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The Control of Communicable Diseases Manual, published by the American Public Health Association, defines a carrier as a person or animal that harbors a specific infectious agent without discernable clinical disease and serves as a potential source of infection. Several varieties of carrier are recognized.


These are persons who harbor an infectious agent but never fall ill or manifest any overt evidence that they are infected. This commonly happens with certain virus diseases, such as several forms of viral hepatitis and poliomyelitis, and with some bacterial diseases, including diphtheria and meningococcal meningitis. The pathogenic organisms responsible for these and other diseases in this category live as commensal organisms in the carrier's respiratory and/or gastrointestinal tract, apparently coexisting without causing disease because the host is not susceptible to infection or because the organisms are not virulent. Carriers of the diphtheria bacillus, meningococcus, or other organisms in this category manifest no symptoms or signs of infection, but the organisms can be recovered from their nose, throat, or from their feces. Moreover, appropriate serological tests may reveal evidence of inapparent infection. Animals and birds can be carriers of some human diseases. For instance, jungle yellow fever is carried by monkeys and possibly other jungle-dwelling small mammals. The rabies virus, which is almost invariably fatal when humans are infected and not protected immediately by antirabies vaccine, is carried by bats who seem to suffer no ill effects at all. Salmonella organisms may be carried by many varieties of animals and birdscattle, rodents, pets such as dogs and cats, tortoises, chickens, ducksand of course by humans. Some may be healthy carriers, and others are chronic carriers who were infected at some time in the past and have not stopped harboring and excreting the infectious agent.


The pathogenic organisms that cause many diseases can infect healthy people who come into contact with the person harboring the pathogen either during the incubation period or during convalescence. One of the reasons that measles is so highly infectious is that it is at its most contagious stage shortly before the characteristic rash appears. Experienced family physicians and pediatricians soon learn how to recognize children in the incubation period of measles and do their best to minimize transmission by isolating children with a dry cough, red eyes, and fever. Although we should no longer have to be concerned about the risks of transmitting measles when virtually all children are immunized, occasional outbreaks still occur, so continuing vigilance is necessary. Some types of the common cold can similarly be transmitted during the incubation period.

Many diseases remain infectious for a time after the acute stage has passed and the sick person has become apparently well again. Persons in this category are convalescent carriers, and are the most frequent source of infection for others. The common cold is very often transmitted by incubatory and convalescent carriersand, of course, by those who carry on with their normal activities without acknowledgment and treatment of their cold. Convalescent carriers can be a serious problem with many forms of diarrheal diseases, notably shigella and sonne dysentery. Investigation of outbreaks of diarrhea often reveals that the source of infection is a carrier who works as a cook or food handler in a restaurant. Among the best known, though rare, carrier states in this category, is typhoid. Convalescent cases can remain infectious for long periods, especially when typhoid bacilli lurk in such organs as the gall bladder, whence they are excreted in the feces. Typhoid carriers commonly have had overt disease at some time in the past and continue to carry typhoid bacilli, which they excrete and thereby expose others to infection. But some typhoid carriers have no history of overt disease in the past. The infamous Typhoid Mary may have been an example. The convalescent carrier state may be temporary, lasting only until residual symptoms disappear, or it may be prolonged, chronic, or even permanent.

A very important category of carrier state occurs with many sexually transmitted diseases (STDs) and with HIV (human immunodeficiency virus) infection. Persons with STDs and HIV are more often outwardly well than overtly unwell, and all too often they are sexually active. There are many recorded instances of a sexually promiscuous person with gonorrhea infecting one hundred or more people over a relatively short period.

John M. Last

(see also: Sexually Transmitted Diseases; Typhoid; Typhoid Mary; Universal Precautions )


Chiu, J., ed. (2000). Control of Communicable Diseases Manual, 17th edition. Washington, DC: American Public Health Association.

Last, J. M. (1997). Public Health and Human Ecology, 2nd edition. Stanford, CA: Appleton and Lange.

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The Carrier are an American Indian group located in north-central British Columbia along the numerous lakes and rivers in the region. The estimated precontact population of roughly eighty-five hundred decreased to a low of about fifteen hundred by 1890 and has since increased to about six thousand. The Carrier were composed of fourteen named subtribes, which on the basis of cultural, territorial, and linguistic evidence have been classified into two or three divisions such as the northern, central, and southern Carrier. Seventeen bands are recognized by the Canadian government today. The Carrier use the subtribe names in reference to themselves. They speak an Athapaskan language.

Carrier prehistory is unclear. The Carrier were involved in intensive trade relations with groups to the west, which eventually involved indirect trade with White traders making port on the northwest coast to seek beaver, fox, and other furs supplied by the interior groups. Contact with Northwest Coast groups such as the Gitksan and Bellacoola resulted in the Carrier adopting the social stratification/potlatch complex of these groups. First contact with Whites was in 1793. Within fifteen years, North West Company fur trade posts were established in Carrier territory and the traditional Carrier hunting and fishing economy began to change. Fur trade activity was joined by gold mining in 1858, then farming and ranching, and finally lumbering of Carrier lands.

Prior to White settlement, families followed an annual cycle of congregating in settlements to visit, potlatch, prepare food for storage, and live off of stored food or separating in order to hunt and trap. Beginning in the late 1800s, the Government began setting aside land for the Carrier, which now includes some sixty-three thousand acres in over two hundred reserves. Traditional dwellings included A-frame houses and plank houses modeled after those of the Northwest Coast.

