Identifying children who suddenly display muscle weakness, often not moving one or more of their limbs as a result, forms the cornerstone of polio surveillance. Such children could have “acute flaccid paralysis” (AFP) that is symptomatic of polio, a disease caused by a virus. But AFP can also arise for other reasons, including infection by non-polio pathogens.
No child in India has been diagnosed with polio for nearly two years now and all the indications are that the virus responsible for it is no longer circulating here. However, the country’s polio surveillance system has indicated a sharp increase during recent years in the number of non-polio AFP cases.
Data published by the World Health Organisation show that close to 8,000 non-polio AFP cases were identified in India during 2003. They went up to over 12,000 the following year, more than 26,000 in 2005 and crossed 40,000 by 2007. In 2011, there were more than 60,000 non-polio AFP cases.
A good polio surveillance system ought to pick up all AFP cases among children so that they can be screened for poliovirus infection. On average, only about one child out of every 200 children carrying the poliovirus develops AFP. Such cases must be identified so that appropriate immunisation measures can be undertaken.
India’s polio surveillance shows that the country is polio-free. But it also indicates that the country now has the world’s highest rate of non-polio AFP cases. According to data published in WHO’s Weekly Epidemiological Record , India’s annualised non-polio AFP rate for 2011 stood at 15.06 per one lakh children below 15 years of age, compared to a global rate that year of 5.48.
Moreover, most of the country’s non-polio AFP cases occur in just two States — Bihar and Uttar Pradesh. They accounted for about 61 per cent of the 53,000-odd non-polio AFP cases identified in the country in 2012, according to data from WHO’s National Polio Surveillance Project. As a result, the two States have far higher annualised non-polio AFP rates than other States — around 34 for Bihar and about 23 for Uttar Pradesh. The rate for the country as a whole is slightly over 12.
“The increased non-polio AFP rate is due to increased reporting of AFP cases due to deliberate efforts of the programme to increase the sensitivity of the surveillance system since 2004,” according to the WHO Country Office for India. In a written response provided to this correspondent, the health body said these efforts were more intense and closely monitored in the traditionally polio-endemic states of Bihar and U.P., resulting in even higher rates of reporting of AFP cases in those States.
In 2004, a number of steps were initiated to strengthen surveillance in order to accurately and more rapidly detect all polio cases in the country, it said. Those measures included expanding the definition of AFP; increasing the number of AFP reporting sites; increasing the number of active surveillance visits; and more training for health professionals on what constituted an AFP case.
Since then, the number of AFP cases that were reported and investigated continued to increase, it noted. This was not due to an increase in the incidence of a specific disease that might cause these symptoms. Rather, it was the direct result of surveillance activities for AFP cases being strengthened.
The programme in India had taken a much broader interpretation of what would qualify as an AFP case than other countries have. Although facial paralysis would not be part of a standard definition of AFP, it was included in that definition for India. Other similar examples were diseases like meningo-encephalitis, Bells palsy, post-diphtheria polyneuritis and spinal muscular atrophy. Data had shown that broadening the case definition led to the detection of some polio cases that would have otherwise been missed, the WHO Country Office noted.
Moreover, in the remaining polio-endemic countries of Nigeria, Pakistan and Afghanistan too, efforts to strengthen polio surveillance were resulting in increased non-polio AFP cases being reported, it added.
The high non-polio AFP rates in the country ought to be a “red flag”, remarked T. Jacob John, a leading virologist who was with Christian Medical College, Vellore, and is known for his work on polio eradication.
With heightened polio surveillance, sick children with suspected paralysis or possible neurological maladies were being identified and tested by the polio surveillance system, he remarked. However, the neurological disorders given by the WHO Country Office as examples of the expanded definition of AFP were likely to account for only a small part of the increase in non-polio AFP cases being seen in India.
No clear picture
Unfortunately, the cases of children with non-polio AFP were not being monitored by either the polio eradication programme or the larger state health care system. As a result, there was no clear picture of what was causing the AFP, the kind of diseases these children displayed, or how many of them were seriously affected, he pointed out.
A range of non-polio pathogens could produce AFP, said Dr. John. With many such pathogens, the paralysis they caused would often disappear in a short period of time. However, others were capable of causing quite serious diseases, disability and even death.
Two teams of Indian scientists recently studied the sorts of enteroviruses found in children with non-polio AFP. Enteroviruses are a diverse group, most of which replicate in the alimentary tract. The poliovirus is part of this group. Several non-polio enteroviruses have been associated with a range of acute and chronic human diseases, including polio-like paralysis.
In a study published in 2009, a team at the Sanjay Gandhi Postgraduate Institute of Medical Sciences in Lucknow tested over 46,000 stool samples from children with AFP in U.P., Bihar and other northern States between 2004 and 2007. In the other study, C. Durga Rao of the Indian Institute of Science, Bangalore, and his colleagues looked for enteroviruses in stool samples collected from more than 2,700 children with non-polio AFP in Kerala, Karnataka and Uttar Pradesh between 2007 and 2009.
Both groups found that only about 30 per cent of the non-polio AFP cases were associated with enteroviruses. These viruses could therefore only partially explain the non-polio AFP cases being detected.
In a paper published early last year in the Indian Journal of Medical Ethics , Neetu Vashisht and Jacob Puliyel of the St. Stephens Hospital, Delhi, gave another perspective on the issue. Children in Bihar and U.P. have received more doses of oral polio vaccine than elsewhere in the country. The oral vaccine, it was found, became less efficacious in the face of gut infections and diarrhoea that were widely prevalent in those States.
In their paper, Dr. Vashisht and Dr. Puliyel analysed the non-polio AFP rates across all States over 10 years up to 2010, and found that the rate “increased in proportion to the number of polio vaccine doses received in each area.” In 2012, the number of doses of oral vaccine given to children in Bihar and U.P. had come down and, for the first time, there was a decrease in the non-polio AFP cases in those States, Dr. Puliyel told this correspondent.
There was need for “a critical appraisal to find the factors contributing to the increase in non-polio AFP with increase in OPV [oral polio vaccine] doses — perhaps looking at the influence of strain shifts of entero-pathogens induced by the vaccine,” said Dr. Vashisht and Dr. Puliyel in the paper.
The non-polio AFP rate was not correlated with the number of oral vaccine doses that were administered, countered the WHO Country Office in its response. The largest number of oral vaccine doses given in India was in 2004, which had the lowest non-polio AFP rate in the last eight years. Moreover, although the number of oral vaccine doses given in the country had shown a continuous decline since 2007, the non-polio AFP rate had increased during the same period. In Bihar and U.P. too, there were similar trends of reduced oral vaccine doses and rising AFP rates during 2007-2011.
“The ICMR [Indian Council of Medical Research] is leading the investigations into non-polio causes of AFP,” the WHO Country Office stated.