results of seroepidemiologic studies carried out recently on the same population, which showed high levels of immunization coverage,7 similar to those shown in the Italian population.8 No evidence of sabin-like poliovirus circulation was found, even though it has been highlighted several times in recent years in investigations conducted on environmental matrices in Italy.6,9
These results seem to confirm the theory of the so-called healthy migrant. Emigration could in fact be considered as a selective process in which only the “strongest of the weak” undertake the journey. Of all potential migrants in a country of origin, those who leave are capable of bearing the financial, emotional, and psychological costs of the feat. We therefore generally deal with the healthy, young, motivated, educated, and those able to speak or learn more languages, who therefore have greater access in the country of origin to health services such as vaccinations. The subjects examined in our study are in fact on average young and therefore likely to have been subject to immunization intervention in their country of origin, extensively launched for more than 20 years, which have reduced the circulation of poliovirus.
Nevertheless, the current epidemiological poliomyelitis worldwide situation means there is still a risk of importing poliovirus; during 2010, imported WPV cases were reported in 11 countries and during January–March 2011, the number of WPV cases was substantially higher than during the same period in 2010.2
Given the uncontrolled and widespread geographic transmission of both remaining WPV serotypes (WPV2 was last seen in 1999 and is considered eradicated), historical spread to neighboring countries and recent geographic expansion of WPV1 across Chad, the WHO rates as high the risk of further international spread. With the Hajj (pilgrimage to Mecca, Kingdom of Saudi Arabia) expected to begin in early November and Ramadan in early August, it is anticipated that pilgrims are now beginning to move across west and central Africa, further increasing the risk of polio spread.10
In this epidemiological context and considering migration inflow, the level of attention given by public health care systems must be high. Research on environmental wild and sabin-like polioviruses, together with an Acute Flaccid Paralysis active surveillance system and the vaccination of migrants represent the key risk assessment strategies.
Declaration of Interests
The authors state that they have no conflicts of interest to declare.