Wild-caught and colonized tampan ticks, Ornithodoros moubata (Murray), were fed on hepatitis B virus (HBV)-positive blood-means in a series of four experiments. Hepatitis B surface antigen (HBsAg) persisted in nymphal and adult ticks for up to 779 days, while the epsmark antigen (HBeAg) persisted in mature nymphs up to 13 days, in adult males up to 11 days and in adult females up to 16 days. HBsAg was transmitted trans-stadially through two moults during the life cycle but transovarial transmission did not occur. The surface antigen was transmitted by two out of fifteen single ticks into 0.4 ml aliquots of HBV-negative blood, although six groups of ticks failed to transmit into 5.5 ml aliquots of blood: this antigen was not transmitted to hamsters. HBsAg was detected in samples of the ticks' coxal and rectal fluid secretions always at the infecting feed and usually at the second feed. HBeAg was only detected in one of two samples of coxal fluid collected at the infecting feed. The results as a whole indicate that no biological multiplication of virus occurs in O.moubata but that mechanical transmission from ticks to man could occur by: (i) contamination of a person when crushing infected ticks; (ii) infection by bite; (iii) contamination with coxal fluid, especially by scratching bites. This is thought to take place among the Kavango tribe in their village huts in north-eastern Namibia where infestations of infected O.moubata occur.
Abstract:The Orange River, with an average annual runoff of 11 500 million m 3, is the largest among South Africa's rivers, drains 48 % of the total area of the country and provides for 22 % of the total South African downflow. Not only does the average annual precipitation of the drainage basin vary from 2 000 mm in the upper reaches to 40 mm at the river's mouth in the Atlantic, but large deviations from the average are the rule rather than the exception over most of the area. The correspondingly low reliability in the discharge of the Orange master stream is demonstrated by a 0,6 coefficient of variability. For utilising the river's water efficiently, periodic and seasonal runoff deficits may be overcome by building large storage dams. This is the purpose of the H.F, Verwoerd Dam, near the confluence of the Caledon and the Orange Rivers, and the P.K. le Roux Dam 130 km lower downstream. They form part of the R490 million (1974 estimate) Orange River Project by which water is stored and distributed in canals and tunnels (one 82 km long) reaching beyond the basin boundaries to Bloemfontein in the north and Port Elizabeth in the south. The implementation of the Orange River and Tugela-Vaal Schemes shifted the spatial focus of water development upstream along the Orange, Caledon and Vaal Rivers towards the plateau blocks of Lesotho.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.