Article

Chiggers
February 03, 201901,931

What are chiggers?

Chiggers are the larvae of some types of mites. In the English-speaking world, chiggers are also commonly called harvest bugs, harvest mites, harvest lice, red bugs, red mites, orange tawnies, berry mites or scrub-itch mites.1 They are often mistaken for Mower’s mites or jiggers, which belong to two entirely different families of insects.1

Chiggers are tiny, six-legged insects, ranging in size from 0.2 to 0.4 millimeters – barely bigger than the width of a human hair.2,3 As their common names suggest, they are usually red in color, though they may also be orange or yellow.1

 

Figure 1: Drawing of a chigger. Morphart Creation/Shutterstock.

 

Chiggers are parasitic and eat the lymph and tissue fluids (not blood!) of birds, reptiles, amphibians and mammals, including humans.1 Chiggers are only parasitic for a short time, eating for a few hours or days before dropping off to become adults. They do not live in skin.1

Chiggers appear to attack the first available animal that they can feed on. No species of chigger is known to only feed from a single kind of host animal.1

Species of chiggers

Though there are over 3,000 species of chigger mites, only 50 are known to be able to bite humans. Of these, only 20 are believed to have any health consequences.1 The bites of nearly all of these species simply cause a local allergic reaction in the skin around the chigger bite. Some species found in east Asia, however, can transmit the infectious bacteria O. tsutsugamushi. These bacteria cause scrub typhus, which is a potentially serious disease.1,2

How can you get a chigger bite?

Humans are usually bitten by chiggers after accidently coming into contact with them during outdoor activities. These activities include farm work (hence “harvest” bug), as well as leisure activities, such as camping, hiking, or rafting.1

Where are you likely to come into contact with chiggers?

Chiggers are found everywhere in the world. However, the seasons and times during which they are present depend on the climate.2

Chiggers hatch from mite eggs during warm, humid weather. Chiggers live best in temperatures ranging from 25-30°C (77-86°F) and in a humidity around 80 percent.1,2

In areas far from the equator, temperatures and humidity only allow chiggers to hatch during the late summer or early fall months. In areas closer to the equator, chiggers may be present through much longer stretches of the year.1,2

Chiggers sit in clusters at the tops of blades of grass or at the of the ends of branches to wait for an animal to pass. Therefore, they are most often found in areas of thick vegetation, such as can be found in parks, gardens, yards or areas around rivers, lakes or marshes.1

 

Figure 2: Life-cycle of harvest mites. The larva, called chiggers, are the only stage in the life-cycle that is parasitic.
Adults, nymphs and eggs do not bite or infect humans in any way. “The life cycle of a harvest mite from eggs (1) through larva (2) and nymph (3) to adult imago (4)” by Bugby52.4 is licensed under CC0 1.0.

How common are chigger bites?

It is difficult to know the number of people world-wide bitten by chiggers each year. Not everyone who is bitten visits a doctor and the bites are hard to tell apart from other bug bites, skin rashes, scabies or allergies.1,4 It is likely that many cases of chigger bites are misdiagnosed, even among those that see a doctor. However, at least one million people get scrub typhus each year. Since only a small percentage of chigger bites cause scrub typhus, tens of millions of people are likely bitten each year.2

 

What are chigger bites? What do chigger bites look like?

Visible chigger bites are immune reactions in the skin to chigger saliva following a bite. Most bites begin as red dots, similar to most red bug bites or a rash caused by any allergy. Many then develop the appearance of a small blister or pimple, with a raised clear or yellow center.1

 

Figure 3: Chigger bites on human skin with typical blister-like raised centers.
Trombiculosis sores from chigger bites on human ankle skin, Alabama, USA.” by Wilson44691 is licensed under CC0 1.0.

 

Since chiggers cluster together to wait for an animal to come past, most individuals will have multiple bites in a single area.1 This may cause people to think the bites are a rash, but really, they are all single bites from many different animals. Chigger bites are also easily mistaken for hives, scabies or skin sensitivities. 1,4

Chiggers like warm, moist areas and areas where clothing gets tighter. Chigger mite bites are often located on the stomach or back, in armpits, around the genitals, or along the edges of underwear or socks.1

What causes chigger bites?

Chigger bites are caused by an immune reaction to chigger mite saliva and skin damage, which causes redness, itching and swelling of the skin around a bite site.5

How do chiggers bite?

