the risk of transmitting the human immunodeficiency virus, hepatitis B virus, and other blood-borne pathogens through nonsterile finger-prick methods, such routine mass screening cannot be recommended.

In countries where malaria is highly endemic, the epidemiology is focal, the burden of disease varies greatly, and surveys that evaluate the prevalence of malaria infection can be particularly deceptive. For example, areas of both Papua New Guinea and the Gambia are highly endemic for malaria and have similar prevalences of malaria infection, yet the levels of malaria-related mortality in the two countries appear to be quite different. On the north coast of Papua New Guinea, few deaths can be traced to malaria, even among very young children (Moir et al., 1989), while in the Gambia, a quarter of all deaths in children one to four years of age are believed to be malaria related (Greenwood et al., 1987). Some of the differences may be explained by the fact that the population around Madang, Papua New Guinea, is relatively advantaged and has better access to antimalarial drugs.

Not all people in malarious areas are at the same risk of becoming sick or dying from the disease. Indeed, the risk of severe and potentially fatal infection with Plasmodium falciparum falls principally on nonimmunes, such as young children, immigrants from malaria-free areas, and pregnant women, in whom immunosuppression during pregnancy appears to be associated with a higher frequency of malaria infection and adverse pregnancy outcomes (Breman and Campbell, 1988). Despite this general pattern, and for reasons not well understood, not all individuals within these groups are at equal risk of becoming seriously ill or dying. Much of the most recent work in malaria epidemiology has thus concentrated on the identification of the variables that place certain groups at greater risk of illness and death. Central to this work has been a better understanding of the acquisition of immunity.

Acquired immunity appears to be relatively short-lived and depends on repeated exposure to the parasite over time. It is directly related to the level of malaria endemicity in a given area, transmission patterns, frequency of human-vector contact, and the length of time a person resides in an endemic area. The species of parasite present, the level of endemicity, and the biologic, behavioral, and socioeconomic characteristics of the human population determine the prevalence of infection and the distribution of disease.

An increasingly important issue in understanding the epidemiology of malaria disease is the availability and use of antimalarial drugs. With the spread of drug-resistant parasites, the effects of drugs on immune status and on drug resistance itself are issues of paramount concern.

By looking at malaria as a disease, epidemiologists are better equipped to assess the short- and long-term impacts of various control strategies,



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