Introduction:
Trombiculosis is a skin infection caused by the larval stage of various species of mites, particularly mites belonging to the genus Trombicula. Trombicula (chiggers, red bugs, or scrub-itch mites) are eight-legged arthropods or tiny arachnids of the Trombiculidae family. These microscopic mites measure around 0.4 millimeters (0.01 inch) and are chrome-orange in color. Trombicula alfreddugesi is a common species of harvest mite found in North America. In the United Kingdom, the most common mite is Trombicula autumnalis.
The rash formed due to the manifestation of this infection is commonly known as chigger bites.
During the larval stage, these mites attach themselves to various animals and humans, feeding on their skin and leading to itching and trombiculosis.
Where Is Trombiculosis Found Commonly?
The mites are more prevalent in temperate and humid environments, including temperate woodlands and low-lying moist places. However, they can also occur in drier areas like golf courses or lawns, particularly during late warm summers. At the end of autumn, the eggs usually hatch, and new mites grow on the skin of small rodents. During the larval stage, these obligate parasites feed and thrive on them by releasing lytic enzymes to digest cutaneous cells.
Outdoor activities or individuals involved in the countryside for recreational or professional purposes usually become the host for this ectoparasite (parasites that thrive on the external surface of hosts). However, the infection is more likely to occur in farmers, hunters, or children.
The optimum ground temperature needed for the survival of these mites ranges between 77 to 86 degrees Celsius, and they are killed at a temperature below 42 degrees Celcius.
What Are the Clinical Features of Trombiculosis?
The peculiar clinical feature is the presence of a rash or chigger. The skin surrounding the tiny holes created by the mites hardens and leads to the formation of a feeding tube known as style some present below the surface of the skin. This hole causes itching and urges the patient to dig or scratch the rash. If left untreated, these chiggers can thrive on the affected skin cells for days or weeks. Initially, the bite goes unnoticed, but symptoms begin 1 to 3 hours later.
A reddened blister or pustules develops at the site of the bite. Symptoms like intense itching usually occur after 1 or 2 days and may continue for up to 2 weeks. Scratching of the rash can lead to infection and pain.
How Is Trombiculosis Diagnosed?
Trombiculosis is an underreported infection and is usually misdiagnosed. Clinical features include skin rash, which is nonspecific, and an accurate anamnesis (a patient's personal medical history) is important for making the correct diagnosis.
In certain cases, where the recent history of exposure to mites is not recorded, video dermatoscopy (a non-invasive technique mainly used for the examination of cutaneous skin lesions) is helpful to reach a correct diagnosis and acts as a valuable diagnostic aid. Furthermore, sharing this diagnostic data helps to collaborate with experts and ensures rapid recognition of parasitic disorders in tropical countries or other geographical areas. In addition, video dermatoscopy is a noninvasive way to diagnose diseases that cause itching. Therefore, it helps avoid unnecessary and expensive investigations and treatments.
Healthcare professionals who cannot access this equipment should refer the patients to a video dermatoscopy diagnostic center for prompt management.
How Can Trombiculosis Be Prevented?
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Trombicula or chiggers are usually found on the tips of the grass. Therefore, keeping grass short helps to limit the growth of these mites. In addition, sunlight penetrating the grass will make the lawn drier and provide a less favorable environment for the development and survival of these mites.
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The bites usually occur below the knees since the mites ate present in low-lying vegetation, short grass, trails, paths, or roads. Therefore, the repellent should be applied to the shoes, lower legs, and skin to prevent the disease.
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Commercially, sulfur is used for mite control and is dusted in yards to control chiggers. In addition, dusting socks, shoes, and trouser legs with sulfur can be highly efficient in chigger repulsion.
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Common household vinegar (5 % acetic acid) can also be used to treat chiggers.
What Is the Lifecycle of Trombicula?
The lifecycle of Trombicula consists of four stages:
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Egg.
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Larva.
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Nymph.
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Adults.
The adults usually have eight legs and thrive on plants, and do not cause infections in humans. It is the larval stage that is responsible for causing infection in humans. These larvae are six-legged and grow on skin cells. These larvae thrive on mammals, ground-dwelling birds, toads, box turtles, and insects. These chiggers do not bite the victims. Instead, they make tiny holes in the skin by using their sharp claws. Then they deposit their saliva through this opening. The skin cells are dissolved by the digestive enzymes in their saliva.
How Is Trombiculosis Managed?
The treatment of Trombiculosis includes the following:
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A warm, soapy shower should be taken immediately after exposure to chigger.
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The skin should be scrubbed properly.
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Clothes exposed to the mites should be washed in hot water, and shoes or boots must be cleaned appropriately.
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Topical corticosteroids or calamine lotions are used to suppress the itching.
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Patients are prescribed antihistamines like Benadryl, taken orally to relieve symptoms.
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Other itch-relief treatments that show positive results include cool compresses, cool showers, or using products with colloidal oatmeal as the main ingredient.
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Insect repellents that contain permethrin, DEET (N, N-diethyl-meta-toluamide), catnip oil extract (nepetalactone), citronella oil, or eucalyptus oil extract should be administered. In 1993, a study was conducted on two commercial repellents, DEET (N, N-diethyl-meta-toluamide) and citrus oil. The filter papers treated with DEET killed the chiggers. On the contrary, the filter paper treated with citrus oil did not kill the chiggers. Hence, it was proved that DEET was more effective than citrus oil.
Conclusion:
In North America, these chiggers are not vectors of this infection but a species that carries the bacterium that can cause scrub typhus. In addition, men who get this infection in the groin area risk developing summer penile syndrome. It is characterized by itching, swelling, and a problem urinating, which may last for weeks.
