TICKS

Ticks are of importance to veterinary medicine because they can be an annoyance, cause harm due to their blood feeding activities and because they can transmit many pathologic organisms.

Most common ticks can be identified microscopically to the generic level by examining the mouthparts (above). This consists of a spined hypostome surrounded by a pair of palps. The area where the mouthparts are attached to the cephalothorax (base of the mouthparts) is called the basis capituli.

There are two families of ticks. The Ixodidae or hard ticks and the Argasidae of soft-bodied ticks.

1. Ixodidae - Hard ticks. Characterized by having a visible scutum with mouth parts originating on the anterior margin.
2. Argasidae - Soft ticks. Characterized by lacking a scutum and having mouth parts that originate on ventral surface.

The life cycle of all ticks include four stages (egg - larvae - nymph - adult). In the majority of species, the ticks drop off the host animal between stages (exceptions are one-host ticks that remain on the same animal). The larvae (seed ticks)(above, left) hatch from the eggs and attach to vegetation in order to be in easy reach of passing animals. Attraction to the host is due to heat and carbon dioxide concentrations. Once on the new host, they attach and feed on blood. Nymphs and adults employ the same methods of host seeking. Mating of adults (above, right) takes place on the host while attached and feeding. Egg laying by the female occurs after detachment.

Heavy tick infestations (above) are often responsible for considerable morbidity and mortalities in both domestic livestock and wildlife.

Male and female adult hard ticks can be separated by observing the presence or absence of a complete scutum covering the entire dorsal surface of the male and a partial scutum on the female.

(Females are on top, males below) Left to right-Dermacentor andersoni, Amblyomma americana, Dermacentor variabilis(above).

Common hard ticks include:

• Ixodes scapularis (dammini)- Black-legged tick (3 host). Once thought to be separate species, I scapularis and I dammini are now considered to be the same species. This tick is the most common vector for Lyme disease in North America. The adults are cool weather ticks, appearing in the fall and usually remaining on the host throughout the winter. Larvae and nymphs are abundant in the summer and feed on small mammals and lizards as well as humans. Typically, the life cycle for this tick requires 2 years to complete. Members of this genus are also involved in the transmission of tularemia, human and rodent babesiaosis, human ehrlichiosis (HGE). and paralysis. Adults can be identified by the presence of large mouthparts (longer than the basis capituli) and an anal grove in the ventral side that forms an arch over the anus.

• Ixodes pacificus- Western Black-legged tick (3 host). This is the common vector for Lyme disease in western states, especially California, Oregon, Washington, Utah and Nevada. Adults are abundant on the host in late winter to summer with nymphs and larvae appearing in spring and summer.

• Dermacentor andersoni- Rocky Mountain wood tick (3 host). Adults of this species are common on most large animals. Larval and nymphal stages feed on a wide variety of hosts. Adult ticks appear in March, peak in May, declining by July. Larvae and nymphs appear later than adults, disappearing by late summer. The is the tick most commonly involved in RMSF, anaplasmosis, and paralysis cases in western states.

• Dermacentor spp (left) and Rhipicephalus spp(right) are similar in appearance. Members of the genus Dermacentor can be recognized by the short mouthparts and non-flarred basis capituli.

• Dermacentor variabilis-American dog tick (3 host). Adults are common on a variety of hosts but dogs appear to be the preferred host. This species is widely distributed over the eastern two-thirds of the United States. Adult tick activity begins in mid-April and peaks in June, declining until September. In southern states, all stages may be found on the host throughout the year. A common vector for RMSF, anaplasmosis, feline cytauxzoonosis, and tick paralysis in eastern and southern states.

• Dermacentor albipictus-A cool-weather or winter 1 host tick. This species is common on large animals including domestic and wildlife species. Although common in most areas that experience freezing winter weather (including Oklahoma), it is also responsible for "ghost moose" in northern areas due to heavy infestations and the resulting loss of hair. This tick is known to be responsible for tick paralysis cases as well as the transmission of "winter" anaplasmosis in domestic cattle.

• Rhipicephalus sanguineus- Brown dog tick (3 host). This is an extremely common tick with a preference for feeding on dogs. It is perhaps the most widely distributed tick species in the world. In spite of its abundance, it is an uncommon parasite on man. Adult activity is usually from spring until autumn. Adults have a tendency to crawl upward and can often be found in roofs and in cracks of kennels or dwellings. This common tick is frequently involved in infestations of houses and is also a common vector for canine babesiosis, canine haemobartonellosis, canine ehrlichiosis (E. canis), and paralysis.

• Amblyomma americanum-Lone-Star tick (3 host). This is an extremely common tick in south-eastern United States. It is primarily a problem as a pest but is also involved in the transmission of canine ehrlichiosis (E. ewingii), human ehrlichiosis (E. chaffeensis) tularemia, Q fever, and cervid theileriosis. It is not a vector for Rocky Mountain Spotted Fever. Tick activity begins in March or April and continues throughout the warm months. Larvae and nymphs are most active in mid-summer. Adult females are easily recognized by the white spot on the dorsal scutum. Mouth parts for this genus are large and they lack an anal groove.

