The Dynamics and Environmental Influence on Interactions Between Cassava Brown Streak Disease and the Whitefly, Bemisia tabaci.

Cassava brown streak disease (CBSD) is currently the most significant virus disease phenomenon affecting African agriculture. In this study, we report results from the most extensive set of field data so far presented for CBSD in Africa. From assessments of 515 farmers' plantings of cassava, incidence in the Coastal Zone of Tanzania (46.5% of plants; 87% of fields affected) was higher than in the Lake Zone (22%; 34%), but incidences for both zones were greater than previous published records. The whitefly vector, Bemisia tabaci, was more abundant in the Lake Zone than the Coastal Zone, the reverse of the situation reported previously, and increased B. tabaci abundance is driving CBSD spread in the Lake Zone. The altitudinal "ceiling" previously thought to restrict the occurrence of CBSD to regions <1,000 masl has been broken as a consequence of the greatly increased abundance of B. tabaci in mid-altitude areas. Among environmental variables analyzed, minimum temperature was the strongest determinant of CBSD incidence. B. tabaci in the Coastal and Lake Zones responded differently to environmental variables examined, highlighting the biological differences between B. tabaci genotypes occurring in these regions and the superior adaptation of B. tabaci in the Great Lakes region both to cassava and low temperature conditions. Regression analyses using multi-country data sets could be used to determine the potential environmental limits of CBSD. Approaches such as this offer potential for use in the development of predictive models for CBSD, which could strengthen country- and continent-level CBSD pandemic mitigation strategies.

WHO cancer control programme in the African region.

The control of communicable diseases, malnutrition and birth complications has been the main preoccupation of the Member States of the African Region of WHO. As a result of these control measures, death rates, particularly among infants and young children, have continued to decline. This has increased life expectancy to the extent that we are now witnessing the emergence of the diseases prevalent in the industrial world: they have already become a major public health problem in Africa. Carcinoma of the cervix and hepatocellular carcinoma are the commonest forms of cancer afflicting the people of this Region. Others include cancers of the breast, skin, prostate, oesophagus, stomach and bladder. Burkitt's lymphoma is the commonest childhood malignancy. The causal factors of some of these tumours are known, and can therefore be eliminated by primary prevention. This is shown by the almost total absence of carcinoma of the penis in those communities that practise male circumcision, and the decrease in the incidence of squamous-cell carcinoma of the skin that resulted from the prevention of tropical ulcer, thanks to effective care of injuries and wounds. The priorities of the WHO cancer programme are therefore primary prevention, early detection and the provision of adequate pain relief. The success of the programme will depend mainly on whether the services provided will benefit the majority of the population.