Tick-Borne Diseases in Sub-Saharan Africa: A Systematic Review of Pathogens, Research Focus, and Implications for Public Health

Abstract

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.

Keywords: pathogens; public health; research; sub-Sahara Africa; systematic review; tick-borne diseases.

Figure 1

PRISMA flow diagram.

Figure 2

Number of studies according to types of pathogens.

Figure 3

Pathogens studies according to target population. Legend: “Screened” refers to the total number of studies that investigated the presence of each pathogen, regardless of whether the pathogen was detected or not. “Detected” indicates the number of studies in which the pathogen was actually detected.

Figure 4

Temporal evolution of studies on tick (A), animal (B), human (C), and combined (D) target populations.

Figure 5

Venn diagram of screened (A) and detected (B) pathogens in animals, ticks, and humans. Legend: “Screened” refers to the total number of studies that investigated the presence of each pathogen, regardless of whether the pathogen was detected or not. “Detected” indicates the number of studies in which the pathogen was actually detected.

Figure 6

Bacteria (A), parasite (B), and virus (C) families according to tick genus. Legend: “Screened” refers to the total number of studies that investigated the presence of each pathogen, regardless of whether the pathogen was detected or not. “Detected” indicates the number of studies in which the pathogen was actually detected.

Figure 7

Methods used to detect a domain’s pathogens in ticks (A), animals (B), and humans (C). Legend: This figure represents the number of times each method has been used to detect pathogens belonging to each pathogen domain (bacteria, parasites, and viruses) in ticks (A), animals (B), and humans (C). The various methods include the following: cPCR: conventional polymerase chain reaction; cPCR+sequencing: conventional polymerase chain reaction followed by the sequencing of the positive amplicons; nPCR: nested polymerase chain reaction; nPCR+sequencing: nested polymerase chain reaction followed by the sequencing of the positive amplicons; qPCR: quantitative polymerase chain reaction; qPCR+sequencing: quantitative polymerase chain reaction followed by the sequencing of the positive amplicons; RT_PCR: reverse transcription polymerase chain reaction; nRT_PCR: nested reverse transcription polymerase chain reaction; RT_PCR+sequencing: reverse transcription polymerase chain reaction followed by the sequencing of the positive amplicons; RT_qPCR: reverse transcription quantitative polymerase chain reaction; HRM_PCR: high-resolution melting polymerase chain reaction; HRM_PCR+sequencing: high-resolution melting polymerase chain reaction followed by the sequencing of the positive amplicons; LAMP: loop-mediated isothermal amplification; RLB: reverse line blot hybridization assay; and Metagenomic.

Figure 8

Distribution of tick-borne zoonotic bacteria and parasites in ticks (A), animals (B), and humans (C). Legend: These figures illustrate the geographical distribution and frequency of studies reporting the presence of zoonotic bacterial and parasitic agents transmitted by ticks in ticks (A), animals (B), and humans (C) in sub-Saharan Africa. Each pathogen is represented by a distinct color. The pie charts superimposed on the different countries indicate the frequency of studies reporting each pathogen in each country. The underlying map shows the average density of the ruminant population (cattle, sheep, goats) between 2012 and 2022, based on FAO statistics [36]. The density is expressed as the number of animals per square mile.

Figure 8

Distribution of tick-borne zoonotic bacteria and parasites in ticks (A), animals (B), and humans (C). Legend: These figures illustrate the geographical distribution and frequency of studies reporting the presence of zoonotic bacterial and parasitic agents transmitted by ticks in ticks (A), animals (B), and humans (C) in sub-Saharan Africa. Each pathogen is represented by a distinct color. The pie charts superimposed on the different countries indicate the frequency of studies reporting each pathogen in each country. The underlying map shows the average density of the ruminant population (cattle, sheep, goats) between 2012 and 2022, based on FAO statistics [36]. The density is expressed as the number of animals per square mile.

Figure 9

Distribution of tick-borne viruses. Legend: The figure illustrates the geographical distribution and frequency of studies reporting the presence of viruses transmitted by ticks in in sub-Saharan Africa. Each virus is represented by a distinct color. The pie charts superimposed on the different countries indicate the frequency of studies reporting each virus in each country. The underlying map shows the average density of the ruminant population (cattle, sheep, goats) between 2012 and 2022, based on FAO statistics [36]. The density is expressed as the number of animals per square mile. The red stars indicate a zoonotic virus; BDTPV: Brown dog tick phlebovirus; BOGV: Bogoria virus; PERV: Perkerra virus; JMTV: Jingmen tick virus; BPSV: Bovine papular stomatitis virus; PCPV: Pseudocowpox virus; KPTV: Kaptombes virus; BTV: Balanbala tick virus; BoTV: Bole tick virus.