Issued October 1938 Revised February 1946 E-454 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine COMBATING THE AMERICAN DOG TICK, CARRIER OF ROCKY MOUNTAIN SPOTTED FEVER IN THE CENTRAL AND EASTERN STATES By F. C, Bishopp, assistant chief of Bureau, and Carroll N. Smith and Harry K, Gouck, Division of Insects Affecting Man and Animals The American dog tick or common wood tick ( Dermacentor variabilis (Say)) of the Mississippi Valley and the region eastward carries the dread hximan disease known as Rooky Mountain spotted fever and is capable of carrying rabbit fever (tularemia) and of inflicting annoying bites. It occasionally causes a type of paralysis in man or dogs and is extremely troublesome by its attachment in great numbers to dogs. The annoyance from this tick's habit of craY/ling on people and the fear of its bite tend to drive vacationists away from otherwise attractive outing places. It does not infest houses, although a few ticks may be carried into houses from time to time on clothing or by dogs. If a house is contin- uously tick-» infested, and especially if the ticks are found in considerable numbers, a different species is probably concerned, namely, the brown dog tick ( Rhipioephalus sanguineus (Latr.)). l/ With its proved record of disease transmission, obviously the bite of this tick should be avoided and efforts should be put forth to control the pest. Rocky Mountain spotted fever does not occur among the ticks in every locality, and only a small percentage of them are infected. In most instances, therefore, the attachment of a tick will cause no serious consequences. However, this disease appears here and there in unexpected places, and when a person does happen to be bitten by an infected tick the results may be serious, as the mortality in the East usually runs from 20 to 25 percent. Stages and Development of the Tick The American dog tick and related species pass through four stages-- the egg, the seed tick or larva, the nymph, and the adult. The brown eggs are laid in a dense mass in some protected place on the ground. The eggs hatch in 1 to 2 months, depending on the temperature, producing tiny 6-legged seed ticks. Under experimental conditions the seed ticks may live as long as 18 months without food, but in nature their longevity seldom exceeds 12 months. When opportunity offers, they attach to small \J For information on the control of this species see Bishopp, F.C., The brown dog tick, with suggestions for its control. U. S. Bur. Ent. and Plant Quar. E-292, 3 pp., illus. (rev.) 1939. - 2 - wild rodents, such as meadow mice. They fill themselves with blood in 2 to 13 days, the majority requiring about 4 days, then drop and hide in some protected place. After 6 days to 8 months, depending on the tempera- ture, they molt their skins. The resulting nymphs are larger than the larvae amd have 8 legs. They also attach to small animals and engorge in 3 to 11 days. If a host animal is not at hand they may live for as long as 19 months, but in nature they are seldom active for more than a year. In 17 days to 10 months, depending on the temperature, the engorged nymphs molt to adult males and females. These are the flat, brownish, active creatures, known as wood ticks, iivhich attach to larger animals including dogs smd man. The males have a network of white lines on their backs (fig. r). The females have a hard shield marked with white on the fore part of the back; the rear part is softer and reddish, stretches,, and becomes grayish as blood is ingested (fig. 2). The adult ticks may live nearly 3 years without food under experimental conditions, but in nature only a few are active, for two reasons — engorgement of the females requires from 5 to 13 days, and mating takes place during this time. In from 3 to 58 days, depending on the temperature, after the engorged females drop from the host, egg laying begins. An engorged female may lay from 3,000 to 6,500 eggs, after which she dies. Wood ticks are most active in spring and in the early part of the summer. There are relatively few ticks abroad after August 1. In the South their activity is not so sharply restricted seasonally. Where the American Dog Tick is Found The American dog tick occurs here and there over the country from eastern Montana, Kansas, and Texas, eastward to the coast, and also in parts of western California. It is most commonly found in parts of Minnesota, Wisconsin, Iowa, and Texas, and along the Atlantic coast from Cape Cod to Florida. It is most abundant in damp areas that are covered with vmderbarush and tall grass and weeds* Animals Attacked The young ticks (seed ticks and nymphs) engorge upon small wild