Dengue can turn deadlier as all of its four strains can circulate together, scientists have established. The viruses can also circulate with malaria and chikungunya virus.

The disease is caused by the mosquito-borne dengue viruses consisting of four serotypes (strains)—DENV 1, DENV 2, DENV 3 and DENV 4.

The Indian Council of Medical Research (ICMR) has confirmed that DEN 3 is circulating this year in the national capital, while the National Institute of Malaria Research (NIMR) has recently established in its research, An Epidemiological Study of Dengue and its Coinfections in Delhi, that in previous years, all the four strains were circulating together. The research was also published in the International Journal Of Infectious Diseases

As many as 1,536 (28%) of the 5,536 patients tested during the study in the NIMR clinic had confirmed dengue. The peak dengue positivity was seen during September and October, said the study.

“Of the 60 samples analysed, 10 (16.7%) had concurrent infection with multiple dengue serotypes; one of them had all the four serotypes. Co-infection of dengue with malaria and chikungunya was also observed. Infection with more than one serotype was also observed. Dengue and malaria co-infection was also found though malaria transmission is very low in Delhi," said Deepali Savargaonkar, a scientist with NIMR and the author of the study.

“Delhi being hyper-endemic to dengue and other vector-borne diseases, the occurrence of concurrent infections with multiple DENV serotypes has become a frequent finding. There is a need for strong surveillance to monitor trends in dengue distribution, seasonal patterns and circulating serotypes to guide dengue control activities," she said.

There is a significant association of peak in dengue positivity and high larval indices with the post-monsoon period, the scientists have pointed out.

Dengue is seen to be common in the age groups of 11-20 and 21-30 as they are more prone to mosquito bites because of the nature of their daily routine, they said.

“Dengue is prevalent in at least 128 countries. With increased globalization and major travelling, the possibility of co-infection of virus’s strains has largely increased. As people travel, they can bring different strains from other places," said Himmat Singh, a scientist with NIMR.

“If a mosquito carrying one strain bites a person carrying a different strain, the mosquito gets the new strain as well and further spreads it. Dengue co-infection with its own strains and malaria and chikungunya can be much more severe than thought," Singh said.

“In areas endemic for dengue, chikungunya and malaria, there is a need to have a higher degree of suspicion of co-infection to ensure prompt treatment, especially for malaria. With frequent outbreaks in Delhi, there is a need to conduct epidemiological and entomological surveillance, which will help in early warning of outbreak and control of dengue," said Savargaonkar.

At least 40,868 cases of dengue have been reported with 83 deaths till 30 September 2018, according to the National Vector Borne Disease Control Programme under the ministry of health and family welfare. The highest burden of the disease is in Maharashtra (4.667 cases), Odisha (3,883) and Kerala (3,660). Kerala has recorded the highest number of deaths, 35, followed by Maharashtra (18) and Chhattisgarh (10). There have been 1,156 cases this season in Delhi.

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