The prevalence of hepatitis B (Australia) antigen in Southern Africa

The prevalence of hepatitis B (Australia) antigen (HBAg) in 38 941 apparently healthy persons of various ethnic groups living in the Transvaal was determined by countercurrent immuno-electrophoresis or by complement fixation. The prevalence was 0,09 - 0,6% in  healthy Whites, 0,9% in Coloured donors, 2,0% in urban Negroes and 7"10 in rural male Blacks. The positivity rate in 444 healthy Black subjects and in 423 Sana (Bushmen) inhabiting areas in the northern and north-western regions of Southern Africa ranged from 2,7 to 15,8%. An assessment of the frequency of HBAg in various tribal groups of either Sana (Bushmen) or rural Blacks indicated that geographical environment might be one of the factors influencing antigenaemia in healthy persons. The prevalence was highest in persons originating from the west coast regions of Southern Africa, in adjoining territories proceeding from the central plateau, and those countries north of this area (9,1 - 13,6%) An intermediate prevalence of 6 - 7% was noted in some regions abutting on the east coast strip, and a lower prevalence was recorded for inland regions, including Lesotho, the eastern Orange Free State, Natal Midlands and Zululand (4 - 4,7%), while the lowest frequency was found in northern Natal and the central Transvaal areas (2 - 3%). A small group of Sana in the north-eastern corner of South West Africa who had an incidence of 2,7% was the only one which did not fit in with the general geographical distribution of HBAg observed.S. Afr. Med. J., 48, 941 (1974)

Oscillations and waves of cyclic AMP in Dictyostelium: a prototype for spatio-temporal organization and pulsatile intercellular communication.

The amoebae Dictyostelium discoideum aggregate after starvation in a wavelike manner in response to periodic pulses of cyclic AMP (cAMP) secreted by cells which behave as aggregation centers. In addition to autonomous oscillations, the cAMP signaling system that controls aggregation is also capable of excitable behavior, which consists in the transient amplification of suprathreshold pulses of extracellular cAMP. Since the first theoretical model for slime mold aggregation proposed by Keller and Segel in 1970, many theoretical studies have addressed various aspects of the mechanism and function of cAMP signaling in Dictyostelium. This paper presents a brief overview of these developments as well as some reminiscences of the author's collaboration with Lee Segel in modeling the dynamics of cAMP relay and oscillations. Considered in turn are models for cAMP signaling in Dictyostelium, the developmental path followed by the cAMP signaling system after starvation, the frequency encoding of cAMP signals, and the origin of concentric or spiral waves of cAMP.Historical ArticleJournal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: re.jinfo:eu-repo/semantics/publishe