ani- mals, particularly meadow mice, but pine mice, white-footed mice, cotton rats, rice rats, and sometimes rabbits suad squirrels are also satisfactory hosts. The adults prefer dogs and various kinds of wild animals, such as raccoons, opossums, and coyotes. They also infest horses eoid, to a lesser extent, cattle, hogs, and other domestic and wild animals. Man, although frequently bitten, is not a preferred host. Methods of Control Methods of control applicable to many of the conditions under which this tick occurs have not been developed. Several things may^ be done, however, to reduce the number of wood ticks, especially around habitations. - 3 - (1) Since the dog is the principal host upon which the adult ticks feed, an effort should be made to prevent the ticks from engorging thereon. Each female tick engorged on a dog is capable. olLproducing from 3,000 to 6,500 young. Therefore, dogs should be kept away from tick- infested areas, the ticks hand-pioked daily, or better, a derris dip applied to the dogs regularly every 4 days. If but few ticks are present and hand picking is employed, it is best to use tweezers or forceps rather than to pick them off with the fingers. If the fingers are used, the hands should immediately be carefully washed to reduce the danger of acquiring infection from the ticks. Rubbing the eyes or nose while the hands may be contaminated should be avoided. Rotenone-bearing materials, such as derris end cube, are effective in killing the tick on dogs when applied as a dir> or dust. The dip is made by mixing 2 ounces of fine derris or cube pov;der» 1 ounce of neutral soap, suid 1 gallon of tepid water. The powder should contain at least 3 percent of rotenone. The dog may be put in a tub containing the dip, or it may be applied thoroughly with a brush, sponge, or dipper. The dip is allowed to dry on; if necessary, the surplus liquid may be removed with a towel. The dip can be kept for at least a week without deteriora- tion. If the dip cannot be used conveniently, derris powder may be applied to the skin on. all infested parts. To prevent ticks from engorging, the powder must be applied every other day. The persistence of either the dip or the dust depends on the type of dog, and the interval between trea-bnents can be determined best by experience. The powder or dip should not be permitted to get into the eyes. (2) Near habitations, parks, etc., rodents, especially meadow mice and rats should be destroyed by trapping or poisoning. Poisoning operations should be carried on only under the direction of competent authorities. (3) Underbrush, grass, and weeds around dwellings, schools, parks, and other places frequented by the public should be kept closely cut. This practice tends to drive out rodents and removes protection favorable to the ticks. (4) Close gracing of brushy and weedy areas with sheep will do much to reduce tick abundance. If sheep with fine v/ool are used, relatively few ticks become engorged on them and many ticks are killed by the wool grease. (5) Clearing and burning over vacant overgrown lots in towns and cities reduces the tick hazard. (6) Many of the ticks in an infested area can be killed by applying spray or dust to the ground and vegetation. The most satisfactory material to use for this purpose is DDT, as it provides a high initial kill and a lasting residual action. It may be applied as a spray or as a dust, irtiichever is more convenient. By either method from 2 to 3 pounds of DDT per acre should be applied. A convenient dust to use is one containing 10 percent of DDT in pyrophyllite. At this concentration from 20 to 30 - 4 - pounds of dust per acre would be used, which is sufficient to assure adequate coverage* Sprays containing DDT in various fonaulations with different solvents and eraulsifiers have been found satisfactory and it seems probable that any water-mi soible preparation will be effective. The following prepara- tions iriien used in 100 gallons of water per acre have given excellent results: (l) 2 l/2 pounds of technical DDT dissolved in 12 l/2 pints of soluble pine oil; (2) 2 l/2 pounds of technical DDT dissolved in 6 l/4 pints of xylene and 1 l/t pints of Triton X-100 (an aralkyl polyether alcohol). The amount of spray needed to secure adequate coverage varies with the type of vegetation. If 100 gallons per acre is not convenient, the quantity of water used may be increased or decreased, but the amount of DDT used should remain between 2 and 3 pounds per acre. At this rate DDT will not injure vegetation, and most of the solvents and emulsifiers used in water-misoible commercial preparations will also be harmless, but no assurance can be given that this will be