What is Chigger Bites and Trombiculiasis?

Chiggers are a type of mite from the Trombiculid family. When the larvae of these mites bite, it can cause itchiness and irritation, known as trombiculiasis or trombiculosis. While this is usually mild and goes away on its own, there can sometimes be complications such as transmitting diseases or causing a bacterial infection.

There are many species of these mites all over the world. In the United States, you’ll often hear about the Eutrombicula alfreddugesi, whereas in Europe, it’s the Trombicula autumnalis. In the Asia-Pacific region, the focus is primarily on the Leptotrombidium genus.

The larvae of these mites feed on the skin of various animals, including humans. Adult mites dig into the soil and eat decaying plant and animal material. The larvae gather on leaves and grass waiting to latch onto a host that passes by. They then move to their preferred spot, attach to the skin, and release enzymes to break down skin cells. This process leads to an inflammatory response, making the area red, swollen, and itchy.

Scratching can easily dislodge the larvae and they rarely stay attached to a human for more than two days. However, the intense itchiness, inflammation, and localized allergic response can last for weeks. Sometimes, the small, light-red to orange-colored larva, measuring 0.15 to 0.3 mm in length, can be identified on the skin. But generally, trombiculiasis is diagnosed based on history of being in an area known to harbor these mites, the pattern of the skin reaction, and ruling out other possible diagnoses.

The treatment of chigger bites focuses on controlling the symptoms. This could involve taking oral antihistamines or applying topical corticosteroid creams to ease the itch and inflammation.

What Causes Chigger Bites and Trombiculiasis?

Trombiculiasis is a condition that occurs when you are bitten by trombiculid mites, which are tiny bugs found in certain habitats. When these mites bite you, they release digestive enzymes that turn your skin into a liquid. This causes your body to have a strong reaction in the area of the bite, and you might notice bumps (papules), redness (erythema), and hives (urticaria).

Risk Factors and Frequency for Chigger Bites and Trombiculiasis

Larval mites, known as chiggers, grow into their parasitic stage from June to September in the Northern Hemisphere. That’s why most chigger bites occur in summer and fall. In tropical areas, though, chiggers can bite at any time of year. People of all ages are at risk if they visit places where chiggers live, such as overgrown fields, forests, or damp soil near water sources.

Traditionally, trombiculiasis (the medical term for a chigger bite) was thought to be common among people who work outdoors, like farmers. But it can also occur in suburbs or cities, where people have contact with grassy fields, overgrown lawns or gardens. It’s hard to say exactly how many cases of trombiculiasis there are, because it usually goes away on its own and people may not report it.

Chiggers are known to spread a bacterial infection called scrub typhus in humans.
There’s a lack of definite data on the risk of the disease in urban areas. However, a recent study from Bangkok found chiggers on nearly 77% of animals captured in public parks.
The bacteria causing scrub typhus was not found in the Bangkok study.
Scrub typhus was once thought to be primarily in the Asian-Pacific region and Northern Australia, an area called the “Tsutsugamushi Triangle.”
However, reports of scrub typhus in Africa, southern Chile, and the Middle East suggest the disease is more widespread.
Recent findings have even indicated the presence of Rickettsia infections (a group of bacteria that includes the one causing scrub typhus) from chiggers in North Carolina, US.

Signs and Symptoms of Chigger Bites and Trombiculiasis

Chigger bites can happen to anyone who spends time in certain environments during the summer, such as yards, gardens, or parks. These bites are common among people who work outdoors but can occur even during a casual park stroll. The result is a skin condition known as trombiculosis, characterized by skin inflammation and intense itching, followed by a rash. Symptoms often appear a few days after exposure, with itchy bumps grouped or arranged in a line on exposed skin or near tight clothing. These bumps can develop into dark red spots or blisters, typically around the legs and waist. In rare cases, large blisters may form. The itch usually fades away in a few days, but occasionally, it can persist longer.

