Hidden threat of tortoise ticks: high prevalence of Crimean-Congo haemorrhagic fever virus in ticks Hyalomma aegyptium in the Middle East
© Široký et al.; licensee BioMed Central Ltd. 2014
Received: 17 January 2014
Accepted: 3 March 2014
Published: 11 March 2014
It is the first time that Crimean-Congo haemorrhagic fever virus (CCHFV), causing potentially lethal disease of humans, has been reported from the Middle East region and from the tortoise tick Hyalomma aegyptium from a tortoise host, whose epidemiological significance may have remained almost completely overlooked so far. We used RT-PCR to screen for 245 ticks collected from 38 Testudo graeca tortoise individuals. Results of our genetic screening provide unambiguous evidence of occurrence of CCHFV in this region and host, suggesting a potentially important role of H. aegyptium in CCHF epidemiology.
Crimean-Congo haemorrhagic fever (CCHF) is a potentially fatal viral infection of humans with a distributional range covering the largest geographical area of all medically important tick-borne viral zoonoses . Wildlife rodents, hares and hedgehogs are the most common hosts in endemic areas, while migratory birds can spread CCHF virus (CCHFV) over long distances into new regions . Ticks of the genus Hyalomma, particularly H. marginatum, are considered principal vectors of CCHFV . Hyalomma ticks mostly feed on mammals, although pre-adult stages of some species also parasitize on birds. H. aegyptium, a three-host tick species, represents a single exception, in which the adults are host-specific, feeding on tortoises of the genus Testudo. On the other hand, larvae and nymphs show lower host-specificity and commonly infest various reptiles, small mammals, and birds. Ticks with such a wide host spectrum have greater potential for transmitting pathogenic agents among various vertebrate groups; they can thus act as “bridge vectors” and significantly contribute to spreading its natural foci. Despite this fact, ticks parasitizing reptiles have traditionally been considered epidemiologically and economically less important than ticks of mammals and birds, and as a result, they have been understudied and their vector capability may have been overlooked. However, a relationship between H. aegyptium and some important zoonotic agents has recently been suggested .
Distribution and prevalence of CCHFV-positive Hyalomma aegyptium ticks at studied localities in Syria (SY) and Turkey (TR)
Sampled tortoises/carriers of positive ticks
Krak des Chevaliers, SY
Kafr Takharim, SY
Qalat Samaan, SY
Our results revealed 30.2% (74/245) prevalence of CCHFV in studied H. aegyptium (Table 1). Interestingly, the only reptile species detected as a CCHFV antibody carrier so far, was another tortoise species Testudo horsfieldii, which, similar to T. graeca, belongs to H. aegyptium hosts. Despite these results, it remains unknown whether tortoises can serve as a reservoir of CCHFV in natural circulation or can only carry infected ticks; to resolve this it would be necessary to confirm a viremic tortoise host. However, since the pre-adult stages of tortoise tick H. aegyptium also feed on humans , this species can potentially play an important role in CCHF epidemiology, at least in the region of the Middle East.
This study was supported by the project “CEITEC – Central European Institute of Technology” (CZ.1.05/1.1.00/02.0068) from the European Regional Development Fund. Ivan Bartík assisted during the fieldwork. Anna Papa provided viral RNA for positive controls. Karolína Stratilová helped with laboratory processing of some samples.
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