Ectoparasite Control in Small Ruminants

UPDATE ON SMALL RUMINANT MEDICINE

0749-0720/01 $15.00

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ECTOPARASITE CONTROL IN SMALL RUMINANTS David P. Gnad, DVM, and Donald E. Mock, PhD

Small ruminants throughout the world are subject to ectoparasitism by many species of insects, mites, and ticks. In North America, only a few species of ectoparasites commonly cause serious problems for sheep and goats, but several others may be locally or occasionally significant. When numerous, ectoparasites that suck blood from their mammalian hosts cause anemia, resulting in poor performance, abortion, or death. Many bloodsucking ectoparasites can also serve as biologic or mechanical vectors for infectious organisms (i.e., bluetongue virus). Non-bloodsucking ectoparasites can cause a wide range of problems in small ruminants, such as annoyance by house flies, myiasis by nasal bots and blow flies, alopecia and irritation from chewing lice, and mild to fatal primary and secondary effects of several kinds of mange mites. Host immune responses to ectoparasites, whether localized, systemic, or both, can also exacerbate the deleterious effects of ectoparasitism. Increasingly, serious economic and social consequences can affect livestock owners through litigation arising from flies from livestock facilities becoming a nuisance to neighbors. Each kind of ectoparasite may be categorized as permanent or intermittent with respect to its host. Permanent ectoparasites include sheep keds, mange mites, and lice; they normally occupy the host animal continually throughout their life cycles. Such parasites are spread from animal to animal and herd to herd primarily by direct contact and secondarily by fomites ranging from bedding, transportation facilities, grooming or shearing equipment, and clothing of personnel, including

From the Section of Agricultural Practices, Department of Clinical Sciences, Kansas State University College of Veterinary Medicine (DPG); and the Department of Entomology, Kansas State University (DEM), Manhattan, Kansas

VETERINARY CLINICS OF NORTH AMERICA: FOOD ANIMAL PRACTICE VOLUME 17 • NUMBER 2 • JULY 2001

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veterinarians. Such permanent ectoparasites can be eradicated from a farm and, through rigorous attention to isolation and closed-herd tactics, the farm can be maintained free from such pests without additional use of insecticides. Intermittent ectoparasites are free-living species such as flies, mosquitoes, and ticks that are often highly mobile and live most of their lives off the host, rendering closed-herd tactics unsuccessful if used exclusively. Some species that are intermittent with respect to their entire life cycle occupy their hosts for such long durations that the problems they cause and opportunities for control may be more similar to those relating to permanent ectoparasites. Examples of these are spinose ear ticks that may be deep in an animal's ear canal for several months, winter ticks and blacklegged ticks that often reside on the same host for several months during the colder times of the year, and sheep nasal bots. In sections on specific ectoparasites, some general geographic and seasonal distributions are provided; however, each veterinarian should try to become aware of these factors as they apply to his or her practice. For example, in Gulf Coastal and Atlantic seaboard states, adult Gulf Coast ticks parasitize hoofed animals primarily in late summer and fall, whereas in northern Oklahoma and in Kansas, they do so in March through mid-June. In some locations, stable flies may be common throughout most of the year; in other locations, they are mostly a May-June pest, and in other states they may be considered a mid- to late summer problem. Correct identification of a pest species is key to assessing its potential for causing injury or loss and is requisite for choosing and implementing avoidance, control, or eradication strategies. It is not within the scope of this article to provide sufficient detail to determine the species identification of the ectoparasites discussed. For many of them, however, the descriptions taken in consideration of the circumstances in which they are found may allow the reader to make adequate identifications. Where identifications beyond the expertise of the practitioner are needed, the authors recommend consultation with a veterinary diagnostic laboratory or department of entomology within a university. In assessing problems with ectoparasites, and especially in selecting strategies to negate their effects, one must consider the scope of the operation and the goals and capabilities of the operator. Control strategies such as power spraying or dipping may be economical for a large commercial stockgrower, but they are not feasible in a small farm flock or herd. Conversely, some labor-intensive, hand-application methods may be easy to use with a few animals but not feasible in an operation with thousands of sheep or goats. Although insecticides and acaricides are often necessary to control a current infestation of ectoparasites, the practitioner and herdsman should consider opportunities to avoid or minimize their use through cultural or management practices. Ideally, the use of chemicals should complement cultural and management practices to provide the most cost-effective overall outcome. Largely because the sheep and goat in-

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dustries do not constitute as large of a potential market for such products, there are not as many insecticidal and acaricidal products registered for use on these animals compared with cattle and swine. Many practitioners regularly prescribe off-label use of cattle products on small ruminants. Although this practice may sometimes be required, one who is adequately informed about appropriately labeled products seldom needs to assume the risk that accompanies off-label drug use. Many considerations should be made in selecting and using chemical products for ectoparasite control, including the following: What are the relative toxicities of various choices to the animals being treated and the person applying treatment? Does this kind of ectoparasite require direct treatment of the animal, treatment of the premises, or both? Does the practitioner need a fast-acting uknock-down" product, or is it more important to have residual activity? Which formulation can be best targeted where it is needed, and does this client have the equipment to use the formulation? Does this pest species have known resistance to some kinds of insecticides, or, even if not known, is such resistance likely to develop in the pest population? How can use of this product be integrated with other pest management practices and with overall management? And, of course, what are the relative costs of the materials and of the labor to apply them? LICE

