Parasites

Although all disease-causing microorganisms are technically parasites, the word is usually used to describe disease-causing organisms--such as protozoa and worms--that are larger than microscopic. Such organisms can cause terrible diseases such as blindness, and malaria, especially in underdeveloped countries with poor water supplies and sanitary systems. Clear, easy-to-understand explanations and microphotographs help readers understand the nature of these germs.