Objective: To investigate the effect of pre-existing Schistosoma haematobium(S. haematobium) infection on malaria disease severity.Methods: The study involved the use of twenty-i ve imprinting control region mice, i fteen of which were initially infected with S. haematobium. Five of the remaining ten schistouninfected mice together with i ve schisto-infected mice were infected with Plasmodium berghei(P. berghei) after four weeks(acute stage) of schistosoma infection. The remaining i ve schisto-uninfected mice together with i ve schisto-infected mice were also infected with P. berghei after seven weeks(chronic stage) of schistosoma infection. The last i ve schistoinfected mice were used as control group. They were then monitored for changes in P. berghei parasitaemia on Days 3, 5, 7, 9 and 11 post-infection. Records on their survivability were also taken.Results: The co-infected mice had signii cantly higher malaria parasitaemia, compared with the mono-infected mice during acute S. haematobium infection. In contrast, the co-infected mice had signii cantly lower malaria parasitaemia during chronic S. haematobium infection and a higher survival rate.Conclusions: Co-infection of mice with P. berghei during acute S. haematobium infection resulted in rapid P. berghei development and increased malaria parasitaemia. However, the co-infection resulted in slower P. berghei development and decreased malaria parasitaemia with enhanced survivability of the mice during chronic S. haematobium infection. Therefore, pre-existing chronic S. haematobium infection may provide some protection to the host by reducing parasitaemia. Objective: To investigate the effect of pre-existing Schistosoma haematobium (S. haematobium) infection on malaria disease severity. Methods: The study involved the use of twenty-i ve imprinting control region mice, i fteen of which were initially infected with S. Five of the remaining ten schistounincted mice together with i ve schisto-infected mice were infected with Plasmodium berghei (P. berghei) after four weeks (acute stage) of schistosoma infection. The remaining i ve schisto-uninfected mice together with i ve They were then monitored for changes in P. berghei parasitaemia on Days 3, 5 , 7, 9 and 11 post-infection. Records on their survivability were also taken. Results: The co-infected mice had signii cantly higher malaria parasitaemia, compared with the mono-infected mice during acute S. haem atobium infection. In contrast, the co-infected mice had signii cantly lower malaria parasitaemia during chronic S. haematobium infection and a higher survival rate. Conclusions: Co-infection of mice with P. berghei during acute S. haematobium infection resulted in rapid P However, the co-infection resulted in slower P. berghei development and decreased malaria parasitaemia with enhanced survivability of the mice during chronic S. haematobium infection. Therefore, pre-existing chronic S. haematobium infection may provide some protection to the host by reducing parasitaemia