Lice infestation is commonly encountered in small ruminant practice. Lice of small ruminants can be divided into two categories: chewing (Bovicola species) and sucking (Linognathus species). Species of chewing lice affecting small ruminants include B. ovis (sheep), B. crassipes (Angora goats), B. caprae (goats and sheep), and B. limbatus (Angora goats). Species of sucking lice affecting the bodies of small ruminants include L. ovillus (sheep); L. stenopsis (goats); L. africanus (goats and sheep); L. vituli (goats); and the foot louse (L. pedalis), which generally affects the legs and ventrum of sheep.3 Biting lice are pale yellow and sucking lice are bluish gray. Lice found on small ruminants range from 1/20 of an inch to 1/10 of an inch in length and prefer to reside close to the body, making detection difficult in animals with dense wool or long hair. Although parasites are present throughout the year in an infested herd, the percentage of animals infested and certainly the number of lice per animal are much greater during the colder months of the year. During warm weather, the female louse lays fewer eggs, therefore decreasing lice populations. Diagnosis is much easier when lice are abundant, but the effects of such infestations are best minimized when treatment is initiated before seasonal increases occur. The life cycles of chewing and sucking lice are similar in that it takes 21 to 32 days for them to develop from an egg (nit) to an adult louse. A notable exception is the sucking foot louse (L. pedalis), which takes 40 to 45 days to complete its life cycle. Lice are permanent, obligatory ectoparasites that spend their entire

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Lives on their host. Lice are species specific, so each species of louse thrives only on a specific host species or a closely related species. 3 Eggs are laid by mature lice and cemented to the wool or hair fibers. The white-colored eggs develop during a period of 9 to 14 days. Nymphs emerge from the egg and go through three nymphal instars before becoming sexually mature, a process that takes approximately 2 to 3 weeks. Lice remain on the animal, and female lice lay eggs (50-100 eggs/ day) throughout their life cycle (4-5 weeks). Lice can survive for short periods (3-7 days) off the animal but prefer to spend all their time on the animal. 16 Lice generally spread through direct contact but can also be spread by fomites such as combs, brushes, feed bunks, trailers, bedding, and pastures (L. pedalis). Early infestations may not be detected until animals begin to scratch or become nervous from the constant irritation. Other clinical signs such as wool or hair loss, poor-quality wool or hair, stunted growth, anemia (sucking lice), interrupted feeding, and skin irritation may be encountered. While small, lice can be identified grossly if a diligent physical examination is performed. Identification of species can be achieved under routine light microscopy. Animals being introduced into a new flock or herd should be examined thoroughly or treated with appropriate insecticides before being exposed to resident animals. Treatment of louse infestations is best accomplished by direct application of insecticide to the animal. A wide range of insecticides are available, and many more are in the development stages (Table 1). When choosing an insecticide for the treatment of lice, it is important to consider several factors. First, what type of working facilities does the operator have? For example, it may be more appropriate to use dip vats or power dusting units for large numbers of animals versus applying powders by hand for single animals. Other options for insecticide application are spot treatments or sprays. It is important to remember that the skin of sheep and goats has different absorptive and transport capabilities compared with that of cattle, so products approved for one species may be less effective for or dangerous to other species. It is recommended by the authors to use products as directed or under the direct recommendation of the company manufacturing the product. If insecticide is applied by spraying, it is recommended that insecticide solutions be applied under spray pressures of 200 to 300 psi for sheep and 40 to 80 psi for goats if wool or hair is thick 16 High-pressure spraying may cause undesirable tangling or matting of wool if the fleece is more than 1 inch in length. Individual animal washing with dilute insecticide is a popular and effective means to treat show sheep or goats. Second, are there other parasites with which the animals are infected? For example, animals with a heavy internal parasite load may benefit from a product that kills internal parasites and external parasites. Once again, the authors suggest consulting the product label for its exact spectrum of activity. Third, cost and duration of action should be considered when choosing an insecticide. This issue will become increasingly important as new insecticides with longer durations of action are devel-

~

N

1.0

Ectiban 5.7% EC, Insectrin 5.7% EC; spray

Permectrin 25% WP; spray, paint, dip

PY

AV

OP

CH

PY

PY

Fenvalerate

Invermectin

Malathion

Methoxychlor

Permethrin

Permethrin

Pests

pyrethroid; EC

0

0

0

0

11

30

14

15

Days to Slaughter

Remarks

ultra-low volume (aerial

Do not use on animals younger than 1 month old or on lactating dairy goats. Do not spray or dip lactating dairy goats; do not use as dust on goats. Many other trade names with various of the target pest species listed.

Do not use on lactating dairy goats. Use only on sheep.

Do not use on animals younger than 3 months old or on lactating dairy goats. Do not use on goats.

emulsifiable concentrate; ULU

Keds, lice, ticks, black flies, eye gnats, house flies, hom flies, face flies, stable flies, horse flies, mosquitoes Blow flies, ticks, fleas

Lice, hom flies, fleas, and temporary relief of keds

Keds, lice, ticks, hom flies

Sheep nasal bots

Keds and lice

Keds and lice

Keds, ticks, lice, wool, maggots, horn flies

AV = avermectin; CH = chlorinated hydrocarbon; OP = organophosphate; PY application); W = wettable; WDC = water-dispersible liquid; WP = wettable powder.

Marlate 50 WP; spray, dip, dust

Diazinon 50 Wand 50 WP; sprinkle, spray Ectrin 10% WDL; pour-on sprinkle, spray, dip, ULV Ivomec Sheep Drench 0.08% solution Malathion 54% or 57% EC; spray

OP

Diazinon

Co-Ral 25% WP; spray, dip

Sample Formulations and Application

OP

Class

Coumaphos

Chemical Name

Table 1. PRIMARY INSECTICIDES AND ACARICIDES REGISTERED FOR DIRECT USE ON SHEEP AND GOATS

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oped and marketed. An understanding of the life cycle of the louse is critical when developing treatment and control programs because the embryo in the egg is generally unaffected by current treatment methods and may develop unharmed in the absence of retreatment. Retreatment of the animal should take place 12 to 14 days after the initial treatment to kill any nymphs that may have emerged. Louse resistance to insecticides should be monitored after treatment. If louse infestations are severe, the environment should also be addressed, which can be accomplished by maintaining basic hygiene protocols. Bedding should be changed, blankets should be washed, and grooming utensils should be disinfected routinely if animals are commingled frequently, as with show or club animals. FLIES, MOSQUITOES, AND GNATS

