Hyalomma species

The ixodid tick species of the genus Hyalomma (giant tick) are of great medical and veterinary importance in terms of health and economic impact in tropical and subtropical regions (Bakheit MA et al. 2012).

The natural distribution of Hyalomma species is restricted to the Asian, African and European continents (Sands et al. 2017). Of the 27 valid Hyalomma species, five species are widespread and recorded on all three continents, seven species are restricted to Asia, five to Africa, nine to Asia-Africa and one to Africa-Europe. Recently, Hylommma species have also been recorded in Germany. They were probably introduced to Germany by migratory birds. According to the Robert Koch Institute (RKI), the first specimens were discovered in 2007. In 2018, a large number of these tropical ticks were documented in Germany for the first time. In 2024, a large number of Hyalomma marginatum were reported in northern Italy (Friuli-Veneto). Many Hyalomma species have been recorded in humans and are considered zooanthrophilic, i.e. they occasionally infest humans. Apart from many unreported cases of tick bite reactions by Hyalomma ticks, some cases are well documented, namely by H. marginatum (Keirans JE et al. 2001) and H. truncatum (Mathison BA et al.2015).

Note: As Hyalomma species are not native to Germany and Italy, they may not be considered in the differential diagnosis by physicians, diagnostic microbiologists and parasitologists when identifying ticks removed from patients treated in the USA. Due to their morphological characteristics (elongated mouthparts, eyes present, festoons present), they are often misidentified as Amblyomma. Many Hyalomma species have a characteristic striation of the legs, the legs being dark with white spots at the joints.

Note: As with other ectoparasites, a detailed travel history may be important to obtain a definitive diagnosis of ticks and to assess the risk of vector-borne diseases.

About 50 % of the species can infect and transmit pathogens, mainly the Crimean-Congo hemorrhagic fever (CCHF) virus in humans and Theileria annulata in cattle (theilerosis). Apart from these, Hyalomma species are also known to maintain and transmit many other viruses, bacteria and protozoan pathogens to animals and humans.

Case report- (Mathison BA et al. 2015): A previously healthy 59-year-old man presented to his GP's surgery after discovering a tick on his lower back the previous day. He initially thought the tick was a skin bite and carefully removed it. After identifying it as a possible tick, he placed it in a plastic bag with a moistened napkin and put it in the fridge. The patient had returned from a photography trip to Ethiopia, where he had visited several rural towns and villages about five days before the performance. After returning to the US, he had spent some time in California, but had not hiked or camped. The patient reported a self-limiting headache the day before and chills during the return flight. Otherwise, he was asymptomatic and had no arthralgias or myalgias. On examination, the patient was afebrile and appeared healthy. The area around the puncture site was raised, firm and tender, surrounded by a reddened, concentric rash 3 cm in diameter. The case was discussed by telephone with the local infectious disease specialist. Given the patient's mild symptoms, serology was not recommended unless the symptoms worsened. Due to the risk of rickettsial infection from this tick species, the patient was treated with 100 mg doxycycline twice daily for a total of 21 days.

Ticks and tick-borne diseases (TTBDs) are the biggest barriers to increasing livestock productivity globally, with the threshold being much higher in developing countries. The cumulative global losses resulting from the control of TTBDs are estimated at 22-30 billion US dollars per year (Kumar B et al. 2020). The direct effects of tick infestations on hosts include pyaemia, toxicosis and paralysis, which are estimated to cause a cumulative loss of USD 500 million annually. In addition, production losses due to tick infestation in terms of growth and milk production have been estimated at 8.9 ml of milk or 1 g live weight gain per attached female tick per day.

Anyone who finds a conspicuous "giant tick" should send it to the Robert Koch Institute, ZBS 1, keyword "tick", Seestraße 10, 13353 Berlin, for documentation.

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