Urticaria, commonly known as hives, presents as raised, intensely itchy welts that can appear anywhere on the body. These skin reactions occur when a substance triggers a localized release of inflammatory chemicals beneath the skin’s surface. While many cases of hives are linked to common triggers such as specific foods, medications, or viral infections, a less frequent but documented cause involves internal parasitic infections. When hives persist for six weeks or more, a systematic investigation often includes looking for a parasitic cause. Understanding the specific immune response provoked by these organisms is important for determining the correct underlying cause of the skin reaction.
The Biological Connection: How Parasites Trigger Hives
The mechanism by which parasites provoke hives involves a specific branch of the immune system designed to combat large invaders like worms. When parasitic antigens—molecules released by the parasite—enter the bloodstream, they stimulate an immune response characterized by the activation of T-helper 2 (Th2) cells. This activation pathway leads to the abundant production of a particular antibody known as Immunoglobulin E (IgE).
IgE antibodies circulate until they attach to specialized immune cells called mast cells, which are abundant in the skin and mucous membranes. The mast cells become armed and ready to detect the specific parasitic antigens that initially caused the sensitization. When a person is re-exposed to these antigens, the molecules link the IgE antibodies on the surface of the mast cells.
This cross-linking action triggers the mast cell to degranulate, releasing its stored chemical contents into the surrounding tissue. The primary chemical released is histamine, a potent inflammatory mediator. Histamine causes the blood vessels in the immediate area to dilate and become more permeable, allowing fluid and other immune cells to leak into the skin. This localized fluid accumulation and inflammation manifest externally as the characteristic raised, red, and intensely itchy wheals of urticaria.
Common Parasites Associated with Urticaria
The parasites most frequently linked to chronic urticaria are those that live within the human body, known as endoparasites, particularly the group of organisms called helminths, or parasitic worms. These infections are often systemic, meaning the parasites release their antigens throughout the host’s system, triggering a widespread skin reaction. Toxocara canis, or roundworm, is a common helminth repeatedly associated with chronic hives, particularly in cases where the larvae migrate through the tissues.
Other parasitic worms, such as Strongyloides stercoralis and certain tapeworms like those causing hydatid disease (Echinococcus), are also implicated. These parasites can maintain a long-term presence, providing a continuous source of antigens that perpetually stimulate the allergic pathway. The skin reaction can sometimes be the only overt symptom of the internal parasitic presence.
Protozoa, which are single-celled organisms, are also sometimes identified in patients with chronic urticaria. Blastocystis hominis and Giardia intestinalis are examples of protozoa that colonize the gastrointestinal tract and have been linked to persistent skin symptoms. These organisms may cause hives because their presence irritates the gut lining, potentially leading to a systemic immune response.
Diagnosis and Management of Parasite-Induced Hives
A medical professional investigating chronic hives will look for clues suggesting a parasitic origin, often beginning with a comprehensive medical history. Important factors to explore include recent travel to endemic areas, consumption of raw or undercooked foods, and concurrent gastrointestinal complaints like abdominal pain or unexplained diarrhea. The physical examination may also reveal signs of an ongoing infection.
Diagnosis
Laboratory testing is necessary to confirm a parasitic infection is driving the skin condition. A complete blood count often shows an increase in a type of white blood cell called eosinophils, a finding known as eosinophilia, which is a common defense mechanism against parasites. Testing total Immunoglobulin E levels often reveals an elevated concentration, reflecting the robust immune response to the parasite’s antigens.
Specific diagnostic tests include examining stool samples for the presence of ova and parasites, a process that may require multiple samples to confirm an intermittent infection. Blood tests that look for specific IgE antibodies against known parasitic species, such as those from Anisakis or Toxocara, can also provide supporting evidence.
Management
If a parasitic cause is confirmed, the treatment approach becomes two-pronged. Antihistamines are typically prescribed to manage the immediate symptoms and provide relief from the itching and swelling. To achieve a lasting resolution of chronic hives, the underlying infection must be eliminated. This requires the use of specific prescription anti-parasitic medications targeted against the identified organism. Hives that are caused by a parasite usually resolve once the infection is successfully treated and the antigenic stimulus is removed.