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Microfilariae, which are the larvae of filarial worms show a nocturnal periodicity of entering into blood in south Asia and China. This coincides with the biting habits of its vector. The same very species in Malaysia, the larvae are present throughout the day and night but peak at specific time points (subperiodic). The vector there hase different feeding habits.

This understandably is beneficial to the worm.

What are the cues that the worm uses to understand day and night?

Reversing the sleep wake cycle also apparently reverses the periodicity of the larvae from nocturnal to diurnal.

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  • $\begingroup$ The circadian clock is one of the primary drivers for most day-night cycles. Additional factor entrain the clock. This would be one place to start. $\endgroup$ – WYSIWYG Oct 21 '16 at 9:36
  • $\begingroup$ @WYSIWYG the problem here is that the microfilariae, figure out the 'absolute' night and not relative to the hosts sleeping habits. Isn't the circadian rhythm relative? $\endgroup$ – Polisetty Oct 21 '16 at 9:40
  • $\begingroup$ Circadian clock is an endogenous clock. It can operate without stimulation by light. However, light exposure regulates circadian clock so that it can adjust to the natural light-dark i.e. day-night cycles. Host/vector sleeping habits are also affected by circadian clock. When you say that reversal of sleep wake cycles affects the worms then it is likely that they are controlled by some molecules produced by host. Cortisol would be my wild wild guess. $\endgroup$ – WYSIWYG Oct 21 '16 at 10:27

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