Identification and distribution of Rhipicephalus microplus in selected high- cattle density districts in Uganda
Authors: Etiang Patrick , Atim Stella A , Nkamwesiga Joseph , Nalumenya David , Byaruhanga Charles , Odongo Steven , Vudriko Patrick , Ademun Anna Rose , Biryomumaisho Savino , Erume Joseph , Masembe Charles , Thomson Emma C , Muhanguzi Dennis , Tweyongyere Robert 
Published: December 2023

Background: Rhipicephalus (Boophilus)microplus (Canestrini, 1888), the Asian blue tick, is a highly invasive and adaptable ectoparasite. It has successfully established itself in most regions of the world, with movement of cattle being a major driver for its spread. In the recent past, R. microplus ticks have been reported in three districts of Uganda. Information on its spread and distribution are vital in deepening our understanding of the ecological scenarios that lead to tick persistence and in the formulation of control strategies. This is especially important in the cattle-dense districts.
Methods: We randomly collected tick specimens from 1,461cattle spread across seven cattle dense districts located in the Central, Karamoja and West Nile regions of Uganda from January to September 2020. The ticks were identified using standard morpho-taxonomic keys and the R. microplus tick species identities were confirmed by sequencing of the ITS2 region, 12S rRNA and 16S rRNA genes and phylogenetic analyses.
Results: Adult ticks (n = 13,019) were collected from 1,461 cattle. Seventeen tick species were identified and the majority (47.4%; n=6184) of these were R. appendiculatus. In total, 257 R. microplus ticks were found infesting cattle in 18 study sites in the districts of Amudat, Kaabong, Napak (Karamoja region) and Arua (West Nile region). No R. microplus tick was recorded in the districts of Lyantonde and Nakaseke (Central region). Arua District accounted for 82.1% (n=211) of the R. microplus ticks recorded followed by Napak District at 16.3% (n=42), while Amudat and Kaabong Districts accounted for 1.5% (n=4).
Rhipicephalus microplusand R. decoloratus co-existed in 6 of the 13 study sites in Arua District, while in another 6 study sites, no R. decoloratus was recorded. In the Karamoja region districts R. decoloratusco-existed with R.microplus. Of the total 618 ticks belonging to four species of the subgenus Boophilus recorded in this study, R. decoloratus accounted for 50.04% (n=334), followed by R. microplus at 41.58% (n=257), R. geigyi at 2.75% (n=17) and R. annulatus at 1.61% (n=10). In the districts of Amudat, Kaabong and Napak, R. decoloratuswas more dominant (76.1%; n=179) of the three Rhipicephalus (Boophilus) species recorded, followed by R. microplus (19.5%; n=46) and R. geigyi(4.2%; n=10). Contrariwise, R. micropluswas more dominant (84%; n=211) in Arua District followed by R. decoloratus (10.7%; n=27), R. annulatus (3.9%; n=10) and R. geigyi (1.1%; n=3). Phylogenetic analyses of the ITS2 region, 12S rRNA and 16S rRNA genes revealed subgrouping of the obtained sequences with the previously published R. microplus sequences from other parts of the world.
Conclusion: Rhipicephalus microplus ticks were found infesting cattle in four additional districts of Uganda. The absence of R. decoloratus, an indigenous tick, in six sites in Arua District probably suggests its displacement by R. microplus. Rhipicephalus microplus negatively affects livestock production, and therefore, there is a need to determine its distribution and molecular characteristics so as to deepen the understanding of the ecological factors that lead to its spread and persistence in an area.