The 24-hour periodicity of microfilariae: biological mechanisms responsible for its production and control
The 24-hour periodicity of microfilariae: biological mechanisms responsible for its production and control
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微丝蚴的24小时周期性：负责其产生和控制的生物机制
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发表时间：
1967
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影响因子：
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通讯作者：
F. Hawking
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文献类型：
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作者：
F. Hawking
一个解释，它涵盖了大部分的实验数据的机制，其中微丝蚴的周期性保持：在夜间（与吴策线虫班氏丝虫和类似的丝虫）的微丝蚴均匀分布在整个血液中，因此，它们可用于摄食和传播的蚊子。在白天，它们聚集在肺的小血管中，因此它们在外周血中很少;这个阶段可能是为了让微丝蚴在肺中享受有利的生理条件。这种聚集是由于微丝蚴自身的主动反射所致;它可能依赖于通过微动脉的毛细血管前网络的侧向迁移。肺中阻碍微丝蚴通过，使其聚集在肺中（优先于其他器官的毛细血管）的因素是氧张力的极大增加，这可称为"氧屏障"。微丝蚴的24 h周期与宿主的24 h周期一致，宿主的某些节律变化可作为微丝蚴的线索。每一个微丝蚴都有自己的微弱的内源性昼夜节律，但是个体微丝蚴的节律受宿主的节律支配，所以所有不同的个体在同一时间做几乎相同的事情，并且它们在正确的时间做（即正确的传播）。不同种类的微丝蚴对相同的刺激有不同的反应，它们依赖于不同的安排来维持它们的节律。周期性微丝蚴可分为三大类。（а）W.这些取决于静脉-动脉（VA）氧压差（“氧屏障”）的绝对大小，其在夜间（例如40 mmHg）比在白天（例如55 mmHg）低，因此微丝蚴在夜间通过肺，但在白天在那里积聚。如果在夜间使病人吸氧，动脉血氧含量就会上升;如果使病人进行剧烈的肌肉锻炼，静脉血氧分压就会下降;在这两种情况下，VA差都会增大，微丝蚴就会在肺中积聚。(b)人的Loa loa，泰国猴子的Edesonfilaria malayensis和东非猫鼬的Monnigofilaria setariosa。在这组中，微丝蚴对氧屏障的敏感性通过宿主体温的24小时变化而大大增加或降低。因此，这类微丝蚴的周期间接地取决于宿主的温度周期。(c)犬恶丝虫（Dirofilaria immitis）、犬恶丝虫D. repens of dogs，D.这些微丝蚴可能仅对较低范围的氧张力敏感，例如30至60 mmHg。总的来说，它们的周期取决于氧屏障的昼夜变化，就像W。班克罗夫特，但在特殊情况下（如文中所述），给氧可能导致微丝蚴从肺中释放，而不是蓄积。太平洋型W.由于实验证据不足，尚不能确定班克罗夫特的身份。微丝蚴的行为是为了促进传播而调整的，在节肢动物媒介可能叮咬的时候，通过安排外周血中微丝蚴的最大数量来促进传播。实现这一点的最复杂的安排是通过24小时的节奏-经典的“连续性”。一种不太复杂的安排是以啮齿动物的各种丝虫为例，例如卡氏溪螨和维特氏双瓣线虫，其中寄生虫通过在巢穴或洞穴中吸血的螨或蜱传播，当动物安静地坐在巢穴中时，体温下降会刺激微丝蚴在外周血中聚集。仍不太复杂的丝虫，例如持久棘唇线虫和纤细双瓣线虫，不具有任何调节外周血中微丝蚴供应以适应媒介摄食习性的安排。此外，某些微丝蚴，如D. immitis和D.在一年的变化以及24小时之一，他们是最多的血液在7月和8月（当蚊子是最多的温带）。有些宿主（如狗）的24小时节律比其他宿主（如人和猴）的24小时节律不明显，其微丝蚴的周期也同样不明显。
An explanation is presented which covers most of the experimental data about the mechanisms by which the periodicity of microfilariae is maintained: During the night-time (with Wuchereria bancrofti and similar filariae) the microfilariae are evenly distributed throughout the blood and they are thus available for ingestion and transmission by mosquitoes. During the day-time they accumulate in the small vessels of the lungs, and hence they are few in the peripheral blood; this phase is probably adapted to allow the microfilariae to enjoy favourable physiological conditions in the lungs. The accumulation is due to an active reflex by the microfilariae themselves; and it probably depends on a sideways migration through the precapillary network of arterioles. The factor in the lungs which holds up the passage of the microfilariae so that they accumulate there (in preference to the capillaries of other organs), is the great increase in oxygen tension, which may be termed the ‘oxygen barrier’. The 24 h cycle of the microfilariae is orientated to the 24 h cycle of the host; and some rhythmic change in the host acts as a cue to the microfilariae. Each microfilaria has a weak endogenous circadian rhythm of its own, but the rhythms of the individual microfilariae are dominated by that of the host, so that all the different individuals do