The basic manifestation of an acute miasm in homoeopathy refers to the sudden onset of symptoms that are typically intense but short-lived. These symptoms are often related to infectious or epidemic diseases and can include:

1. Sudden Onset: Symptoms appear abruptly and progress rapidly.
2. Intensity: The symptoms are usually severe and pronounced.
3. Specificity: The disease has almost fixed manifestations, meaning it presents in a consistent manner.
4. Prodromal Period: There is often a short period of initial symptoms before the full disease manifests.
5. Recovery Tendency: There is a natural tendency for the body to recover once the acute phase passes.

Examples of diseases caused by acute miasms include measles, chickenpox, and whooping cough.