Young boys can experience a local allergic reaction to chigger bites on the genital area, known as “Summer Penile Syndrome” or “Lion’s Mane Penis.” This condition, which happens seasonally, leads to penile swelling, itchiness, and painful urination. Symptoms resolve on their own after a few days but can last for up to two weeks.

Chiggers can also transmit a bacterial infection called scrub typhus. Symptoms of scrub typhus include headache, loss of appetite, and generally feeling unwell. Some patients may also develop high fever, severe headache, and muscle pain. A rash that often starts on the stomach and extends to the limbs and face is common but is not itchy. Other symptoms can include nausea, vomiting, diarrhea, swollen lymph nodes, and slow heart rate. Severe cases, especially in older patients, may lead to kidney problems or cognitive changes.

Chigger bites
Trombiculosis symptoms (skin inflammation, intense itch, rash)
Summer Penile Syndrome in boys (itching, swelling, painful urination)
Scrub typhus symptoms (headache, loss of appetite, malaise)

Testing for Chigger Bites and Trombiculiasis

The diagnosis of chigger bites typically does not need medical tests, as it can be identified through a medical check-up. This is especially true if you’ve been outdoors during the summer or early fall and present with scattered, red, itchy bumps or hives (urticarial papules) on your skin. This usually suggests that the issue might be trombiculiasis, the medical term for the skin condition caused by chigger bites.

Similarly, when it comes to identifying scrub typhus – a disease one can contract from chigger bites – there are no lab tests that can detect it in its early stages. The diagnosis is mostly based on a clinical assessment; in other words, a healthcare provider reviewing your symptoms and medical history. However, if scrub typhus is suspected, a type of blood test called serology can be used to confirm the diagnosis. This test would be carried out twice, with at least a two-week gap in between. A diagnosis of acute scrub typhus is made if the blood samples show a four-fold increase in substances called titers, detected by a method known as an indirect fluorescent antibody (IFA).

Additionally, an advanced test called Polymerase Chain Reaction (PCR) can detect scrub typhus, but it is not widely available. PCR is a technique where a small sample of DNA is amplified to create thousands to millions of copies of a particular DNA sequence, making it easier to diagnose diseases.

Treatment Options for Chigger Bites and Trombiculiasis

When you have chigger bites, the focus is on relieving your symptoms. This can be done by taking oral antihistamines, like allergy pills, or using creams that contain corticosteroids, which are a type of medication that reduces inflammation. Cold compresses, such as a cloth dipped in cold water, can also help minimize discomfort and reduce swelling.

Although you might have heard of the idea of smothering the parasite by using things like nail polish, vaseline, or normal cream, it is not recommended by healthcare professionals.

For itching, you may apply gels or lotions containing ingredients like menthol or calamine. If the itching is very severe, a strong corticosteroid cream under a bandage might be used. In some instances, corticosteroid injections can be an option if the symptoms don’t improve with cream. However, most of the time, this is not necessary. It’s important to wash your clothes in hot water or treat them with insecticides to kill off the chigger larvae.

Scrub typhus, a type of disease that can be caused by the same pests that cause chigger bites, is often managed with a medication called doxycycline. Studies show that other medicines, such as azithromycin, rifampin, and chloramphenicol, could also work. For pregnant individuals, azithromycin is preferred because other antibiotics may not be safe during pregnancy. If the condition is very severe, a combination of different drugs may be required.

If you’ve been outside and later notice that there are scattered spots on the exposed parts of your skin or that there are clusters of them around areas where your clothing is tight, you might think that you’ve been bitten by bugs. Doctors will also consider this possibility, but there are several other conditions that could cause similar symptoms. They might look for signs of scabies, bites from bedbugs, and bites from mosquitoes or ants. If you have pets, they might also consider the possibility that fleas which often bite following the lines of tight clothing could be the cause.

