The spread of tick-borne borreliosis in West Africa and its relationship to sub-Saharan drought.

In West Africa, tick-borne relapsing fever is due to the spirochete Borrelia crocidurae and its geographic distribution is classically limited to the Sahel and Saharan regions where the vector tick Alectorobius sonrai is distributed. We report results of epidemiologic investigations carried out in the Sudan savanna of Senegal where the existence of the disease was unknown. A two-year prospective investigation of a rural community indicated that 10% of the study population developed an infection during the study period. Transmission patterns of B. crocidurae to humans and the small wild mammals who act as reservoirs for infection were similar to those previously described in the Sahel region. Examination of 1,197 burrows and blood samples from 2,531 small mammals indicated a considerable spread of the known area of distribution of A. sonrai and B. crocidurae. The actual spread of the vector and the disease has affected those regions where the average rainfall, before the start of the extended drought in West Africa, reached up to 1,000 mm and corresponds to the movement of the 750-mm isohyet toward the south from 1970 to 1992. Our findings suggest that the persistence of sub-Saharan drought, allowing the vector to colonize new areas in the Sudan savanna of West Africa, is probably responsible for a considerable spread of tick-borne borreliosis in this part of Africa.

Tick-borne borreliosis in west Africa: recent epidemiological studies.

Tick-borne borreliosis in West Africa is classically considered a rare disease whose geographic distribution is limited to Saharan and Sahelian regions. We report results of epidemiological investigations which indicate that tick-borne borreliosis is endemic in all regions of Senegal north to the 13 degrees 30'N latitude and is a major cause of morbidity in these areas. Our findings indicate a considerable range extension for the vector tick Alectorobius sonrai and suggest that the persistence of Subsaharan drought is responsible for a large spread of tick-borne borreliosis in West Africa.

Microcalorimetric study of the interaction of human and bovine serum albumins with tryptophan and tryptophan analogs.

The thermodynamic parameters for the protein-ligand binding have been obtained by microcalorimetry on three albumin samples (fatty acid free human serum albumin (I), fraction V human serum albumin (II), and fraction V bovine serum albumin (III)) bound with l-tryptophan (A) and three-ring tryptophan analogs (B and B*). The percentage, mu, of binding molecules (equivalent to the number of sites) is found to be 1.0 for I and 0.65 for II (in good agreement with dialysis results on the same systems) and 1.0 for III. The large negative delta H(bind) (-27.2 to -33.2 kJ . mol-1) constitutes the main contribution to delta G(bind) (-23.0 to -31.2 kJ . mol-1). The better binding of I-III towards B and B* compared with A is due to delta S(bind) being less negative. This is interpreted as a lesser loss of entropy for the three-ring ligands than for the normal tryptophan when they are bound. Data obtained on the proteins (heat of dilution; Huggins' constant, k') correlate well with mu or Qmax. This indicates that these physicochemical data could be used to characterize and compare rapidly some albumins of different sources. The unexpected finding that the parameters of I and III are nearer to each other than they are from II is discussed.