Chiggers attach to the skin using short mouth-pieces, called chelicerae.1,5 They usually attach at the opening to a pore or hair follicle in the skin.2 The actual biting process is painless.1

Once attached, the chigger secretes saliva into the skin. Parts of the saliva mix with parts of the skin and form hard walls of a “feeding tube”, called a stylostome.1,5 At the end of the feeding tube, other parts of the chigger’s saliva digest the skin, forming a food cavity.5 The liquid formed in the food cavity is eaten by the chigger.

Dying tissue and the chigger’s saliva activate the immune system.1,2 The immune reaction causes itching, redness, swelling and pain around the bite.5

 

Figure 4: Chigger biting. The chigger attaches to the skin using its small, pincher-like mouth-parts (chelicerae).
It secretes saliva into the skin, forming a feeding tube (stylosome). Immune reaction to damaged tissue and chigger saliva leads to bite symptoms.
A diagram of the stylostome, or the hardened tube of dead cells formed by chiggers (Larval form of the Trombiculidae) when feeding on them” by Bugboy 52.40 is licensed under CC0 1.0.

 Do chiggers burrow?

Do chiggers burrow into your skin? No. In nearly all cases, only their mouth parts enter the skin when biting. The animal itself remains on the surface of your body.1

Some species are able to partially or completely burrow into skin, but this is uncommon and is usually only seen in lizards, amphibians and small rodents.1 Chiggers that do burrow will only remain in the skin for a short period of time – they do not live in skin as adults.1

What are the symptoms of chigger bites?

Normal chigger bites

For most people, chigger bites will be rash-like clusters of small, red, itchy bumps on the skin.1 These are likely to be located on frequently exposed skin, such as arms, legs, feet, ankles or abdomen. Chiggers like warm, damp skin, so bites also often appear near the armpits or groin.1 Bites are also common in areas where clothes tend to get tighter, such as along underwear lines or sock lines.1

The primary symptom of normal chigger bites is intense itching.1 This usually goes away within a week, though it may take up to three weeks for the bites to heal entirely.1

Scrub Typhus

If you were bitten while in south-east Asia, you are at risk for getting scrub typhus. Also known as tsutsugamushi disease, this infection may become life threatening if left untreated.1,2

Early symptoms of scrub typhus begin between five and 20 days after being bitten. The first symptoms are vague and include1:

  • Swelling of the bite site
  • Fever
  • Headache
  • Muscle pain
  • Generally feeling unwell

Frequently in scrub typhus, but not always, the center of the infected bite turns from yellow or white to black during the first few days of symptoms.1,6 This is called an eschar and is a good sign that you may have scrub typhus.6 Finding a bite with an eschar will help a doctor diagnose you.

In most cases, scrub typhus resolves itself before getting any worse. In some people, however, scrub typhus progresses to more serious symptoms when left untreated. These symptoms may include1,6-7:

  • swelling and pain in lymph nodes, especially those near the bite
  • coughing
  • rash
  • nausea, vomiting, abdominal pain or blood in stool
  • brief loss of hearing or sight
  • changes in mood or personality
  • confusion
  • stiff neck
  • swelling in the brain
  • kidney failure
  • abnormal heart beat
  • shock
  • death

Studies show that up to 30 percent of untreated cases of scrub typhus may be fatal.7 Early diagnosis and treatment reduces the risk of dying.6 If you think you may have scrub typhus, you should see a doctor as soon as possible.

Summer Penile Syndrome

Boys may experience summer penile syndrome if they are bitten by a chigger in the groin.8

Summer penile syndrome is most common in young boys between the ages of 3 and 7.8

This syndrome causes a sudden swelling of the penis. Luckily, it rarely effects the boys’ ability to pass urine and they are almost always able to fully empty their bladders.8

As with the chigger bites themselves, this condition is usually self-limiting and goes away on its own. Parents may help ease their child’s symptoms through the use of cold compresses, oral antihistamines and/or anti-inflammatory creams.8

Other infections

If you scratch bug bites a lot and opened a wound in them, some bites may become infected.9 If a bite becomes infected, you may need antibiotics.

Chigger bites vs bed bug bites

Though they both produce red bug bites, chigger bites and bed bug bites have some unique traits that may help you tell them apart.

