quarantine, isolation of persons, animals, places, and effects that carry or are suspected of harboring communicable disease. The term originally referred to the 40 days of offshore wait during which incoming vessels could not discharge passengers or cargo in the era when plague and other great epidemics swept across Europe. The practice has been changed by developments in medical science. Usually the word of the ship's officer that the passengers are free of disease and presentation by the passengers of certificates of inoculation against certain diseases are now sufficient to permit passage of travelers from one country to another. Some nations still maintain extended periods of quarantine for cattle and household pets coming from another country to guard against such diseases as foot-and-mouth disease and rabies. Plant life may also be held for assurance that fungus and other plant diseases are not being introduced.

Local quarantine regulations are also in effect to guard against the spread of communicable disease. Public health laws require that physicians report certain infections to the authorities. The patients (and those who have come in contact with them) may be isolated and their effects disinfected, condemned, or destroyed, if it is in the public interest, since quarantine laws supersede even property rights. Although antibiotics, vaccinations, and other treatments have greatly reduced the use of quarantine in public health, persons with newly recognized or hard to treat communicable diseases may still be isolated by health officials. For example, quarantine was used effectively to control the spread of SARS (severe acute respiratory syndrome), a sometimes deadly pneumonialike illness, in 2003.

Detention of humans or animals suspected to have communicable disease until they are proved free of infection. The term is often used interchangeably with isolation (separation of a known infected individual from healthy ones until the danger of transmission passes). It derives from the 40-day (quarantina) isolation period instituted in an attempt to prevent spread of plague in the Middle Ages. Though appropriate in some cases (e.g., diphtheria), it is ineffective for diseases that are spread by other means (e.g., plague) or are contagious before symptoms appear. In some cases, contacts (e.g., the family of a hepatitis patient) are notified, educated on precautions, and monitored for development of illness. Quarantine is more often applied to animals (e.g., for rabies).

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