A comprehensive survey of the prevalence and spatial distribution of ticks infesting cattle in different agro-ecological zones of Cameroon

Abstract

Background Ticks and tick-borne diseases are a major impediment to livestock production worldwide. Cattle trade and transnational transhumance create risks for the spread of ticks and tick-borne diseases and threaten cattle production in the absence of an effective tick control program. Few studies have been undertaken on cattle ticks in the Central African region; therefore, the need to assess the occurrence and the spatial distribution of tick vectors with the aim of establishing a baseline for monitoring future spread of tick borne-diseases in the region is urgent. Results A total of 7091 ixodid ticks were collected during a countrywide cross-sectional field survey and identified using morphological criteria. Of these, 4210 (59.4%) ticks were Amblyomma variegatum, 1112 (15.6%) Rhipicephalus (Boophilus) microplus, 708 (10.0%) Rhipicephalus (Boophilus) decoloratus, 28 (0.4%) Rhipicephalus (Boophilus) annulatus, 210 (3.0%) Hyalomma rufipes, 768 (10.8%) Hyalomma truncatum, and 19 (0.3%) Rhipicephalus sanguineus. Three ticks of the genus Hyalomma spp. and 33 of the genus Rhipicephalus spp. were not identified to the species level. Cytochrome c oxidase subunit 1 (cox1) gene sequencing supported the data from morphological examination and led to identification of three additional species, namely Hyalomma dromedarii, Rhipicephalus sulcatus and Rhipicephalus pusillus. The finding of the invasive tick species R. microplus in such large numbers and the apparent displacement of the indigenous R. decoloratus is highly significant since R. microplus is a highly efficient vector of Babesia bovis. Conclusions This study reports the occurrence and current geographical distribution of important tick vectors associated with cattle in Cameroon. It appears that R. microplus is now well established and may be displacing native Rhipicephalus (Boophilus) species, such as R. decoloratus. This calls for an urgent response to safeguard the livestock sector in western central Africa.

First detection of Theileria parva in cattle from Cameroon in the absence of the main tick vector Rhipicephalus appendiculatus

“…These findings are in agreement with previous studies using the same techniques (Byaruhanga et al, ; Kiara et al, ; Njiiri et al, ). As previously mentioned, this difference could be explained by more frequent transmission of T. mutans in the field, by contrast with T. parva for which the main vector is apparently absent in Cameroon (Silatsa, Simo, et al, ), and for which transmission still needs to be demonstrated, although it seems likely based on the 23% T. parva seroprevalence such transmission may occur. Furthermore, unlike T. parva , T. mutans undergoes limited lymphocytic merogony.…”

“…This could explain why most infections were detected in these areas. (Silatsa, Simo, et al, 2019b). It is, however, possible that other Rhipicephalus and Hyalomma species that are present in Cameroon for which the ability to transmit T. parva infection has been demonstrated experimentally could potentially evolve to become vectors in future (Norval et al, 1992;Theiler, 1909;Uilenberg, 1981 (Silatsa, Simo, et al, 2019b), the infected animals do not currently pose any risk of infection to naive cattle, although this situation could change in future, since certain AEZs, such as the Adamawa plateau, the western highlands and the coastal belt are climatically suitable for establishment of the major vector R. appendiculatus (Walker et al, 2003).…”

“…This is of great potential epidemiological importance since infected cattle may act as a reservoir for transmission of the disease in future if a competent tick vector either colonizes Cameroon from an adjacent country, or a novel tick species evolves the capacity to transmit T. parva . Fortunately, the major T. parva tick vector R. appendiculatus was not found in Cameroon, during a recent comprehensive survey of ticks present in all agro‐ecological zones in the country (Silatsa, Simo, et al, ). It is, however, possible that other Rhipicephalus and Hyalomma species that are present in Cameroon for which the ability to transmit T. parva infection has been demonstrated experimentally could potentially evolve to become vectors in future (Norval et al, ; Theiler, ; Uilenberg, ).…”

“…Although serology does not indicate whether T. mutans is still present in an animal, RLB indicates active infection with T. mutans which are transmitted by ticks of the genus Amblyomma . A recent study on ticks infesting cattle in Cameroon ranks Amblyomma variegatum as the most prevalent and ubiquitous tick species in Cameroon (Silatsa, Simo, et al, ). Therefore, we hypothesise that T. mutans is actively transmitted in Cameroon, due to the combined presence of host, vector and pathogen and that severe ECF is not observed in infected cattle, at least in part, because T. mutans infection decreases the pathology associated with T. parva infection.…”

Tick Cell Lines in Research on Tick Control

“…Globally, the most economically important species, the invasive Asian cattle tick Rhipicephalus (Boophilus) microplus, is also the most notorious for rapid development of resistance to every new acaricidal product brought onto the market (Jonsson and Hope, 2007;Abbas et al, 2014). Acaricide-resistant R. microplus are widespread throughout tropical and sub-tropical Asia, Latin America and Australia (Abbas et al, 2014), and are rapidly spreading in Southern, Central and West Africa (Nyangiwe et al, 2018;Silatsa et al, 2019).…”