The Calliphoridae family of flies has a significant effect on small ruminants, most commonly sheep, in the United States. Some common adult calliphorids are blow flies, bottle flies, and screwworm flies. 8 Screwworm myiasis has been eliminated from the United States through eradication programs, so it is not discussed further. The blow fly life cycle can vary depending on environmental conditions. For example, in early spring it takes blow flies 3 to 4 weeks to develop from the egg to a mature fly and only 10 to 14 days during warmer periods of the year. Blow fly numbers are highest during spring and fall; thus the threat of infestation is highest during these periods, although infestation is possible during summer months. 16 Female blow flies are able to travel several miles and prefer to lay eggs in necrotic tissue and carrion, although certain types lay eggs in and use a wide range of decomposing plant material to lay eggs. Calliphorides also lay eggs in wool that becomes matted and soiled from feces, urine, or sweat. Necrotic tissue resulting from surgical procedures such as castration, dehorning, and docking is also attractive for egg deposition by these flies. A wound from shearing is another common situation resulting in egg deposition. Once eggs are deposited, larvae emerge (wool maggots) and begin to feed on necrotic tissue. Larvae of some species may also invade intact tissue, causing irritation, poor appetite, and restlessness and may result in the death of the animal in severe cases. 16 The fully grown larvae fall to the ground and pupate for several days, resulting in emergence of an adult fly. Treatment of "wool maggots" consists of removal of wool or hair around the affected area and debridement. Once the larvae have been removed, the authors recommend spot treatment with an appropriately labeled insecticide until healing has occurred. Management practices can also decrease the incidence of infestation. Practices such as good hygiene around livestock facilities and housing help to decrease fly populations. If possible, performing surgical procedures in the early spring before flies emerge decreases the incidence of infestation. If surgical procedures are performed during fly season, the authors recommend application of

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a protective insecticide to the wounds until healing has occurred. All wounds received during shearing should also be treated with an insecticide wherever practicaL In warm, arid areas, it is suggested that udder and vulvar areas be monitored for fly attack after lambing. Retained placental membranes can also be a site for egg deposition, so removal of retained membranes may be needed in high-risk areas. Black flies (Simuliidae) (Fig. 1) are small, biting flies. They are widely distributed and are generally found in areas of running water. The adult female flies attach their eggs to stationary objects along clear, running water. Larvae and pupae mature in the aquatic environment. Adults may travel up to 10 miles in search of an animal on which to feed. 16 It is common for large swarms of black flies to develop and attack sheep or goats. The flies swarm around the eyes, nose, mouth, and ears of sheep and goats, eventually biting the animal and feeding on the blood. Animals may stand huddled together with their heads down, often congregating in thick brush. Grazing and drinking time are decreased in areas heavily infested with black flies. Control of black flies is extremely difficult because of their vast area for reproduction and the environmentally sensitive nature of their aquatic developmental sites. Insecticide application to animals is of little value for large herds because of the impracticality of frequent treatments. Spot treatment of favored anatomic sites of the host, such as the ears, with permethrin spray or pour-on products is helpful for smaller herds. Small herds or pets may be locked up in buildings during the daylight hours of late spring and early summer, which offers protection because the black flies prefer not to enter buildings and generally feed in the daytime. 1s Some species of black flies have also been implicated in the transmission of vesicular stomatitis.6, 20 The bot fly species, Oestrus avis, is a nonbiting fly that deposits larvae (nasal bots) in the nostrils of sheep and goats. These flies are persistent and decrease grazing and feeding times, subsequently decreasing performance if fly numbers are high enough. ls During the season in

Figure 1. A black fly, Simulium vittatum, feeding on a white mouse. (Courtesy of Eddie Cupp, PhD, Auburn University, Auburn, AL.)

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which nasal bot flies are larvipositing, animals may huddle together, holding their heads down or burying their nostrils in each others' fleece. Once larvae have been deposited in the nostril, they migrate to the sinuses for development and then back down to the nostrils. This migration can cause irritation and potentially obstruction. A nasal mucopurulent discharge is usually evident in sheep and goats infected with nasal bots. Once the larvae reach the nostril, they fall or are coughed out onto the ground, where they pupate. This life cycle can range from 6 months to 1 year, depending on the climate. Bot flies prefer warm, sunny weather. At the time of this writing, the only drug labeled for control of sheep nasal bots in the United States is Ivomec Sheep Drench (0.08% ivermectin, administered at 0.2 mg/kg). Experimentally, ivermectin controlled-release capsules,24, 26 injectable ivermectin (subcutaneously, 0.2 mg/kg),4 1% injectable moxidectin solution,5 and oral closantel (10 mg/ kg)5 have all shown efficacy for the treatment of Oestrus ovis larvae. Closantel and ivermectin (subcutaneous) have demonstrated the added benefit of residual activity against Oestrus ovis larvae. 4 Sheep keds (Melophagus ovinus) (Fig. 2) are tick-like in general appearance and movement, but because they have only six legs they are characterized as insects. They spend their entire lives on their host (sheep) and are spread by direct contact. The adult female ked carries her larvae, which are developed singly, until they are mature, at which time the female ked attaches them to the fleece, where they pupate. Sheep keds are blood feeders and cause irritation to the skin. This irritation to the skin causes significant discomfort to the animal, decreases wool quality, and can permanently damage the hide (cockle). Ked populations generally increase through the fall months and peak during the winter, then numbers decrease through the summer. Control of sheep keds is generally rewarding. Timing of treatment may coincide with other ectoparasite treatments. For example, fall treatment for lice also kills keds, preventing the normal rise in ked numbers through the winter. The authors suggest a late fall treatment of all animals in the

Figure 2. A sheep ked (female), Melophagus ovinus. (Courtesy of John Lloyd, PhD, University of Wyoming, Laramie, WY.)

