SAN ANTONIO (Reuters Health) - Microscopic aquatic animals known as copepods, one of the most widespread and abundant life forms on Earth, could be a source of gastrointestinal and other allergies, researchers report.
In fact, nearly half of patients already allergic to other substances also tested positive to proteins extracted from a species of copepod, according to Dr. Steve Kagen of the Kagen Allergy Clinic in Appleton, Wisconsin.
Copepods (Latin for "oar feet") are related to much larger crustaceans, such as crabs or shrimp, and are found wherever there is water--from the deep ocean and freshwater streams to the moist undersides of leaves and grass. Ranging in size from microscopic to barely visible, they feed on algae, bacteria and other organisms, and taken together comprise one of the largest sources of protein on the planet.
Because other small animals--such as dust mites or cockroaches--can shed proteins known to trigger allergy, Kagen wondered if the lowly copepod might do the same. After extracting suspected protein allergens from two species of copepod, he and his colleagues used a highly sensitive antibody test to see if any of 75 patients already allergic to other substances were allergic to copepod protein, too.
The result? Thirty-three of the patients--44%--showed evidence of antibodies suggesting prior reactions to copepod. To help rule out "cross-reactivity"--the possibility that other allergens might have triggered the antibody response--Kagen also ran tests for common allergens such as ragweed, birch, grass, midge, shrimp and dust mites. They found no evidence of cross-reactivity.
All of us have ingested--and will continue to ingest--proteins shed by copepods, Kagen said. "If you go swimming in a lake and you swallow some water, you just swallowed some copepods," he told Reuters Health. And even in tap water sourced from municipal water supplies, "the copepod itself may not get through, because there are sand filters and other techniques that are being used, but the proteins themselves will come through," he said.
Of course, developing antibodies to an allergen does not mean a patient will develop noticeable symptoms of allergy. But because copepod proteins ingested through swimming or drinking water will most certainly come into direct contact with the gastrointestinal system, Kagen believes they could be an as yet unidentified trigger for Crohn's disease or ulcerative colitis--serious chronic illnesses whose causes are not always clear.
Kagen's team is currently investigating the prevalence of copepod allergy in patients with these conditions, known collectively as inflammatory bowel disease, and so far every one of the Crohn's patients in his practice have tested positive for copepod allergy.
"What we're going to do next is isolate the copepod proteins, sequence them if we can, clone the genes, so we can really find out what these proteins are," Kagen said. In the meantime, he hopes to alert allergists to the fact that these tiny, ubiquitous creatures could be a cause of hitherto-unexplained allergic illness.