Public-Health Pest Control

Public-Health Pesticide Applicator Training Manual

MITES AND TICKS


I. Mites - Bionomics - Detection and Control
II. Ticks - Developmental Stages - Bionomics - Detection and Control


The order Acarina (class Arachnida) includes mites and ticks. Members of this order differ from other arachnids in that the body is not segmented, and the cephalothorax and abdomen are combined into one body region. Larval mites and ticks have three pairs of legs, whereas nymphs and adults have four pairs.

Mites inhabit most ecological settings, ranging from deserts to rain forests, mountain tops to tundra and saltwater ocean floors to freshwater lakes. The relatively few species parasitic on humans in the U.S. produce dermatitis, often followed by allergic reactions.

Ticks are parasitic during their life cycle. They are annoying pests whose bites are irritating. When a tick is forcibly removed, its mouthparts frequently remain in the skin, resulting in a sore, an infection or even blood poisoning. In the U.S. ticks, unlike mites, transmit many serious diseases.

I. MITES

Mites that attack humans with some frequency in the U.S. originate in a variety of habitats. Some, including the chicken mite and the tropical fowl mite, migrate to humans from birds. Others, such as grain mites and mushroom mites, are found in food materials or stored products. The straw itch mite and furniture mite come from plant material, and the chigger mite is found in lawns and open woodlands. The tropical rat mite and the mouse mite come from rodents, whereas the itch mite and follicle mite are permanent residents on humans. Mites develop by gradual metamorphosis.

Bionomics
Chicken mite (Dermanyssus gallinae). Best-known of the mites infesting poultry, the chicken mite is found on the birds only when it is feeding, which is normally at night. In the daytime it hides in cracks and crevices in the vicinity of the roost. The chicken mite will feed freely on many other birds, including pigeons, canaries, sparrows, swallows, doves and wrens. When the mite attacks humans it causes mild dermatitis and itching. Cases of dermatitis caused by this mite are common in rural areas, but infestations also occur in urban areas. These include instances where the infestations can be traced to pet canaries, pigeons and nests of other wild birds or in which the death of the bird host or its departure from the nest instigated the attack on humans. It is believed that this species can live for several months without food.

Northern fowl mite (Ornithonyssus sylvarium). Although very similar to the chicken mite in appearance, the northern fowl mite differs in that it breeds among the feathers of the host and may complete development without leaving the host. It is not necessary for this mite to stay on the host, however, and it may be found in nests, or roost areas, and in surrounding cracks and crevices. It can survive for two or three weeks away from the host. This mite may bite humans, causing some annoyance but infrequently dermatitis. The problem most frequently is irritation from the occasional bites inflicted by wandering mites. The mite is a general parasite of birds, being found on domestic fowl, sparrows, swallows and many other avian species throughout the temperate region. Human annoyance is frequently associated with the absence of the normal host bird, leaving an infestation of mites in the nest area without a convenient source of food.

Tropical rat mite (Ornithonyssus bacoti). This mite is associated with rats throughout the U.S., where it feeds also on humans and many other warm-blooded animals. The bite is painful, causing intense itching and a skin irritation known as rat-mite dermatitis. This mite has not been proven to be a transmitter of typhus or other diseases, although its habits appear to suit it well for such a role. Attacks on humans are almost always associated with rats in buildings, and complaints are common from areas that may be infested with rats, such as warehouses, stores, theaters and apartments. Rat control may intensify the attack on humans, but this mite will bite humans even when there is an abundance of host rats on which they can feed. The mite drops from its host after each feeding and may be found on a variety of surfaces near rat-infested areas. It can survive for several days without a blood meal.

House mouse mite (Liponissoides sanguineus). This mite in the U.S. is primarily a parasite of mice. It tends to leave its rodent host to wander throughout buildings and bite people. Its major importance is that it has been identified as the vector of rickettsial pox, a mild and nonfatal human disease.

