Two months after the country earned its polio-free tag, a mosquito has emerged as a fresh concern. Mosquito-borne West Nile virus has been found to be causing acute flaccid paralysis (AFP), the main symptom of poliomyelitis, for the first time in India. The symptom is the most common sign of acute polio and is used for surveillance during polio outbreaks.

However, unlike polio which is a childhood disease, West Nile induced AFP is seen in adults. So, the finding is not going to undermine the success of polio-free certification, say researchers, but is still reason for concern. Nationwide AFP surveillance is the gold standard to detect polio cases.

Neurologists from hospitals in Kochi, Kerala along with virologists from Indian Council of Medical Research (ICMR) designated virology laboratory Manipal Centre for Virus Research (MCVR), Manipal University have reported three laboratory confirmed cases of West Nile virus induced AFP, a syndrome historically associated with infection by polio virus.

"The findings are bewildering. While polio virus is a member of enterovirus family transmitted by water, the WNV is an arthropod-borne virus from the arbovirus family, which is transmitted by mosquitoes. However, the devastating effects are found to be the same," said virologist G Arunkumar, professor and head, Manipal Centre for Virus Research and one of the main researchers who reported the first three cases of West Nile virus induced AFP.

The emerging threat from the West Nile virus is being looked at with concern given that the country earned its polio-free certification from wild polio virus transmission only in March this year.

The case reports of three patients, all in the age bracket of 42 to 55 years, have the doctors flummoxed. The three patients were suffering from extreme muscle weakness of limbs, reduced muscle tone, impaired breathing and fever which are primarily the characteristics of polio.

Only after running blood tests and performing a battery of radiology tests that record activity in nerves and in spinal cord cells, did the doctor reach their diagnosis: AFP caused by West Nile virus.

"Previously, severe cases of West Nile had been characterised by meningitis and encephalitis, the brain swelling that is regarded as the most serious consequence of the virus. But the muscle weakness and other problems associated with AFP were not evident," said Arunkumar.

Asked what limitations the study suffer, Arunkumar said, "Our diagnosis is well accepted and there is no flaw. However, detailed epidemiological studies involving human, mosquitoes, birds, animals and environment are need of the hour to understand the burden and plan prevention and control strategies. There is no specific antiviral or vaccines available against West Nile as of today."

In polio, the gray matter of the patients' spinal cord, which contains the neurons responsible for carrying information to the muscles is attacked by the virus. The attack crushes the neuron fibers causing the muscles to turn flaccid, often producing uneven results - a leg gone weak on the right side, an arm on the left. It also results in bladder and bowel dysfunction, along with respiratory complications that can leave patients attached to artificial breathing machines.

The Annals of Indian Academy of Neurology, official journal of Indian Academy of Neurology published the research article 'Acute flaccid paralysis due to West Nile virus infection in adults: A paradigm shift entity' on the AFP link in January-March edition of 2014.

"It is extremely important that the findings circulate among physicians to avoid misdiagnosis that could become life-threatening. West Nile-induced AFP cannot go untreated and unreported," the researchers said in their article.

Further, in the post-polio eradication era it may be worthwhile testing AFP cases for WNV. "A high level of clinical suspicion, active clinical case detection and appropriate laboratory confirmation is the way forward to increase the hospital based surveillance of WNV infection in India," researchers have said.

A virologist from National Institute of Virology (NIV), a premier virology institute in India commenting on the study said, "We have to see whether they have used single serum sample to conclude the West Nile positivity as normally we need convalescent sera to confirm the results. Besides, as per our sero-survey study almost 40-50% of people are seropositivity to either Japanese encephalitis or West Nile virus in Kerala region."