CCHF detection in ticks
We detected CCHF virus in ticks removed from cattle destined for
slaughter at two SHs. This is the first description of CCHF virus in Rh. decoloratus ticks in Kenya, with previous studies reporting
detection only in Hyalomma ticks from the north-eastern region (Sang et
al., 2011). This suggests that other tick species besides Hyalomma spp. may be supporting the local transmission of the
virus. As the infected Rhipicephalus spp. ticks in this study
were blood-fed and collected from livestock, we also tested the blood of
the livestock from which they came from for CCHF virus, but they were
negative. Association between infected ticks and seropositivity is
common; however, ticks can also be found on seronegative animals and
vice-versa (Spengler et al., 2016). Domestic animals, especially sheep,
have been shown to be asymptomatic carriers of the virus (Spengler et
al., 2016), acting as reservoirs of infection (via ticks) to humans, who
suffer significant morbidity (Ergönül, 2006). While Hyalomma ticks are the natural vector and reservoir of CCHF virus, other tick
genera such as Rhipicephalus, have been found infected with the
virus (Fakoorziba et al., 2015; Hoogstraal, 1979). Rhipicephalus spp. have also transmitted CCHF virus in laboratory settings and have
been implicated in the transmission of CCHF virus (Balinandi et al.,
2018; Ergönül, 2006). Therefore, Rhipicephalus spp. ticks may
support transmission of the virus in areas where Hyalomma spp.
are absent. However, confirmation of this requires comprehensive
competency studies, and an understanding of the landscape epidemiology
of this virus and its transmission is in its early stages.
In Africa, there are three distinct clades of CCHF virus and the close
phylogenetic relationship between our isolates and the Nakiwogo strain
isolated in Uganda is not surprising (Ergönül, 2006; Lukashev et al.,
2016) given the geographical proximity of our study site to Uganda and
the extensive trade in live animals between the two countries. This
finding supports the circulation of a single strain of virus between the
two countries, which may be facilitated through cross-border movement of
infected livestock. At-risk groups for CCHF virus infection include
farmers, veterinarians, and abattoir and health-care workers (Cook et
al., 2017; Ergönül, 2006). CCHF outbreaks have not been reported in
Kenya since the year 2000 when a fatal case in Western Kenya showed the
possibility of the virus circulating in the region. However, Lwande et
al. (2012) found a 23% human seroprevalence of IgG antibodies to CCHF
virus in North Eastern Kenya, Infection has been reported after skin
contact with livestock, blood spatters during slaughtering, tick bites,
and when health care workers take care of haemorrhaging patients
(Ergönül, 2006). Our findings therefore highlight the potential for
human exposure to CCHF virus at these and other LMs and SHs, and at
public health facilities, and emphasise the need for routine
surveillance for this pathogen and adopting a One Health approach. Other
LM/SH-based surveillance studies in Kenya have described the occurrence
of other arboviruses in ticks, which indicates the importance of ticks
in their epidemiology (Lwande et al., 2013; Sang et al., 2011, 2006).
While most of these studies targeted pastoralist regions, our findings
demonstrate that the risk of human exposure to tick-borne arboviruses is
also present in tropical small-holder systems in East Africa.
While Hyalomma spp. ticks are the chief vectors of CCHF virus,
other species may also be important to transmission ecologies due to
co-feeding transmission between infected and non-infected ticks, even in
the absence of viraemia in the host. An infected tick may transmit a
virus to a non-infected co-feeding tick without the host having
detectable virus in its blood (Kazimírová et al., 2017). Such
non-viraemic transmission is presumed to contribute to amplification of
CCHF virus in nature because the virus can be transmitted among ticks
even without detectable viraemia in the host (Bente et al., 2013).