Grain mite. Grain mites (including the furniture mite and the mushroom mite) are commonly found infesting all types of grain flour, stored foods, cheese and mushroom beds. They prefer a moist location and under favorable conditions develop rapidly and in great numbers, completing the life cycle in as little as 17 days. Under adverse conditions this period may be considerably extended. In some species the second nymphal form may be replaced by a special stage known as the hypopus. In this stage the mite is highly resistant to unfavorable conditions, insecticides and fumigation, and may exist for several months without feeding. The hypopus is transported from place to place by clinging to small animal forms such as insects or mice. When it encounters favorable conditions it sheds its skin and resumes normal growth and development. The peculiar adaptation through the hypopus stage makes control very difficult.

Grain mites are reported to have been the cause of mild dermatitis in humans, known under various names as "grocers' itch," "vanillism" (from infestations on vanilla beans), and "copra itch." These cases are reported where products infested with the mites are handled by humans. These mites are not bloodsucking forms and thus are the cause of only mild irritations, very easily remedied once the source of exposure is identified.

Straw itch mite (Pyemotes ventricosis). The straw itch mite normally lives on other arthropods. Common hosts are the larvae of several insects, including the wheat jointworm; the wheat strawworm; the Angoumois grain moth; the rice, granary, bean and pea weevils; and the pink bollworm. It reproduces rapidly and in enormous numbers. This mite has an unusual development in which the eggs hatch and the young are matured within the body of the female. They are released as sexually mature adults. It is reported that a single female may give birth to more than 200 adult mites and that in one week the females of this brood will have produced another brood in the same manner. Homes with beetle-infested beans or cereals in cupboards often have problems with this mite. Pyemotes causes severe bite reactions.

People engaged in threshing straw or handling grains or other material infested with the insect hosts often are overrun by these mites. Their bites produce a rashlike dermatitis that may cover large areas of the body. The rash appears about 12 hours after the attack and is accompanied by severe itching. The attack is often so intense that vomiting, headache, sweating and fever follow.

Chiggers (Eutrombicula alfreddugesi). Larvae of chiggers, commonly called redbugs, attack humans and dogs during the larval stage. These mites are distributed over approximately the eastern half of the country. They are most common in the southern states where breeding may be continuous but frequently are abundant during the summer in the more northern states with one to three generations per year. They infest a variety of areas ranging from overgrown brush to well-kept lawns. Adults overwinter in earthen cells in the soil, scavenge on decaying matter and emerge from the soil in the spring to lay their eggs. These hatch into tiny, oval, orange-colored larvae that normally feed on snakes, turtles, rabbits, birds and other wildlife. These larvae, barely visible to the naked eye, are very active. When humans come in contact with infested vegetation, the larvae swarm over the entire body and it might be several hours before they settle down to feed. Their attack seems to be concentrated at points where the clothing is pressed against the skin, such as under belts or garters.

They attach, frequently near a hair follicle, by their mouthparts and first pair of appendages. The mites inject a fluid that liquefies the immediately adjacent tissues, which are then ingested. The surrounding tissues become hardened and, as feeding progresses, form a tiny tube through which further liquefied tissue may be withdrawn. The larvae become fully fed in four to six days when they drop off the host, leaving behind the tubes that have developed from the feeding activity. The digestive fluid of the mites causes a severe itching and a definite dermatitis. Itching may last for a week or more. Scratching these areas may lead to secondary infection. After leaving the host, the larvae transform into nymphs and later into adults. Neither of these forms attacks humans or other animals. Both feed on vegetable matter. Chiggers are not associated with disease transmission in the U.S.

Itch mite (Sarcoptes scabiei). This mite causes scabies or itch in humans and is parasitic on dogs, pigs, horses and sheep. There are several closely related forms on animals that may sometimes transfer to humans, but usually close contact is required. Favored sites are in the skin between the fingers, the folds at the wrists, at the bend of the elbow or knee, and under the breasts. Crowded conditions encourage the spread of scabies infestations. The female mite cuts into the skin, makes a burrow under the skin and lays eggs. The larvae return to the surface of the skin to molt, and the nymphal and adult stages then live on the surface. Unnoticed at first in newly infested people, sensitivity and itching build up at the end of the first month of infestation.

