TNF and viral infectious disease: The subjective nature of pain means that it is ultimately defined by the individual experiencing it, making it difficult to measure objectively but studied extensively in fields such as neuroscience, psychology, and medicine.Viral infections can cause muscle pain through various mechanisms, including cytokine activation such as IL-1, IL-6, IL-12, IFN-γ, and TNF-α and stimulation of adrenergic receptors found in skeletal and smooth muscle fibers (25).