Are fewer antifungal and antiprotozoal agents because

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are fewer antifungal and antiprotozoal agents because the eukaryotic cells of the host and those of the parasite have close metabolic and structural similarities. Nevertheless, hosts and parasites do have some significant differences, and effective therapeutic agents have been discovered or developed to exploit them.
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Specific therapeutic attack on viral disease has posed more complex problems, because of the intimate involvement of viral replication with the metabolic and replicative activities of the cell. Thus, most substances that inhibit viral replication have unacceptable toxicity to host cells. However, recent advances in molecular virology have identified specific viral targets that can be attacked. Scientists have developed some successful antiviral agents, including agents that interfere with the liberation of viral nucleic acid from its protective protein coat or with the processes of viral nucleic acid synthesis and replication. The successful development of new agents for human immunodeficiency virus has involved targeting enzymes coded by the virus genome. The success of the "antibiotic era" has been clouded by the development of resistance by the organisms. The mechanisms involved are varied but most often involve a mutational alteration in the enzyme , ribosome site, or other target against which the antimicrobial is directed. In some instances, organisms acquire new enzymes or block entry of the antimicrobic to the cell. Many bacteria produce enzymes that directly inactivate antibiotics. To make the situation worse, the genes involved are readily spread by promiscuous genetic mechanisms. New agents that are initially effective against resistant strains have been developed, but resistance by new mechanisms usually follows. The battle is by no means lost but has become a never-ending policing action. Prevention The outcome of the scientific study of any disease is its prevention. In the case of infectious diseases, this has involved public health measures and immunization. The public health measures depend on knowledge of transmission mechanisms and on interfering with them. Water disinfection, food preparation, insect control, handwashing, and a myriad of other measures prevent humans from coming in contact with infections agents. Immunization relies on knowledge of immune mechanisms and designing vaccines that stimulate protective immunity. Immunization follows two major strategies—live vaccines and inactivated vaccines. The former uses live but attenuated organisms that have been modified so they do not produce disease, but still stimulate a protective immune response. Such vaccines have been effective but carry the risk that the vaccine strain itself may cause disease. This event has been observed with the live oral polio vaccine. Although this rarely occurs, it has caused a shift back to the original Salk inactivated vaccine. This issue has reemerged with a debate over strategies for the use of smallpox immunization to protect against bioterrorism. This
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