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flock. Another option for treatment is at the time of shearing. Multiple application methods are available for the treatment of keds (Table 1); the production system determines which method is most appropriate. Once again, coordination with other ectoparasite control programs is suggested when treating for keds. Stable flies (Stomoxys calcitrans) can affect sheep and goats by inflicting painful bites. House flies (Musca domestica) do not bite, although they annoy sheep and goats, potentially causing a decrease in performance. These species of flies are most commonly associated with operations containing confined animals (Le., feedlots). The most important means of controlling stable flies and house flies is through good sanitary practices. Both stable flies and house flies lay eggs in decaying vegetation or manure, so removal of such debris is the best method for control. Horse flies and deer flies (Tabanidae family) cause distress to sheep and goats by inflicting painful bites and loss of blood. They prefer to lay eggs in wet soil adjacent to ponds, streams, lakes, and rivers. This large area for rearing offspring makes control difficult in sheep and goats. Residual insecticides can be applied to individual animals, but this is not always practical in large production systems. Mosquitoes are common to extremely abundant throughout the world and affect many species of animals, including small ruminants. Female mosquitoes generally bite and feed on blood in the early mornings and evenings, although some species feed during mid-day hours. Water is an essential component of the mosquitoes' life cycle. Mature adults lay their eggs in stagnant water or areas that hold water at some time during the year (i.e., flood plains). Lagoons, ponds, water troughs, water buckets, or standing pools of water in fields or pastures are just a few examples of ideal breeding areas for mosquitoes. Because of the wide array of breeding opportunities for mosquitoes, it is difficult for most operations to control them. Efforts to minimize standing or stagnant water can aid in controlling mosquito populations. The use of a topical insecticide is generally impractical for a production setting with large numbers of animals, especially considering the short duration of insecticidal activity. Gnats of the family Ceratopogonidae, most notably Culicoides spp. (Fig. 3), are common pests affecting small ruminants in North America. These bloodsucking insects prefer feeding on the legs, belly, head, and ears of animals, usually from noon to late evening. 11, 13, 16 Gnats swarm in large groups, causing significant skin lesions on small ruminants. In addition to causing skin lesions, Culicoides sonorensis of the Culicoides variipennis complex is the primary vector of bluetongue virus in North America 11, 15, 16 and may also vector New Jersey serotype vesicular stomatitis virus. 13, 21 Gnats lay their eggs in moist soil near water. The larval stages need an aquatic environment to mature. Gnats use a variety of standing-water sites for oviposition, ranging from pond edges to human sewage, making environmental control difficult and often impractical. Individual animals can be sprayed with insecticides, although this becomes impractical for large flocks or herds.

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Figure 3. A gnat, Culicoides variipennis, feeding on a blood meal.

MITES

Psoroptic mange, caused by Psoroptes ovis, is a reportable condition affecting sheep. Psoroptic mange is commonly known as "sheep scab" because of the profound scab lesions produced by serum drainage after the mites pierce the skin with their pointed, elongated mouthparts. This mite has been declared "eradicated" from the United States since 1973.10 Although eradicated, it is important that diligent surveillance continues owing to the potential threat of the mite entering the country again. Clinical signs of psoroptic mange consist of crusted scabs on the wool portion of the animal's body, prorates, and alopecia. Diagnosis of Psoroptic ovis, as with all mange mites, is accomplished by light microscopy. If a presumptive diagnosis of psoroptic mange is made, federal authorities should be notified before any treatment is instituted so a definitive diagnosis can be made and the animals can be quarantined. Synthetic pyrethroids, organochlorines, and organophosphates have historically been used for successful treatment of psoroptic mange. Since avermectins have been discovered, they have been used for treatment and control as well. Ivermectin failed to clear Psoroptes ovis infestations in sheep when given subcutaneously as a single dose at 0.2 mg/kg? although excellent control was achieved with two subcutaneous injections (7 days apart) at a dose of 0.2 mg/kg. 27 Moxidectin administered subcutaneously, at a dose of 0.2 mg/kg, twice at 10 days apart, cleared 100% of infected sheep.23 Dormectin has been found to have beneficial effects if injected once at 0.3 mg/kg. 22 Sarcoptic mange, caused by Sarcoptes scabiei, is also a reportable disease in sheep and goats. This mite burrows under the superficial skin layers, laying eggs within the tunnels it forms. Mite burrowing causes intense inflammation and irritation to the animal, leading to extreme pruritus. Sarcoptic mites appear to have a preference for nonwooled portions of the body. Beads of dried serum and reddened skin may be apparent on physical examination. As with other mange mites, the

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most common mode of transmission is through direct contact. Light microscopy of skin scrapings should be used to identify mites. Treatment with moxidectin 1% injectable solution at a dose of 0.2 mg/kg given twice at 10-day intervals was effective against sarcoptic mange in one study? Ivermectin injected subcutaneously at a dose of 0.2 mg/kg also provides satisfactory treatment for sarcoptic mange. 12, 19 Chorioptic mange is caused by Chorioptes ovis in sheep and Chorioptes caprae in goats. Chorioptes spp. prefer to reside on the legs, ventrum, and scrotum of sheep and goats. The mites are surface feeders (skin scurf and secretions) and generally cause minimal damage to wool or hair. Skin lesions may be present but are not as severe as with sarcoptic mange. It has been reported that severe scrotal skin lesions caused by Chorioptes mites reduced fertility in rams. 2S Ivermectin given at a dose of 0.2 mg/kg subcutaneously is described as being an effective treatment for chorioptic mange. 1 Otodectes cynotis is a mite that can infest the ears of goats. Animals may shake or hold their heads to one side if infested with O. cynotis. This mite has a life cycle similar to Sarcoptes spp. and can be treated by topical acaricide applied to the ears. Demodex caprae is a mite that can inhabit hair follicles in goats. In goats, pustules may form around the mites, causing skin lumps around the head, neck, and shoulders. These pustules can be differentiated from other infectious processes by microscopically evaluating the exudate for the presence of the cigar-shaped mite. Demodectic mange is generally not harmful and treatment is usually not necessary.16 TICKS

