NEW DELHI: Next time you wake up with crushing fatigue, a high fever, a raw throat and swollen glands, take note. The trigger behind it could be something as simple as a kiss.Infectious mononucleosis, or the ‘kissing disease’, is caused by the Epstein-Barr Virus (EBV) – one of the most common human infections worldwide. It spreads through saliva, not just kissing, but every day close contact.A US study using records from the Mayo Clinic-led Rochester Epidemiology Project, tracking nearly 19,000 people, has found those who develop mono are over three times more likely to develop multiple sclerosis (MS) later. The risk remains small – 0.17% among those with mono versus 0.07% without – but the disease also appeared earlier in those infected.MS is a chronic condition in which the immune system attacks the protective covering of nerves, disrupting signals between the brain and body. It can begin with fatigue, vision problems, numbness and imbalance and may worsen over time.Experts said the link is strong but not causal. Dr Sudhir Kumar, neurologist at Apollo Hospital, Hyderabad, said the apparent rise in younger MS cases likely reflects better awareness and earlier MRI-based diagnosis, not a true shift in onset. While EBV is closely linked to MS, it infects most people, whereas the disease remains uncommon. “EBV may act as a trigger in genetically susceptible individuals, but it is not sufficient on its own to cause MS,” he said, adding it is still unclear if earlier infection leads to earlier disease in practice.He cautioned against routine long-term monitoring after mono, noting the absolute risk is low and over-testing may cause unnecessary anxiety. Instead, awareness is key. Early symptoms – such as blurred or painful vision, tingling or numbness, unexplained fatigue, brief weakness, imbalance, or a shock-like sensation down the spine – are often missed as they come and go, but any neurological symptom lasting over 24 hours should be evaluated.Prof Manjari Tripathi, head of neurology at AIIMS, Delhi, said EBV is widespread in India, especially among children and adolescents. She said, “MS is a complex disease with multiple risk factors – genetic, environmental and immune. EBV may act as a trigger, but it is not the sole cause, and most people with the infection will never develop MS.”Scientists say the findings strengthen the case for preventive strategies, including a potential EBV vaccine.