Comment
320 0169-4758/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0169-4758(00)01730-0 Parasitology Today, vol. 16, no. 8, 2000 All of the cited parasite genome
jects are successful, collaborative pro-jects between their respective, generally overlapping, research communities and the sequencing centres. The centres and public funding agencies must continue to support the immediate sharing of se-quence data and annotation when the sequence is completed: getting the DNA sequence is the ‘easy’ bit.
NB. The views expressed in the above are those of the author, and do not necessarily represent those of the Wellcome Trust.
References
1Knowlton, R.G. et al. (1985) A polymorphic DNA marker linked to cystic fibrosis is located on chromosome 7. Nature318, 380–382 2Brookes, A.J. et al.(1999) HGBASE: a database
of SNPs and other variations in and around human genes. Nucleic Acid Res.28, 356–360 3Dunham, I. et al.(1999) The DNA sequence
of human chromosome 22. Nature 402, 489–495
4Hattori, A. et al. (2000) The DNA sequence of human chromosome 21. Nature405, 311–319 5 Fleischmann, R.D. et al. (1995) Whole-genome random sequencing and assembly of Haemophilus influenzae Rd. Science 269, 496–512
6 Cole, S.T. et al. (1998) Deciphering the biology of Mycobacterium tuberculosisfrom the complete genome sequence. Nature393, 537–544
7Parkhill, J. et al. (2000) Complete DNA sequence of a serogroup A strain of Neisseria meningitidisZ2491. Nature404, 502–506 8Goffeau, A. et al. (1996) Life with 6000 genes.
Science 274, 546–567
9The C. elegans Consortium (1998) Genome sequence of the nematode C. elegans: a platform for investigative biology. Science282, 2012–2018 10Venter, J.C. et al. (1998) Shotgun sequencing of the human genome. Science280, 1540–1542 11Myers, E.W. et al. (2000) A whole-genome
assembly of Drosophila. Science287, 2196–2204 12Loder, N. (2000) Rival demands sink genome
alliance plans. Nature404, 117
13Butler, D. (2000) US/UK statement on genome data prompts debate on ‘free access’. Nature404, 324–325
14Smaglik, P. (2000) Shareholder sues Celera over loss. Nature405, 3
15Smaglik, P. (2000) … as US tightens up on ‘speculative’ claims. Nature403, 3
16Dickson, D. (2000) NIH opposes plans for patenting ‘similar’ gene sequences. Nature405, 3 17Smaglik, P. (2000) Critics challenge Celera’s claims over human genome sequence … Nature404, 691–692
18Butler, D. (2000) Celera in talks to launch private sector human proteome project. Nature403, 815–816
19Marcotte, E.M et al. (1999) A combined algorith for genome-wide prediction of protein function. Nature402, 83–86 20Enright, A.J. et al. (1999) Protein interaction
maps for complete genomes based on gene fusion events. Nature402, 86–90
21Brazma, A. et al. (2000) One-stop shop for microarray data. Nature403, 699–700
22Johnston, D.A. et al. (1999) Genomics and the biology of parasites. BioEssays21, 131–147 23Brindley, P.J. (ed) (2000) Parasite Genomes.
Int. J. Parasitol.30, 327
24Gardner, M.J. et al. (1998) Chromosome 2 sequence of the human malarial parasite Plasmodium falciparum. Science282, 1126–1132 25Bowman, S. et al. (1999) The complete nucleotide sequence of chromosome 3 of Plasmodium falciparum. Nature400, 532–538 26El-Sayed, N.M. et al. (2000) The African
trypanosome genome. Int. J. Parasitol. 30, 329–345 27Verdun, R.E. et al. (1998) Gene discovery through expressed sequence tag sequencing in Trypanosoma cruzi. Infect. Immunol. 66, 5393–5398
28Myler, P.J. et al. (1999) Leishmania major Friedlin chromosome 1 has an unusual distribution of protein-coding genes. Proc. Natl. Acad. Sci. U. S. A.96, 2902–2906
29Blaxter, M. and Ivens, A. (1999) Reports from the cutting edge of parasite genome analysis. Parasitol. Today15, 430–431
30Bhattacharya, A. et al. (2000) Identification of parasitic genes by computational methods. Parasitol. Today16, 127–131
31Ginsburg, H. (2000) Biochemistry of Plasmodiumon the web. Parasitol. Today 16, 87–88
32Ivens, A. et al. (2000) Functional websites for parasite genome projects. Parasitol. Today16, 93–94
Al Ivensis at the Pathogen Sequencing Unit, Sanger Centre, Hinxton, UK CB10 1SA. Tel: +44 1223 494851, Fax: +44 1223 494919, e-mail: alicat@sanger.ac.uk
Twelve years ago, Julia Walsh com-mented1that ‘the wide array of imper-fect tests for the diagnosis of amebiasis severely limits our understanding of the magnitude and epidemiology of this in-fection’. While the suffering from amebi-asis of even a single child in the devel-oping world is unacceptable, burden of disease figures are an important tool for the allocation of limited public health resources for efforts at treatment and prevention. Current WHO estimates of 40–50 million cases of amebic colitis and liver abscess and up to 100 000 deaths per annum are based in large part on
Walsh’s utilization of these imperfect parasitologic and seroepidemiologic sur-veys from different parts of the world2. These estimates may not be far from the mark: taking as an example just one country, the Mexican national sero-survey demonstrated that 8.4% of the population had been exposed to amebi-asis, resulting in an estimated 1 million cases of amebiasis and 1216 deaths3. Infection in the developed countries of the world is not rare either, as illustrated in May 1998 by the outbreak of amebic liver abscess from a contaminated mu-nicipal water supply in Tbilisi, Republic of Georgia (R.S. Barwick et al., Abstract)*.
