Distribution and Prevalence of Anaplasmataceae, Rickettsiaceae and Coxiellaceae in African Ticks: A Systematic Review and Meta-Analysis

Abstract

In Africa, ticks continue to be a major hindrance to the improvement of the livestock industry due to tick-borne pathogens that include Anaplasma, Ehrlichia, Rickettsia and Coxiella species. A systemic review and meta-analysis were conducted here and highlighted the distribution and prevalence of these tick-borne pathogens in African ticks. Relevant publications were searched in five electronic databases and selected using inclusion/exclusion criteria, resulting in 138 and 78 papers included in the qualitative and quantitative analysis, respectively. Most of the studies focused on Rickettsia africae (38 studies), followed by Ehrlichia ruminantium (27 studies), Coxiella burnetii (20 studies) and Anaplasma marginale (17 studies). A meta-analysis of proportions was performed using the random-effects model. The highest prevalence was obtained for Rickettsia spp. (18.39%; 95% CI: 14.23-22.85%), R. africae (13.47%; 95% CI: 2.76-28.69%), R. conorii (11.28%; 95% CI: 1.77-25.89%), A. marginale (12.75%; 95% CI: 4.06-24.35%), E. ruminantium (6.37%; 95% CI: 3.97-9.16%) and E. canis (4.3%; 95% CI: 0.04-12.66%). The prevalence of C. burnetii was low (0%; 95% CI: 0-0.25%), with higher prevalence for Coxiella spp. (27.02%; 95% CI: 10.83-46.03%) and Coxiella-like endosymbionts (70.47%; 95% CI: 27-99.82%). The effect of the tick genera, tick species, country and other variables were identified and highlighted the epidemiology of Rhipicephalus ticks in the heartwater; affinity of each Rickettsia species for different tick genera; dominant distribution of A. marginale, R. africae and Coxiella-like endosymbionts in ticks and a low distribution of C. burnetii in African hard ticks.

Keywords: Africa; Anaplasma; Coxiella; Ehrlichia; Rickettsia; tick-borne disease.

Figure 1

Papers included in our analyses according to our original search.

Figure 2

Number of studies on the detection of bacteria in ticks, belonging to the families Anaplasmataceae, Rickettsiaceae and Coxiellaceae, published from 1992–2022.

Figure 3

Number of datasets grouped per the variable sample type (individual ticks vs. pooled ticks).

Figure 4

Geographic distribution of Anaplasmataceae species detected in African ticks. Countries where the pathogen was investigated, but not detected, are represented in white, while countries where the pathogen has not been investigated are represented in grey.

Figure 5

Number of tick species within each genus infected with different pathogen species.

Figure 6

Geographic distribution of Rickettsiaceae species detected in African ticks. Countries where the pathogen was investigated, but not detected, are represented in white, while countries where the pathogen has not been investigated are represented in grey.

Figure 7

Geographic distribution of Coxiellaceae species detected in African ticks. Countries where the pathogen was investigated, but not detected, are represented in white, while countries where the pathogen has not been investigated are represented in grey.

Figure 8

Relative percentage of the studies reporting infection with at least one Anaplasmataceae, Rickettsiaceae or Coxiellaceae species.

Figure 9

Choropleth maps showing the molecular prevalence of Anaplasmataceae, Rickettsiaceae and Coxiellaceae in African ticks. Only the estimates showing a significant association sampling country are here displayed. CLEs were reported only from two countries (Sao Tome and Principe and Algeria), hence their distribution is not represented here.

Figure 10

Contour-enhanced funnel plots of prevalence estimates that showed significant funnel plot asymmetry (Egger’s test p < 0.05). Solid-filled circles indicate the studies included in the original meta-analysis; empty circles indicate studies added by the trim-and-fill method to adjust for funnel plot asymmetry. (A) A. centrale; (B) A. bovis; (C) Rickettsia spp.; (D) R. aeschlimannii.