Chigger bites

Chigger bites often appear on only one part of the body at a time. They usually do not have a pattern. They are likely to be found on frequently exposed skin (arms, lower legs, feet, ankles), or near the groin, abdomen, armpits, pant-line and/or sock line.1 Chigger bites usually begin itching within hours of the bug attaching.1

A good sign that your bug bites are from chiggers is that they appeared between three hours to one day after unprotected outdoor activities in areas that might have chigger populations.1

Bedbug bites

Bedbug bites often appear in a semi-circle or line of three bites.9 They are more likely to be located on skin exposed while sleeping and frequently in areas that spend much of the night in direct contact with the bed. Since bedbugs do eat blood, bed bug bites often have small blood-colored puncture wounds at the center. Bedbug bites may take seconds or days (up to 11) to appear on the skin.9

Bedbug bites are likely if they appeared within 11 days after having slept in a strange bed.9

 

 

Figure 5: Comparison of chigger bites to bed bug bites

 

Left: Chigger bites on foot and ankle. “Bites on a foot from the Harvest mite Trombicula alfreddugesi” by  TimVickers is licensed under CC0 1.0.

Right: Bed bug bites on back; note the typical lines/clusters of three bites. “Bed bug (Cimex lectularius) bites (from a hotel in Amsterdam)- Ludwigshafen, 26.11.2015” by Hermann Luyken is licensed under CC0 1.0. Image has been cropped from original.

How do you treat chigger bites?

Treating normal chigger bites

Normally, you do not have to do anything to get rid of chigger bites. They will heal on their own within about three weeks.1

To decrease the itching and discomfort, oral antihistamines or topical anti-itch creams may be helpful. They may help prevent scratching and help ensure you don’t get an infection.1

Treating infected chigger bites

If your bites are not healing well on their own, you should seek medical attention. This may be a sign you have an infection and you may need antibiotics.

Treating scrub typhus

If you were in Asia and one of your bites is not healing, rather is turning black in the center, you should see a doctor as soon as possible. This may be a sign of scrub typhus. If you have other symptoms of scrub typhus, but cannot find a black chigger bite, you should still seek medical treatment.1

Treatment for scrub typhus is usually oral doxycycline or tetracycline, which are common antibiotics.6 You may also need other medications to help with specific symptoms, if they have become severe.

 Other important information

Though there is little to be done after chigger bites have occurred, you can decrease your risk of bite symptoms and infections by preventing the bites in the first place. According to the CDC10, there are a number of effective ways to prevent chigger bites. These include:

  • Wear proper clothing. Wear long sleeves and long pants if possible. Tuck pant legs into the tops of your socks. Tuck your shirt in. Choose closed shoes, rather than sandals, to protect your feet.
  • Use chemical repellents on clothing. Clothes may be treated with permethrin, a strong insect repellent. This only needs to be reapplied after washing the clothes several times. You may also buy clothes that have been pre-treated with permethrin.
  • Protect exposed skin. Repellent sprays and creams may be put on exposed skin. When doing so you should:
  • take care not to apply sprays or creams to open wounds, irritated skin or eyes, as this may cause you harm.
  • avoid inhaling or eating them; applying sprays in open spaces and protecting your face by first spraying your hands and then rubbing the repellent on your face can help protect your lungs and mouth from exposure.
  • avoid putting sprays or creams on skin under clothing.
  • follow the label instructions on the repellent.
  • Shower. Showering in warm, soapy water within two hours of being in an area believed to have chiggers may get rid of any chiggers on your body before they can bite you. This especially helps reduce the risk of getting scrub typhus from a bite.1,10

If you are planning outdoor activities in the areas of south-east Asia where scrub typhus is common, these protective measures are very important and you should follow them with care. The areas where scrub typhus is common include1,2:

  • Eastern Russia
  • Japan
  • Southern China
  • Pakistan
  • Afghanistan
  • India
  • Korea
  • Islands of the Indian and Pacific Oceans (including Sri Lanka, New Guinea, Taiwan and the Philippines)
  • Northern Australia

 

Figure 6: Areas of the world where scrub typhus is common.
Epidemiologists call this region the “tsutsugamushi triangle” after the bacteria responsible the disease. Modified from “World Pacific Ocean centered” by d-maps.com11

 

Chiggers FAQ

  • Do chiggers spread on your body?

No! After feeding, chiggers fall off and develop into adult mites. Mites breed and lay eggs in soil.1,2 They cannot reproduce on your skin. If it appears the bites are spreading, it likely means you have been exposed to new chiggers, or you are just beginning to see older bites.

