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Planes, trains and vehicles: The neglected role of passive transportation!

July 17, 2014 - 20:27 -- Bart G.J. Knols
I still remember the day ten years ago in a workshop in Sudan on the establishment of the Sterile Insect Technique (SIT) project for the control of An. arabiensis in northern Sudan. The discussion was mainly about the isolation of the area, in the middle of which old Prof. Osman Abdelnour, chief entomologist of Sudan who passed away two weeks ago, raised his hand and hardly pulled his body from the chair and asked: and what about passive transportation?...

Getting back to my very busy life I still remember that very simple direct question and wonder whether its significance has been overlooked. It is not only the absence of scientific research determining the impact on Sterile Insect Technique Studies, but also more generally as a factor that might affect our understanding of the dynamics of mosquito populations in any part of the world. 
With respect to Sudan the sole published paper about the isolation of northern Sudan mentioned the expectation of passive transportation of An. arabiensis mosquitoes into the control area as improbable. However, field observations from Sudan show that luggage cabinets in big buses are places that are frequently found to accommodate mosquitoes, in addition to areas underneath seats inside “air conditioned” buses. The journey by bus between Khartoum in central Sudan and Khariema in northern Sudan through the desert takes around 4.5 hours. Only one train a week travels from Khartoum to Wadi Halfa at the Egyptian border. Despite the trip taking 12 hours Egyptian authorities spray it with insecticide when the train reaches Wadi Halfa to limit the possibility that passive transportation disrupts their successful An. gambiae control programme. This leads me to wonder how the numerous short bus trips might compare to 12 hours by train in terms of the risk of passive transportation.
Another obvious potential passive transportation route are airplanes. Luckily, in northern state they are not favoured as it is very costly in comparison to buses and small vehicles. However, the image of an air hostess on certain plane routes taking two bottles of insecticide fluid and spraying the inside of a plane is one familiar to many travelers around the world. This activity has always made me wonder about the scientific basis of such precautions (and what insects are being targeted).
It has been stated that “SIT site[s] should be an island or an area on the main land as isolated as possible so that reinfestation does not occur or is so slight that it does not distort the evaluation of the experiment”1. Conceptually it seems that passive dispersion may be more of an issue when the objective is local stable eradication (where releases may stop after success) and might be less important where the objective is long term suppression (based on continuous long-term releases of sterile males). However despite my sustained interest in passive transportation I consider that there is a lack of suitable scientific studies to determine if we underestimate or overestimate its role in SIT projects? In addition I wonder what is the evidence of the relative effectiveness of risk reduction techniques such as the spraying of planes and trains?
Personally I think that more scientific studies should be carried out to increase our understanding of passive transportation of mosquitoes to better anticipate its impact on control efforts. Primarily to identify factors which have the biggest impact on the frequency of passive transportation e.g. seasonal climatic conditions, socioeconomic factors or the design of vehicles? Once there is this type of knowledge we will be in a much better position to assess the value (if any) of current control techniques or if it is necessary to develop new ones.
Planes, trains or vehicles? This is a plea for more scientific input on passive transport.
1. Knipling E F, Laven H, Craig GB, Pal R, Smith CN, Brown AWA: genetic control of insects of public health importance. Bull World Health Organ 1968, 38: 421-438.
The views expressed in this article are the authors' alone and not intended to reflect those of their organizations.

 Rasha Azrag is a medical entomologist working in the department of Zoology/ University of Khartoum, Sudan and used to teach basic entomology courses to undergraduate students and molecular entomology to master students in the Medical Entomology and Vector Control program. She has experience from working in different vector control programmes, from basic classic control methods to the use of genetic methods. 
Guy Reeves is a research scientist at the Max Planck Institute for Evolutionary Biology in Plön, Germany. Part of his research involves the exploration of genetic methods to control vectored diseases.

Our shared vision is to play a part in bridging the gap between scientists working in different fields and countries, promoting discussion on stimulating topics.           



Submitted by MURLIDHAR J. MENDKI (not verified) on

I agree with Rasha and Guy. In India we have experienced many times; while travelling by train especially the Sleeper class compartments. Except in sever winter, generally it is found that when the train halts in station (average halting period is 3 mins to 15 mins) the passengers normally suffer the biting nuisance by the mosquitoes. They are quite clever they hide under the berths and passengers may thought that trains speed will drive away the mosquitoes. It is quite possible that the means of transportation may be /are the good source of mosquito dispersion from one place to another. But ist is quite a daunting task to keep track on the passive transportation of mosquitoes. Recently in India the railway passenger services were extended in Jammu and Kasmhir and I do fear that the days are far away the mosquitoes are next tourists visiting in this region from coming other region by passive transportation.

Submitted by Rasha Azrag and... (not verified) on

Dear Murlidhar Mendki
Thanks for your very relevant observations from a very different part of the globe and also for your insight.
We agree that while it may appear a daunting task to look at passive transportation , as you allude to, we think that passive transportation (particularly by trains) might generate hypotheses that can then be tested in different geographical regions. Maybe looking at the historical presence or absence of mosquito species in the context of changing transportation links might be one way to start exploring impact of passive transportation that might not be so challenging ? we also need to develop appropriate scientific designs that can help testing such hypothesis.
Thanks again
Rasha and Guy

Jeff Juel's picture
Submitted by Jeff Juel on


Yet another thought-provoking post.

Civil Engineering, as taught at my alma mater, was divided into three areas of study: Structures, Transportation, and Water & Air Resources. Your latest post is related to transportation, and just the other day you posted a story about leaking water pipes. That makes two out of three.

Is a blog about using screened doors and windows and mosquito-proof structures in the offing?

Your recent posts reinforce my contention that civil engineering is vital to the eradication of Malaria.

Flood control and the associated drainage infrastructure is my particular area of interest. This has obvious and extremely important implications for LSM.

Dr. Israel Kligler's eradication work in Palestine entailed an array of civil engineering works. The TVA work in America was a massive civil works effort which ultimately played a central role in eradication malaria in the Tennessee Valley.

In my humble opinion, attempting regional eradicate of malaria without a good helping of civil engineering is a Sisyphean task.

Jeff Juel, PE

Bart G.J. Knols's picture
Submitted by Bart G.J. Knols on

Dear Jeff,
Please note that I did not write this column. The credit goes to Rasha and Guy...
Best, B

Submitted by Rasha Azrag and... (not verified) on

Dear Jeff
We definitely see your general point about the value of engineering solutions but we suspect that currently we are still at the stage of trying to determine in what circumstances passive transportation is of practical importance. Only then will we be in a position to determine where and when might warrant resources devoted to preventing it.
While, whatever effective approaches that are resource efficient should be part of control programs, with respects to sterile insects technique (SIT) it might be notable that the most spectacular achievement of this approach, the eradication of screwworm from North and Central America, occurred through a fairly singular application of SIT (though other might know more about this). We anticipate for the SIT program in Sudan that considering impact of passive transportation in its final stages might has good prospects to sustain the control efforts of An. arabiensis in the region.
We will definitely consider doing our next Colum on ‘structures’ to fulfil your hat-trick of ‚’ Structures, Transportation, and Water & Air Resources’.-is there a prize?
Rasha and Guy

Submitted by Prof. Z. N. Mahmoud (not verified) on

Thanks Rasha and Guy for your interesting article. In harmony with what you wrote, the role of steamers as well as lorries carrying vegetables (usually covered by wet broad or massiveleaves)deemed to be investigated. To avoid being attacked by mosquitoes, I will go for small uncomforable vehicles!