But a lot of other conditions can also cause rashes that look similar, including infections, autoimmune conditions (where the body’s immune system attacks itself), or reactions to things you’re allergic to. To figure out if the bites are caused by trombiculiasis (a condition caused by mite larvae), they will consider things like whether you’ve been outside recently, if the symptoms come and go with the seasons, and whether the rash keeps coming back. Trombiculiasis is less likely if you’re feeling sick, your vital signs like temperature and blood pressure are abnormal, the rash has turned into blisters or bullae (large blisters), or if the bite marks are painful instead of itchy.

There’s a special type of trombiculiasis called summer penile syndrome, which affects the penis. When considering whether this is the cause, doctors will also rule out other conditions that can affect this area such as:

Balanitis: This is when the head of the penis is painfully inflamed. This might also be paired with pus leaking out and the skin on the head of the penis wearing away.
Phimosis: This is when the foreskin is too tight and can’t be fully pulled back over the head of the penis.
Paraphimosis: This is when the foreskin gets stuck after being pulled back over the head or body of the penis, which then restricts the blood flow to the head of the penis. Both of these conditions can also lead to a swollen penis.

In cases of summer penile syndrome, the swollen skin should be only a bit sensitive and should be easily pulled back over the head of the penis in males who aren’t circumcised. Doctors will also ensure that conditions like cellulitis (skin infection) and abscesses (pockets of pus) are not causing this syndrome.

What to expect with Chigger Bites and Trombiculiasis

Typically, trombiculiasis, or chigger bites, gets better on its own within a few weeks if there’s no additional exposure. The chances of getting a bacterial infection from chigger bites or the bites passing on a bacterial disease are usually very low. So, the outlook for people with chigger bites is generally good.

However, if there’s a chance of getting bitten again, it’s best to stay away from places where chiggers live. If you have to move through areas that are infested with chiggers, make sure to cover your skin to protect it from bites. You can also use bug sprays and insecticides to avoid getting bitten.

Possible Complications When Diagnosed with Chigger Bites and Trombiculiasis

Problems that can arise from trombiculiasis, a skin condition caused by mite larvae, can include skin infection due to scratching, a condition known as summer penile syndrome, and the spread of a disease called scrub typhus. If scrub typhus is not addressed properly, it could lead to a dangerous situation where multiple organs fail, and could even cause death. Other body-wide effects of scrub typhus can include heart rhythm abnormalities, reduced blood supply, and longer time intervals necessary for heart muscle repolarization (referred to medically as QT prolongation).

Potential Consequences:

Skin infection from scratching
Summer penile syndrome
Spread of scrub typhus
Multiorgan failure
Potential death
Heart rhythm abnormalities
Reduced blood supply
Longer-than-normal heart muscle repolarization

Chigger Stylostome. Illustration of a chigger using its stylostome during
feeding.

Preventing Chigger Bites and Trombiculiasis

The best way to avoid getting sick from chigger bites is to prevent the bites altogether. Stay clear of places where chiggers are known to live if you can. If you can’t avoid these places, there are some precautions you can take. Try using elastic bands to tighten the ends of your sleeves and pants against your skin, or tuck your pants into your socks or boots. Make sure to cover your skin as much as possible. You could also use specific insect repellents like DEET and permethrin to keep chiggers away.

DEET, which is a short term for N,N-diethyl-meta-toluamide or N,N-diethyl-3-methylbenzamide, is a very effective bug spray that works well against chiggers. People have been using DEET for over 60 years to protect against ticks, mosquitoes, and other bugs, and it’s highly regarded for its effectiveness. Although DEET is available in different strengths, it doesn’t seem to work better if it’s stronger than around 30%. However, stronger DEET does tend to keep working for a longer period of time. Serious side effects from DEET are rare but can include skin irritation, allergic reactions, and in very rare cases, seizures. DEET is safe to use on children older than 2 months, but make sure it doesn’t accidentally get into their mouth.

Permethrin is another type of bug spray that can be helpful. It’s a human-made chemical that’s toxic to insects but not to people. You can spray permethrin on your clothes or your bedding to deter ticks and chiggers. Clothes sprayed with permethrin will stay effective even after you wash them several times. But permethrin is not as good at keeping bugs away as DEET spray is.