Follicle mite (Demodex folliculorum). This mite is found in the skin pores of humans, especially around the nose and eyelids. It is likely that most people harbor this species. The mite is entirely parasitic, spending the entire life cycle on the host.

House dust mite (Dermatophagoides spp.). House dust mites can be a problem in any building occupied on a regular basis. They are generally found in mattresses, pillows, overstuffed furniture, rugs, floors or other protected places where people sleep or sit for long periods. They require a damp environment and are often found in floors where moist air may enter a room. Eggs are laid singly and the life cycle takes about a month. Adults live for one to three months, feeding on a variety of foods including dog food, cereals, yeast and especially the scaling of the skin of humans and their pets. In some sensitive people, they cause an allergic reaction.

Detection and Control
Detection. Survey methods vary with the habits of the species being investigated. Various household ectoparasites can generally be found in structures.

To survey for chigger mites, use 12-inch squares of black or white paper placed on the ground for one to five minutes at intervals of 100 feet, perhaps, throughout the area, or in 400x400-foot grids. Count and record the number of mites aggregating at the upper edge of the squares. Collect the mites with a fine-pointed brush and vials of alcohol for later identification. Use Berlese funnels to collect flour and grain mites and other free-ranging species, such as bird mites in nesting material.

Estimates of chigger, bird and rodent mite population densities can be based on data gathered by stunning or killing the ectoparasites (with ether or chloroform) on dead or trapped animals, and combing (or beating) the parasites into a white enameled pan or picking them off with forceps. Alternatively, live hosts in cages with hardware cloth bottoms can be placed so that mites will drop into a pan of water after engorging, or the ectoparasites can be floated from a dead animal by immersion in water containing detergent and then collected on filter paper.

Scabies mites are detected by making skin scrapings for microscopic examination.

Control. Do not attempt control for the scabies (human itch) mite. This pest is controlled by laundering bedding and underwear and use of pesticide ointments prescribed by a physician. These may be recommended for application from the neck down for all family members.

For mites that migrate from bird nests or coops, remove the nests or caulk to exclude mite movement into dwellings. Wear protective clothing (gloves, eyeglasses, etc.) to prevent mites and nest debris from contaminating workers. Apply approved pesticide sprays or dusts indoors to cracks and crevices near or leading to mite sources, and outside at nest areas. Habitat alteration to remove birds from nest areas coupled with pesticide application should immediately eliminate the problem.

For chigger mites, avoid infested locations or use repellents on pants legs and shoes and tuck trousers into boots. When possible, keep vegetation cut low. Not only does this remove chigger harborage, it also eliminates harborage for rodents and other animals that serve as wild hosts. These sanitation practices are especially important for chigger management in fields, vacant lots, recreational areas and parks. Chiggers can also be controlled in lawns and other infested areas by careful and thorough treatment with granules or sprays of residual pesticides that are effective against mites. The miticides will work best if applied after the infested area has been mowed.

II. TICKS

From a public-health standpoint ticks are important as vectors of diseases of humans and other animals. Many species are quite resistant to environmental stresses and may live for many years. They have few natural enemies and have a wide range of hosts. Ticks typically take one blood meal in each of the three parasitic stages: larva, nymph and adult. Both sexes are blood feeders, the female becoming greatly distended with blood after mating and then producing many eggs. Most ticks feed on a different host during each parasitic stage. After exposure to ticks, the body should be carefully searched, including the scalp.

Several characteristics of ticks make them outstanding vectors of pathogenic agents. Wide host range and tendency to feed on several hosts during their lifetime ensures ample opportunity to acquire and transmit pathogens. Hardiness and longevity allow them to survive periods of unfavorable environmental conditions. High reproductive potential ensures large populations and a high frequency of host-vector contact. Finally, they feed slowly and attach to the host for relatively long periods. This allows sufficient time for pathogen acquisition and transmission as well as vector dispersal by means of host movement.

Hard ticks (family Ixodidae) are responsible for transmission of the majority of tick-borne diseases of humans in the U.S. They are the vectors of babesiosis, Colorado tick fever, Lyme disease, ehrlichiosis, Rocky Mountain spotted fever and tularemia. While soft ticks (family Argasidae) do not directly transmit these diseases to humans, they may be involved in the maintenance of natural cycles among reservoir hosts, as in the case of Colorado tick fever. In addition, soft ticks of the genus Ornithodoros are vectors of tick-borne relapsing fever.

