Each parasite has two names, one general and one particular, with the former beginning with a capital letter and the latter beginning with a tiny letter, followed by the designator's name, punctuation, and lastly the year. The generic and particular names are italicized, but not the name of the designer. For example, the general name of a tapeworm is Tegumental organ with hooks, and the particular name is Hymenolepsis nana. The term "parasite" is often used interchangeably with "endoparasite" and "exoparasite". Endoparasites include viruses and bacteria, while exoparasites include worms and other organisms that live in the body but do not eat food, such as lice or fleas. Parasites can also be defined as any organism that obtains nutrients from another organism without providing any useful service in return. Humans are not alone in being parasitized by other organisms; parasites may be pathogens (disease-causing organisms) or symbionts (organism that live within another organism and provide benefits). Examples of pathogenic parasites that infect humans include malaria parasites, which cause malaria; roundworm parasites, which cause ascariasis (roundworm infection) and trichuriasis (hairworm infection); and hookworm parasites, which cause anemia due to their ability to extract blood proteins through their intestinal walls.