Mosquitoes on a plane: Disinsection will not stop the spread of vector-borne pathogens, a simulation study

Abstract

Mosquito-borne diseases are increasingly being recognized as global threats, with increased air travel accelerating their occurrence in travelers and their spread to new locations. Since the early days of aviation, concern over the possible transportation of infected mosquitoes has led to recommendations to disinsect aircraft. Despite rare reports of mosquitoes, most likely transported on aircraft, infecting people far from endemics areas, it is unclear how important the role of incidentally transported mosquitoes is compared to the role of traveling humans. We used data for Plasmodium falciparum and dengue viruses to estimate the probability of introduction of these pathogens by mosquitoes and by humans via aircraft under ideal conditions. The probability of introduction of either pathogen by mosquitoes is low due to few mosquitoes being found on aircraft, low infection prevalence among mosquitoes, and high mortality. Even without disinsection, introduction via infected human travelers was far more likely than introduction by infected mosquitoes; more than 1000 times more likely for P. falciparum and more than 200 times more likely for dengue viruses. Even in the absence of disinsection and under the most favorable conditions, introduction of mosquito-borne pathogens via air travel is far more likely to occur as a result of an infected human travelling rather than the incidental transportation of infected mosquitoes. Thus, while disinsection may serve a role in preventing the spread of vector species and other invasive insects, it is unlikely to impact the spread of mosquito-borne pathogens.

Fig 1. Distributions of the parameters for the average number of humans (A) and mosquitoes (B) on aircraft.

The dark shaded areas in each distribution indicate the interquartile range. The median and interquartile range (IQR) of each distribution is shown in the corresponding panel.

Fig 2. Distributions of parameters in the branching process for P. falciparum and dengue virus introduction.

The prevalence of infection in humans and mosquitoes is characterized by Bernoulli distributions with parameters p_IH (A and C) and p_IM (B and D), respectively. Transmissibility for humans to mosquitoes and mosquitoes to humans are characterized by Poisson distributions with parameters R_0HM (E and G) and R_0MH (F and H), respectively. The dark shaded areas in each distribution indicate the interquartile range. Each panel provides the median and the interquartile range (IQR) of the corresponding distribution.

Fig 3. Step by step probabilities of success for each introduction pathway.

For each sequential step in the mosquito (A) and human (B) introduction processes, we calculated the median (points) and 95% Credible Interval (vertical lines) for the probability of at least one event occurring. For example, the median probability that at least one human is on an aircraft is approximately 1.0 while the median probability that there is at least one human on an aircraft AND who is infected with a dengue virus is approximately 0.5. Note that for the introduction pathway via infected mosquitoes, the probabilities of success at each step (as well as the 95% CI) are nearly identical for both malaria and dengue.

Fig 4. Distributions for the probability of introduction by each pathway.

The density (log scale) for the probability of introduction via each pathway across 1 million simulations for P. falciparum (left column) and dengue virus (right column) and for the two pathways of introduction: infected mosquitoes (top row) and infected humans (bottom row). Each panel provides the median and 95% credible interval.

Fig 5. Sensitivity of introduction pathways to each individual step.

Sensitivity coefficients indicate the percent change in the probability of introduction given a 1% change in each individual parameter (S1 Text). The probability of travel and the prevalence of infection are combined in the parameters λ_ITM and λ_ITH.