Vaccine and Infectious Disease Division

The mosquito flies anyway, with dengue

Aedes aegypti mosquito

Aedes aegypti mosquito, the vector that transmits dengue virus.

Graphic by M. Miner

The WHO estimates that 50-100 million people worldwide are infected annually with dengue virus, the pathogen that causes dengue fever. It is a vector-borne disease transmitted via the mosquito Aedes aegypti, which is endemic mainly in parts of South America, Africa and Southeast Asia. There are 4 dengue serotypes, all of which cause disease.

Approximating the likelihood of dengue transmission (also referred to as the attack rate) is challenging because not only human variables must be taken into account, but also those of the vector itself. A recent study by VIDD Senior Staff Scientist Dennis Chao, Affiliate Investigator Ira Longini and Member Betz Halloran developed what is referred to as an individual-based mathematical model to study the effect of mosquito movement and spatial distribution on dengue incidence. The model was designed to determine dengue transmission rates and patterns of mosquito-based interactions with humans at home, school and workplace for a rural area in Thailand using published census data, representative geographic grids and estimates of serotype prevalence from Thailand for the past 4 decades. The attack rate is proportional to the mosquito population size, amount of time a person spends at a given location, and whether a mosquito’s travel is constrained to small distances, which is typical, or unconstrained by distance. The authors found that a mosquito’s tendency to travel small distances had a larger effect on dengue transmission than the mosquito population size at any given location.

The authors then applied their mathematical model to a mass vaccination simulation and found robust effectiveness over the entire human population, even when the assumed vaccination rate was only 70%. The study concludes that mosquito mobility patterns can highly affect dengue transmission and, based on these assumptions, vaccination on a population-wide level can provide effective protection. This study can be used to model mass vaccination to prepare for the (hopefully) imminent availability of a dengue vaccine.

  

Chao DL, Longini IM Jr, Halloran ME. The effects of vector movement and distribution in a mathematical model of dengue transmission. PLoS One. 2013 Oct 21;8(10):e76044.