true in every case* At this dosage an initial reduction in tick abundance of better than 90 percent may be expected, and the treated area should remain practically free of ticks for a month or more. CAUTION : DDT is poisonous if taken by mouth, and to a lesser extent by contact. Oil solutions of DDT, particularly the more concentrated ones, should not be allowed to raaain on the skin. Methods of Avoiding Tick Attack and Infection The reduction of t^e number of ticks in a given area by the methods described lessens the danger of attack, but the following precautions against being litten, or otherwise infected, should be taken when one is in a tick- infested cure at (1) Wear high-top shoes over the bottoms of the trousers, or^ if such shoes are not at hand, weeur the socks over the bottoms of the trousers. Host ticks crawl up from the ground or low vegetation, and this arrangement keeps them from crawling beneath ihe clothing. (2) Train yourself to feel the ticks irtien they start to orawl on the neck or body, and remove them. (s) Occasionally glance over the clothing, especially when two people are together, to flotaot the presence of ticks before they reach the neck or get into the clothing. Light-colored clothing aids in this* (4) After walking in ticky areas examine the outer clothing and look underneath the collar before entering an automobile or house. (5) If ticks are abundant, it is well to remove all clothing upon coming in from the field. Drop the garments loosely into a large metal container, such as a 25-pound lard can, pour 2 teaspoonfuls of carbon - 8 - tetrachloride on top of the clothing or in a saucer set on the clothing, and put the lid on over a sheet of wrapping paper or seal it with adhesive tape. This- will kill all ticks in 8 hours. Carbon disulfide may be used in the same way but, being inflammable, it is more dangerous. If this fumigation cannot be carried out, examine the clothing carefully for ticks, including folds and seams. (6) Never sleep in clothing worn during the day, as ticks sometimes lide in the folds and attach at night. (?) Do not lay field clothing on the bed. (8) Examine the body thoroughly upon arising, again at noon, ajid upon retiring. Individuals should examine each other, and a long mirror is an aid. Pay particulair attention to the hairy parts, especially the back of the head. Ticks often lie very close to the skin when first attached and are easily overlooked. Combing the hair upward with a moderately fine-toothed comb helps reveal the presence of ticks. (9) If a tick is found attached, remove it at once by grasping it with the fingers or tweesers and pulling steadily. There is no danger of the mouth parts of this species being broken off in removal. Ticks should not be left attached any longer than can be helped. Infected ticks are not likely to produce the disease unless they have been allowed to feed for several hours, usually 6 to 8. (10) Cauterize the point of attachment with a solution of carbolic acid or of silver nitrate. This can be done best by dipping the point of a round wooden toothpick in the solution and then drilling it lightly into the skin at the exact point of attachment. Iodine may be used if the other materials are not at hand, (11) The blood from crushed ticks may be a source of infection if it gets into the eye or into a skin abrasion. Therefore, the use of insecticides on dogi is advised, rather than hand picking. If the ticks a|*e picked, remove them carefully with small forceps and drop them at once into kerosene or boiling water. Do not rub the eyes. Wash the hands thoroughly when the job is finished, (12) Do not allow ticks that have been resioved from animals to escape, because they may attach to man, and the infected ones are capable of conveying the disease very soon after attachment. (13) If Rocky Mountain spotted fever is suspected, all unnecessary physical exeirtion should be avoided, a competent physician should be con- sulted, and prompt ho spita ligation is desirable. The incubation period of spotted fever in man is 2 to 12 days, (14) A preventive vaccine has been developed by the United States Public Health Service, but the produetion is limited bnd the material is being used in special cases only. Digitized by the Internet Archive in 2013 http://archive.org/details/combatingamericaOOunit Figure l.~The male Amerioan dog tick as seen from above. About 13 times natural size. Figure 2, --The female Amerioan dog tick as seen from above. About 13 times natural size. After attachment to an animal for a few days the body of the female becomes greatly distended with blood. ,,,^,[Ji,\,^«S;TV OF FLOR,DA ■III illillllll 3 1262 092S 6627 ■'•