All ticks have four life forms: egg, six-legged larva (protonymph), one or more eight-legged nymphal stages, and eight-legged adult. North American ticks are separated into two families: the soft ticks (Argasidae family) and hard ticks (Ixodidae family). Various tick species have varying degrees of host specificity. Although no tick is host-specific to sheep or goats, both hard and soft ticks parasitize these ruminants. Ticks have life cycles requiring a few months to 3 or 4 years to complete, but most species spend relatively little time actually on their hosts. With the blood-feeding habit and the multihost acceptance of many species, it is not surprising that ticks commonly vector zoonotic disease agents (i.e., tularemia-Francisella tularensis, Q fever-Coxiella burnetti, Lyme disease-Borrelia burgdorferi, and ehrlichiosis-Ehrlichia spp.). In addition to their role as disease vectors, female ticks of many species have a neurotoxic factor in their saliva that can cause an ascending paralysis in many kinds of mammals, including small ruminants and humans. Although tick paralysis is more common when many ticks are attached, in dogs, sheep, goats, and humans even a single tick has been known to cause fatal paralysis. Tick paralysis is generally caused by certain populations of the Rocky Mountain wood tick, Dermacentor ander-

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Figure 4. Dorsal view of a spinose ear tick, Otobius megnini. (Courtesy of Donald E. Mock, PhD, Kansas State University, Manhattan, KS.)

soni, in Montana, Idaho, Oregon, and British Columbia,28 but at least 43 species of hard ticks and soft ticks have been demonstrated or suspected of causing it. 9 Soft ticks that affect sheep and goats in North America are limited to two species with different life strategies and effects on their hosts. They are Otobius megnini (spinose ear tick) (Fig. 4) and Ornithodoros coriaceus (pajaroello tick) (Fig. 5). Spinose ear ticks are native to warm, arid regions of western and southwestern United States. They are established, but less uniformly, well into colder parts of the country as far northeast as central Kansas and northward on the High Plains to Torrington, Wyoming. They creep into the host's ear as larvae and stay there for all of the feeding they will ever do. The larvae feed on blood for about a week and molt to first-stage nymphs. After approximately 10 days, they molt again. Second-stage nymphs are covered with short, sharp spines. They feed slowly or intermittently on blood from 2 to 6 months and attain the size of a large pea before dropping out of the ear. On the ground,

Figure 5. Various sizes of pajaroello ticks, Ornithodoros coriaceus. (Courtesy of Nancy C. Hinkle, PhD, University of California, Riverside, CA.)

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they seek dry, dark hiding places such as under tree bark or in cracks in fence posts or barn walls. After 12 to 41 days in hiding, they molt, become adults, and continue to remain in protected sites. This species is incapable of feeding in the adult stage. They mate and, during a period of about 6 months, the female tick lays from a few hundred to 1500 eggs, which hatch 2 or 3 weeks later. Newly hatched larvae crawl out of the crevices, seek hosts, and the cycle continues. Favored hosts of spinose ear ticks are hoofed mammals, including cattle, horses, sheep, goats, deer, elk, bighorn sheep, and swine, but they also infest dogs, coyotes, rabbits, cats, and humans. There is no distinct season of animal exposure to spinose ear ticks except that in northern extensions of its range, infestation is initiated only during warm months. Infestations may first be noticed because of incessant head tossing, head shaking, and ear rubbing as a result of irritation. Secondary bacterial infection involving the middle and inner ear is common. Ear drum perforation and deafness can result. Severe cases may include permanent nerve damage and death from meningitis. In areas of known or potential infestation, the ear canals of sheep and goats should be inspected routinely for ticks during opportune situations such as vaccinating, deworming, and shearing. Effective treatment and a few weeks' subsequent protection can be achieved with ear washes of permethrin, fenvalerate, coumaphos, or lindane, or with coumaphos or permethrin dust. Ear-wash solutions (at labeled sprayconcentration rates) or dusts should be applied with a squeeze bottle fitted with a curved plastic cannula; both ears of all animals should be treated. Acaricide sprays of confinement premises are recommended where repeated infestations have occurred; the spray should be applied to wooden fences and sides of barns, tree trunks, feed troughs, and other structures to which livestock have access. The practitioner should ensure penetration of cracks and crevices with the spray. Primary acaricides for this purpose include coumaphos, permethrin, and fenvalerate. Other premise sprays include diazinon, chlorpyrifos, cyfluthrin, and lambdacyhalothrin. It is important to notice whether the product label calls for animal exclusion from the premises during treatment. Ornithodoros coriaceus, known more commonly as "coriaceus tick" or "pajaroello tick," is present only in California, Nevada, southern Oregon, and possibly southwestern Idaho. These ticks are most abundant in brushy foothill terrain on both sides of the Sierra Nevada Range between altitudes of 600 and 8000 feet. 17 Unlike spinose ear ticks, pajaroello ticks spend only a short time on hosts and are unlikely to be shipped a long way from their point of origin. Cattle and deer are the most common hosts of pajaroello ticks, but horses, sheep, goats, and even humans incur its bites. They are a grounddwelling species that seldom climb. Although adults range up to one half inch long, their drab, gray-brown color, pebble-textured integument, and habit of lying motionless most of the time make them difficult to see in their off-host habitat. All stages seek hosts, usually while the animal is lying down. Larvae can live up to 5 months without feeding.

