Dermacentor is a genus of hard ticks that affects wild and domestic mammals worldwide: cattle, sheep, goats, horses, dogs, cats, and humans as well. There are about 30 Dermacentor species worldwide. The most relevant for livestock and pests are the following:
- Dermacentor andersoni, the Rocky Mountain wood tick; North America
- Dermacentor marginatus, the ornate sheep tick; Europe, temperate and Mediterranean; Northern Africa
- Dermacentor nitens (= Anocentor nitens), the tropical horse tick; important for horses; tropical America
- Dermacentor reticulatus, the marsh tick, the ornate cow tick, the European meadow tick; important for dogs; Europe
- Dermacentor variabilis, the American dog tick, the wood tick; important for dogs; parts of North America
As a general rule, Dermacentor ticks are less relevant for cattle and other livestock than those of the genus Amblyomma, Boophilus and Rhipicephalus. But several species are important dog andhorse parasites.
Biology and life cycle of Dermacentor ticks
As all hard ticks, Dermacentor ticks are obligate parasites: they cannot survive without feeding blood of their hosts.
Dermacentor ticks are medium-sized, i.e. engorged adult females are usually 1 to 1.5 cm long. They have short mouthparts, typical dull enamel ornamentation, and the abdomen is bordered by typical festoons.
Most Dermacentor ticks are three-host ticks, i.e. larvae, nymphs and adults can be found free-living in the environment waiting for a suitable host to pass by. Larvae and nymphs usually infect small mammals (e.g. rodents, rabbits, etc.), whereas adults prefer larger ones, often dogs, but also livestock and humans. Their life-cycle takes usually 12 to 24 months to complete, depending on the climate. All stages can survive for 10 months and longer without feeding, and are capable of overwintering in cold regions. All these species can feed on almost any mammal. Larvae and nymphs prefer small animals (rodents, rabbits, moles, etc.), whereas adults will prefer larger ones, often dogs, but also livestock and humans. Due to their preferred habitats they are seldom a problem for cattle, but may affect sheep on summer grazelands. They are more active and from spring to early autumn.
In contrast with this Dermacentor nitens is a one-host tick, i.e. only larvae are infective. It occurs in Southern USA, Mexico, Central America, several Caribbean Islands and in tropical and subtropical South America. It affects mainly horses but can also feed on cattle and other livestock. It is typically found in the ears, which can be virtually filled with ticks. They can also congregate in the nostrils, in the mane, around the anus und in the underbelly. Such highly infested animals attract screw-worm flies that ley their eggs on the tick wounds.
Within the European species, Dermacentor marginatus prefers bushlands and steppes but is also found in deciduous forests, often in meadowland; Dermacentor pictus prefers deciduous forests and in the mountains is often found close to the streams. Dermacentor reticulatus is found mainly in riverside woods, but can also inhabit cosatlands.
Within the North American species, Dermacentor variabilis is found in the western half of the USA, from the Gulf Coast up to Canada. It prefers woodlands, shrublands and grasslands, but preferential habitats can vary depending on predominant ecologic and climatic conditions. Dermacentor andersoni is found in the the Rocky mountain states.
Click here to learn more about the general biology of ticks.
Harm and economic loss due to Dermacentor ticks
As for all ticks, Dermacentor bites cause stress and blood loss to the hosts. A few ticks are usually well tolerated by livestock and pets, but infestations with dozens or hundreds of ticks can significantly weaken affected animals and cause weight loss, reduced fertility, decreased milk production, etc.
Dermacentor ticks are all vectors of several tick-borne diseases of increasing importance for dogs and humans in Europe and North America.
- Dermacentor andersoni transmits Rocky Mountain spotted fever, tularemia, Colorado tick fever, and Q fever in the USA, and can cause tick paralysis.
- Dermacentor marginatus transmits Q fever, tularemia, dog babesiosis, cattle anaplasmosis, various Rickettsia species, etc.
- Dermacentor nitens transmits horse and cattle babesiosis.
- Dermacentor reticulatus transmits dog, cattle and horse babesiosis, sheep anaplasmosis, sheep and horse theileriosis, brucellosis, toularemia, Boutonneuse fever, etc.
- Dermacentor variabilis transmits human Rocky Mountain spotted fever and tularemia, cattle anaplasmosis, and can caused tick paralysis.
It seems that these ticks are expanding their range, possibly due to climate changes, but also to increased environmental protection that helps preserving or even extending their habitats. Wildlife protection and climatic changes also contribute to increase the number of potential hosts for these ticks. On the other side, more and more people visit the environments where these ticks prevail, either in recreational areas, or in peri-urban residential areas.
Dermacentor ticks are usually only a minor issue for the cattle industry compared with Amblyomma and Boophilus ticks. In endemic areas it can by a problem for sheep and goats on summer grazelands where these ticks prevail. Dermacentor nitens can be a serious problem for horses in Latin America.
Non-chemical prevention and control of Dermacentor ticks on livestock
Where these ticks are a problem for cattle, a proven method to reduce such problems is to increase the amount of B. indicus "blood" in the herds. Cebu cattle (Bos indicus) and numerous indigenous breeds are naturally resistant to ticks and tick-borne diseases, whereas European breeds (Bos taurus) are not. Unfortunately, in many regions the opposite is more frequent. The reason is that producers are often urged to increase the productivity of their properties. Since they can neither reduce their costs, nor increase the cattle density of the farm, a rather cheap and easy option is to introduce more European "blood". It doesn't need significant investments or changes in the infrastructure and management of the property. Social and cultural factors also play a role: European breeds are often perceived as high-tech and prestige livestock.
