The variation of tick abundance on ruminants had received little attention in West Africa before Rhipicephalus (Boophilus) microplus started to invade this region in the early 2000s. Ten years later, R. microplus was suspected to have replaced the native ticks. In addition to testing this hypothesis, this study investigated the interactions between native and invasive ticks and the relative role of climatic and geographical variables in the variations of tick community composition (beta diversity) on cattle herds. A one-year-long survey was performed in Benin and Burkina Faso during which adult ticks were collected from 144 steers from 12 localities in four different areas once a month. Morphological features were used to assign the collected ticks to different species (A. variegatum, R. annulatus, R. decoloratus, R. microplus and R. geigyi). Beta diversity analyses and generalized linear models allowed characterizing the geographical variations in species assemblage and the effect of co-infestation patterns on the seasonal variations in the abundance and incidence rates of each taxon. About 68 % (22,491/32,148) of all the adult ticks collected in one year were R. microplus. The most heterogeneously distributed taxa were Hyalomma spp and R. microplus and the lowest specific diversity was found in Central Burkina Faso. Although climatic variables did not provide any additional information on the variation in species assemblages compared with the sampling geography, adult tick abundance tended to peak during the late (Boophilus subgenus) or early (other taxa) rainy season. In most taxon-per-locality analyses, the abundance and incidence rate of a given tick taxon significantly increased when the host was co-infested by other taxa. The comparison with previous estimates (when possible) did not support the hypothesis that R. microplus invasion led to a decrease in native tick species abundance. The co-infestation patterns among native and invasive tick species are key factors for the determination of the community structure and the infestation dynamics of each tick taxon in West African cattle.

A meeting, sponsored by the Bill and Melinda Gates Foundation (BMGF) and organised by Clinglobal, was held at The International Livestock Research Institute (ILRI) in Nairobi, Kenya, from 19th – to 21st October 2022. The meeting assembled a unique group of experts on tick control in Africa. Academia, international agencies (FAO and ILRI), the private Animal Health sector and government veterinary services were represented. The significant outcomes included: (i) a shared commitment to standardisation and improvement of acaricide resistance bioassay protocols, particularly the widely used larval packet test (LPT); (ii) development of novel molecular assays for detecting acaricide resistance; (3) creation of platforms for disseminating acaricide resistance data to farmers, veterinary service providers and veterinary authorities to enable more rational evidence-based control of livestock ticks. Implementation of enhanced control will be facilitated by several recently established networks focused on control of parasites in Africa and globally, whose activities were presented at the meeting. These include a newly launched community of practice on management of livestock ticks, coordinated by FAO, an African module of the World Association for the Advancement of Veterinary Parasitology (WAAVP-AN) and the MAHABA (Managing Animal Health and Acaricides for a Better Africa) initiative of Elanco Animal Health. Graphical Abstract

Ticks and tick-borne diseases (TTBD) are constraints to the development of livestock and induce potential human health problems. The worldwide distribution of ticks is not homogenous. Some places are ecologically suitable for ticks but they are not introduced in these areas yet. The absence or low density of hosts is a factor affecting the dissemination of the parasite. To understand the process of introduction and spread of TTBD in different areas, and forecast their presence, scientists developed different models (e.g., predictive models and explicative models). This study aimed to identify models developed by researchers to analyze the TTBD distribution and to assess the performance of these various models with a meta-analysis. A literature search was implemented with PRISMA protocol in two online databases (Scopus and PubMed). The selected articles were classified according to country, type of models and the objective of the modeling. Sensitivity, specificity and accuracy available data of these models were used to evaluate their performance using a meta-analysis. One hundred studies were identified in which seven tick genera were modeled, with Ixodes the most frequently modeled. Additionally, 13 genera of tick-borne pathogens were also modeled, with Borrelia the most frequently modeled. Twenty-three different models were identified and the most frequently used are the generalized linear model representing 26.67% and the maximum entropy model representing 24.17%. A focus on TTBD modeling in Africa showed that, respectively, genus Rhipicephalus and Theileria parva were the most modeled. A meta-analysis on the quality of 20 models revealed that maximum entropy, linear discriminant analysis, and the ecological niche factor analysis models had, respectively, the highest sensitivity, specificity, and area under the curve effect size among all the selected models. Modeling TTBD is highly relevant for predicting their distribution and preventing their adverse effect on animal and human health and the economy. Related results of such analyses are useful to build prevention and/or control programs by veterinary and public health authorities.

The invasion of West Africa by Rhipicephalus microplus during the past decade has changed the ecological situation of the agent of heartwater Ehrlichia ruminantium in this area. Before, its local vector, Amblyomma variegatum, was the most abundant tick species found on livestock. Today, the abundance of the R. microplus is one magnitude higher than that of A. variegatum in many west-African localities. We investigated the potential of this new ecological situation to impact the circulation of E. ruminantium in West Africa. Ehrlichia ruminantium infections were assessed with the specific PCR-diagnosis targeting the PCS20 region. This screening was applied on field samples of 24 R. microplus adults, on four females from a laboratory strain that had been blood-fed since larvae on one E. ruminantium-infected steer as well as on the offspring of these females at egg and larval stages. The PCR detected E. ruminantium in 29 % of the field-collected R. microplus, i.e. twice as much as reported for A. variegatum with the same protocol. Regarding the laboratory strain, the PCR-diagnosis performed showed that all females were infected and passed the rickettsia to their progeny. Sequencing of the PCR product confirmed that the maternally inherited rickettsia was E. ruminantium. According to the present findings, the invasive dynamic of R. microplus in West Africa is currently impacting the local evolutionary conditions of E. ruminantium since it offers new transmission roads such as maternal transmission in R. microplus.

Sub-Saharan Africa, with its hot and humid climate, is a conducive zone for tick proliferation. These vectors pose a major challenge to both animal and human health in the region. However, despite the relevance of emerging diseases and evidence of tick-borne disease emergence, very few studies have been dedicated to investigating zoonotic pathogens transmitted by ticks in this area. To raise awareness of the risks of tick-borne zoonotic diseases in sub-Saharan Africa, and to define a direction for future research, this systematic review considers the trends of research on tick-borne bacteria, parasites, and viruses from 2012 to 2023, aiming to highlight the circulation of these pathogens in ticks, cattle, sheep, goats, and humans. For this purpose, three international databases were screened to select 159 papers fitting designed inclusion criteria and used for qualitative analyses. Analysis of these studies revealed a high diversity of tick-borne pathogens in sub-Saharan Africa, with a total of 37 bacterial species, 27 parasite species, and 14 viruses identified. Among these, 27% were zoonotic pathogens, yet only 11 studies investigated their presence in humans. Furthermore, there is growing interest in the investigation of bacteria and parasites in both ticks and ruminants. However, research into viruses is limited and has only received notable interest from 2021 onwards. While studies on the detection of bacteria, including those of medical interest, have focused on ticks, little consideration has been given to these vectors in studies of parasites circulation. Regarding the limited focus on zoonotic pathogens transmitted by ticks, particularly in humans, despite documented cases of emerging zoonoses and the notable 27% proportion reported, further efforts should be made to fill these gaps. Future studies should prioritize the investigation of zoonotic pathogens, especially viruses, which represent the primary emerging threats, by adopting a One Health approach. This will enhance the understanding of their circulation and impact on both human and animal health. In addition, more attention should be given to the risk factors/drivers associated to their emergence as well as the perception of the population at risk of infection from these zoonotic pathogens.