Control of scabies and chiggers on humans
Scabies are caused by the microscopic mite (Sarcoptes scabei var. hominis). This mite, which is not a true insect but is more closely related to spiders, is widely distributed.
It will infest and prefer certain parts of the body such as the skin between the fingers, the bend of the elbow and knee, the breasts, the penis, and the shoulder blades. It is not found above the neck. Apparently, newly infested persons experience no itching, so an infestation may progress extensively before being noticed.
In about a month, a rash appears and intense itching is felt. This usually occurs at night and is caused by toxic secretions and excretions directly associated with burrowing by the mite. Scratching may cause secondary infection and helps the mites spread. The mites are transmitted by person-to-person contact, or by coming in contact with bedding, towels, or articles of clothing used by an infested individual.
The fertilized female mite deposits oval eggs at intervals in the tunnel she makes in the upper skin layer (epidermis). Usually, she will remain in the tunnel for her lifetime, depositing eggs at 2- to 3-day intervals for a 2-month period. Larvae hatch in 3 to 5 days and move freely over the skin. They and nymphs often are found in hair follicles. Within 4 to 6 days after egg hatch, the nymph transforms into a male or an immature female. The female makes a temporary burrow in the skin before mating. Maturity is reached 10 to 14 days after hatching.
Diagnosis and treatment
If you suspect an infestation of the mite, skin scrapings from the affected area should be taken by a physician or dermatologist and analyzed. Without this analysis, scabies cannot be accurately diagnosed.
Once an infestation is positively diagnosed as scabies, it is desirable to use an insecticide called Kwell. Medical advice is recommended since a prescription is required for this insecticide. When used as directed, Kwell is extremely effective, and repeated applications are not required.
Besides insecticide treatment of the body below the neck, clothing and bedding should be washed in hot water (125 degrees F) for 10 minutes. Clothes dryers exceed this temperature and will kill the scabies mite and eggs.
Caution: Insecticidal control of scabies should be carried out only after positive diagnosis. You are applying an insecticide directly to the body; it is a poison and should be handled carefully.
Chiggers are unique among mites affecting humans and animals in that the immature stage (the larva) is the only parasitic stage. The six-legged larva may attach itself to a variety of hosts to feed. Once engorged, it leaves the host to become a nymph and eventually an adult; both nymph and adult are eight-legged. It is likely that nymphs and adults feed on insect eggs or small, soft and inactive soil invertebrates. The common North American chiggers require 50 to 70 days to develop from egg to adult. In Minnesota there is only one generation per year.
Typical host-seeking behavior by the larva consists of congregating in a shaded area near the top of an object in close contact with the earth, such as a blade of grass or a fallen leaf. Here they are activated by an increase in carbon dioxide as a vertebrate host approaches.
People who have been outdoors in chigger-infested vegetated areas may suffer intense itching 3 to 6 hours after exposure, followed by a dermatitis (skin inflammation). A careful search of the skin after a trip through tall grass, weeds, or berry brambles will reveal minute, red mites, either moving fast or attached to the skin. The itching is usually along sock tops, behind the knee, around the waistband, or other places where clothing fits tightly, although most bites occur below the knees. The itching may persist for many days.
Chigger larvae do not burrow into the skin, nor do they feed primarily on blood. Their food usually consists of watery elements of tissue broken down by their digestive fluids; a few blood cells may be ingested. During larval feeding, the skin of the host becomes hardened, and a tube forms in which the mouthparts remain until feeding stops. It is probably the action of the digestive fluid that causes itching at the site of mouthpart attachment.
You may not know that you have been attacked by chiggers until welts appear and itching begins. Take a bath as soon as possible upon returning from a chigger-infested area. Apply a thick lather, rinse, and then repeat. This action kills most attached chiggers and ones not yet attached. Next, apply an antiseptic to the welts; this kills any remaining chiggers and prevents infection.
Destroying the chiggers reduces the itching but does not stop it. The fluid injected by the chiggers causes the itching, and no practical way to remove it has been found. For temporary relief of itching, apply ointments that contain benzocaine, hydrocortisone, or those used for relief of poison ivy itching.
Before going into a place where chiggers may be present, protect yourself with a repellent. Look for the active ingredient DEET (N,N,-diethyl-m-toluamide). A drugstore, hardware or garden store should have this insect repellent in stock.
Apply the repellent to clothing by rubbing or spraying it on. Do not saturate the cloth with repellent. Some kinds of rayon and other synthetic fabrics may be damaged by the repellents, so use caution; nylon, cotton, and wool will not be harmed.
In treating clothing, apply repellent along the inside and outside edges of all openings, such as cuffs, neck, and waistband areas. Be sure to treat all the way around the upper edges of socks. Cotton and wool socks absorb repellent better than other materials. Apply the repellent lightly to the arms or legs if they are not covered by clothing. Read the label for specific instructions and cautions.
Chiggers can infest inanimate objects lying on the ground, such as clothes and blankets. Avoid setting such articles on the ground if you believe chiggers are present. Clothes and blankets suspected to be infested with chiggers should be washed in hot water.
Before applying insecticides to outdoor areas you must have an idea where the chiggers are. A simple survey is needed. The chiggers may be concentrated in a small area, making treatment easy, less expensive, and safer to pets, humans, and wildlife.
Place a piece of black cardboard edgewise on the ground and observe it for a few minutes. If chiggers are present, they will climb to the top edge and congregate there. Make this test in 8 to 12 spots over the area.
Unless the entire area is infested, treat only the parts in which control is desired, such as grass around picnic tables or lawn chairs. An insecticide such as permethrin is effective against chiggers.
The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the University of Minnesota. Mention of a pesticide or use of a pesticide label is for educational purposes only.
A pesticide label is a legal document. Always follow the pesticide label directions attached to the pesticide container you are using. Pesticide labels may change frequently. Internet labels may not match the label on the container you are using. The site of use or plant to which the pesticide is to be applied must be listed on the label or the pesticide cannot be used. Remember, the label is the law.
Reviewed by Jeff Hahn 2016