Freshwater snails of Africa and their medical importance

It is a great pleasure to see this revised edition of David Brown's Freshwater snails of Africa and their medical importance appear in print. The second edition follows the layout of the first but has been extensively re-written to provide a masterly up to date review. Above all, the book is immensely readable for although it is packed with pertinent facts Brown manages to present these in a lively and informative way which is easily understood and assimilated. The high quality of the text is matched by the production of the book. The binding, paper, print halftones, figures and layout are all of extremely good quality. Of course, such a product does not come cheap and it is unfortunate that the price at which the book sells will inevitably restrict its readership.

Approximately half the book deals with a systematic account of African freshwater snails and half with matters which could broadly be classed as ecological although this second half also includes the chapters on schistosomiasis. It is in the second half that the bulk of updated text is to be found. The systematic account gives keys to generic levels and figures and accounts at species level for all the African freshwater snails, including species from marginal habitats such as mangrove swamp. In all, some 400 species are dealt with. As mentioned above, the illustrations, which are predominantly found in this part of the book, are excellent and are also appropriately positioned within the text. This portion of the work contains a checklist and is concluded by a set of maps showing some distribution patterns.

Although Africa is a vast continent, embracing several climatic zones from the Mediterranean in the north through desert, lowland and upland tropics to the temperate uplands of southern Africa, the families Thiaridae and Planorbidae dominate the freshwater snail fauna. It is of course, the planorbiid genus Bulinus which is the subject of much of the second half of the book because of its pre-eminence as the intermediate host for schistosomiasis, the complexity of the forms and their distribution over all of the continent. Chapters include discussion ofschistosome and other snail-transmitted diseases, the biology of Bulinus and snail control. More removed from the medical aspects are chapters on local snail faunas (including that of the great African lakes), chemical and physical factors, life cycles and populations and biogeography. It is in this second half, particularly, that Brown guides us with such ease through the complexities of the literature. I was disappointed that we hear no more of the parasite S. hippopotami than its mammalian host, fascinated by the accounts of polyploidy in Bulinus and its relevance to distribution and resistance to schistosome infection, and not surprised that the forms of Bulinus that are so variable in shell characters, appear to be as complex at the protein and DNA level. It appears that attempts to control schistosomiasis by using molluscicides have been unsuccessful but the use of molluscan predators of Bulinus offers an exciting possibility for control.

Only at one point did I feel that Brown's scholarship faltered and that was when discussing the relationship between equivalents, molarity and mg per litre of Ca++ and calcium bicarbonate where he suffers from the apparent convention that biologists have of writing CaCO3 (calcium carbonate) but talking of (calcium) bicarbonate. As a chemist the habit jars horribly in my mind and, as written, is in fact incorrect although it does not affect subsequent discussion in any way. Readers should also note that mM is already a unit of concentration i.e. moles per litre. However, this is a minor point and I recommend everyone who is interested in freshwater snails, their ecology and relevance to disease to buy the book.

David Brown is to be congratulated on this second edition of a classic work and no less praise go to the publishers for their excellent production.