Amoebic disease is characterized by massive tissue destruction resulting in ulcerative colitis or liver abscesses. Within the last year, investigations exploring the mechanisms involved in this process resulted in some interesting findings: (i) Using the technique of "Differential Display RT-PCR" genes encoding ferredoxin- and cyclophilin-like molecules were found to be overexpressed in amoebae isolated from liver abscesses of artificially infected rodents; (ii) comparison of DNA sequences revealed that the gene for a particular cysteine proteinase (CP5) located on the surface of E. histolytica trophozoites is present but completely degenerated in E. dispar, thus explaining the missing of this important pathogenicity factor in this non-pathogenic but closely related amoeba species; (iii) pore-forming peptides also known as "amoebapores" are the main cytolytic effector molecules of E. histolytica. Interestingly, analogous peptides were found to be present in two other pathogenic amoeba species, namely Naegleria fowleri and Acantamoeba culbertsoni. The comparison of the various molecules might help to resolve their precise mechanism of action.

Further activities were dealing with the mechanism of amoeba metronidazole resistance as well as with questions concerning chromosome assignment and karyotype analysis. Metronidazole resistance in E. histolytica was found to be associated with impaired expression of certain antioxidant enzymes suggesting that the mechanism of resistance greatly differs from those described for other organisms. Karyotype analysis of E. histolytica chromosomes indicated the presence of 14 independent linkage groups which are distributed on 31 to 35 distinguishable chromosomes with a calculated haploid genome size of about 20 megabases. In light of current initiatives to determine the genomes of various protozoan parasite, these results are of considerable importance for the design of strategies to sequence the entire E. histolytica genome.

According to recent WHO recommendations, more information and accurate data on the prevalence of E. histolytica, on the incidence of amoebiasis as well as on possible risk factors for infection and for progression into disease are urgently needed. Taken these recommendations into account, the BNI and the Medical College of the University of Hue have signed an agreement to establish a collaborative research unit in aim to perform comprehensive analyses on the epidemiology of amoebiasis. As Hue is one of the areas with the highest incidence for amoebiasis in the world, it is expected that this newly established research initiative will provide new insights into the epidemiology of E. histolytica and might pave the way for the design of more rational control strategies to prevent amoebic disease.

Egbert Tannich