The Carrier were hunters, fishers, and fur trappers. Salmon was the primary fish taken in basket traps, and Beaver, bear, caribou, and other animals were hunted. The fur trade, at first indirect through the Northwest Coast groups and later direct with the North West Company and then Hudson's Bay Company, quickly replaced hunting and fishing as the primary economic activity. As the fur trade became more and more lucrative, purchase of food and equipment replaced hunting for food and traditional manufactures to a large extent. Today wage labor (mostly seasonal work in canneries, on ranches, or in lumbering) and government assistance are the major sources of income supplemented by trapping and crafts by some families.

Prior to extensive contact with Northwest Coast groups, the patrilineally extended family (sadeku ) was probably the basic social unit. Northwest Coast influences produced somewhat different forms of social organization among the northern and southern Carrier subtribes. Though subtribe variation existed, in the North social organizational units went from subtribe to phratries to clans to matrilineages. Social ranking was based on wealth (largely obtained through the fur trade) and was signified by personal and clan crests and potlatching. Control of subtribe land was allocated to the phratries. In the South, the system was less elaborate with crest groups (who conducted potlatches), bilateral descent groups, and sadeku. Potlatching, banned by the government and discouraged by Catholic missionaries, has largely disappeared. Marriage was usually preceded and followed by a period of bride-service. Polygyny, the sororate, and levirate were practiced in the past.

The Carrier are now mostly Roman Catholic in belief, if not entirely in practice. Traditional beliefs and practices (taboos, dreaming, quests, and so on) focused on spirits.


Jenness, Diamond (1943). The Carrier Indians of the Bulkley River: Their Social and Religious Life. U.S. Bureau of American Ethnology Bulletin no. 133. Anthropological Papers, no. 25, Washington, D.C.

Morice, Adrien G. (1905). The History of the Northern Interior of British Columbia (Formerly New Caledonia ), J 660-1880. 3rd ed. Toronto: William Briggs.

Tobey, Margaret L (1981). "Carrier." In Handbook of North American Indians. Vol. 6, Subarctic, edited by June Helm, 413-432. Washington, D.C.: Smithsonian Institution.

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car·ri·er / ˈkarēər/ • n. 1. a person or thing that carries, holds, or conveys something: water carriers. 2. a person or company that undertakes the professional conveyance of goods or people: Pan Am was the third U.S. carrier to cease operations in 1991. ∎  a vessel or vehicle for transporting people or things, esp. goods in bulk: the largest timber carrier. ∎  an aircraft carrier. ∎  a company that provides facilities for conveying telecommunications messages. 3. a person or animal that transmits a disease-causing organism to others. Typically, the carrier suffers no symptoms of the disease. ∎  a person or other organism that possesses a particular gene, esp. as a single copy whose effect is masked by a dominant allele, so that the associated characteristic (such as a hereditary disease) is not displayed but may be passed to offspring. 4. a substance used to support or convey another substance such as a pigment, catalyst, or radioactive material. ∎  Physics short for charge carrier. ∎  Biochem. a molecule that transfers a specified molecule or ion within the body, esp. across a cell membrane.

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carrierbarrier, carrier, farrier, harrier, tarrier •Calabria, Cantabria •Andrea • Kshatriya • Bactria •Amu Darya, aria, Zaria •Alexandria •Ferrier, terrier •destrier •aquaria, area, armamentaria, Bavaria, Bulgaria, caldaria, cineraria, columbaria, filaria, frigidaria, Gran Canaria, herbaria, honoraria, malaria, pulmonaria, rosaria, sacraria, Samaria, solaria, tepidaria, terraria •atria, gematria •Assyria, Illyria, Styria, SyriaLaurier, warrior •hypochondria, mitochondria •Austria •auditoria, ciboria, conservatoria, crematoria, emporia, euphoria, Gloria, moratoria, phantasmagoria, Pretoria, sanatoria, scriptoria, sudatoria, victoria, Vitoria, vomitoria •Maurya •courier, Fourier •currier, furrier, spurrier, worrier •Cumbria, Northumbria, Umbria •Algeria, anterior, bacteria, Bashkiria, cafeteria, criteria, cryptomeria, diphtheria, exterior, hysteria, Iberia, inferior, interior, Liberia, listeria, Nigeria, posterior, Siberia, superior, ulterior, wisteria •Etruria, Liguria, Manchuria, Surya

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1. (in medicine) An individual who harbours a particular disease-causing microorganism without ill-effects and who can transmit the microorganism to others. Compare vector.

2. (in genetics) An individual with an allele for some defective condition that is masked by a normal dominant allele. Such individuals therefore do not suffer from the condition themselves but they may pass on the defective allele to their offspring. In humans, women may be carriers of such conditions as red–green colour blindness and haemophilia, the alleles for which are carried on the X chromosomes (see sex linkage).

3. (in biochemistry) See carrier molecule; hydrogen carrier.

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carrier (ka-ri-er) n.
1. a person who harbours the microorganisms causing a particular disease without experiencing signs or symptoms of infection and who can transmit the disease to others.

2. (in genetics) a person who bears a gene for an abnormal trait without showing signs of the disorder.

3. an animal, usually an insect, that passively transmits infectious organisms from one animal to another or from an animal to a human being. See also vector.

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1. See modulation.

2. of an algebra. See signature.

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