A countrywide molecular survey leads to a seminal identification of the invasive cattle tick Rhipicephalus (Boophilus) microplus in Cameroon, a decade after it was reported in Cote d’Ivoire

Abstract

The cattle tick Rhipicephalus microplus is the most important arthropod vector of livestock diseases globally. Since its introduction in West Africa a decade ago, it has been reported in Ivory Coast, Benin, Togo, Mali, Burkina Faso and Nigeria with potentially far-reaching adverse impacts on the livestock sector in the region. Cameroon is located on a major route for transboundary cattle trade between Central and West Africa and it is therefore at risk from R. microplus invasion. This study investigated the occurrence of R. microplus in Cameroon, the genetic polymorphism of the tick and population structure of isolates from different regions of the country to provide data that underpin the design of future vector control programs. A cross-sectional survey was conducted in which ticks were collected from cattle at 54 sites across the five Agroecological zones (AEZs) within Cameroon. Tick identity (sex and species) was assigned using taxonomic keys. Species identity was confirmed through amplification and sequencing of the mitochondrial COI and 16S rRNA genes. A total of 7091 ticks were collected out of which 1112 (15.6%) were morphologically identified as R. microplus . The presence of R. microplus was confirmed in 4 out of 5 agroecological zones. Only two haplotypes were identified by both COI and 16S rRNA genes, indicating a very low divergence in the genetic structure of the R. microplus population in Cameroon. 16S rRNA sequence analysis revealed a new haplotype specific to Cameroon. Phylogenetic trees revealed that all isolates of R. microplus from Cameroon were grouped into the previously described Africa/Americas clade. Application of a niche modelling algorithm to R. microplus distribution in Cameroon predicted that suitable habitat for the tick extended into southern Nigeria. This study demonstrated for the first time the presence of R. microplus in Cameroon. Genetic diversity tests indicate that the tick has not evolved significantly since the initial introduction to West Africa. We suggest further longitudinal studies to better define the spatial and temporal expansion of the range of the tick and the drivers of this spread.

Molecular evidence confirms occurrence of Rhipicephalus (Boophilus) microplus in Kenya and suggests that an undifferentiated genotype is prevalent in the African continent

“…Low et al, (2015) [20] reported a relatively low but signi cant genetic differentiation of R. microplus in Malaysia while in S. African a low variation within the species was observed with COI and 16S rDNA genes [38]. A similar low divergence was also recently observed in Cameroonian R. microplus ticks by Silatsa et al, (2019) [10] using the two mitochondrial genes. Low levels of genetic differentiation and lack of population structuring amongst R. microplus populations based on microsatellite markers has also been observed [38][39][40].…”

“…6). The same low divergence has also been observed with the 16S rDNA gene [10,20]. R. microplus, a one-host tick that completes its entire life cycle attached to a single vertebrate host can be classi ed as a host specialist [41].…”

“…The invasive Rhipicephalus Boophilus microplus, a highly e cient vector of tick fevers caused by Babesia bovis, Babesia bigemina, and Anaplasma marginale has rapidly spread into many African countries over the last decade [3][4][5][6][7][8][9][10][11]. In many areas, it has been reported to progressively displace, the indigenous R. decoloratus and R. annulatus [3,5,11,[32][33][34][35] sometimes establishing itself in areas predicted to be climatically unsuitable for its survival [7,32,35].…”

“…In many areas, it has been reported to progressively displace, the indigenous R. decoloratus and R. annulatus [3,5,11,[32][33][34][35] sometimes establishing itself in areas predicted to be climatically unsuitable for its survival [7,32,35]. The latest ndings of widespread occurrence of R. microplus in eastern Uganda [11] and recent introduction and spread of the tick in Cameroon [10] have been attributed to uncontrolled live animal movements from neighbouring countries and cross-border animal trade.…”

“…It was originally introduced into the African continent from southern Asia through Madagascar during the rinderpest epidemic in 1896 when R. microplus-infested cattle were imported into South Africa [2]. In the last decade it has been reported in many West African countries [3][4][5][6][7][8] and more recently in Angola [9], Cameroon [10] and Uganda [11].…”