Wild animals may be responsible for the continuing spread of African sleeping sickness, scientists have claimed.

The West African form of the sleeping disease, also known as Gambiense Human African trypanosomiasis affects around 10,000 people in Africa every year and can be fatal if left untreated.

The disease is caused by a parasite that invades the human brain. The parasite in transmitted by bites of the tsetse fly. The sleeping sickness gets its name from hallmark symptoms of drowsiness and altered sleeping patterns that affect late-stage patients. Other physical and neurological symptoms include manic episodes and hallucinations that can eventually lead to coma and death.

While past studies revealed that animals could also be infected with the parasite, most still believe that the disease persisted in its traditional areas mostly because of human-to-human transmissions.

However, a new study published in the journal PLOS Computational Biology challenges the general assumption. After using a mathematical model, researchers from the London School of Hygiene and tropical Medicine found that the disease can persist in the area even when there are no human cases. Furthermore, the model revealed that the disease would only need the presence of infected wild animals to maintain the chain of transmission.

The model used in the latest study was based on data collected in active screening campaigns between 1998 and 1999 in the Bipindi area of Cameroon.

Researchers say that the latest findings can explain why sleeping sickness manages to survive in places that have undergone intensive efforts to find and treat infected people in the community.

The study suggests that efforts to eliminate the disease must also factor in the wild animal populations.

"This research suggests that targeting human populations alone, the main current control strategy, might not be enough to control the disease," lead researcher Sebastian Funk said in a statement. "Maintenance of transmission in wild animal populations could explain the reappearance of sleeping sickness in humans after years without cases."