MÁS DATOS SOBRE LA «FIEBRE HEMORRÁGICA CRIMEA-CONGO». Vector : la Garrapata

Genus Hyalomma (Bont-leg ticks)

Identification: Unfed Hyalomma ticks are large at 5 to 6mm including mouthparts. The integument texture has striations. The mouthparts are anterior and palp article 2 are longer than articles 1 and 3. The basis capituli has medium angular lateral margins. Eyes are always very convex. The scutum /conscutum are coloured brown. Enamel is usually absent. The slender legs usually have pale rings and pulvilli pulvilli are always present. Festoons Festoons are present in both sexes but are unclear in females when fed. Spiracular plates Spiracular plates are large and posterior to legs, and ventral plates are present in males only. The anal groove is posterior to the anus. Coxae 4 are of normal size and coxae 1 have large and equal paired spurs.

Dorsal view of female and male Hyalomma anatolicum excavatum
Photo: Alan Walker

There are about 30 species of Hyalomma which are found in Asia, Europe and Africa. Many have a 3-host life cycle but some have either a 1-host or 2-host life cycle. They may be the most abundant tick parasites of livestock in warm arid and semi-arid habitats. Several are of considerable veterinary or public health importance. The primarily Asian and North AfricanHyalomma anatolicum transmits the causative agents of a wide range of animal diseases as well as the human-infective Crimean-Congo haemorrhagic fever. Other important disease vectors are Hyalomma detritum and Hyalomma marginatum.

 

Hyalomma rufipes (= Hyalomma marginatum rufipes) (Hairy bont-legged tick)

Identification: Both sexes have the scutum/conscutum dark and have legs with pale rings. In the male the cervical fields depression is not apparent and the lateral grooves are short. Posterior ridges are absent and a caudal depression is absent. The central festoon is dark coloured. The posteromedian and paramedian grooves are absent. Punctation are small and dense. In the female the scapular grooves profile is steep and the scutum posterior margin is distinctly sinuous. The genital aperture posterior lips have a broad V shape. The adanal plates have square ends.

Dorsal view of male Hyalomma rufipes
Photo: Alan Walker

Hyalomma rufipes has been recorded from a wide range of habitats and climatic regions from desert to rain forest. It has an extensive distribution in Africa, southern Europe and through to central Asia. The wide distribution probably results from the dispersal of birds infested with the immature stages of this tick.

Hyalomma rufipes is a two host tick. The larva attaches to the first host (a bird), feeds, and then moults to a nymph while on the host. After engorgement at the nymphal stage, the ticks drop off from the bird and moult on the ground before attaching to their second and final host which is usually a large mammal.

This tick is the most important vector in southern Africa of the virus causing Crimean-Congo haemorrhagic fever in humans. It also transmits the bacterium Anaplasma marginale to cattle causing bovine anaplasmosis, the bacterium Rickettsia conorii causing tick typhus in humans and the protozoan Babesia occultans to cattle. The feeding of adults on cattle causes large lesions at the attachment sites, leading to the formation of severe abscesses.

Hyalomma impeltatum

Identification: Both sexes have the scutum/conscutum dark and have legs with pale rings. In the male the cervical fields depression is apparent but small and the lateral grooves are long. There are two posterior ridges and a caudal depression is present. The central festoon is pale coloured (this is more obvious in the picture of ticks feeding immediately below these). The posteromedian groove is present and long and paramedian grooves are large. Punctation size is large and punctuations are localized on the cervical fields and lateral grooves; punctations may be numerous around the caudal depression. In the female the scutum posterior margin is distinctly sinuous. The scapular grooves profile is shallow and is marked by columns of punctations and a rough surface. Punctation size is large and the punctations are localized on the scapulae and at scapular grooves. The genital aperture posterior lips have a narrow V shape, and the adanal plates have square ends.

 

Male (left) and female (right) Hyalomma impeltatum
Photos: InfluentialPoints (Joel Kanunga)

Hyalomma impeltatum is a dry country species found in Mediterranean, steppe and desert climates. It is found widely through North Africa including along camel trade routes through the Sahara desert. It is also found in Sudan, Eritrea, Somalia, northern Kenya, northern Tanzania, Chad and the Middle East.

Hyalomma impeltatum is a three-host tick. The immature stages of Hyalomma impeltatum feed on small animals like rodents, hares and ground birds. The adults feed on wild ungulates as well as large domestic animals, particularly cattle on which high infestations are recorded. Camels are also commonly infested. The picture below shows a group of male and female Hyalomma impeltatum ticks feeding on a zebu cow in south-west Kenya.

Hyalomma impeltatum feeding on cow in Kajiado District, Kenya
Photos: InfluentialPoints (Joel Kanunga)

Two other Hyalomma species (H. truncatum and H. rufipes) are found commonly in the area, but we can see that these are Hyalomma impeltatum from the white central festoon which is diagnostic for this species.

It is still not clear whether Hyalomma impeltatum should be considered as an important disease vector. It certainly can transmit Theileria annulata to cattle, and has been implicated as the main vector of malignant theileriosis caused by Theileria hirci in sheep (El Azazy et al., 2001 ). On human diseases, Al-Khalifa et al (2007) has shown that Hyalomma impeltatum is infected with two other viruses transmissible to man, Sindbis virus and Dhori virus. It has also been shown that it can transmit the virus of Crimean-Congo haemorrhagic fever to humans. However Camicas et al. (1990)  note this is unlikely to be of much epidemiological importance because of the rarity of human infestation by adult ticks.

 

Engorged Hyalomma impeltatum female removed from cow (left), and ticks impaled on Acacia thorn in Kenya (right)
Photos: InfluentialPoints (Joel Kanunga)

Being a large common tick the direct blood loss effect is probably important, and certainly pastoralist livestock keepers remove them from cattle when present. The first picture above shows an engorged female Hyalomma impeltatum removed from a cow in south-west Kenya. Disposing of removed ticks can be more difficult as they are quite resistant to squashing, so Maasai livestock keepers often impale them on Acacia thorns as shown in the second picture. The alternative method is a large rock!

Acknowledgements Whilst we try to ensure that identifications are correct, we do not warranty their accuracy. We have mostly made identifications using Walker (2001).  We fully acknowledge this author as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections.

References  Al-Khalifa, M.S. et al. (2007). Man-threatening viruses isolated from ticks in Saudi Arabia. Saudi Medical Journal 28 (12), 1864-1867. Abstract   Camicas, J.-L. et al., (1990). Ecology of ticks as potential vectors of Crimean-Congo hemorrhagic fever virus in Senegal: epidemiological implications. Archives of Viro1ogySuppl 11, 303-322. Abstract   El-Azazy, O.M.E. et al. (2001). Hyalomma impeltatum (Acari: Ixodidae) as a potential vector of malignant theileriosis in sheep in Saudi Arabia. Veterinary Parasitology 99, 305-309. Full text   Walker, A.R. (2001). Ticks of domestic animals in Africa: a guide to identification of species. Bioscience Reports. Full text

Last updated 3 January 2013