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Those that find a host feed for approximately 9 days, drop from the host, and molt to become nymphs. There may be from three to seven nymphal stadia, each requiring a single blood meal that takes from a few minutes to nearly 2 hours. Adults feed from 5 to 50 minutes. Nymphs can survive for several months off the host between blood meals, and unfed adults can survive for up to 2 years, but the average life cycle is probably about 1 year. Female ticks live for approximately 5 years and produce three or four batches of 150 to 300 eggs each. Larvae hatch from eggs in 10 to 20 days after oviposition. As with hard ticks, control of this tick in its off-host environment is seldom feasible for livestock production operations. Animals can be provided some protection with whole-body spray treatments as described for hard ticks. Hard ticks include many species more familiar to outdoorsmen, ranchers, and veterinarians and are generally referred to as "wood ticks," "dog ticks," or "deer ticks." Hard tick species universally have only one nymphal stage between the larval stage and the adult. Most are three-host ticks; that is, they feed once in each crawling stage (larva, nymph, adult) and must find a new host (whether of the same or different species) for each feeding. Typically, they attach to their host and feed for 3 to 7 days as larvae, 4 to 7 days as nymphs, and 5 to 12 days as adults. Most are capable of a complete life cycle in a year, but in more northerly climates or when a larva or nymph does not readily find a host, 2 or 3 years is common. Male ticks expand little during feeding. Female ticks, larvae, and nymphs expand greatly as they feed, becoming bulbous ("fat as a tick") and weighing many times more than their unfed weight. Color markings are reliable characteristics for identification of species and distinguishing male ticks from female ticks. The Rocky Mountain wood tick, Dermacentor andersoni, is an ornate, three-host tick that is a major ectoparasite of livestock (including sheep and goats) and humans throughout the Rocky Mountain and Great Basin States and western Canada-the big sheep-ranching region. Hosts of larvae and nymphs are primarily rodents; the adults parasitize mediumsized and large animals. Mating occurs on the host as the female tick feeds. They may be found anywhere on the host, but on sheep they apparently find it easiest to attach to the ventrum and head. After engorging, mated female ticks drop to the ground, lay from 5000 to 6000 eggs within a month, and die. Egg hatching begins about a month later. Larvae seek rodent hosts, feed, drop off, molt, and become nymphs. Nymphs seek shelter from the summer heat and usually overwinter before seeking another rodent host, feeding, dropping off, molting, and becoming adults. Adult activity and recruitment to animals may occur throughout the warm months, but peak activity is April through June. Two other ornate, three-host Dermacentor ticks, D. variabilis (the American dog tick) and D. occidentalis (the Pacific Coast tick), have similar life strategies. They have similar effects on small ruminants in the regions where they occur, although they seldom parasitize sheep and goats in as great a number as D. andersoni. D. variabilis ticks occur

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from the High Plains east of the Rocky Mountains to the Atlantic Coast and also in various parts of Washington, Oregon, and California. D. occidentalis ticks occupy the Pacific Coastal area from Baja California through Oregon. Yet another Dermacentor species, D. albipictus (the winter tick), is present throughout most of the United States and northward into central Canada. Population densities of this species seem to be greater in the timbered mountain slopes of the Rockies and in the northern part of its range. This is one of two species most likely to infest sheep, goats, and other livestock between November and March (see discussion of Ixodes scapularis in the following paragraphs). There are two color morphs of D. albipictus-ornate and inornate. The inornate morphs are more common in the southern United States, but both forms are present in many parts of the country. They were formerly considered to be a separate species, D. nigrolineatus. 29 D. albipictus is a one-host tick. Large, hoofed animals are favored hosts, although they have been taken from a wide array of other wild and domestic animals. In autumn and early winter months, larvae quest from brush or other vegetation, mostly at heights of 3 to 5 feet from the ground, waiting for a host to pass by. Once on the host, they stay there through larval and nymphal feeding and molting and until they have fed and mated as adults. In dense infestations they may practically cover the host's body, but they prefer the ventrum, neck, and head. Female winter ticks drop off the host during the first warm weeks of late winter or early spring and lay eggs. After hatching, larvae remain clustered and inactive on the soil beneath vegetation and leaf litter until cool fall weather arrives. They then seek hosts, and the cycle is renewed. Next to D. andersoni, the tick species that probably has the greatest effect on sheep and goat production is Amblyomma americanum, commonly known as the lone star tick. This is an ornate, three-host tick that uses a broad host range. The egg and larval stages of this species require more than 65% relative humidity for survival,I4 thus precluding its distribution from arid parts of the country. This species is common to abundant east of a line from approximately the lOOth meridian in south central Texas, northeasterly through southeastern Nebraska, and mostly south of a line from there through New Jersey. Within this region, they are more abundant in semi-open woodlands, woods-grassland interfaces, or along windbreaks of trees and shrubs. Lone star ticks overwinter in both the adult and nymph stages, and both are active from late-winter warmup through the autumn months. Months of annual activity depend on the climate of the location and the annual seasonal variation. Peak adult activity wanes after the onset of hot, mid-summer weather. Nymphs are active from early spring through the autumn months. Larval activity peaks from June through August in central Texas and from mid-July through mid-September in eastern Kansas. Most larvae use rodents, other small mammals, and ground-nesting birds as hosts; nymphs use the same hosts and virtually any medium-