Hard ticks have a hard upper surface called a shield or scutum that covers the entire back of the male but only partly covers the female. Mouthparts are visible from above. They attach securely and may feed for extended periods, using a different host in each life stage. The female produces as many as 6,000 to 7,000 eggs.

Soft ticks do not possess a shield, so the sexes look alike. Their mouthparts are beneath the anterior end of the body and are not visible from above. Principal hosts are birds, domestic animals, bats and small mammals. These ticks feed intermittently at night. The female oviposits following the blood meal and produces 500 to 1,000 eggs during her lifetime.

Developmental Stages
Larvae. Normally, thousands of tiny larvae, commonly called "seed ticks," hatch from an egg batch and crawl randomly in search of a host. Fortunate ones attach to a small mammal or lizard. Feeding time is generally short, a few hours or a day, but up to three days for Ixodes scapularis. During feeding, the host wanders and the tick is transported to a new location where, when engorged, it drops off.

Nymphs. After molting, hard tick nymphs climb grass leaves or plant stems and await a host. Because they are higher than ground level, they tend to attach to larger hosts than before. Soft tick nymphs burrow in and await the arrival of a host. After several days of feeding they drop off and again molt.

Adults. Ticks sometimes wait for months or more than a year for a suitable host. When finally engorged, they drop off to oviposit. Ticks that tend to feed on the same host species at each stage are referred to as 1-host ticks, whereas those that feed on different hosts each time are called 3-host ticks.

Bionomics
Hard ticks and some species of soft ticks seek their hosts by climbing vegetation and awaiting vibrations or shadows to announce the arrival of a host. The first pair of legs is extended and used to grasp the host when contact is made. This behavior is known as questing. If heat or carbon dioxide is detected by the tick, it will seek it out and climb onto the host as it passes. The height at which questing takes place determines the size of the host and therefore, to some extent, the species selected. There is considerable variation between species, and the different life stages of some species, in the height at which they quest.

Many soft ticks, in contrast, inhabit caves, dens, stables and other places used by potential hosts. They typically secrete themselves in loose soil, cracks or crevices by day and attack their host at night, usually while it is asleep. They crawl to the host, engorge in a few minutes or hours, and return to their hiding places.

All ticks orient to potential hosts in response to products of respiration. Carbon dioxide, in particular, is attractive at a distance. This characteristic is helpful in surveillance studies because many species can be collected using traps baited with dry ice.

When feeding, the tick uses its chelicerae (teeth) to cut the victim's skin and then inserts its mouthparts. The hypostome (feeding tube) has many rows of recurved barbs that become cemented in and anchor the tick to its host (making it very hard to withdraw by external force). Blood is pumped by a muscular pharynx (pump), and the salivary glands produce an anticoagulant that allows long periods of feeding without the host's blood coagulating. The tick usually moves to the highest part of the host to attach and feed on the head or ears.

American dog tick (Dermacentor variabilis). The American dog tick, a 3-host tick, is widely distributed east of the Rocky Mountains and along the Pacific coast. Dogs are the preferred host of adult ticks, although they feed readily on many large mammals, including humans. This tick species transmits the causative pathogen of Rocky Mountain spotted fever and possibly Q fever to humans. Adult ticks are commonly found in spring on grass and other low vegetation in their questing position. The adult stage is identified by the ornate pattern (i.e., pale markings) on the scutum (shield). Also, they have simple eyes, short mouthparts and 11 ridges, or festoons, on the edge of the abdomen.

American dog ticks prefer overgrown urban and rural vacant lots, wood-lined creeks, waste farm fields, weedy roadsides and edges of paths and hiking trails. They wait on grass and weeds for a suitable host to brush against the vegetation and are commonly encountered by sportsmen and recreationalists. Larval activity begins in early spring when they feed on rodents such as meadow voles and white-footed mice, whereas the eight-legged nymphs may be found on white-footed mice, cotton rats, and rabbits during winter months. Adults are most abundant from mid-April to mid-July. Once on the host, they crawl upward, seeking a place to attach and take a bloodmeal. The adult male may remain on the host for an indefinite period of time, alternately feeding and mating. The female feeds, mates, becomes engorged and drops off to lay several thousand eggs. The entire life cycle requires from four months to more than a year.

