This is an article I've been waiting years for. Via the University of New South Wales School of Public Health and Community Medicine, an article by Ronan Kelly of FluTrackers: Acute Encephalitis Syndrome Outbreaks in India – an ongoing puzzle.Excerpt:
Between Jan 1, 2008 and Aug 27, 2014; 44,097 cases and 5,728 deaths were reported due to AES in India. This figure represents a significant increase in the recent annual number of reported cases even as the CFR has dropped to around 13%. An average of 8,139 cases per year have been reported for 2011-2013 an increase of 220% over the period 2003-2007.(8,9) This is likely an underestimate.
Government statistics do not generally include cases that never make it to hospital, and AES outbreaks predominantly affect rural communities with poor access to healthcare who are less likely to be notified as AES cases. Much of the recent increase is accounted for by a surge in reported cases in Assam (cases tripled in 2011 and stayed at that level ever since) and West Bengal (cases jumped sevenfold in 2011 and doubled again since then).
Nationally, since 2008, only 6,825 (15.5%) patients tested positive for JE. In many cases, the causative agent remains elusive.
The State of Uttar Pradesh has experienced periodic AES outbreaks since 1978, but following a major outbreak in 2006, the annual case load has exceeded 3,000 patients, three times the level prior to that year.(10) The State has accounted for almost half (over 20,000) of cases and 3,560 deaths since 2008. Only 8.1% of the cases have been confirmed for JE and the State has annually hosted a variety of investigative teams.
In recent years, various enteroviruses such as EV-76, EV-89 as well as coxsackievirus B5 and echovirus 19 have been found associated with AES cases.(11,12) It has been suggested that shallow wells pumping up contaminated drinking water are a major problem.
However, making any conclusions about what is causing AES outbreaks in Uttar Pradesh is hampered by poor patient record systems. A study from Kushinagar in 2011-2012 found that record keeping, test results and vaccination history were so poor that “inferences about the epidemiology and etiology of AES could not be made”.(13)
One of the conclusions that can be drawn from the various studies in Uttar Pradesh is that the cause of AES outbreaks can vary from location to location. This is also true for the country at large. For example while outbreaks in Assam have consistently tested >35% positive for JE since 2008, Chandipura Virus has been implicated in outbreaks in Gujarat. West Nile Virus (WNV), as in Kerala in 2011, may also be playing a part.(14)
But some outbreaks remain a mystery. One intriguing outbreak has drawn much attention. The State of Bihar has seen periodic outbreaks for over twenty years. Recent recurrent outbreaks centered on Muzaffarpur appear unusual. One such outbreak of unknown aetiology occurred in 2012. Rather than peaking in September as is usual for JE, on this occasion the peak happened in June. None of the 334 patients tested positive for JE and at least 118 (35.3%) of them died.(15)
This year (2014), the outbreak lasted through June and early July and resulted in around 200 deaths. None tested positive for JE, Chandipura, Nipah or WNV. The victims were mostly children, mostly poor, mostly malnourished.
The outbreak coincided with the litchi (lychee) picking season. One hypothesis is that a toxin in unripe litchis leads to hypoglycaemic syndrome in under nourished children causing symptoms that are being diagnosed as AES. (16) Others suggest that the outbreak is really a form of encephalopathy brought about by heatstroke. (17) In parallel with Uttar Pradesh, most cases got their drinking water from shallow hand pumps, but I am not aware of any enteroviruses being identified.(18)
Investigations over the past two years have resulted in local treatment recommendations such as rapid assessment for and correction of hypoglycaemia. Preliminary study suggests that this may have reduced the mortality rate in Muzaffarpur this year down to 26%.