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sized or large mammal. Thus, all crawling stadia of this species may parasitize the same host either simultaneously (during larval season) or sequentially. The immature stages are more commonly found on the legs and ventrum. The adults may attach on any anatomic site, but they often aggregate in great numbers in and around a host's ears and eyes and on the perineum. Lone star ticks sometimes elicit a dramatic cutaneous response in the host. In heavy infestations, serum may ooze from tick bites, and suppurative lesions may occur. A related ornate, three-host species is the Gulf Coast tick, A. maculatum. This species was historically associated with the lowlands along the Gulf of Mexico-mostly within 200 miles of the coast, and along the Atlantic Coast northward through South Carolina. Within the past few decades, this species has become established northward through the Southern Plains of Texas and Oklahoma and nearly to the Nebraska border in the eastern half of Kansas. A. maculatum populations appear to thrive best in a prairie habitat. Larvae and nymphs attack small animals but are most numerous on ground-dwelling birds such as meadowlarks and quail. Adults of this species commonly parasitize cattle, horses, and mules but may be found on swine, small ruminants, dogs, and humans as well. Adult Gulf Coast ticks have a strong predilection for the ears of hoofed animals, commonly attaching midway along the inside of the pinna. Their feeding results in extreme tissue trauma in the middle part of the ear; the ear becomes thickened, and the tip of the ear bends sharply forward or downward from that point. The deformity is permanent; it is commonly known as "gotch ear." Heavy infestations can cause exsanguination, morbidity, and death in domestic animals. 28 In its traditional southern range, A. macula tum adults may infest large animals from early spring, but peak activity occurs during August and September. In northern Oklahoma and Kansas, peak activity is from first warmup in March through mid-June. Intermediate timing of adult activity has been reported in Georgia. 29 Gulf Coast tick infestations can be treated in individual animals as described for spinose ear ticks, but the cannula on the squeeze bottle is unnecessary. It is easier, faster, and just as effective to use low-pressure spray in and around the ears and on the neck, shoulders, and briskets of animals to protect them from this species. The black-legged tick, Ixodes scapularis, is an inornate, three-host species that occupies much of the same range that lone star ticks do, as well as the northeastern and north central states. Their egg and larval stages require high humidity for survival; thus, they are even more confined to moist regions and close to wooded areas within those regions. Their western distribution lacks approximately 100 miles of coming as far west as that of lone star ticks. Any crawling stage can attack even large hosts, but most larvae and nymphs parasitize small animals, birds, and lizards. These stages are most common in spring and summer. Adults also use any size host, but most of them parasitize large animals such as deer, cattle, horses, swine, sheep, goats, canines, and humans. They may attach anywhere on the host, but on hoofed animals most are

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found on the head, neck, and ears.16 Adults seek hosts primarily in the cool fall and early winter months. They feed slowly or intermittently and remain on the host until warm days arrive. Black-legged ticks can vector tularemia (Francisella tularensis), Lyme disease (Borrelia burgdorferi), human babesiosis (Babesia spp.), human granulocytic ehrlichiosis (Ehrlichia spp.), and Powassan viral fever. Although several helpful options are available for control of hard ticks, including many insecticides in formulations ranging from dusts and sprays to pour-ons, ear tags, and injections, lasting control is difficult to achieve. Where herd owners have regularly experienced problems with infestations of ticks, they should consider a multipronged, integrated approach incorporating cultural, managerial, and chemical methods. Where ownership of land and ecological considerations make it acceptable, brush control by herbicides or burning reduces populations of ticks. Acaricidal control of ticks in their vast, off-host habitats is not feasible. In most of the United States, protection of sheep and goats from ticks remains primarily dependent on direct application of acaricides to the animals. Treatment should be timed to protect animals during peak tick activity. Even then, such activity commonly extends through several weeks, and retreatment may be necessary if ticks are abundant. Where tick season is prolonged or involves different tick species sequentially, it may not be feasible to protect sheep and goats except during limited periods of most intense infestation. Pour-on and sprinkle treatments administered for keds and lice are helpful in controlling ticks if the timing required for both kinds of pests is coincident. Extralabel applications of endectocides such as moxidectin and dormectin provide some reduction in parasitism by ticks. Ivermectin is rapidly metabolized by sheep and provides little control of ticks beyond those that are on the animal at the time of application and for approximately 3 days afterward. Dips and high-pressure sprays can be used on sheep and goats but are usually not feasible except in large operations. Less acaricide is required to treat sheep or goats that recently have been shorn, and it is easier to monitor the efficacy of treatment on shorn animals. Fortunately, the traditional shearing season comes just before peak tick season in many parts of the country. Table 1 lists insecticides and acaricides registered for use on sheep and goats. SUMMARY

Ectoparasites are a common problem in small ruminants of North America. Management of ectoparasites in small ruminants can be challenging for producers and veterinarians. It is important for the veterinarian to make an accurate diagnosis of the type of ectoparasite that is infesting the animal, then to develop a plan that most effectively and economically controls the ectoparasite. Effective and economic control of an ectoparasite infestation begins with an understanding of the ectoparasite's life cycle and how that life cycle affects the animal. It should

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be noted that climate and geographical area can affect the life cycle of specific ectoparasites, so it is important for veterinarians to educate themselves about their specific environment. Once the life cycle has been addressed, then the veterinarian should decide which intervention will provide the best control. Intervention possibilities may range from insecticides to environmental management or a combination of several methods. The veterinarian should provide the producer with realistic goals that define specific limitations of ectoparasite control. ACKNOWLEDGMENTS The authors thank Clifford Spaeth, PhD, Professor in the Department of Animal Sciences and Industry, Kansas State University, and Sonny Ramaswamy, PhD, Professor and Head, Department of Entomology, Kansas State University, for their helpful comments in the preparation of this article. This article's contribution number is 01-175-B from the Kansas Agricultural Experiment Station.