Brown dog tick (Rhipicephalus sanguineus). The brown dog tick creates severe annoyance when it infests domestic pets and becomes established inside buildings. This is the most widely distributed tick in the U.S. and is characteristically a reddish-brown species that attacks dogs and other mammals, but rarely humans. It is not known to transmit human diseases. It most often attaches to the ears and between the toes of dogs. The engorged female ticks, sometimes about inch long, are particularly noticeable as they crawl on walls, window frames, or around baseboards and cracks looking for protected areas in which to deposit their 1,000 to 3,000 eggs. The entire life cycle can be completed in less than two months. Homes and yards can become heavily infested after the passing of a single dog that drops an engorged female tick with thousands of eggs, eventually reaching a high density in the resident dogs' sleeping areas. This tick does not survive outside in cold climates.

Rocky Mountain wood tick (Dermacentor andersoni). The Rocky Mountain wood tick is the major vector of Rocky Mountain spotted fever, a rickettsial disease of humans. It is common in the Rocky Mountain states and in southwestern Canada, where it is a vector of bovine anaplasmosis and canine babesiosis (blood parasites of animals). The toxins injected as it feeds may cause host paralysis. Hides punctured by tick feeding are downgraded because of reduced tensile strength.

This tick is a 3-host species. Adult ticks appear in the spring. They climb on low vegetation along animal trails in pasture or forested areas and attach to passing animals (usually cattle or horses). This tick mates during feeding, after which the female detaches from the host and deposits several thousand eggs over a period of a month. Hatched seed ticks attach to small rodents, feed, detach and develop into the nymphal stage. Nymphs seek shelter and are inactive until the following spring, when they attach to another animal, feed, drop off and molt into the adult stage. The adults overwinter, and the following spring they attach to a large animal, feed and start the life cycle over. The entire procedure takes three to four years.

Lone star tick (Amblyomma americanum). The lone star tick is mainly found in the southeastern sector of the U.S., but reaches as far north as New Jersey. Due to its long mouthparts, the bite is quite painful and may itch for a long time. It is a vector of ehrlichiosis, tick-borne typhus and tularemia. Females of this species are easily recognized by the conspicuous silvery-white spot on the back or scutum. The male tick has horseshoe-shaped markings on the posterior region of its reddish-brown body.

All parasitic life stages are commonly encountered by recreationalists and people who work outside. Nymphal and adult activity begins in March and April, ceasing in August. Larval activity begins about mid-May and subsides in November. Common hosts for all life stages are livestock, dogs, deer, birds and humans. This tick, like many other species, is attracted by the scent of animals, hence it is numerous along roads, paths and trails. Female ticks that drop from animals along bedding areas, pathways, and trails further increase the concentration at these sites.

Deer tick (Ixodes scapularis). The deer tick or blacklegged tick inhabits the eastern two-thirds of the U.S., and its close relative, I. pacificus, is found on the West Coast. These ticks are the main vectors of Lyme disease, human granulocytic ehrlichiosis and babesiosis. Lyme disease signs and symptoms include a ring-shaped rash at the point of the bite, which usually appears within a few days to a month after the bite. The deer tick prefers wooded areas, feeding on a wide variety of birds, mice, deer, domestic animals and humans. It is a 3-host tick, the adult reaching only the size of a sesame seed. Overwintering adults produce eggs in the spring, and the larvae feed primarily on white-footed and other mice during the summer. They molt into nymphs the following spring and feed on larger animals in the woods and grasslands. This is the primary stage that transmits the Lyme disease pathogen to humans, following a feeding period of up to 48 hours or more. Adults feed on deer and other large mammals.

