Life, from scratch, of a bitesize killer


二月 22, 2002

Mosquitoes hold a special place among insects in that they have been responsible for more deaths over the centuries than any other group. Surprisingly, most people in Britain think only of mosquitoes as a biting nuisance that affects them on summer evenings and are completely unaware that related insects are responsible for at least 2 million deaths from malaria annually, mostly children in sub-Saharan Africa. Few people who go to exotic holiday locations seriously consider mosquitoes in their travel preparations, and no doubt this is why the increasing number who travel abroad bring about 2,000 cases of malaria into the United Kingdom every year. Most of the 2,500-plus species of mosquitoes are harmless and never bother us, because they either feed from birds or animals or do not take blood, but it is the nuisance and disease-carrying species that are the subject of this book. It aims to set the record straight and provide a better understanding for the general reader of why mosquitoes and the diseases they carry still constitute a major international health hazard, and in many cases are expanding their range despite our efforts to contain them.

The book starts with a jovial insect's-eye view of life as an Egyptian house mosquito: from being laid as an egg, through larval life in a puddle, pupation, emergence as a winged adult, to death a few weeks later, in the kind of docu-soap style that has come to dominate natural-history television programmes. Given the hazards experienced by this chapter's heroine - only female mosquitoes suck blood - it may seem remarkable that any mosquitoes survive at all. However, the rest of the text gets down to more serious stuff, recounting first some of the ways that mosquitoes and the diseases they carry have helped to shape history, and then mankind's heroic and sometimes pathetic attempts to eliminate or control the insects. Given that the lead author is a Harvard professor, it is understandable that much of this is recounted with a strong American slant, but his personal reminiscences lend much to the readability of the book.

For the modern observer looking back, it may appear obvious that mosquitoes and other insects could play a significant role in disease transmission. However, until the development of germ theories by Pasteur and others in the late 19th century, the idea that insects could pass disease from one person to another appeared ludicrous, especially to physicians. Even after acceptance of these concepts, it was almost miraculous that discoveries were made of the role of mosquitoes in disease transmission given the lack of basic knowledge of many of the workers concerned. For example, it helps if you can differentiate between species of mosquito when working with them. Ronald Ross, who serendipitously observed the ability of mosquitoes to transmit human malaria, was apparently completely unaware of what he was dealing with and only chanced to try a species of anopheline mosquito, the only group capable of transmission, because his assistant stumbled upon them as larvae. This book is also a salutary reminder of how much of the globe is still potentially subject to the influence of mosquito-borne diseases and how the advances that have been made in disease elimination have been achieved at a cost. In the early days this was in human life - the lives of the investigators who submitted themselves to being bitten and their helpers who also acted as guinea pigs. More recently, the cost has been environmental - in the abortive attempts to eliminate malaria vectors after the discovery of synthetic insecticides. Our lessons have been ill-learned on that front. Finally, the book looks more philosophically at surviving in a world with mosquitoes and diseases that can move across oceans, such as the recent and unexpected ingress of West Nile fever virus into North America.

As an introduction to the mosquito vectors of malaria - filarial worms that cause elephantiasis, and the yellow fever, dengue, and encephalitis viruses - the narrative is easy to follow, but it is not always entirely systematic and sometimes jumps about with snippets of information slipped into the text almost as afterthoughts. No doubt these inconsistencies arise from the joint authorship of a respected international scientist and a prizewinning journalist. There are passages where I can clearly identify the thought patterns and dry wit of Andrew Spielman, but others where the line of reasoning becomes muddled and repetitive, apparently as a result of textual simplification by another hand. I am afraid that I am never happy with such unions because it is often not difficult to see the "seams".

There are a limited number of illustrations but they do not add much to the text and the quality of some could be better. I also found a few scientific inaccuracies and more than just a few simple editorial blemishes, the majority of which are of no consequence such as a few lines of concatenated words. However, to state twice that the yellow fever mosquito, Aedes aegypti, is "strictly a dawn and dusk feeder" is potentially hazardous if people base their behaviour on the information. This insect, one of the most aggressive and widespread transmitters of non-malarial diseases, is actually active throughout most of the hours of daylight with a peak in its biting rate up to two hours after sunrise and two hours before sunset. Consequently, it is one of the few reasons for wearing an insect repellent during the day. These problems aside, Mosquito is a useful introduction to one of the most important groups of insects in public health for students and general readers alike. Its low cost and good layout add to the book's accessibility.

Ian F. Burgess is director, Medical Entomology Centre, Cambridge.

Mosquito: The Story of Mankind's Deadliest Foe

Author - Andrew Spielman and Michael D'Antonio
ISBN - 0 571 20980 7
Publisher - Faber
Price - £10.99
Pages - 247



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