Hard ticks (Acari: Ixodidae) and tick-borne diseases of sheep and goats in Africa: A review

Ticks are leading vectors of economically important pathogens that affect small ruminants due to favourable climatic conditions across different regions of the African continent. They are responsible for both direct and indirect economic losses in the livestock industry. This review focuses on the species diversity of hard ticks, their biology, tick-borne diseases of sheep and goats including non-infectious disease, and risk factors to tick infes-tation in Africa. Furthermore, our review provides recent updates on distribution of ticks and tick-borne path-ogens of small ruminants in Africa. It was observed that several species and subspecies of hard ticks belonging to the genera Hyalomma (Hy), Rhipicephalus (Rh), Ixodes (I) and Amblyomma (Am) were found infesting small ru-minants across the different regions of the continent. Of these genera, Rhipicephalus ticks accounts for the ma-jority of the registered species, with exactly 27 different species infesting small ruminant stocks comprising of different developmental instars and adults of the tick. Rhipicephalus decolaratus, Rh. e. evertsi and Rh. appendi-culatus were the three most common Rhipicephalus species reported. Both protozoal (Babesia and Theileria) and bacterial (Anaplasma, Rickettsia, Ehrlichia, Coxiella and Mycoplasma) pathogens have being reported to be amplified in several hard tick species and/or small ruminant hosts. Furthermore, tick paralysis and lameness were non-infectious conditions attributed to tick infestations. Amblyomma hebraeum and Rh. glabroscutatum may cause lameness in goats, while Hy. rufipes is responsible for the same condition in Merino sheep. Host paralysis due to a neurotoxin released by female Rh. e. evertsi and I. rubicundus has been documented within the continent. We therefore advocate for the need of integrated control measures against tick-borne pathogens (TBPs) including their arthropod vectors, to be performed simultaneously to ease the burden of vector-borne diseases in small ruminant production.

Automated summary

Ticks are significant vectors of economically important pathogens affecting small ruminants in Africa. This review focuses on the diversity of tick species, tick-borne diseases, and risk factors in Africa. Various species of hard ticks belonging to the genera Hyalomma, Rhipicephalus, Ixodes, and Amblyomma were found infesting small ruminants. Tick-borne protozoal and bacterial pathogens have been reported, as well as non-infectious conditions like tick paralysis and lameness. Integrated control measures are necessary to alleviate the burden of vector-borne diseases in small ruminant production.