In what could be an alarming revelation about the behaviour of chikungunya virus, the causative organism that is transmitted in humans by the Aedes mosquito, a study conducted in the national capital has revealed that the virus has the capability to survive within the mosquitoes for generations, without actually going into humans.
The chikungunya virus goes through a mosquito-human-mosquito cycle for its survival, where the humans act as the host for transmission of the virus. However, the latest study reveals that even without that mosquito-human- mosquito cycle, the chikungunya virus has developed the capability to survive within the vector mosquito for generations through “vertical transmission”.
The study reveals “vertical transmission” of chikungunya virus takes place in case of the Aedes mosquito, which act as a reservoir – where the viruses are transmitted from the mother to the offspring, resulting in the Aedes mosquito maintaining the virus within the population for generations.
The findings have been revealed in the study conducted in Delhi and NCR region by researchers from the International Centre for Genetic Engineering and Biotechnology, National Institute of Malaria Research, and the Indian Council of Medical Research, and has been reported in the journal ‘Acta Tropica’.
“In vertical transmission, the viruses are transmitted from the mother to the offspring. In the case of chikungunya virus for Aedes, the virus goes through mosquito-human-mosquito cycle for its survival. But the study for the first time has revealed that vertical transmission takes place in chikungunya virus. Now, even without the human-mosquito cycle, the virus is able to survive within the vector until it reaches a conducive environment for it become infective. This feature of the virus changes the whole paradigm of how you control vector transmission. Therefore it is very important to begin the vector control and vertical surveillance even before the peak period during the monsoons,” Dr Sujatha Sunil, head of Vector Borne Diseases Group at ICGEB and principal investigator of the study told The Indian Express. “Identification of breeding sites and timely control of vector population before the onset of monsoon and during the dry summers is extremely important.”
The study was carried out in south and west Delhi, and Bahadurgarh and Bhadana in Haryana. During the study, freshwater samples were collected at the beginning of every month between May and October and the four sites identified for the study presented different water storage containers. Also, Aedes mosquito immature stages (larvae and pupae) collections were made in 2012, over six months. The collected larva and pupae were transferred to plastic jars filled with fresh water and the adults were collected by suction tube transferred into small plastic containers covered with net. During the study, the adult mosquitoes were provided with normal blood meals.
In south Delhi, containers were primarily for water storage due to acute water shortage, where plastic containers were the predominant type. In west Delhi, desert coolers were a major source of water storage and primary breeding site. The study revealed in south Delhi, “even though water storage was extensive in plastic containers, these were not preferred breeding sites, while permanent breeding sites like underground cement tanks have higher larval indices”.