WordNet

(especially of medicine) of disease or anything resembling a disease; attacking or affecting many individuals in a community or a population simultaneously; "an epidemic outbreak of influenza"
a widespread outbreak of an infectious disease; many people are infected at the same time

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(病気などが)『伝染性の』,急速に広がる / (一般に)流行している / (一時的な)流行病,伝染病 / 流行,はやり
『いたる所ににある』,流行している

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/09/16 20:42:00」(JST)

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In epidemiology, an infection is said to be endemic (from Greek ἐν en "in, within" and δῆμος demos "people") in a population when that infection is maintained in the population without the need for external inputs. For example, chickenpox is endemic (steady state) in the UK, but malaria is not. Every year, there are a few cases of malaria reported in the UK, but these do not lead to sustained transmission in the population due to the lack of a suitable vector (mosquitoes of the genus Anopheles).

For an infection that relies on person-to-person transmission to be endemic, each person who becomes infected with the disease must pass it on to one other person on average. Assuming a completely susceptible population, that means that the basic reproduction number (R₀) of the infection must equal 1. In a population with some immune individuals, the basic reproduction number multiplied by the proportion of susceptible individuals in the population (S) must be 1. This takes account of the probability of each individual to whom the disease may be transmitted actually being susceptible to it, effectively discounting the immune sector of the population.

For the disease to be in an endemic steady state:

\ {R_0} \times {S} = {1}

In this way, the infection neither dies out nor does the number of infected people increase exponentially but the infection is said to be in an endemic steady state. An infection that starts as an epidemic will eventually either die out (with the possibility of it resurging in a theoretically predictable cyclical manner) or reach the endemic steady state, depending on a number of factors, including the virulence of the disease and its mode of transmission.

If a disease is in endemic steady state in a population, the relation above allows us to estimate the R₀ (an important parameter) of a particular infection. This in turn can be fed into the mathematical model of an epidemic.

While it might be common to say that AIDS is "endemic" in Africa—meaning found in an area—this is a use of the word in its etymological not epidemiological form. AIDS cases in Africa are still increasing, so the disease is not in an endemic steady state. It is correct to call the spread of AIDS in Africa an epidemic.^{[citation needed]}

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1. 妊娠中のマラリアの概要 overview of malaria in pregnancy
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5. 東アフリカへの旅行によって感染する可能性のある疾患 diseases potentially acquired by travel to east africa

English Journal

Prevalence and dynamics of antibodies against Toxoplasma gondii in kids born from naturally infected goats.

Rahman M1, Alauddin M2, Hossain KM3, Islam MH4, Kitoh K5, Nagamune K6, Takashima Y7.
Parasitology international.Parasitol Int.2015 Oct;64(5):389-91. doi: 10.1016/j.parint.2015.05.015. Epub 2015 May 28.
We investigated the presence of antibodies against Toxoplasma gondii in domesticated goats intended for human consumption in a rural suburb of Rajshahi, Bangladesh. Antibodies to T. gondii were found in 55.1% (80/145) of the goats tested in our sample. The seroprevalence among goats aged <1year,
PMID 26028431

Predictors for diagnosis of tick-borne encephalitis infection in Poland, 2009-2010.

Zielicka-Hardy A1, Rosińska M, Kondrusik M, Hlebowicz M, Konior R, Stefanoff P.
Infectious diseases (London, England).Infect Dis (Lond).2015 Sep;47(9):604-10. doi: 10.3109/23744235.2015.1042036. Epub 2015 Apr 23.
BACKGROUND: Tick-borne encephalitis (TBE) is a viral infection with no available treatment. Due to its non-specific symptoms, TBE tends to be under-diagnosed and under-reported. We aimed to identify factors predicting TBE diagnosis to develop a diagnostic algorithm for use by physicians.METHODS: We
PMID 25903310

Phylodynamics of Enterovirus A71-Associated Hand, Foot, and Mouth Disease in Viet Nam.

Geoghegan JL1, Tan le V2, Kühnert D3, Halpin RA4, Lin X4, Simenauer A4, Akopov A4, Das SR4, Stockwell TB4, Shrivastava S4, Ngoc NM5, Uyen le TT5, Tuyen NT6, Thanh TT6, Hang VT6, Qui PT5, Hung NT7, Khanh TH7, Thinh le Q7, Nhan le NT7, Van HM8, Viet do C9, Tuan HM9, Viet HL9, Hien TT6, Chau NV5, Thwaites G10, Grenfell BT11, Stadler T12, Wentworth DE13, Holmes EC14, Van Doorn HR10.
Journal of virology.J Virol.2015 Sep 1;89(17):8871-9. doi: 10.1128/JVI.00706-15. Epub 2015 Jun 17.
Enterovirus A71 (EV-A71) is a major cause of hand, foot, and mouth disease (HFMD) and is particularly prevalent in parts of Southeast Asia, affecting thousands of children and infants each year. Revealing the evolutionary and epidemiological dynamics of EV-A71 through time and space is central to un
PMID 26085170

Japanese Journal

Development of Monoclonal Antibodies That Target 1-Cys Peroxiredoxin and Differentiate Plasmodium falciparum from P. vivax and P. knowlesi

Hakimi Hassan,Nguyen Thu-Thuy,Suganuma Keisuke,Masuda-Suganuma Hirono,Angeles Jose Ma. M.,Inoue Noboru,Kawazu Shin-ichiro
Tropical Medicine and Health 41(2), 55-59, 2013
… Differential diagnosis is particularly important in cases of Plasmodium vivax, a species that shares endemicity with P. …
NAID 130003365315

Distribution of Two Subgroups of Human T-Lymphotropic Virus Type 1 (HTLV-1) in Endemic Japan

Otani Masashi,Honda Noritaka,Xia Pin-Cang,Eguchi Katsuyuki,Ichikawa Tatsuki,Watanabe Toshiki,Yamaguchi Kazunari,Nakao Kazuhiko,Yamamoto Taro
Tropical medicine and health 40(2), 55-58, 2012-06-01
… An interesting finding in the present study is the presence of the transcontinental subgroup in Kochi, suggesting the endemicity of the transcontinental subgroup along the Kuroshio Current. …
NAID 10031123158

チクングニアウイルス感染症

高崎智彦
獣医疫学雑誌 15(2), 114-116, 2011
チクングニア熱はチクングニアウイルスを原因とする蚊媒介性急性熱性ウイルス性疾患である。時に激しい関節痛,発疹を伴う。近年,アフリカ,南アジア,東南アジアの熱帯・亜熱帯地域を中心に流行が報告されている。2007年には温帯地域で初めての流行がイタリアで確認され,さらに2010年9月にはフランス南部においても国内流行が発生した。イタリア,フランスにおけるチクングニア熱の国内流行は日本にも生息しており活動 …
NAID 130002098850