• Amblyomma maculatum-Gulf Coast tick (3 host). Once thought to be restricted to areas along the Gulf Coast, this tick is now common in Oklahoma. Because of its large mouth-parts and preference for ataching to the ears of it's host, it is responsible for considerable damage and annoyance. It has become one of the most economically important tick species of horses and cattlle in Oklahoma. Damage and deformity to the ears of the host ("gotch ear") is a direct result of adult tick feeding. Adults appear in late spring and are active throughout the summer. The role of this tick as a vector for diseases is poorly understood.

• Boophilus annulatus-Cattle fever tick (1 host). This is a 1-host tick that is capable of transmitting a variety of diseases. It is the principal vector for bovine babesiosis. It is considered to be eradicated from the U.S. As such, it is a reportable parasite in the U.S. allthough its reintroduction across out southern border is always a threat. Adults can be identified by the laterally produced basis capituli (similar to Rhipicephalus spp), no festoons and ridged palps.

Common soft ticks include

• Otobius megnini- Spinose ear tick ( 1 host, adult free-living). Common in most warm areas of the world. Larval and nymphal stages invade the ears of the host. Adults drop off the animal and are non-parasitic. Hosts are numerous including horses, cattle, rabbits and even man. Individual ticks may remain in the ears of its host for up to 1 year causing considerable damage and annoyance.

• Argus persicus - fowl tick (3 host). A widely distributed tick throughout most of the world. The nymphs and adults are active at night while hiding in trees, under houses, etc., during the day. Ticks may travel long distances to find their hosts. Large numbers may parasitise fowl at night, removing large amounts of blood. During the day, birds will show little indication of infestation but may exhibit striking anemia. This tick can be involved in the transmission of avian borreliosis and paralysis.

• Ornithodoros hermsi- Relapsing fever tick (3 host). This is another common parasite of wild species as well as a major vector of human relapsing fever.

Tick Paralysis

Tick paralysis is a disease caused by numerous species of ticks from several genera and is characterized by an acute, ascending flaccid motor paralysis. The paralysis affects the myoneural junction particularly the conduction rate of slower conducting terminal fibers of small diameter. The paralysis acts on motor nerves by diminishing the liberation of acetylcholine and by causing damage to receptor sites. Although detected worldwide, there are notable variations in the paralytic responses. Localized toxic reactions also have been described often making the separation of paralysis and toxic manifestations difficult. Most investigators believe that tick paralysis is caused by a toxin but its nature is not totally characterized. Generally it is believed that the toxin is produced in the salivary glands of the female tick. Paralysis in both humans and animals has been reported from the attachment of as few as a single female tick.

Prevention of tick infestations appears to be the only sure means of avoiding paralysis. Recovery, following tick removal, is usually complete.

Additional Sites on Tick Biology and Tick Transmitted Diseases:

Fleas and Ticks

Ticks and Tick Transmitted Diseases in Oklahoma

Tick Control

Control of ticks on the host.

There are two ways to control ticks on the animal;

1. Use an acaricide applied to the animals hair (sprays or dips)
2. Bathe the animal with the acaricide.
3. Use a systemic acaricide administered topically.

There are many products available that meet both of these needs. Pyrethrins, Carbaryl, Malathion, Lindane, Amitraz, permethrin and chlorfenvinphos are just a few. Most are effective for 1 to 2 weeks after treatment.

Several new products that are also effective against adult fleas, and now available to pet owners through their veterinarian. Most studies indicate that these products are effective against ticks for one to two months. Products containing phenylpyrazole as an active ingredient appear to provide the best protection.

Collars

Flea and tick collars are made for both dogs and cats. There is an active ingredient (many different ones) impregnated into a resin or plastic which allows the acaricide to be released slowly over time. The efficacy of the acaricide in the collar is related to the toxicity of the ingredient and to the speed of its release. Collars containing propoxur and dichlorvos provide rapid control of ticks with all ticks that were attached being killed by 72 hours after application. Colars with chlorfenvinphos provided the greatest and longest protection against reinfestation.

Control off the host.

Only two products (Chlorphyrifos (Dursban) and tetrachlorvinphos (Rabon, Stirophos)) are EPA approved for area-wide control. These are designed for application in parks, recreational areas, etc. and their use should be timed with the biology of the tick in question.

Various activities such as host reduction and habitat modification are also useful in controlling ticks.

Control and Treatment: Treatment and control of ticks is a problem because of the wide variety of hosts that they can feed on and the fact that different stages feed on different animal species (one-host ticks being the exception). Additionally, all life stages of ticks may live for extended periods of time without feeding.

Various methods of control are employed for different host species. Infestations on companion animals can often be controlled by methods such as the use of treated collars, dusting, or other individual applications. Additionally, the premises (yards, kennels, etc.) can also be treated. This approach does not lend itself to large animal treatment and more extensive methods such as spraying, dipping, habitat clearing, burning, etc. are often employed.

Ivermectin has been shown to have an effect on tick infestations on large animals but generally only on a continuous use basis. During single use applications, many ticks will stay attached and discontinue feeding, resuming feeding again after drug levels are reduced. Several closely related and newly released products with various application methods show a potential for being useful in the control of many tick species on large animals.

Removal of ticks is important in both preventing the spread of disease agents to the animal as well as the person handling the tick. Since ticks often contain infectious particles in both the salivary glands, and hemolymph, ruptured or broken indivivuals can serve as a means of infection.

Removal should be accomplished by grasping the mouthparts close to the attachment point with forceps and slowly removing the tick.

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