Chikungunya upsurge due to 'evolution' of viral strain, say experts

As the number of deaths in Delhi due to chikungunya and its complications have shown a spike,health experts say the sudden "upsurge" of the disease this year could be a result of "evolution" of the viral strain.

Doctors have detected that the viral strain is showing"different behaviour", though it will only be conclusive onceresearch is conducted on the make up of the virus. "Dengue and chikungunya both are caused by the same aedesmosquito but dengue can be contracted through four vira lstrains while chikungunya is caused only by one strain.

"Also, in dengue cases, some strains are more virulentthan other ones. The number of rising cases of chikungunyathis year after the 2006 spike could be due to an evolution inits strain," National Vector Borne Disease Control Programme(NVBDCP) Director A C Dhariwal said. Experts also feel that north Indians could be succumbingto the vector-borne disease because of their "low immunity" to it.

"People in north India haven't been really exposed to thechikungunya strain compared to the population in the southernpart of the country, and therefore they are more vulnerable tothis viral attack," Municipal Health Officer of SDMC, P KHazarika told PTI. He, however, said the probability of evolution of theviral strain will just be a speculation until scientistsestablish it.

IgM-ELISA and Reverse Transcription-Polymerase ChainReaction (RT-PCR) are the two main tests used to detectchikungunya in patients. A senior doctor at Sir Ganga Ram Hospital says the viralstrain in patients diagnosed with chikungunya at its hospitalare "showing different behaviour" for the two tests.

"We used IgM serology on patients earlier but then afterfinding discrepancy between clinical diagnosis and laboratorytests, we started performing molecular test (RT-PCR) to detectthe chikungunya virus from the blood of clinically suspectedpatients from September 1 onwards," the doctor said. "And from Sep 1-13, out of 565 samples of suspected viralfever, 319 came positive for chikungunya virus which is about56 per cent positivity.

So, we found out that a test comingnegative by IgM is coming positive by RT-PCR. And, this couldmean the number of cases in Delhi could be much higher thancurrently reported," he said. Arun R Kaushik, specialist in microbiology andgeriatrics, says, "Chikungunya virus is transmitted by thebite of aedes albopictus and aedes aegypti mosquitoes. Therisk of death is about one in 1,000 especially common amongthe elderly or those with underlying chronic medicalproblems."

According to the Bangalore-based doctor, "The prevalenceof arbovirus infections similar to chikungunya virus in southIndia especially in states like Karnataka, Tamil Nadu havemade people tolerant to these infections." The number of chikungunya cases in the national capitalhave climbed to over 1,700 this season and at least 12 deathshave been reported due to the disease.