Screening of Trypanosoma brucei gambiense in Domestic Livestock and Tsetse Flies from an Insular Endemic Focus (Luba, Equatorial Guinea)

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Abstract
Sleeping sickness is spread over 36 Sub-Saharan African countries. In West and Central Africa, the disease is caused by Trypanosoma brucei gambiense, which produces a chronic clinical manifestation. The Luba focus (Bioko Island, Equatorial Guinea) has not reported autochthonous sleeping sickness cases since 1995, but given the complexity of the epidemiological cycle, the elimination of the parasite in the environment is difficult to categorically ensure. The aim of this work is to assess, by a molecular approach (Polymerase Chain Reaction, PCR), the possible permanence of T. b. gambiense in the vector (Glossina spp.) and domestic fauna in order to improve our understanding of the epidemiological situation of the disease in an isolated focus considered to be under control. The results obtained show the absence of the parasite in peridomestic livestock but its presence, although at very low rate, in the vector. On the other hand, interesting entomological data highlight that an elevated concentration of tsetse flies was observed in two out of the ten villages considered to be in the focus. These findings demonstrate that even in conditions of apparent control, a complete parasite clearance is difficult to achieve. Further investigations must be focused on animal reservoirs which could allow the parasites to persist without leading to human cases. In Luba, where domestic livestock are scarcer than other foci in mainland Equatorial Guinea, the epidemiological significance of wild fauna should be assessed to establish their role in the maintenance of the infection. Sleeping sickness is a neglected disease with an important impact on public health of many countries of Sub-Saharan Africa. It is transmitted by tsetse fly bites (the vector) and mainly affects remote and rural populations. The chronic form, caused by Trypanosoma brucei gambiense, includes almost 90% of reported cases, and it is often misdiagnosed or lately detected after months or years of infection. Many efforts have been carried out to control the disease and interesting advances have been achieved. Although elimination is considered possible, there is an urgent need to understand the disease dynamic, especially in foci with very low rate (or absent) of infection for a long time. We performed a parasite screening in tsetse flies and livestock from Luba focus (Equatorial Guinea), considered to be “controlled” since 1995 (no human cases for fifteen years). The obtained results demonstrate that T. b. gambiense still remains in the environment and entomological data reveal high population density of the vector in some localities. This finding suggests that other intervention ways focused on control of vector populations, combined with the detection of human cases, could be necessary to achieve the total elimination of the parasite in hypoendemic foci.