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Beware of the litre of blood! Bring back the mm3!
TRANSACT~NS
OF THE ROYAL
Socra~
OF TROPICAL
MED~NE
The parasites maintain their viability for long periods at 28 and 32°C. Stained smears from samples taken 17.20 and 30 davs after inoculation revealed the presence’ of amastigotes, sphaeromastigotes and epimastigotes. This easy method should facilitate obtaining clones and would permit genetic and physiological studies on T.
crwi.
A complete study of the behaviour of T. ctwi isolateson this medium will be reported later. NELSON
L~)PEZEYZAGUIRRE
References
Janovy,J., Jr. (1978).Agar plate cultivation of Ttypamsom&due. Progress Report,WHO SpecialProgramme on Leishmaniasis. Geneva:WHO. Keppel, A. D. & Janovy,J. Jr. (1977).Herpetomonas megaseliae andCrithidia hatmosa: growthon blood-agar plates.Parasitology, 63, 872-882.
Beware
of the he
24th April,
of blood!
HYGIENE, VOL.
77, No.
5 (1983).
CORRES~~DENCE
741
be more readily intelligible to your older readers such as myself. T. 77 Strand Road, Portstewart, Co. Londondeny BT55 N. Ireland.
WILSON
7LX,
References
Bruce-Chwatt,L. J. (1983).Bewareof the litre of blood! Transactions of the Rqal Hygiene, 77, 139.
Society
of Tropical Medicine
Medicine
77, 138-139.
and
Ferraroni,J. J., Alencar,F. H. & Shrimpton,R. (1983). Multiple drug resistance in falciparummalariafrom Brazil. Tramactions of the Royal Societyof Tropical
Universidad de Los Andes, Fact&ad de Ciencias, Department0 de Biologia, Mirida 5101, Venezuela.
Accepted for publication
AND
1983.
Bring back the mm3!
May I reinforceProfessorL. J. Bruce-Chwatt’splea for a return to commonsensewhenreporting levelsof parasitaemiain malaria (BRUCE-CHWATT,1983). I agree with the arguments that he puts forward concerningthe quantity of bloodnormally examined, the unavoidable risk of counting errors, and the statisticalabsurdity of multiplying the resultingfigure by a factor of lo6or morein order to expressaparasite count per litre of blood; but I stron Iy disagreewith his preferencefor ul insteadof mmY. Apart from its familiarity after many years of use, the outstanding advantageof using mm3 would be that publishing errors should be reduced to a minimum. ProfessorBruce-Chwatt’sown letter, and the letter from Dr. J. J. Ferraroni and his colleagueson the precedingpageof the sameissueof the Transactions (FERRARONIet al., 1983), provide exampleswell calculatedto bemusethe reader. In his paragraph5, Professor Bruce-Chwatt refers to “the estimated figure per ml”. UnlessI’m much mistakenhe meant “figure per pl’> ashe then mentionsmultiplication by a factor of 10 to indicate parasitecount per litre. Dr. Ferraroni’s letter gives parasite counts as “3,400 parasites/ml blood”, “1,400 parasites/ml blood” and soon. Surely thesecountsought alsoto be “per ul’., otherwise they are incredibly low. As a separateissue,I think that reportsof this type should always specify the number of microscopicfields of thick or thin films that were examined before the blood wasrecordedasnegative, but this report omits to do so. In addition to being a closerapproximationto the practicalitiesof blood examinationfor malaria parasites, a return to counts per mm3would eliminatea distressinglycommonsourceof confusion,and would
and Hygiene,
Accepted for publication
Low
19th May,
cost polycarbonate
1983.
filters
We shouldlike to bring to the attention of Fellews the availability of low cost polycarbonatemembrane filters for use in field surveys to diagnoseurinary schistosomiasis. “Schisto kits”, at a fraction of the commercial price, are availableto non-profit orgnizations from PATH, Canal Place, 130 Nickerson St., Seattle, Washington98109,USA. Each kit contains13 mmdiameterpolycarbonatefilters of 12 or 14 um poresize,plusa few holdersandforceps.Pricesrangefrom $0+4-$0.065per filter dependingon the quantity of filters purchased.Extra holders are also available. The filters facilitate rapid examinationof unstained schistosome ova from urine samples(PETERSet al., 1976). The main drawback of the 13 mm filters is that clogging may occur when 10 ml urine samplesare used, and egg counting is often difficult when the number of eggson a filter is greater than 103. Any clogging/readingproblemcan be overcomeby using12 urn pore-sizefilters of 25 mm diameter.The latter filters arenot yet availablefrom PATH, but can be producedcheaplyfollowing a procedurewhich we have found to be satisfactory. (1) Purchase 12 urn pore-size polycarbonate membranesin 8 in. x 10 in. sheets(availablefrom Nuclepore Corporation, 7035 Commerce Circle, Pleasanton,Ca. 94566, USA). (2) Use a 25 mm-diametermetal punch and flat headhammerto stampout the filters. For the cleanest cuts, sheetsshouldbe placedon top of a smooth,flat, semi-elasticslab, like polypropylene. Using this method, 25 mm, 12 urn polycarbonate filters can be producedeasilyfor $0.10each, an 80% saving compared with the current retail price of pre-cut filters of the samesize. RALPHKLUMPP G.
Dept. of Medical Helminthology, London School of Hygiene & Tropical Medicine, Gower Street, London, WCIE 7HT.
