Is it possible to experience only systemic symptoms without noticeable parotid gland swelling?

Absolutely possible! While not very common, this situation does occur, and we generally refer to it as "atypical mumps."

Here's how to understand it:

The mumps virus is actually a "systemic" virus; it doesn't just attack the parotid glands (the salivary glands on both sides of your face, below your ears). When the virus enters our body, our immune system immediately starts to "fight" it. This "fight" process triggers a series of systemic reactions, such as:

Fever
Headache
General weakness and muscle aches
Loss of appetite

These are what we call systemic symptoms.

Why might the parotid glands not swell?

Individual Differences: Everyone's immune system reacts differently. Some people's immune systems might be stronger or react in a way that controls the virus before it has a chance to "multiply extensively" in the parotid glands and cause noticeable swelling. However, the body's fight against the virus will still cause symptoms like fever and headache.
The Virus "Went Astray": Sometimes, the mumps virus's primary target isn't the parotid glands, but other glands or organs in the body, such as the pancreas, testicles (in males), ovaries (in females), or even the central nervous system. In these cases, patients might experience symptoms like abdominal pain (pancreatitis), testicular pain (orchitis), or more severe headaches and vomiting (viral meningitis), while swelling of the cheeks is very mild or completely absent.

Important Reminder

When only systemic symptoms appear, it's easy to mistake it for a "common cold" or "flu." However, if any of the following situations occur, it's best to see a doctor for a diagnosis:

Fever that doesn't subside after several days.
Severe headache.
Testicular pain and swelling in males.
Unexplained abdominal pain.

Doctors can confirm whether the mumps virus is the culprit through professional tests (e.g., blood antibody tests), which allows for targeted treatment and proper isolation to prevent transmission to family and friends.

So, in summary, while parotid gland swelling is the most characteristic symptom of mumps, its absence does not necessarily rule out mumps. If you experience discomfort, seeking timely medical attention is always the safest approach.