 Having been a first-hand eyewitness of epidemics at Cádiz, Málaga and Gibraltar, he then published "Reports of the pestilential disorder of Andalusia, which appeared at Cádiz in the years 1800, 1804, 1810, and 1813" (1815).Arthur Wellesley appointed Fellowes deputy county lieutenant for Hampshire and Mrs Piozzi left Fellowes her manuscripts and copies of her writings with handwritten notes in 1821, with Fellowes becoming her literary executor.He was elected to the Royal Society of Edinburgh in 1800, the Royal College of Physicians in 1805 and the Royal Society in 1816.