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As shown in twin studies, the inherited predisposition plays an important role in tuberculosis. Genetic influences may be specified in two ways. First, variants of genes whose products are involved in apparently disease-relevant pathways may be tested in population-based studies. Applying this approach, associations with pulmonary tuberculosis have been reported for variants of the genes encoding mannose-binding protein, the vitamin-D receptor, natural-resistance associated macrophage protein 1, interferon-gamma, of HLA alleles and of the interleukin-1 gene cluster. Second, genetic influences can be identified by genome-wide studies of members of affected families. Thus, linkage has been found between pulmonary tuberculosis and as yet undefined genetic variants on chromosome 15q and the X chromosome. Further genomic regions of interest have been identified in mouse models.

Entamoeba histolytica is the causative agent of human amoebiasis. During recent years, research in amoebiasis has concentrated on two subjects: 1. the dual manifestation of the infection as harmless colonization of the intestinal cavity or pathogenic tissue invasion and 2. the molecular analysis of functions of E. histolytica that are considered essential for pathogenicity. Besides epidemiological studies and isoenzyme analyses, molecular genetics have revealed additional evidence that two genetically distinct forms of E. histolytica do exist, named "pathogenic" and "nonpathogenic" forms, respectively. Both can infect humans but only the "pathogenic" form is able to invade the tissue and cause disease whereas the "nonpathogenic" is not. Questions remain open about the mechanism that triggers "pathogenic" E. histolytica to become invasive and about the molecules that are involved. Current data indicate that at least three functions of the amoebae are considered essential for pathogenic tissue invasion. Pathogenicity is viewed as a result of 1. adherence of the amoeba to host cells, predominantly mediated by a galactose- and N-acetylgalactosamine-inhibitable lectin, 2. killing of host cells by a pore-forming peptide known as amoebapore, and 3. proteolysis of the host's extracellular matrix mediated by cysteine proteinases. Structural detailed molecular analysis including cloning of the corresponding genes have led to a better understanding of the function of these proteins.

Clinical and pathological data on 25 fatal cases of tropical malaria were obtained from several hospitals in a retrospective survey. The patients originated, without exception, from non-malaria endemic regions (non-immunes). Death occurred in nine patients despite elimination of the parasitaemia with schizontocides. Life threatening complications were complex and apparently interacting. Manifestations of the disease included (1) initial acute renal failure, (2) disturbance of water and electrolyte balance, (3) cerebral oedema resulting in microhaemorrhages, (4) lung oedema, and increasing respiratory insufficiency even after elimination of the parasitaemia (in 4 cases there was histological evidence of shock lung), (5) myocarditis (histological evidence of cellular myocardial infiltration obtained in 4 cases), (6) hepatocellular damage, (7) complications associated with intensive-care treatment in 2 cases. The data allow no conclusions on the intensity and nature of blood clotting disturbances. According to this analysis the clinical manifestations of advanced malaria resemble protracted shock conditions having other aetiologies. However, specific cerebral and cardiac complications and homeostatic disturbances do apparently occur, the treatment of which requires experience with the clinical syndrome.