She worked for 33 years in East Africa, where she focused on tuberculosis and HIV/AIDS prevention and treatment, campaigns for eradication of female genital mutilation, and special schools for hearing-impaired, blind and disabled children.

[6] After "six years of service to poor people of the suburbs, to orphan children, mentally or physically disabled or abused kids" of her own town,[7] in 1969, the then 25-year-old Tonelli went to Africa supported by the Committee Against World Hunger of Forlì, that she had helped to start its activity.

After some years she studied to be a nurse too and spent over a decade in the town of Wajir caring for the destitute and ill.[6] Already in 1976, Tonelli became responsible for a World Health Organization (WHO) pilot project for treating tuberculosis in nomadic people.

[10] In 1984, following political and inter-clan clashes, the army of Kenya started a repression campaign against the Degodia Somali clan in the Wajir area known as the Wagalla Massacre.

The Kenyan military rounded up 5000 men and boys and brought them to the Wagalla Airstrip and forced them to lie on the stomachs naked for 5 days.

[11] Annalena brought a couple lorries and her Toyota Serf to the Wagalla Airstrip and attempted to collect the bodies and treat the wounded but was refused.

[6] Tonelli first settled in the southern port town of Merca, which during the colonial period was part of Italian Somaliland.

In November 2002, hundreds of protesters marched in front of her Borama hospital throwing stones and shouting "Death to Annalena."

[17] Two weeks after Tonelli's assassination, Dick and Enid Eyeington were murdered in their flat at the SOS Sheikh Secondary School in the town of Sheekh, situated in northwestern Somaliland.