Chikungunya cases dip in Delhi but experts say threat looms

The municipal corporations of Delhi, according to their weekly reports, have recorded at least 109 cases of chikungunya this year (till October 20).

The number of recorded chikungunya cases this year is 40 times less than those recorded in 2016, data available from municipalities said. In 2016, at least 4,464 cases had been reported till October third week, when Delhi witnessed a chikungunya outbreak.

A total of 7,760 laboratory confirmed cases of chikungunya were reported from Delhi in 2016.

Chikungunya is a viral infection transmitted by the bite of the aedes aegypti mosquitoes, which is also known to spread other viral infections like dengue and zika. The symptoms of chikungunya are very similar to that of dengue — fever, chills, fatigue, headache, and skin rashes. But, chikungunya also causes severe debilitating joint pains, which sometimes persists for months.

Unlike dengue, there is only one strain of the chikungunya virus and an infection is said to confer lifetime immunity to the affected person.

Can there be another outbreak? Experts believe that it is quite possible.

“There is always a possibility of another outbreak. The virus is in circulation — a few cases are reported every year — the mosquito is also there and the people are also there. In 2016, a few thousand cases were reported by the authorities, but unofficial estimates put the number at more than a lakh as many people might not have been tested for the disease altogether,” said Dr Pradeep K Sharma, a consultant of paediatric critical care at Sri Balaji Action Medical Institute, Paschim Vihar, west Delhi.

“Delhi has a population of almost two crore people. Add to that the large population of migrants and you have a huge number of people who are not immune to the infection. As soon as the herd immunity goes down in a couple of years, there is a possibility of another outbreak,” he said.

Do people die of chikungunya? Not a single death was reported in 2016 when India reported more than 64,000 cases of chikungunya, of which at least 26,000 were laboratory confirmed.

In fact, the government has not reported any chikungunya deaths in India so far. They maintain that the people with chikungunya who do succumb, die because of other simultaneously occurring co-morbid conditions.

The World Health Organisation too states that the disease can only ‘contribute’ to death.

“It is very unusual for people to die of chikungunya alone. The viral infection can deteriorate pre-existing conditions like diabetes or hypertension or heart diseases. However, with proper management of the co-morbid conditions, along with the infection, deaths can be prevented,” said BK Tripathi, professor and head of department of medicine at Safdarjung hospital.

“The viral infection also puts people at risk of developing secondary bacterial infections, which if not treated properly, can lead to death,” added Tripathi.

However, a study conducted by a city hospital that retrospectively looked at the patient data from the paediatric intensive care unit during the 2016 chikungunya outbreak, spotted that a 14-year-old with no co-morbid conditions died of chikungunya.

Of the total 49 children admitted to the hospital with laboratory confirmed chikungunya, 11 got septic shock.

Of these children (all less than one-year-old or between 11 to 14-year-olds), the symptoms relieved with the fever in those who had been admitted early. Three children who were admitted after a few days of the infection developed multi-organ failure and needed to be put on ventilator.

One of the three children later died.

“The child was completely healthy and did not have any co-morbid conditions, so it was viral infection that led to the death. We need more studies to see how the virus reacts, especially in infants and children undergoing puberty,” said Dr Sharma.

In India, 5,789 confirmed cases of chikungunya were reported till September end , 2018, according to the data provided by the National Vector Borne Disease Control Programme (NVBDCP). Of these, the highest number of cases were reported from Karnataka (1,866), Madhya Pradesh (1,150), and Jharkhand (736).

“Theoretically, it is believed chikungunya confers lifetime immunity, meaning another outbreak in the same region must not happen till another generation comes along in 30 or 35 years. But, in Kerala, for example there was an outbreak in 2007 and it happened again within two years. So, clearly something changed — there is no research to show whether it was a mutation in the virus, change in population composition or something else; we don’t know,” said an expert, who did not want to be named.

Chikungunya cases are usually reported from Andhra Pradesh, Karnataka, Maharashtra, Madhya Pradesh, Tamil Nadu, Gujarat and Kerala.

“And it might have happened in other places too. Who knows? There is no way to clinically diagnose someone with chikungunya conclusively. An antigen test, which needs to be done within the first few days of the infection, has to be done to know for sure whether cases are occurring,” said the expert.

Since the first recognised outbreak in East Africa in 1952, the disease has spread other countries countries, according to the World Health Organisation.

Chikungunya usually occurs in Africa, Asia and the Indian subcontinent. Around 1.9 million cases have been reported from India, Indonesia, Maldives, Myanmar and Thailand since 2005.

The disease was reported for the first time in Europe in 2007 in a localised outbreak in northeastern Europe.

First Published: Oct 26, 2018 16:15 IST