While as many as 300 million dengue virus (DENV) infections may go unnoticed because they are asymptomatic or associated with mild symptoms only, it has been assumed that these infections contribute little to onward transmission. However, recent blood-feeding studies with Aedes aegypti mosquitoes have found that people with asymptomatic and pre-symptomatic DENV infections can infect mosquitoes. The authors therefore used models of within-host viral dynamics and human demographic projections to quantify the net infectiousness of all patients with DENV infection and estimate the fraction of transmission attributable to patients with differing severities of disease. They found that the net infectiousness of patients with asymptomatic infections is 80% of people with apparent or inapparent symptomatic infections. However, because of the high numbers of patients involved, clinically inapparent infections in total could account for 84% of DENV transmission. Of the infections that ultimately result in any level of symptoms, the authors estimated that 24% of onward transmission results from mosquitoes biting patients during the pre-symptomatic phase of their infection. Only 1% of DENV transmission is attributable to patients with clinically detected infections after they have developed symptoms. This demonstrates that current prevention practices need to be pre-emptive to account for the contributions of undetected infections and new methodologies are needed to include currently undetected infections in surveillance programmes.
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