Updated June 23, 2015.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

A brain infection spreading among kids is just plain scary. It's even scarier when we don't know the cause.This has happened for families in parts of India again and again.

Unexplained outbreaks of acute encephalitis syndromes - which cause fevers and brain swelling with possible brain damage and death - have occurred around the world, but particularly in India. Such outbreaks have also occurred in Vietnam, Malaysia, and other locales, to varying degrees.

Sometimes the cause isn't known because the testing isn't available. Sometimes the disease is caused by a new virus that testing can't identify. Sometimes testing happens, but too late in the outbreak. 

We also might not know the cause because data collection can be a bit messy. Entries may seem off. Testing might also not be fully recorded. Vaccination histories may not be clear. Many cases may not be reported - or families might not bring patients into care.

This is particularly complicated as outbreaks close in time and place may be cause by different diseases. It's hard to figure out the causes of these outbreaks.

What is clear is that there are many cases of unexplained encephalitis in children in India. A database from January 2011–June 2012 recorded 812 cases, almost half in children under 5. These are just the cases that are recorded.

What is Acute Encephalitis?

The virus causes an encephalitis, or brain swelling, It can cause a high fever and brain involvement, seizures, coma, and other changes.

Some cases can cause paralysis; some twitches; some loss of reflexes.

So many diseases

Most cases in India were thought to be caused by Japanese Encephalitis which leads to fever, neurologic changes, and death. However, with increased vaccination for Japanese Encephalitis and an increase number of cases recorded, there must be other causes as well.

Less typical cases of Dengue can be to blame. Likewise, atypical West Nile, which is often asymptomatic, can be the cause.

Common diseases can present in uncommon forms;  Herpes, Varicella, Measles, Mumps, Leptospirosis, and Enterovirus can also cause a similar picture, though usually lead to milder illnesses. Malaria often causes fever, neurologic changes, and death quickly in children. Rabies can also be to blame.

Sometimes specifics of the disease, like paralysis with no relfexes (West Nile) or psychiatric symptoms (HSV) can identify which hint to which disease is which. Usually, though, it's hard to identify the cause.

Novel diseases

There are also likely new viruses which are to blame. This has been the case when Nipah first arrived in Malaysia - and even West Nile in New York City.

For any disease, we know what syndrome a patient has, but we can't find what's responsible. Sometimes we have a potential cause (a virus or bacteria) but we don't know if it's just a bystander - or the cause.

One such virus that seemed to cause encephalitis - but maybe it didn't - was Chandipura virus.

Where was Chandipura found? 

The disease had first been identified in two people with fevers in 1965 in a village called Chandipura, in Maharashtra state, India.

How was Chandipura identified as a potential cause?

It was known for a long time as cause of fever without it being associated with encephalitis. However,by the 1980s it was beginning to be seen as the cause of some cases of encephalitis. There wasn't however any proof that it caused encephalitis outbreaks.

There were however outbreaks for which no cause could be found. In 2003, in Andhra Pradesh state in southern India, many children became ill and many died (183 out of 329 cases). Tests were negative for common causes (Japanese encephalitis, West Nile, dengue, and measles viruses, and for RNA of coronavirus, paramyxovirus, enterovirus, and influenza viruses.) However, some - but not all - cases were positive for Chandipura by PCR, Antibody, and other testing.

?Another with a similar high mortality rate in kids (78.3%) was noted in Gujarat in 2004. Likewise, no other cause could be found; 9 to of 20 samples showed Chandipura.

It seemed to be that Chandipura was the cause. The thing is, even if it is the cause, there isn't, a treatment or a vaccine to offer. It did not change the course of the disease for these children.

What did the disease seem to be like?

The disease is striking in who it strikes.

About 55 to 75% of children infected will die. Adults were not affected.

Death if it occurred happened quickly, within 48 hours.

Illness seemed to include an influenza respiratory disease with neurologic changes (including lack of reflexes and other changes). The disease seemed to affect the liver and cause skin eruptions, with vesicles. 

Some cases likely caused no apparent symptoms.

How is it spread?

The virus is thought to be spread primarily through sand flies. The virus has been found in sand flies in India and West Africa (though the human illness hasn't been identified there). (It was also thought to be spread by mosquitoes).

How is it diagnosed?

A PCR can be done on CSF (cerebrospinal fluid) as well as respiratory samples. Antibody testing can be carried out after - or late into - infection.

What type of virus is it?

Chandipura is a Rhabdovirus (negative-sense single-stranded RNA virus). Another famous Rhabdovirus is the virus that causes Rabies. Another Rhabdovirus is Vesicular Stomatitis Virus (VSV or also called Vesicular stomatitis Indiana virus (VSIV) which is being used to develop an Ebola vaccine.