INTRODUCTION
Tick-borne pathogens have been identified as the etiologic agents of
emerging important human diseases especially in many tropical countries
in Africa, Asia and South America (Parola et al., 2013). In many
sub-Saharan Africa countries, these diseases are rampant in rural
communities where there are frequent contacts between humans and
domestic animals that are hosts to these ticks (Parola et al., 2013;
Raoult and Roux, 1997). Rickettsioses are zoonotic diseases that are
caused by some pathogenic Rickettsia spp. They are one of the
oldest known vector-borne zoonotic diseases whose severity varies from
one etiologic agent to another. There are many recognized species ofRickettsia that are delineated into four major groups namely; the
typhus group consisting of two species which are R.typhi andR.prowazekii, the spotted fever group which contains many species
that are wholly transmitted to humans through ticks bite, the
transitional group comprising of R.australis , R.
akari and R.felis that are associated with ticks, mites and
fleas and the ancestral group made up of R.bellii and R.canadensis . Beside these groups, there are also many otherRickettsia species that do exist but have not been fully
characterized (Raoult and Roux, 1997; Bogovic et al., 2016). The current
guidelines for the classification, delineation and description of novel
rickettsial isolates are based on the 16S rRNA gene, the differences in
nucleotide sequence of glt A, omp A, omp B, and the D
genes that encodes for essential proteins in the organisms (
Portillo et
al., 2017). The global distribution of tick-borne rickettsioses varies
from one region to the other as their geographical spread are determined
by their ticks vectors whose distributions are generally governed by
suitable environmental conditions like relative temperatures, humidity
and biotopes which varies from one region to the other (Socolovschi et
al., 2009; Tomassone et al., 2018).
Members of the genera Amblyomma, Hyalomma, Rhipicephalus, Ixodes,
Dermacentor and Haemaphysalis are the species of tick that are
generally involved in the transmission of tick-borne rickettsioses in
the tropical regions of the world. Transmission of tick-borne
rickettsioses could be either transstadial or transovarial transmission
thus making some tick species such as Amblyomma to be a known
reservoir of R. africae (Tomassone et al., 2018). In the Eastern
Cape of South Africa, the most common species of ticks are members of
the genera; - Amblyomma, Rhipicephalus, Haemaphysalis, andHyalomma (Iweriebor et al., 2017; Yawa et al., 2019) and all
these ticks’ genera have the ability to transmit one or multitudes of
zoonotic pathogens. While most tick-borne pathogens are linked to known
tick vectors, it is possible in some cases for an etiologic agent of a
particular disease to be indeterminate.
Members of the SFG of the genus Rickettsia are the etiologic
agents of tick-borne rickettsioses a group of diseases that its ticks
vectors and clinical severity varies from one geographic location to
another (Tomassone et al., 2018). The epidemiological and clinical
attributes of tick-borne diseases are tied to the ecology and biotopes
of their tick vectors (Tomassone et al., 2018) as each of these diseases
are confined to different geographical regions though their distribution
and redistribution keep varying overtime as well as the species of ticks
that transmit them. Prior to the development of molecular approaches
which are highly selective and sensitive in disease diagnoses, severalRickettsia spp. had been detected in ticks but their roles in the
etiology of disease in humans were unrecognized. However, in recent
times such species that were previously thought innocuous have now been
directly linked to the etiology of human diseases (Parola et al., 2005;
Bogovic et al., 2016).
The Eastern Cape of South Africa is predominantly rural with intensive
animal husbandry where the animals are kept in close proximity to homes.
Couple with this is that there are many game reserves where these
animals are in close contact with those in the wild. There exist great
possibilities of these domesticated animals being infested with ticks
from those originating from the wild thus making the spread of zoonotic
pathogens possible in these localities. Also, with the very high
prevalence of HIV/AIDS in these rural communities, the chances of these
immunocompromised patients coming down with zoonotic infections are
equally very probable as they lack the competent immune system that
ordinarily fights off these infections in healthy folks. Besides, most
of the SFGR infections present with symptoms that are very much similar
to flu and could thus be misdiagnosed by clinicians who might not
consider them as top priority in diagnoses and treatments due to lack of
laboratory diagnosis prior to commencement of treatments. This study
therefore, was aimed at epidemiological surveillance for tick-borneRickettsia pathogens in ticks collected from domesticated animals
in communities which are close to natural game reserves and human
habitations in order to assess the likelihood of zoonotic diseases in
humans who might be infested with ticks.