Publisher Summary
This chapter provides an overview of parasites, bacteria, and viruses. Flat worms that may affect a man's health are the trematodes or flukes and the cestodes or “tape-worms.” There are two groups of trematodes—(1) those that are hermaphrodites, and (2) those that are non-hermaphrodites. The chapter discusses how parasites can affect a man's health and it also explains their diagnosis, prevention, and control. A large number of bacteria do not cause disease. Some live in dead organic matter and are called saprophytes. Saprophytes are important in industrial and agricultural microbiology. Saprophytes are responsible, for the ripening of cheese, the fermentation of carbohydrate leading to alcohol production, and the acidification of milk. In nature, bacteria are involved in carbon, nitrogen, and sulfur cycles. Thus, decomposition of organic matter is associated with the action of bacteria. Viruses differ from the other obligate intracellular parasites in certain important respects. Viruses are spread from patients, carriers, and healthy individuals who are in the incubation stage of the disease.