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Genus Amblyomma

Unfed Amblyomma ticks are large at 6 to 7mm in length including mouthparts. The mouthparts are anterior and palp article 2 is longer than article 1 and 3. The basis capituli (basal part of the mouthparts) has straight lateral margins. The slender legs usually have pale rings and pulvilli are always present. A scutum (dorsal shield) is present in the female with a conscutum in the male. Enamel is present on the scutum and conscutum of many species. The colour of the enamel is predominantly pink to orange, or orange to red. Eyes are always present and may be flat or convex. Festoons (wrinkles in the posterior margin) are present in both sexes, but unclear in fed females. Spiracular plates are large and posterior to legs. Ventral plates in males are indistinct. The anal groove is posterior to the anus. Coxae 4 are of normal size and coxae 1 have unequal paired spurs.

 

Amblyomma americanum (Lone Star Tick) male and female
Photos: Courtesy of Centres for Disease Control (James Gathany).

There are over 130 species of ticks in the genus Amblyomma. Most live in hot climates, occupying a range of habitats. The early stages may feed on birds, rodents or reptiles, but adults mainly feed on larger mammals. The genus Amblyomma includes important disease vectors. Diseases transmitted to man or domestic animals include Rocky Mountain spotted fever caused by Rickettsia rickettsii, ehrlichiosis and anaplasmosis. We concentrate on three African species below. Amblyomma gemma which has recently been found to be a major reservoir of viral livestock diseases, Amblyomma hebraeum and Amblyomma variegatum which is a major pest worldwide.

 

Amblyomma gemma

Both sexes have the primary punctation on the scutum/conscutum localized between the eyes. The eyes are flat and close to the margin of the scutum/conscutum. Enamel ornamentation is pink to orange and the legs have pale rings. In the male (pictured below) the conscutum has extensive ornamentation with the mesial area elongate, and the lateral median areas large and complex. Festoon enamelling is partial occurring on only 6 of the 11 festoons. The posteromedian stripe is broad and usually joins with the falciform stripe which runs transversely below the mesial area of enamel. In the female (not pictured here) the mesial and lateral areas of pink to orange enamel ornamentation on scutum are large. There are fine connections between the central and lateral spots. The scutum sides are straight and the scutum posterior angle is broad. The genital aperture posterior lips have a narrow V shape.

Side view of male Amblyomma gemma
Photo: InfluentialPoints (Joel Kanunga).

This tick has been recorded from areas with climates ranging from temperate (highland), through steppe to desert but it is especially associated with arid zones. It is mainly distributed in eastern Ethiopia, northern and southern Somalia, Kenya and north-eastern Tanzania.

Amblyomma ticks are easy to distinguish from most other genera by the presence of often elaborate ornamentation on the scutum or conscutum. It is not always so easy to distinguish the species of Amblyomma because they show a fair degree of within species variability. For example the tick below is from the same locality as that shown above, but the distributions of cream and orange enamel are rather different.

Dorsal view of male Amblyomma gemma
Photo: InfluentialPoints (Joel Kanunga).

Nevertheless we can confirm this tick as A. gemma because the eyes are flat and (more visibly) in males the posteromedian stripe joins with the falciform stripe - unlike in the other Amblyomma species which occur in East Africa (Amblyomma lepidum and Amblyomma variegatum).

The preferred hosts of Amblyomma gemma are large herbivores such as giraffes and buffaloes, but adults will also feed on domestic animals such as cattle and camels. It shows marked seasonal changes in abundance with highest numbers found during and shortly after the main rains. The ticks pictured here were found on the cattle shown above in Kajiado District, Kenya towards the end of the rainy season when there was abundant grass.

Cattle grazing in Kajiado District, Kenya during main rains.
Photo: InfluentialPoints (Joel Kanunga).

Various other studies have recorded Amblyomma gemma on cattle in East Africa. Pegram et al (1981)  found 33 species and subspecies of ticks on cattle in Ethiopia with Amblyomma gemma common in drier eastern areas. Regassa (2001)  also in Ethiopia found that about 5% of the tick on cattle were Amblyomma gemma. He suggested that control should aim to reduce the Rhipicephalus pulchellus  burdens whilst allowing a reasonable number of ticks to remain on cattle for the maintenance of endemic stability to tick-borne diseases.

