TROPICAL DERMATOLOGY

Tropical Dermatology

Tropical Dermatology

Thesis Statement

Plant viruses and virus diseases have been studied for more than 100 years and much attention has been given to their control. However, this has been difficult to achieve because of the lack of any effective means of curing virus-infected plants. Chemotherapy, thermotherapy and meristem-tip culture can be successful in eliminating viruses from plant tissue, but they cannot be used on a large scale. Consequently, the main approach has been to prevent or delay virus infection or to ameliorate its effects. Various means have been used to achieve these objectives, including phytosanitation (involving quarantine measures, crop hygiene, virus-free planting material and eradication), changes in cropping practices, the use of pesticides to control vectors, mild strain protection and the deployment of resistant or tolerant varieties.

Introduction

Tropical diseases are diseases of the poor, and investments in control and research to develop more effective intervention tools and strategies have been minimal. For some, however, effective intervention methods have been developed, and successful control has been achieved.

Literature Review: Quarantine

The information available on the geographic distribution of viruses and their vectors is inadequate, especially in the tropics where there is often a lack of adequate facilities and trained personnel to carry out the necessary surveys and virus identifications. This creates difficulties in interpreting reports of a seemingly 'new' disease, or of the apparent 'spread' of a known disease into a new area. Nevertheless, it is apparent that some viruses and vectors are restricted to certain regions and absent from others. Some of the most important of the potential threats to crops in other tropical regions are:

• Rice hoja blanca virus (currently restricted to South and Central America);

• rice tungro viruses (South and South-East Asia);

• Rice yellow mottle virus (Africa);

• Indian cassava mosaic virus (India/Sri Lanka);

• Sri Lankan cassava mosaic virus (Sri Lanka);

• African cassava mosaic viruses (Africa);

• Cassava brown streak virus (Africa);

• Cassava common mosaic virus (South America);

• Cassava vein mosaic virus (South America);

• Maize rough dwarf virus (Mediterranean);

• Maize rayado fino virus (South/Central America);

• Groundnut bud necrosis virus (Asia);

• groundnut rosette viruses (Africa).

There are obvious advantages in adopting quarantine and other measures in attempts to maintain the situation and to avoid introducing viruses or their vectors to other areas where they could become established and cause problems (Foster and Hadidi, 1998). This has long been recognized and there has been considerable expenditure on establishing and operating quarantine facilities at several centres in the tropics or subtropics. In Africa, they include Muguga in Kenya, Ibadan in Nigeria and Pretoria in Republic of South Africa. There are also special quarantine facilities for banana and plantain at the University of Louven, Belgium, and for cacao at the University of Reading, United Kingdom (Hadley et al., 1989). Regulations and procedures are collated and coordinated by the United Nations Food and Agriculture Organization (FAO), which has published a series of guidelines for the safe movement of germplasm (Frison and Putter, 1989). However, there are many difficulties in implementation and enforcement due to the continually increasing scale ...