  • Are chiggers visible?

Unfortunately, chiggers are too small to see.2

Sometimes, they are even missed when using a magnifying glass, especially if they are in hard to see areas of the body or hidden among hairs. With a magnifying glass, chiggers look like small bright-red dots on the skin.

A special type of microscope may be used to see chiggers.4 Using a microscope, you can see the whole animal clearly, and they look like bright-red ticks or mites with six legs.

  • How do you kill chiggers?

Chiggers do not have to be killed in order to stop them from biting you or to remove them from the surface of your skin.1 This can be achieved by using protective clothing, showering or scratching.1,10

If you wish to kill them, however, sprays and creams containing insecticides have been shown to be able kill these larvae.12

  • Are chiggers contagious?

No, there is no evidence of chiggers spreading from infected to non-infected humans. Once they have bitten one person, and are eating, they are not likely to bite anyone else.

Additionally, most individuals who have visible chigger bites no longer have any actual chiggers. The animals normally release from the skin or are scratched off between three hours and two days after attaching, but bites are visible for up to three weeks.1

  • Can chiggers live in your house?

No, chiggers need soil to reproduce.1,2 If they are brought into your house as larva on your body, they cannot continue to live there. You will not find chiggers living in beds, furniture or carpets.

If you keep getting new chigger mite bites even though you are careful when outside and/or avoid infested areas, you might be getting bites from chiggers brought inside by your pets. Though rare, some cases have been reported of people being bitten after allowing pets to sit on their laps for a long time.1

If you think you are being exposed by your pets, preventing them from going into areas where they may be pick up chiggers may help prevent you from getting bitten.

References

  1. Santibáñez P, Palomar AM. The role of chiggers as human pathogens. In: Samie A. eds. An Overview of Tropical Diseases. InTech, 2015:173-202. doi: 10.5772/61978. https://www.intechopen.com/books/an-overview-of-tropical-diseases/the-role-of-chiggers-as-human-pathogens. Accessed June 18, 2017.
  2. Sharma P, Kakkar R, Kaore SN, Yadav VK, Sharma R. Geographical distribution, effect of season and life cycle of scrub typhus. JK Science. 2010;12(2):63-64. PDF
  3. Department of Energy. Scale of Things – Nanometers and More 2012. Accessed June 19, 2017.
  4. Nasca M, Lacarrubba F, Micali G. Diagnosis of trombiculosis by videodermatoscopy. Emerg Infect Diseases. 2014;20(6):1059-1060. doi: http://dx.doi.org/10.3201/eid2006.130767
  5. Shatrov AB, Takahashi M, Nod S, Hitoko M. Stylosome organization in feeding Leptotrombidium larvae (acriformes: trombiculidae). Exp Appl Acarol. Published online April 2014. doi: 10.1007/s10493-014-9809-8.
  6. Chogle AR. Diagnosis and treatment of scrub typhus – the Indian scenario. J Assoc Phys India. 2010;58(-)11-12. http://japi.org/january_2010/Article_01.pdf.
  7. Rajapaske S, Rodrigo C, Fernando D. Scrub Typhus: pathophysiology, clinical manifestations and prognosis. Asian Pac J Trop Med. 2011;5(4)261-264. https://doi.org/10.1016/S1995-7645(12)60036-4.
  8. Schulert G, Gigante J. Summer penile syndrome: an acute hypersensitivity reaction. J Emerg Med. 2014;46(1):e21-e22. http://dx.doi.org/10.1016/j.jemermed.2013.08.081.
  9. Bernardeschi C, Le Cleach L, Delaunay P, Chosidow O. Bed bug infestation. BMJ. 2013;346(138):1-8. doi: 10.1136/bmj.f138.
  10. Protection against mosquitos, ticks & other arthropods. cdc.gov. https://wwwnc.cdc.gov/travel/yellowbook/2018/the-pre-travel-consultation/protection-against-mosquitoes-ticks-other-arthropods. Updated May 31, 2017. Accessed June 19, 2017
  11. World Map Pacific Ocean centered. Date published not available. http://www.d-maps.com/carte.php?num_car=3227&lang=en. Accessed June 20, 2017.
  12. Goodyer LI, Croft AM, Frances SP et al. Expert review of the evidence base for arthropod bite avoidance. J Travel Med. 2010;17(3):182-189. doi: 1111/j.1708-8305.2010.00402.x

 

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