Little to nothing can be done to reduce Dermacentor tick populations on their natural habitats.
Pasture burning is a common practice in many regions of the world. Regarding cattle tick control, the experience is that it contributes to reduce the tick numbers to some extent, but it is certainly not enough to eliminate or substantially reduce the tick populations. But it cannot be practiced in most natural grazelands or woodlands where Dermacentor ticks are a problem.
Livestock alternation doesn't help at all with Dermacentor ticks, because they feed on whatever livestock or wildlife. Reducing the number of wild animals can have an impact on Dermacentor populations, but is usually impossible in natural grazelands.
Pasture rotation or vacation is not feasible with Dermacentor ticks: they can survive very long without feeding and there will always be enough wild animals around to support tick populations.
Biological control of Dermacentor and other ticks using their natural enemies remains a research topic has not yet delivered really effective and sustainable solutions for tick population control. Tick predators such as insects (e.g. ants, wasps), small rodents or birds (e.g. cattle egrets, guinea fowls, oxpeckers, etc.) do in fact consume significant amounts of ticks, but will not eliminate tick populations. One reason is that they are not specific tick predators, but feed on whatever is available. The most promising results have been obtained so far with so called entomopathogenic fungi, i.e. fungi that are pathogenic for ticks and other insects (e.g. Beauveria bassiana, Metarhizium anisopliae, etc.). In certain countries there are commercial products for crop protection based on such fungi, and there are reports that they can effectively control ticks on livestock too. However, a systematic commercial approach to cattle tick control using such fungi is still missing. In addition, such biological control methods target tick population control and not protection of single animals or killing already attached ticks on an infected animal. For the reasons previously mentioned population control of Dermacentor ticks is virtually impossible in endemic regions.
Learn more about biological control of ticks and mites.
There are no specific vaccines against Dermacentor ticks. A few reports have shown efficacy of the Boophilus tick vaccine against other tick species, but little is know about its effect against Dermacentor ticks.
There are no repellents, chemical or natural, that effectively prevent Dermacentor ticks from attaching to livestock or pets, or that cause already attached ticks to detach.
There are no traps that effectively reduce Dermacentor tick populations in the pastures: whatever domestic or wild animals are much more attractive for ticks than any possible trap.
So far there are no herbal remedies commercially available really effective for protecting livestock from Dermacentor ticks in endemic regions.
Chemical prevention and control of Dermacentor ticks with tickicides
Chemical treatment of cattle against Dermacentor ticks is often not needed in most of North America and Europe, simply because cattle seldom graze where these ticks prevail.
Sheep may need tick protection during summer grazing in regions where Dermacentor ticks are endemic. In many places sheep are routinely treated once at the beginning of the outdoor grazing season, often not only for tick protection, but also against other external parasites (e.g. biting flies, blowflies).
Most products approved for tick control and prevention on livestock in these countries or elsewhere are based on veteran contact parasiticides of various chemical classes such as:
- Organophosphates (e.g. chlorfenvinphos, chlorpyrifos, coumaphos, diazinon, ethion, etc.)
- Amidines (mainly amitraz, also cymiazole)
- Synthetic pyrethroids (e.g. cypermethrin, deltamethrin, flumethrin, permethrin)
Some of these products are also approved for use on horses. All are for on animal use. In most countries there are currently no tickicides approved for pasture treatment against cattle ticks. The major reason is that to effectively control the ticks on pasture the dose will be lethal for almost any invertebrate fauna in the pastures and for most of the vertebrates that feed on them (birds, reptiles, rodents, etc.). In addition, pastures would be also contaminated with chemicals, which could be toxic for livestock or leave illegal residues in meat and/or milk.
Organochlorines were vastly used in the past, but are now prohibited for livestock in most countries. Neonicotinoids are not effective against ticks. Carbamates are often not effective enough against ticks.
These veteran acaricides are mostly available as concentrates for topical administration as dips and sprays, or as ready-to-use pour-ons. As a thumb rule, dips are more effective than sprays and pour-ons, simply because sprays and pour-ons do not ensure a complete coverage of the whole body (e.g. ears, udders, perineum, below the tail etc.).
Neither macrocyclic lactones (e.g. doramectin, eprinomectin, ivermectin, moxidectin), nor tick development inhibitors (fluazuron) ensure adequate control of Dermacentor ticks on livestock (or any other multi-host tick species) or horses. This means that there are no systemic tickicides suited for controlling Dermacentor ticks in livestock or horses, and consequently neither injectables, nor drenches nor feed additives.
|If available, follow more specific national or regional recommendations or regulations for tick control.|
Resistance of Dermacentor ticks to tickicides
There are no reports on serious resistance problems of Dermacentor ticks on livestock, horses or pets.
This means that if a tickicide fails to achieve the expected efficacy, chance is almost 100% that either the product was unsuited for Dermacentor control, or it was used incorrectly. Incorrect use is the most frequent cause of failure of antiparasitics.