Diagnostic Medical Parasitology is one of anumber of excellent publications producedby the American Society for Microbiology.The authors are both actively engaged indiagnostic parasitology and this is reflectedin the very practical and authoritativepresentation of the information given in thebook. Given that this is a third edition theauthors have made considerable changesand additions to the text; each chapter hasan extensive bibliography that is up to dateand very relevant to the subject.

The book is divided into two sections,plus an extensive set of appendices. Thefirst section provides an extremelycomprehensive coverage of parasites ofclinical importance with chapters onunusual parasitic infections, those incompromised hosts, nosocomial andlaboratory acquired infections and animproved chapter of medically importantarthropods. Each chapter is provided withexcellent summary tables and diagrams and

very useful algorithms illustrating thecorrect approach to the diagnosis of theparasites covered. All the usual informationis provided, such as life-cycle, disease,diagnosis, epidemiology and treatment. ‘Keypoints’ are summarized within the text,allowing rapid reference for studentsstudying medical parasitology. The authorshave included a new chapter on theimmunology of parasitic infections whichlinks nicely with the following one onappropriate antibody and antigen detectionmethods. This is an area of diagnosis whichis becoming much more important andmore widely used by laboratories. I havealways had some doubts about theusefulness of a chapter on histologicalidentification of parasites in a book such asthis, but this has been improved by theinclusion of more photographs, althoughstill in black and white.

The second section deals with thediagnostic procedures recommended for

the collection, processing and identificationof parasites and is both comprehensive andaccurate. As this is an American book, itdoes emphasize an approach to diagnosiswhich is not commonly found in Europeand other parts of the world. The authorsparticularly emphasize the use ofpermanent stained faecal smears for thediagnosis of faecal parasites and it is easy toargue the case against these being used bybusy microbiology departments required tocarry out ‘ova, cysts and parasite’ screens.There is however a very useful ten pages ofartefacts which can be confused withparasites, something that will be muchappreciated by those who infrequently seepositive specimens. There is also the nowobligatory chapter on safety and qualityassurance, again this tends to have a USbias, but the information should proveuseful to those in other countries whoneed to set up or update their own systems.

The last part of this very comprehensivetext is a collection of appendices showinggeographical distribution, specific bodylocations in which parasites are found, keycharacteristics of different parasites,procedures, quality control, lists of suppliersand an excellent collection of colour plates

Parasitology Today, vol. 14, no. 3, 1998 125

R. Sinden comments in this issue on thelimitations of gene targeting as a tool tostudy malaria parasites. Gene targeting, like any other tool, certainly has limitations.In the best situation, ie. when a mutantdefective phenotype can be reverted to the wild-type phenotype by genecomplementation, then it can be ascertainedthat the observed phenotype is a directconsequence of the lack of the targetedgene product. It is thus incorrect to statethat knockout studies are simply an indirect method to analyse gene function,or that in most studies the phenotypeobserved is not a direct consequence ofthe genetic modification. Perhaps what wasmeant is that genetic studies do notpinpoint the exact function of the geneproduct in the completion of the phenotype.Obviously, this requires analysis of theprotein itself. We certainly accept the factthat understanding the precise function of aprotein is simply beyond the reach ofgenetics alone.

The CS and TRAP knockout studiesillustrate the power of the genetic approach.The CS knockout has suggested a role forCS in sporozoite morphogenesis, a roleuntil then unsuspected despite years ofwork on this protein. I should rectifySinden’s statement that CS knockouts infecthepatocytes or mosquito salivary glands;

they are just not formed or are formed in such small numbers that they do notreach the salivary glands and cannot betested in hepatocyte invasion. The TRAPknockout study has shown the unexpectedrole of TRAP in sporozoite motility. It is thefirst direct evidence of the role ofsporozoite motility in sporozoite infectivityto the host. It further supports thehypothesis of a common mechanism ofmotility and target cell invasion byApicomplexa, as proposed by Russell andSinden1 and others. The model was basedprimarily on structural data and inhibitionstudies, which cannot be viewed as ‘well-established reasons why immobilesporozoites cannot invade hepatocytes’,simply because the actual behavior of anorganism is beyond the reach of structuralconsiderations alone. An analogy can bemade here with recent work onToxoplasma entry into target cells. Muchindirect evidence had been gained over theyears from a variety of approaches thatparasite entry into cells was primarilydependent on the parasite actin cytoskeleton.Dobrowolski and Sibley have now formallydemonstrated this point, using cytochalasinD-resistant mutants2. The fact is thatgenome manipulation in general and genetargeting in particular have provedinvaluable in broadening our understanding

of the biology of any organism where theyare available, from bacteria to the ‘neversimple’ eukaryotic cell.

It is a pessimistic scientist, however, whothinks that data from gene manipulationsmight supplant other data, and thatemergence of this type of technology mightbe deleterious to other approaches to thebiology of the parasite. Data cannot besupplanted (only theories can) and theirfate depends on whether or not they areaccurate and relevant, not the type oftechnology they come from. Moreoptimistically, we should all appreciate thatfrom a ‘holy grail’ technology that Plasmodiumtransfection was a little more than twoyears ago, it is now considered a ‘fashionable’tool. If it succeeds in becoming a common(reproducible and reliable) tool, it shouldinevitably attract new biologists interestedin this and other ways to tackle theparasite. There is thus little reason to fearthat the ex-fashionable tool will not, at leaston average and with time, be used wiselyand be beneficial for the field.

References1 Russell, D.G. and Sinden, R.E. (1981)

J. Cell Sci. 50, 345–3592 Dobrowolski, J.M. and Sibley, L.D. (1996)

Cell 84, 933–939

Robert MénardDepartment of PathologyMichael Heidelberger Division of ImmunologyNew York University Medical CenterNew York, NY 10016, USA

Malaria Transfection: A New Tool to StudyMolecular Function – Reply

Diagnostic Medical Parasitologyby L.S. Garcia and D.A. Bruckner, ASM Press, 1997. £60.00 (xv + 937 pages)

ISBN 1 55581 1167

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