A false-colored electron micrograph shows a malaria sporozoite migrating through the midgut epithelia. Infection is the invasion of an organism’s body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they human digestive system worksheet pdf. Infectious disease, also known as transmissible disease or communicable disease, is illness resulting from an infection.
Infections are caused by infectious agents including viruses, viroids, prions, bacteria, nematodes such as parasitic roundworms and pinworms, arthropods such as ticks, mites, fleas, and lice, fungi such as ringworm, and other macroparasites such as tapeworms and other helminths. Hosts can fight infections using their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response. Specific medications used to treat infections include antibiotics, antivirals, antifungals, antiprotozoals, and antihelminthics.
Infectious diseases resulted in 9. The branch of medicine that focuses on infections is referred to as infectious disease. Symptomatic infections are apparent and clinical, whereas an infection that is active but does not produce noticeable symptoms may be called inapparent, silent, subclinical, or occult. An infection that is inactive or dormant is called a latent infection.
An example of a latent bacterial infection is latent tuberculosis. Some viral infections can also be latent, examples of latent viral infections are any of those from the Herpesviridae family. This fact occasionally creates some ambiguity or prompts some usage discussion.
A short-term infection is an acute infection. A long-term infection is a chronic infection.
Among the many varieties of microorganisms, relatively few cause disease in otherwise healthy individuals. Infectious disease results from the interplay between those few pathogens and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen, depends upon the ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. However a host’s immune system can also cause damage to the host itself in an attempt to control the infection.
Many of the most common primary pathogens of humans only infect humans, however many serious diseases are caused by organisms acquired from the environment or that infect non-human hosts. Primary pathogens may also cause more severe disease in a host with depressed resistance than would normally occur in an immunosufficient host. A primary infection is infection that is, or can practically be viewed as, the root cause of the current health problem. In contrast, a secondary infection is a sequela or complication of a root cause.
Primary pathogens often cause primary infection and also often cause secondary infection. These postulates were first used in the discovery that Mycobacteria species cause tuberculosis. Koch’s postulates can not be applied ethically for many human diseases because they require experimental infection of a healthy individual with a pathogen produced as a pure culture. Often, even clearly infectious diseases do not meet the infectious criteria.
It is less clear that a pure culture comes from an animal source serving as host than it is when derived from microbes derived from plate culture. Epidemiology is another important tool used to study disease in a population. Thus, a contagious disease is a subset of infectious disease that is especially infective or easily transmitted.