vation groups, the United States banned use of the pesticide for all nonpublic health uses. By 1982, production of DDT in the United States had ceased altogether. The removal of this cheap and effective antimalaria weapon from the U.S. marketplace had a negative impact on malaria control efforts worldwide. Subsequent pesticides (e.g., malathion) have proved to be more expensive and more toxic.

Beginning in the early 1970s and continuing to the present, resistance to important antimalarial drugs has become increasingly prevalent. Particularly disturbing is the resistance to chloroquine, once the treatment of choice for P. falciparum malaria. The progressive spread of P. falciparum into areas where other species of the parasite once predominated adds an unfortunate complication to control efforts. Multidrug resistance has become such a problem in some parts of the world, such as Thailand, that malaria control personnel are hard pressed to institute any effective preventive or treatment regimen.

Political and social instability around the world have played a central role in malaria's comeback. From the decades-long civil war in Ethiopia, with its attendant cycles of famine and drought, to the devastation of Brazil's rain forest by urban resettlement, human impact on and interaction with the environment have facilitated the resurgence of the disease. Matters are made worse by the fact that there is a dwindling pool of technically competent malariologists, both nationally and internationally, equipped to manage the complexities of malaria research and control in the coming years.

On the positive side, important research discoveries, such as the development in 1975 of an in vitro culture system for the blood stage of P. falciparum, have facilitated scientific understanding of the malaria parasite (Trager and Jensen, 1976). A series of studies in the early and mid-1970s proved that humans could be protected for short periods of time from infection after being inoculated with irradiated sporozoites, lending considerable support to the notion that a vaccine against malaria is possible. Much of the early vaccine-related work in the United States has been supported by the USAID, which by the mid-1970s established a formal malaria vaccine research project. The agency continues to be the major source of U.S. malaria vaccine research funding. During this same period and continuing into the 1980s, a number of new antimalarial drugs, such as mefloquine and halofantrine, were discovered and developed, adding to the available chemotherapeutic options for treating and preventing the disease. The Special Programme for Research and Training in Tropical Diseases (TDR), founded in 1976 as a joint project of the United Nations Development Programme (UNDP), the World Bank, and WHO, has added both scientific direction and consistent financial and organizational support to worldwide activities in the area of malaria research and control.

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