Amblyomma gemma has until recently been considered unimportant to the health of domestic animals. However, Sang et al. (2006))   have recently demonstrated that in arid areas this species of tick is primarily responsible for the maintenance and transmission of number of cattle and/or human-infective tick-borne viruses.

 

Amblyomma hebraeum (South African Bont Tick)

Identification:Both sexes have the primary punctation on the scutum/conscutum localized between the eyes. The eyes are slightly convex and close to the margin of the scutum/conscutum. Enamel ornamentation is pink to orange and the legs have pale rings. Enamel ornamentation is pink to orange and the legs have pale rings. In the male (pictured below) the mesial area of enamel ornamentation on conscutum is elongate, and lateral median areas of enamel ornamentation on conscutum are large and complex. Festoon enamelling is extensive covering all but the two outermost festoons. The posteromedian stripe is narrow only rarely reaching the falciform stripe. The female (not pictured here) has the mesial area of enamel ornamentation on scutum large and elongate and the lateral areas are large and complex. The scutum sides are convex and the scutum posterior angle is broad. The genital aperture posterior lips have a narrow V shape.

Amblyomma hebraeum male
Photo: USDA Agricultural Research Service (Mat Pound)

Amblyomma hebraeum lives in moderately humid warm savannas in southern Africa.

Adult ticks prefer to feed on large hosts such large hosts such as giraffes, buffaloes, elands and cattle. They will also infest sheep and goats. Preferred feeding sites are the hairless areas under the tail, in the lower perineal region, on the udder and around the genitalia. On sheep and goats they are also found around the feet. The immature stages feed on the same hosts as the adults and also on small antelopes, scrub hares, helmeted guineafowls, and tortoises.

There have been a number of studies on the ecology of, and disease transmission by, Amblyomma hebraeum. On the ecology Norval (1977)  found that larvae of Amblyomma hebraeum Koch occur in well-drained, shaded habitats, with a ground cover of grass. The life cycle is normally of 3 years duration. Bryson et al. (2000)  found these ticks could be sampled effectively with pheromone/ carbon dioxide traps.

Amblyomma hebraeum is one of the main vectors responsible for the transmission of Ehrlichia ruminantium (= Cowdria ruminantium), the cause of heartwater in cattle, sheep and goats and some wild antelope species. This tick also transmits the bacteria Rickettsia africae and Rickettsia conorii, causing tick bite fever in humans, and the protozoan Theileria mutans which causes benign theileriosis in cattle. The bite sites may become infected with bacteria which results in foot abscesses in sheep and goats. The wounds caused by the mouthparts are also attractive to the blowfly Chrysomya bezziana and the larvae of this fly can cause severe myiasis. Norval (1989)  found that there was a direct effect of tick feeding on weight gain of animals - heavily infested cattle had a large and significant lower weight gain than uninfested cattle.

 

Amblyomma variegatum (Tropical Bont Tick)

Both sexes have the primary punctation sizes on the scutum/conscutum small to medium. The eyes are distinctly convex. Enamel ornamentation is pink to orange and the legs have pale rings. In the male (pictured below left) the mesial area of enamel ornamentation on the conscutum is elongate. There are usually no lateral median areas of enamel ornamentation on the conscutum. There is no festoon enamelling. The posteromedian stripe is narrow and does not join with the falciform stripe. In the female (pictured below right) the mesial area of enamel ornamentation on the scutum is elongate, although it may be indistinct in its anterior part. The lateral areas of enamel ornamentation on scutum are small. The scutum sides are straight and the scutum posterior angle is broad. The genital aperture posterior lips have a broad U shape.

 

Amblyomma variegatum male and female
Photo: Alan Walker

This species occurs in a wide variety of habitats and climates from rain forest to temperate (highland) and savanna. It is found throughout West, Central and East Africa and in much of southern Africa. However, it does not seem to coexist in the same areas as Amblyomma hebraeum. It is also found in several Caribbean islands and in Madagascar as a result of cattle transportation.