References 1. Alogninouwa T, Parent R: Ivermectin treatment of mange in goats in Senegal due to mixed infestation with Sarcoptes scabiei and Chorioptes caprae: Clinical observations. Bulletin Mensuel de la Societe Veterinaire Pratique de France 70:399-400, 1986 2. Bates PG, Groves BA: Failure of a single treatment with ivermectin to control sheep scab (Psoroptes ovis) on artificially infested sheep. Vet Rec 128:250-253, 1991 3. Butler JF: Lice affecting livestock. In Williams RE, Hall RD, Broce AB, et al (eds): Livestock Entomology. New York, John Wiley & Sons, 1985, pp 101-127 4. Dorchies P, Alzieu JP, Cadiergues MC: Comparative curative and preventive efficacies of ivermectin and closantel on Oestrus ovis (Linne 1758) in naturally infected sheep. Vet Parasitol 72:179-184, 1997 5. Dorchies P, Cardinaud B, Fournier R: Efficacy of moxidectin as a 1% injectable solution and a 0.1% oral drench against nasal bots, pulmonary and gastrointestinal nematodes in sheep. Vet Parasitol 65:163-168, 1996 6. Francy DB, Moore CF, Smith GC, et al: Epizootic vesicular stomatitis in Colorado, 1982: Isolation of virus from insects collected along the northern Colorado Rocky Mountain Front Range. J Med Entomol 25:343-347, 1988 7. Fthenakis GC, Papadopoulos E, Himonas C, et al: Efficacy of moxidectin against sarcoptic mange and effects on milk yields of ewes and growth of lambs. Vet Parasitol 87:207-216, 2000 8. Georgi JR, Georgi ME: Arthropods. In Parasitology for Veterinarians, ed 5. Philadelphia, WB Saunders, 1990, pp 2-76 9. Gothe R, Kunze K, Hoogstraal H: The mechanisms of pathogenicity in the tick paralyses. J Med Entomol 16:357-369, 1979 10. Graham OH, Hourrigan JL: Eradication programs for arthropod parasites of livestock. J Med Entomol 13:629-658, 1977 11. Holbrook FR, Tabachnick WJ, Schmidtmann ET, et al: Sympatry in the Culicoides variipennis complex (Diptera: Ceratopogonidae): A taxonomic reassessment. J Med Entomol 37:65-76, 2000 12. Ibrahim KE, Abu-Samra MT: Experimental transmission of a goat strain of Sarcoptes scabiei to desert sheep and its treatment with ivermectin. Vet Parasitol 26:157-164, 1987 13. Kramer WL, Jones RH, Holbrook FR, et al: Isolation of arboviruses from Culicoides midges (Diptera: Ceratopogonidae) in Colorado during an epizootic of vesicular stomatitis New Jersey. J Med Entomol 27:487-493, 1990

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14. Lancaster JL Jr: A guide to the ticks of Arkansas. University of Arkansas Agricultural Experiment Station Bulletin 779:1-40, 1973 15. Lloyd JE: Arthropod pests of sheep. In Williams RE, Hall RD, Broce AB, et al (eds): Livestock Entomology. New York, John Wiley & Sons, 1985, pp 253-267 16. Loomis EC: Epidemiology and control of ectoparasites of small ruminants. Vet Clin North Am Food Anim Pract 21:397-409, 1986 17. Loomis EC, Furman OP: The pajaroello tick. Division of Agricultural Sciences, University of California Leaflet 2503:1-3, 1979 18. Lucientes J, Castillo JA, Ferrer LM, et al: Efficacy of orally administered ivermectin against larval stages of Oestrus ovis in sheep. Vet Parasitol 75:255-259, 1998 19. Manurung J, Stevenson P, Beriajaya, et al: Use of ivermectin to control sarcoptic mange in goats in Indonesia. Trop Anim Health Prod 22:206-212, 1990 20. Mead DG, Mare CJ, Ramberg BF: Bite transmissions of vesicular stomatitis virus (New Jersey serotype) to laboratory mice by Simulium vittatum (Diptera: Simuliidae). J Med Entomol 36:410-413, 1999 21. Nunamaker RA, Perez de Leon AA, Campbell CL, et al: Oral infection of Culicoides sonorensis (Diptera: Ceratopogonidae) by vesicular stomatitis virus. J Med Entomol 37:784-786, 2000 22. O'Brien DJ: Treatment of psoroptic mange with reference to epidemiology and history. Vet Parasitol 83:177-185, 1999 23. Parker LD, O'Brien DJ, Bates PG: The use of moxidectin for the prevention and treatment of psoroptic mange (scab) in sheep. Vet Parasitol 83:301-381, 1999 24. Rehbein S, Batty AF, Barth D, et al: Efficacy of an ivermectin controlled-release capsule against nematode and arthropod endoparasites in sheep. Vet Rec 142:331-334, 1998 25. Rhodes AP: The effect of extensive chorioptic mange of the scrotum on reproductive function of the ram. Aust Vet J 52:250-257, 1976 26. Rugg D, Gogolewski RP, Barrick RA, et al: Efficacy of ivermectin controlled-release capsules for the control and prevention of nasal bot infestations in sheep. Aust Vet J 75:36-38, 1997 27. SolI MO, Carmichael IH, Swan GE, et al: Treatment and control of sheep scab (Psoroptes ovis) with ivermectin under field conditions in South Africa. Vet Rec 130:572-574, 1992 28. Strickland RK, Gerrish RR, Hourrigan JL, et al: Ticks of veterinary importance. USDA Agriculture Handbook 485:1-122, 1976 29. Teel PD: Ticks. In Williams RE, Hall RD, Broce AB, et al (eds): Livestock Entomology. New York, John Wiley & Sons, 1985, pp 129-149

Address reprint requests to David P. Gnad, DVM Section of Agricultural Practices Department of Clinical Sciences Kansas State University College of Veterinary Medicine 1800 Denison, Mosier Hall Manhattan, KS 66506 e-mail: [email protected]