However, with the current excite-ment about the feasibility of an amebi-asis vaccine, we are in a situation where a new estimate of the burden of E.
histolytica infection to world health is
urgently needed4,5. Significant resources must be allocated if a vaccine is to be achieved, and this can only come about with timely estimates of impact. One particular area where this is evident is in delineating the contribution of amebiasis to diarrheal diseases in children under the age of five. Diarrheal diseases are a major cause of death of children in countries such as Bangladesh where one in ten children die before their fifth birthday (Fig. 1). The use in the past of insensitive and nonspecific tests for amebiasis make it very difficult to esti-mate the contribution of amebiasis even to crude mortality, much less to future functional status as measured by disabil-ity adjusted life years (DALYs).
It is now possible, and critically im-portant, to arrive at better estimates through the utilization of vastly improved
Estimating the Impact of
Amebiasis on Health
W.A. Petri, Jr, R. Haque, D. Lyerly, and R.R. Vines
Comment
Parasitology Today, vol. 16, no. 8, 2000 321
diagnostic tests (Table 1). Microscopy is an outmoded technique that should not be used to diagnose amebic colitis: it is insensitive, incapable of differentiating pathogenic E. histolyticafrom nonpatho-genic E. dispar, and prone to false positive results. Our experience in Bangladesh has highlighted the danger of relying on microscopy: only 40% of children diagnosed by microscopy were proven to have E. histolytica infection when specific methods were used. Conversely, of all children diagnosed with E. histolytica infection by specific methods, the majority were missed by microscopy6,7!
The new generation of specific diag-nostic reagents for amebiasis is based on the recent delineation of what used to be called E. histolytica into two genetically distinct species, the invasive disease-causing parasite Entamoeba histolytica, and the non-invasive parasite E. dispar8–10.
Entamoeba disparhas never been
docu-mented to cause colitis or liver abscess, but is responsible for many cases of asymptomatic infection, especially in de-veloped countries; E. histolyticacauses col-itis and liver abscess, and can also asymp-tomatically colonize the large bowel. Specific and sensitive means to detect E.
histolytica in stools today include the
TechLab E. histolyticaII stool antigen de-tection kit and nested PCR techniques based on amplification of the parasite rRNA gene6,7.
We are using these tools to define the contribution of E. histolyticato diarrheal disease with a three-year prospective study of 272 children aged 2–5 years in the Mirpur district of Dhaka, Bangladesh. For accurate estimates of the impact of amebiasis on child health, studies using ac-curate diagnostic tools will need to be ap-plied to other populations in the devel-oping world. TechLab, Inc. is providing, at no charge (in cases where funding is otherwise unavailable), the stool antigen detection kit for epidemiologic studies in the developing world. Thus, the recent confusion over amebiasis figures promises to be resolved in the near future.
Acknowledgements
Work from the authors’ laboratories was sup-ported by NIH grant AI-43596. The University of Virginia has licensed diagnostic techniques to TechLab, Inc. WP is a Burroughs Wellcome Fund Scholar in Molecular Parasitology, and RH is a Howard Hughes Medical Institute International Research Scholar.