Wild hosts are buffaloes and other large herbivores. All stages also feed on cattle, sheep and goats. Nymphs may feed on birds. Adults attach on the dewlap, sternum, flanks, areas around the genitalia, and the udders. There have been a number of studies of the ecology of Amblyomma variegatum. In Zambia where the species is indigenous the tropical bont tick has one generation per year with larvae in March to May, nymphs from May to September and adults from October to December (Pegram, 1986 ). In the Caribbean where it was imported along with cattle from Senegal there can be at least two generations per year. Barré & Garris (1990)  review the implications of its ecology in the Caribbean for a regional eradication programme. Yonow (1995)  brought much of the life history information together with a view to modelling populations.

Much like Amblyomma hebraeum, this tick is an important vector of the bacterium Ehrlichia ruminantium which causes heartwater in cattle, sheep and goats. Amblyomma variegatum also transmits the bacterium Ehrlichia bovis, causing bovine ehrlichiosis, and the protozoans Theileria mutans and Theileria velifera causing benign bovine theileriosis. The tick has also been associated with dermatophilosis (also called streptothricosis) caused by the bacteria, Dermatophilus congolensis. The wounds caused by the tick and the immunosuppression that occurs secondary to feeding, predispose entry of the bacteria into the skin (Ambrose et al., 1999 ). Dermatophilosis results in a loss of milk production, poor quality hides, weight loss and sometimes death.

Amblyomma variegatum ticks feeding on udder of young cow in Ghana
Photo: Alan Walker

Heavy infestations also damage teats and directly reduce suckling efficiency and productivity.

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

  •  Ambrose, N. et al. (1999). Immune responses to Dermatophilus congolensis infections. Parasitology Today 15 (7), 295-300. Abstract 

  •  Barré, N. & Garris, G.L. (1990). Biology and ecology of Amblyomma variegatum (Acari: Ixodidae) in the Caribbean: implications for a regional eradication program. Journal of Agricultural Entomology 7: 1-9.  Full text 

  •  Bryson, N.R. et al. (2000). Collection of free-living nymphs and adults of Amblyomma hebraeum (Acari: Ixodidae) with pheromone/carbon dioxide traps at 5 different ecological sites in heartwater endemic regions of South Africa. Experimental and Applied Acarology 24, 971-982. Full text 

  •  Norval, R.A.I. (1977). Ecology of the tick Amblyomma hebraeum Koch in the Eastern Cape Province of South Africa. I. Distribution and seasonal activity. The Journal of Parasitology 63 (4), 734-739. Abstract 

  •  Norval, R.A.I. et al. (1989). The effect of the bont tick (Amblyomma hebraeum) on the weight gain of Africander steers. Veterinary Parasitology 33 (3-4), 329-41. Abstract 

  •  Norval, R.A.I. et al. (1995). The relationship between tick (Amblyomma hebraeum) infestation and immunity to heartwater (Cowdria ruminantium infection) in calves in Zimbabwe. Veterinary Parasitology 58 (4), 335-52. Abstract 

  •  Pegram, R.G. et al. (1981). Ticks (Acari: Ixodoidea) of Ethiopia. I. Distribution, ecology and host relationships of species infesting livestock. Bulletin of Entomological Research 71, 339-359. Abstract 

  •  Pegram, R.G. et al. (1986). Ecology and phenology of ticks in Zambia: Seasonal dynamics on cattle. Experimental and Applied Acarology 2 (1), (1986), 25-45. Abstract 

  •  Regassa A. (2001). Tick infestation of Borana cattle in the Borana Province of Ethiopia. Onderstepoort Journal of Veterinary Research 68, (1), 41-5. Abstract 

  •  Sang, R. et al. (2006). Tick-borne arbovirus surveillance in market livestock, Nairobi, Kenya. Emerging Infectious Diseases 12 (7), 1074-1080. Full text 

  •  Walker, A.R. (2001). Ticks of domestic animals in Africa: a guide to identification of species. Bioscience Reports. Full text 

  •  Yonow T. (1995). The life-cycle of Amblyomma variegatum (Acari: Ixodidae): a literature synthesis with a view to modelling. International Journal for Parasitology 9, 1023-1060. Abstract 

Last updated 3 January 2013