approximately the same thing at the same time, and they do it at the right time (i.e. right for transmission). Different species of microfilariae respond differently to the same stimuli, and they depend on different arrangements for the maintenance of their rhythms. Three main groups of periodic microfilariae may be recognized. (а) W. bancrofti, Brugia malayi, etc. These depend upon the absolute size of the venousarterial (VA) difference in oxygen tension (‘oxygen barrier’) which is lower by night (e.g. 40 mmHg) than it is by day (e.g. 55 mmHg) and so the microfilariae pass through the lungs by night but accumulate there by day. If at night the patient is caused to breathe oxygen, the arterial oxygen rises; or if he is caused to take vigorous muscular exercise, the venous oxygen tension falls; in both cases the VA difference becomes greater and the microfilariae accumulate in the lungs. (b) Loa loa of man, Edesonfilaria malayensis of monkeys in Thailand and Monnigofilaria setariosa of East African mongooses. In this group the sensitivity of the microfilariae to the oxygen barrier is greatly increased or decreased by the 24 h changes in the body temperature of the host. Accordingly, the cycle of microfilariae of this group indirectly depends upon the temperature cycle of the host. (c) Dirofilaria immitis, D. repens of dogs, D. aethiops (corynodes) of monkeys, etc. These microfilariae are probably sensitive only to the lower range of oxygen tensions, e.g. 30 to 60 mmHg. On the whole their cycle depends on day-night changes in the oxygen barrier as with W. bancrofti, but under special circumstances (as explained in the text) administration of oxygen may cause liberation of microfilariae from the lung instead of accumulation. The mechanism controlling the Pacific type of W. bancrofti cannot yet be identified, since the experimental evidence is insufficient. The behaviour of microfilariae is adapted to promote transmission by arranging the maximum number of microfilariae in the peripheral blood at times when the arthropod vector is likely to bite. The most sophisticated arrangement to achieve this is by a 24 h rhythm—the classical ‘periodicity’. A less sophisticated arrangement is illustrated by various filariae of rodents, e.g. Litomosoides carinii and Dipetalonema witei, in which the parasites are transmitted by mites or ticks which suck blood in the nest or burrow, and the microfilariae are stimulated to swarm in the peripheral blood by a fall in body temperature when the animal sits quietly in its nest. Filariae which are still less sophisticated, e.g. Acanthocheilonema perstans and Dipetalonema gracile, do not possess any arrangements for adjusting the supply of microfilariae in the peripheral blood to the feeding habits of the vectors. Furthermore, some microfilariae, e.g. those of D. immitis and D. repens, are adjusted to their vectors on an annual variation as well as on a 24 h one and they are most numerous in the blood during July and August (when mosquitoes are most numerous in temperate zones). Some hosts (e.g. dogs) have a less marked 24 h rhythm than other hosts (e.g. man and monkey) and the cycles of their microfilariae are similarly less marked.