References
1 Walsh, J.A. (1988) Prevalence of Entamoeba histolytica infection, in Amebiasis: Human Infection by Entamoeba histolytica (Ravdin, J.I., ed.), pp 93–105, John Wiley & Sons 2 WHO/PAHO/UNESCO report of a
consultation of experts on amoebiasis. (1997) Weekly Epidemiol. Rep. WHO72, 97–99 3 Caballero-Salcedo, A. et al. (1994)
Seroepidemiology of amebiasis in Mexico. Am. J. Trop. Med. Hyg.50, 412–419
4 Stanley, S.L. Jr (1997) Progress towards development of a vaccine for amebiasis. Clin. Microbiol. Rev.10, 637–649
5 Huston, C.D. and Petri, W.A., Jr (1998) The host-pathogen interaction in amebiasis: Is a vaccine feasible? Eur. J. Clin. Microbiol. Infect. Dis. 17, 601–614
6 Haque, R. et al.(1998) Comparison of PCR, isoenzyme analysis, and antigen detection for diagnosis of Entamoeba histolytica infection. J. Clin. Microbiol.36, 449–452
7 Haque, R. et al. Diagnosis of amebic liver abscess and intestinal infection with the Techlab Entamoeba histolyticaII antigen detection and antibody tests. J. Clin. Microbiol. (in press) 8 Sargeaunt, P.G. et al.(1978) The differentiation
of invasive and non-invasive Entamoeba histolyticaby isoenzyme electrophoresis. Trans. R. Soc. Trop. Med. Hyg. 72, 519–521
9 Tannich, E. et al. (1989) Genomic differences between pathogenic and nonpathogenic Entamoeba histolytica. Proc. Natl. Acad. Sci. U. S. A.86, 5118–5122
10Diamond, L.S. and Clark, C.G. (1993) A redescription of Entamoeba histolytica Shaudinn 1903 (amended Walker 1911) separating it from Entamoeba dispar (Brumpt 1925). J. Euk. Microbiol.40, 340–344
William A. Petri, Jr is at the University of Virginia, Charlottesville VA 22908, USA, Rashidul Haque is at the International Center for Diarrheal Disease Research, Bangledesh, Center for Health and Population Research, Dhaka, Bangladesh. David Lyerly and Richard R. Vines are at TechLab, Inc., Blacksburg VA 24060-6364, USA. Tel: +1 804 924 5621, Fax: +1 804 924 0075, e-mail: wap3g@ virginia.edu
Erratum
In the January issue of Parasitology Today, in the Newsarticle by S.I. Hirst and L.A. Stapley (Parasitology: The Dawn of a New Millennium, Parasitol. Today 16, 1–3), the figures for mortality due to amoebiasis given in Table 1 were inaccurate. The most recent data from the WHO estimate that between 40 000 and 100 000 deaths occur per year due to amoebiasis [WHO (1991) WHO/PAHO informal consultation on intestinal protozoal infections, Mexico, 21–23 October. WHO/ CDS/IPI/92.2, based on Walsh, J.A. (1988) Prevalence of Entamoeba histolytica
infection, in Amoebiasis: Human Infection by Entamoeba histolytica (Ravdin, J.I., ed.), Wiley & Sons]. (See W.A. Petri, Jr, Commentarticle, this issue.)
We apologize to readers for any confusion caused by this error. Fig. 1. Probability of survival from birth to age (x) for children in Matlab, Bangladesh.
Data obtained from the 1994 Demographic Surveillance System (DSS)-Matlab, Health and Demographic Surveillance Programme, Community Health Division, International Centre for Diarrhoeal Disease Research, Dhaka, Bangladesh. Arrow indicates drop off in survival probability at five years.
Parasitology Today 0.0
0.2 0.4 0.6 0.8 1.0
0 10 20 30 40 50 60 70 80 90
Age (years)
Survival probability
Causes of death in children under five years:
Vaccine preventable 10% Prematurity 11% Respiratory disease 18% Diarrhea/Dysentry 30% Other 31%
Table 1. Diagnostic tests for amebic colitis
Sensitivity Specificity Microscopya 5–60% 10–50% Stool Antigen 90% .90%
Detectionb
Stool PCRc 90%
.90%
Serum 70% d
Antibody
aEntamoeba histolyticaand E. disparappear
identi-cal by microscopic ‘O&P’ exam of stool, account-ing for the low specificity of this test.
bTechLab E. histolyticaII test.
cPCR tests are based on the unique DNA
sequence of the multi-copy small subunit ribosomal RNA gene of E. histolytica.
dSeropositivity rates of .25–50% in some regions
