In a tetanus infection, out of all symptoms and signs, why is respiratory problems and muscle spasms the main concerns of doctors?

See answer. The severity of Tetanus varies depending on the amount of toxin that reaches the nervous system, the duration between initial infection and first symptoms(symptoms can develop in 2 days or as long as 38 days after infection....the shorter the interval the more severe the disease). Muscle spasms cause the respiratory failure, which is fatal if not treated.