WEBBE
OF THE ROYAL
Socra~
OF TROPICAL
MED~NE
The parasites maintain their viability for long periods at 28 and 32°C. Stained smears from samples taken 17.20 and 30 davs after inoculation revealed the presence’ of amastigotes, sphaeromastigotes and epimastigotes. This easy method should facilitate obtaining clones and would permit genetic and physiological studies on T.
crwi.
A complete study of the behaviour of T. ctwi isolateson this medium will be reported later. NELSON
L~)PEZEYZAGUIRRE
References
Janovy,J., Jr. (1978).Agar plate cultivation of Ttypamsom&due. Progress Report,WHO SpecialProgramme on Leishmaniasis. Geneva:WHO. Keppel, A. D. & Janovy,J. Jr. (1977).Herpetomonas megaseliae andCrithidia hatmosa: growthon blood-agar plates.Parasitology, 63, 872-882.
Beware
of the he
24th April,
of blood!
HYGIENE, VOL.
77, No.
5 (1983).
CORRES~~DENCE
741
be more readily intelligible to your older readers such as myself. T. 77 Strand Road, Portstewart, Co. Londondeny BT55 N. Ireland.
WILSON
7LX,
References
Bruce-Chwatt,L. J. (1983).Bewareof the litre of blood! Transactions of the Rqal Hygiene, 77, 139.
Society
of Tropical Medicine
Medicine
77, 138-139.
and
Ferraroni,J. J., Alencar,F. H. & Shrimpton,R. (1983). Multiple drug resistance in falciparummalariafrom Brazil. Tramactions of the Royal Societyof Tropical
Universidad de Los Andes, Fact&ad de Ciencias, Department0 de Biologia, Mirida 5101, Venezuela.
Accepted for publication
AND
1983.
Bring back the mm3!
May I reinforceProfessorL. J. Bruce-Chwatt’splea for a return to commonsensewhenreporting levelsof parasitaemiain malaria (BRUCE-CHWATT,1983). I agree with the arguments that he puts forward concerningthe quantity of bloodnormally examined, the unavoidable risk of counting errors, and the statisticalabsurdity of multiplying the resultingfigure by a factor of lo6or morein order to expressaparasite count per litre of blood; but I stron Iy disagreewith his preferencefor ul insteadof mmY. Apart from its familiarity after many years of use, the outstanding advantageof using mm3 would be that publishing errors should be reduced to a minimum. ProfessorBruce-Chwatt’sown letter, and the letter from Dr. J. J. Ferraroni and his colleagueson the precedingpageof the sameissueof the Transactions (FERRARONIet al., 1983), provide exampleswell calculatedto bemusethe reader. In his paragraph5, Professor Bruce-Chwatt refers to “the estimated figure per ml”. UnlessI’m much mistakenhe meant “figure per pl’> ashe then mentionsmultiplication by a factor of 10 to indicate parasitecount per litre. Dr. Ferraroni’s letter gives parasite counts as “3,400 parasites/ml blood”, “1,400 parasites/ml blood” and soon. Surely thesecountsought alsoto be “per ul’., otherwise they are incredibly low. As a separateissue,I think that reportsof this type should always specify the number of microscopicfields of thick or thin films that were examined before the blood wasrecordedasnegative, but this report omits to do so. In addition to being a closerapproximationto the practicalitiesof blood examinationfor malaria parasites, a return to counts per mm3would eliminatea distressinglycommonsourceof confusion,and would
and Hygiene,
Accepted for publication
Low
19th May,
cost polycarbonate
1983.
filters
We shouldlike to bring to the attention of Fellews the availability of low cost polycarbonatemembrane filters for use in field surveys to diagnoseurinary schistosomiasis. “Schisto kits”, at a fraction of the commercial price, are availableto non-profit orgnizations from PATH, Canal Place, 130 Nickerson St., Seattle, Washington98109,USA. Each kit contains13 mmdiameterpolycarbonatefilters of 12 or 14 um poresize,plusa few holdersandforceps.Pricesrangefrom $0+4-$0.065per filter dependingon the quantity of filters purchased.Extra holders are also available. The filters facilitate rapid examinationof unstained schistosome ova from urine samples(PETERSet al., 1976). The main drawback of the 13 mm filters is that clogging may occur when 10 ml urine samplesare used, and egg counting is often difficult when the number of eggson a filter is greater than 103. Any clogging/readingproblemcan be overcomeby using12 urn pore-sizefilters of 25 mm diameter.The latter filters arenot yet availablefrom PATH, but can be producedcheaplyfollowing a procedurewhich we have found to be satisfactory. (1) Purchase 12 urn pore-size polycarbonate membranesin 8 in. x 10 in. sheets(availablefrom Nuclepore Corporation, 7035 Commerce Circle, Pleasanton,Ca. 94566, USA). (2) Use a 25 mm-diametermetal punch and flat headhammerto stampout the filters. For the cleanest cuts, sheetsshouldbe placedon top of a smooth,flat, semi-elasticslab, like polypropylene. Using this method, 25 mm, 12 urn polycarbonate filters can be producedeasilyfor $0.10each, an 80% saving compared with the current retail price of pre-cut filters of the samesize. RALPHKLUMPP G.
Dept. of Medical Helminthology, London School of Hygiene & Tropical Medicine, Gower Street, London, WCIE 7HT.
WEBBE