Epidemiology

Each hantavirus is specific to a different rodent host, and the epidemiology of each virus is therefore closely linked to the ecology of its host. Once infected the rodent will secrete infectious virus for prolonged periods, probably for life. Transmission of virus between rodents and to humans occurs through inhalation of infected animal excreta and fluids, i.e. urine, faeces and saliva. Bites may also be a factor in rodent infections, and have occasionally been reported for human infections. Occupational risk factors are important for infection: trapping, forestry workers, farmers, and military personnel are amongst those in whom infection occurs. Exposure to rodent excreta via working with wood piles and entering/cleaning long abandoned buildings are also associated with a risk for hantavirus infection.

The possibility of exposure amongst campers, hikers and tourists to endemic areas is generally considered to be low, and can be reduced if rodent contact is avoided.

Spring/summer rises in cases in Asia are related to increased rodent contact during seasonal planting and harvesting activities. Puumala virus infection in western Europe tend to occur between March and November, with peaks in August and September.

The bank vole, host to Puumala virus, is a small mammal that eats seeds, fruits of trees and bushes, and green plants. The population dynamics of these animals are directly influenced by the seed production of trees, especially oak, beech and acorn. Years with increased seed production (called 'mast' years), mediated by favourable climatic conditions (including mild winters and dry summers), give rise to increased rodent population densities in the following year. In recent years, particularly 2004-2005, such events have been accompanied by an increase in human hantavirus disease (Eurosurveillance May 2007).