Relapsing fever ticks (Ornithodorus spp.). This is the most important genus of soft ticks from a medical standpoint. Relapsing fever ticks are seldom seen by the average person because they are nest ticks and can survive starvation for months or even years. Bitten people may contract relapsing fever.

Fowl tick (Argas persicus). This soft tick feeds rapidly at night and subsequently oviposits in cracks and crevices. The tick has two or three nymphal stages before molting to the adult stage. Like the relapsing fever tick, this tick may live for months or years without a blood meal. Argus persicus readily attacks humans but does not transmit human disease. It is a vector of fowl spirochaetosis.

Spinose ear tick (Otobius megnini). This soft tick gets its name from the habit of larvae and nymphs to infest the ears of cattle, horses, mules, etc., and occasionally people. This is a 1-host tick.

Rodent tick (Ornithodorus hermsi). This soft tick is a common rodent parasite and a vector of relapsing fever. It is found along the Pacific coast and in the Rocky Mountain region of the U.S. Larvae can expand to three times their normal size after a blood meal and appear bright red. They are sometimes mistakenly referred to as strawberry seed insects.

Detection and Control
Detection. Surveillance for hard ticks is routinely conducted with a tick drag, a soft white cloth (3x3 feet) stapled to a dowel to which a cord is attached, with a second dowel or board at the end to weigh the cloth down. Questing ticks grab onto the cloth as it is dragged over grass and brush. The drag is inspected for ticks at fixed intervals, for example, 10 paces in an area of relatively high tick density or 100 meters in less dense infestations. Tick drags are effective when the vegetation is dry and the temperature exceeds 45ºF.

For many species, carbon dioxide trapping can yield the most ticks per worker-hour expended. This technique relies on the ability of ticks to sense carbon dioxide and move toward the source. Dry ice is placed in ventilated containers or compressed gas is used as the source of carbon dioxide.

Host trapping, as described above for mite surveillance, is also an effective method for detecting ticks. In areas with dense tick populations, simply walking through the habitat is an effective surveillance method.

Prevention. Personal protection is a recommended approach for prevention of tick bites. Tucking trousers into boots and shirts into pants, using repellent for exposed skin and an approved toxicant for clothing, and performing regular clothing and body checks should be routine when in tick habitat.

Removal of attached, embedded ticks should be done carefully as the insertion is deep and provides an entry for pathogens that might be released if the tick is crushed. The portion of the mouthpart (hypostome) that penetrates the skin is long in certain ticks and firmly attached and may break off from the body if the tick is forcibly pulled loose. The attachment results in a continuous itching. The inflamed condition is relieved only when the mouthparts are removed. Secondary bacterial infections may occur at the bite site. Do not force the tick to remove itself by placing a chemical or lighted cigarette on it because the tick will respond by regurgitating into the wound before it pulls out. A pair of fine-tipped forceps should be inserted into the skin at the base of the mouthparts and then the entire tick gently pulled out.

Control. Habitat alteration can be very effective. Exclusion of host animals (e.g., deer) can cause major reductions in populations of ticks that feed on deer. Opening clearings provides better visibility for predators to spot rodents. Keep vegetation short, widen paths and advise users to stay on the paths in order to avoid ticks. Controlled burning and mechanical clearing can reduce infestations temporarily. Reduced cover raises the ground temperature and lowers the humidity, causing the ticks to dry up and die. It eliminates suitable habitat for the larval and nymphal hosts, which include small rodents such as the white-footed mouse and the meadow vole. Also, limit access of dogs and children to tick habitats. Dog control is important to reduce brown dog tick infestations. Dogs should be disinfested daily.

Approved pesticides can be used in conventional applications in high priority areas. Depending on the target species, spray low vegetation thoroughly, apply granulars in heavier vegetation and dust rodent runs and burrows. Self-treatment stanchions are used to control ticks on deer. Control of ticks on mice in the yard with cardboard cylinders, from which the mice take insecticide impregnated cotton balls to the nest where it kills the parasites without harming the rodents, has not proven to be as effective as initially reported.

This chapter printed from the
University of Florida and the American Mosquito Control Association
Public Health Pest Control WWW site at http://entomology.ifas.ufl.edu/fasulo/vector/


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