New Delhi: Next time you wake up with extreme fatigue, high fever, raw throat and swollen glands, pay attention. The reason behind this could be as simple as kissing.Infectious mononucleosis, or the ‘kissing disease’, is caused by the Epstein-Barr virus (EBV) – one of the most common human infections worldwide. It is spread through saliva, not just through kissing, but through every day close contact.A US study tracking nearly 19,000 people using records from the Mayo Clinic-led Rochester Epidemiology Project has found that people who develop mono are three times more likely to later develop multiple sclerosis (MS). The risk remains small – 0.17% in people with mono versus 0.07% in those without mono – but the disease appears earlier in infected people.MS is a chronic condition in which the immune system attacks the protective covering of the nerves, disrupting signals between the brain and body. This may begin with fatigue, vision problems, numbness, and imbalance and may worsen over time.Experts said the relationship is strong but not causal. Dr Sudhir Kumar, neurologist at Apollo Hospitals, Hyderabad, said the apparent increase in young MS cases reflects better awareness and earlier MRI-based diagnosis, and not a real change in onset. While EBV is closely related to MS, it infects most people while the disease remains uncommon. “EBV can act as a trigger in genetically susceptible individuals, but it is not sufficient in itself to cause MS,” he said. It is still unclear whether earlier infection causes earlier disease in practice, he said.They cautioned against routine long-term monitoring after mono, noting that the absolute risk is low and that more testing may cause unnecessary worry. Instead, awareness is important. Initial symptoms – such as blurred or painful vision, tingling or numbness, unexplained fatigue, brief weakness, imbalance, or a shock-like sensation in the spine – are often missed at the time of visit, but any neurological symptoms lasting more than 24 hours should be evaluated.Professor Manjari Tripathi, head of neurology at AIIMS, Delhi, said EBV is widespread in India, especially among children and adolescents. He said, “MS is a complex disease with multiple risk factors – genetic, environmental and immune. EBV can 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.