Answer:
The more pathogens cause the disease the more difficult it will be to eradicate. If a disease is caused by a limited number and closely related pathogens then often same tools and approaches can be used in eradication efforts.Malaria parasites have a complex life cycle, and there is poor understanding of the complex immune response to malaria infection. Malaria parasites are also genetically complex, producing thousands of potential antigens.It's hard because we're talking of a parasite and the biology of the parasite and of the transmission of that parasite is orders of magnitude more complex than anything we've confronted and a disease that would be eradicated before. So a virus like that of polio or smallpox is a relatively simple organism.