Transmission Mode of Chikungunya Fever

Maintenance of CHK Virus in Nature The virus is maintained in nature at a low level in man–mosquito–man cycle. The survival of CHK virus in nature is also through transovarial transmission (TOT) in Aedes aegypti mosquitoes.

The Vectors In India Aedes aegypti is the principal vector of this virus. It can be transmitted by Aedes albopictus & Aedes vitatus.

CHK virus is transmitted from person to person by Aedes aegypti mosquitoes. Aedes aegypti is the most important epidemic vector, but other species such as Aedes albopictus & Aedes vitatus have also been incriminated as a secondary vectors. Aedes aegypti is the main vector species and is common in most urban areas. The rural spread of Aedes aegypti is relatively recent occurrence associated with the development of rural water supply schemes, improved transport systems & scarcity of water. The population of Aedes aegypti fluctuates with rainfall and water storage.

Eggs are deposited singly on damp surface just above the water line. Most female Aedes aegypti lay eggs in several ovi position sites during a single gonotrophic cycle. Embryonic development is generally completed in 48 hours in a warm and humid environment. Once embryonation is complete, the eggs can withstand long periods of desiccation (More than a year). Eggs hatch once the containers are flooded, but not all the eggs hatch at the same time.

Aedes aegypti breeds almost entirely in domestic manmade water reservoirs found in and around households, construction sites and factories. In a hot and dry regions overhead tanks, ground water storage tanks etc. becomes primary habitats. Under the optimal condition the life cycle of aquatic stage of the Aedes aegypti (The time taken from hatching to adult emergence) can be as short as 7 days. At low temperature, it may take several weeks for adults to emerge. Aedes aegypti has an average adult survival of only 8 days. During rainy season when survival is longer (Up to 21 days) the risk of virus transmission is greater.

Feeding Behaviour Aedes aegypti is highly anthropophilic. Being a diarnal species, females have two periods of biting, one in the morning for several hours after day break and the other in the afternoon for several hours before dark. Aedes aegypti generally does not bite at night but it will feed at night in lighted rooms.

Resting Behaviour Aedes aegypti prefers to rest in dark, humid places inside houses or buildings, including bedrooms, bathrooms, and kitchens, The preferred indoor resting surfaces are the underside of furniture, hanging objects such as clothes and curtains & on walls. Less often it can be found outdoor in vegetation or other protected sites.

Flight Range The dispersal of adult female (Aedes aegypti) is influenced by number of factors including availability of ovi positions sites and blood meals, but appears to be often within 100 meters of the sight of emergence.

The Transmission Cycle The female Aedes aegypti usually become infected with CHK virus when takes blood meal from a person in the acute febrile (Viraemia) phase of illness. After an extrinsic incubation period (8 to 10 days), the salivary glands of the mosquito becomes infected and virus is transmitted when the infected mosquito bites and injects the salivary fluid into the wound of another person.