malaria, circadian rhythm

Light hitting the retina suppresses the production of melatonin — and there lies the rub. In this modern world, our eyes are flooded with light well after dusk, contrary to our evolutionary programming. Scientists are just beginning to understand the potential health consequences. The disruption of circadian cycles may not just be shortchanging our sleep, they have found, but also contributing to a host of diseases.

malaria
(mə-lâr'ē-ə)
n.

1. An infectious disease characterized by cycles of chills, fever, and sweating, caused by a protozoan of the genus Plasmodium in red blood cells, which is transmitted to humans by the bite of an infected female anopheles mosquito.
2. Archaic. Bad or foul air; miasma.

[Italian, from mala aria, bad air : mala, feminine of malo, bad (from Latin malus) + aria, air (from Latin āēr , from Greek).]

n.an intermittent and remittent fever caused by a protozoan parasite that invades the red blood cells. The parasite is transmitted by mosquitoes in many tropical and subtropical regions.

malarial adj.

Etymology: mid 18th cent.: from Italian, from mal'aria, contracted form of mala aria ‘bad air.’ The term originally denoted the unwholesome atmosphere caused by the exhalations of marshes, to which the disease was formerly attributed.


^ "Ross and the Discovery that Mosquitoes Transmit Malaria Parasites". CDC Malaria website. Archived from the original on June 2, 2007. http://web.archive.org/web/20070602185153/http://www.cdc.gov/malaria/history/ross.htm. Retrieved 2007-06-15.

malarial ma·lar'i·al or ma·lar'i·an or ma·lar'i·ous adj.
Cinchona bark, used to treat malaria, was brought to Europe in the 1630s from Peru, and by the eighteenth century was widely used, although often incorrectly. Well into the nineteenth century, American doctors also relied on bloodletting and cathartics. The isolation of quinine by French chemists in 1820 made treatment more practicable, and from the 1850s, quinine was also used to prevent malaria from developing. In 1880 a French army surgeon, Alphonse Laveran, demonstrated the parasitic cause of the disease in the blood of humans. Dr. A. F. A. King of Washington, D.C., correctly speculated on its transmission by mosquito in 1882, and William George MacCollum added significantly to knowledge of the complex life history of the plasmodium in 1897. British physician Ronald Ross made the crucial demonstration of mosquito transmission in 1898. Using anti-mosquito measures and prophylactic quinine, William C. Gorgas in 1901 initiated a campaign that reduced the malaria rate in Havana from 909 per 1,000 in 1899 to 19 per 1,000 in 1908. Later he obtained comparable results in the Canal Zone, which made possible the building of the Panama Canal.


English

瘧疾患者多呈現高熱發燒癥狀，由於早期跡象與流行性感冒有 相似之處，許多對該疾病不熟悉的外來旅遊者容易將瘧疾誤認為感冒，從而因為沒有得到及時的藥物治療而使得病情惡化。瘧原蟲生活周期具有很明顯的生理節奏 （circadian rhythm），這使得病患的發燒癥狀呈現周期性反覆的特徵。舉例來說，因為間日瘧原蟲（Plasmodium vivax）導致的瘧疾發熱周期為48小時。

瘧疾患者常有的其他癥狀包括：瘧原性貧血，酸毒症，呼吸窘迫等等。如果瘧原蟲侵入腦部血管，則會導致最為嚴重的腦部瘧疾，這通常會造成病者昏迷。

按照瘧疾病徵的嚴重程度不同，瘧疾可以分為非重症瘧疾（uncomplicated malaria）和重症瘧疾（complicated / severe malaria），能有效治療這兩類瘧疾的藥物不太相同。

如果沒有得到及時和有效的治療，瘧疾患者的死亡率會非常高。這也是非洲瘧疾肆虐的主要原因之一，由於戰亂和經濟發展問題，處於疫區的非洲國家公共衛生和醫療狀況通常非常惡劣，這使得這些地方瘧疾的感染和死亡率一直居高不下。

[編輯] 病源

瘧疾疫區，1996年。^[1]
高危險 中危險 低危險 極低危險 無危險

瘧疾的致病源是瘧原蟲（瘧原蟲屬，Plasmodium spp.），這是一類單細胞真核生物，屬於細胞內寄生蟲，它們以瘧蚊（蚊子的其中一個屬，瘧蚊屬的部分種類）作為傳病媒介，通過雌蚊叮咬吸血來傳播病原體。

瘧原蟲屬生物是頂複合器門（Apicomplexa）的原生生物，這一門的生物幾乎都是寄生蟲。大部分脊椎動物都可以作為瘧原蟲的主要宿主，比如齧齒動物，蝙蝠，蜥蜴，鳥等等。這也使得生物學家可以通過建立生物模型（比方說，用老鼠做瘧疾病理研究）的方式來研究人類瘧疾。

只有四種瘧原蟲能夠感染人類，這包括惡性瘧原蟲(Plasmodium falciparum)、三日瘧原蟲(Plasmodium malariae)、蛋形瘧原蟲(Plasmodium ovale)及間日瘧原蟲(Plasmodium vivax)。其中惡性瘧原蟲是非洲流行瘧疾的主要病原體，亦是造成患者死亡率最高的瘧原蟲。

瘧原蟲的生命周期很複雜。瘧原蟲通過蚊子叮咬進入宿主體內後首先侵入肝臟細胞，再由肝臟進入血液感染紅血球，在紅血球內無性繁殖擴增之後，受外部環境因素的影響，它們可以繼續感染新的紅血球，也可能形成配子體（gametocyte），當蚊子吸取受感染的血液後，雄，雌配子體進入蚊子胃內發育成配子並進行有性繁殖，合子最終在胃壁下形成卵囊（oocyte）。卵囊中瘧原蟲進行無性繁殖，最終形成孢子體（sporozoite）進入蚊子唾液腺，準備感染新的脊椎動物宿主。

根據瘧原蟲所處的環境和自身形態的不同，瘧原蟲的生命周期可以大致分為三個階段：

1 紅血球外階段（Pre-erythrocytic stage）：從寄生蟲的孢子體進入宿主體內到其侵入紅血球為止，這一階段患者無明顯癥狀。

2 無性血內階段（Asexual blood stage）：寄生蟲在紅血球內不斷擴殖，這一階段病人呈現顯著的瘧疾臨床癥狀。由於瘧原蟲具有很明顯的生理節奏，每隔一定的時間所有寄生在紅血球中的寄 生蟲就會一同離開受感染細胞，尋找新的宿主細胞，這是造成瘧疾患者高燒具有周期性的主要原因。另外，瘧原蟲可以改造受感染細胞的表面蛋白結構，使之可以貼 附在血管內壁表面，免於受感染細胞在經過脾臟時受宿主免疫系統攻擊而死亡。這一行為能夠造成微細血管的阻塞，如果阻塞發生在腦部血管，患者很容易陷入昏迷 狀態。

3有性繁殖階段（Sexual stage），瘧原蟲在紅血球內形成配子體，進而經蚊子吸食血液進入蚊子體內完成有性繁殖，再由蚊子叮咬進入新的宿主。對疾病傳播的控制主要針對的就是這一階段。

circadian

(sər-kā'dē-ən, -kăd'ē-, sûr'kə-dī'ən, -dē'-)
adj. Biology
Relating to or exhibiting approximately 24-hour periodicity.

[Latin circā, around; see circa + Latin diēs, day.]

circadianly cir·ca'di·an·ly adv.