Three U.S tick species may trigger a mysterious red-meat allergy

allergy: The inappropriate reaction by the body’s immune system to a normally harmless substance. Untreated, a particularly severe reaction can lead to death.

arachnid: A group of invertebrate animals that includes spiders, scorpions, mites and ticks. Many have silk or venom glands.

bacteria: (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

celiac disease: (also known as sprue) A disorder in which the immune system attacks the small intestine after it encounters foods containing gluten, a wheat protein. People with this disease suffer from stomach pain, constipation, diarrhea and a constant feeling of fatigue. They must avoid gluten-containing products like bread, cake and cookies.

chronic: A condition, such as an illness (or its symptoms, including pain), that lasts for a long time.

compound: (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H₂O.

develop: To emerge or to make come into being, either naturally or through human intervention, such as by manufacturing.

diagnose: To analyze clues or symptoms in the search for their cause. The conclusion usually results in a diagnosis — identification of the causal problem or disease.

diarrhea: (adj. diarrheal) Loose, watery stool (feces) that can be a symptom of many types of microbial infections affecting the gut.

emerging infectious disease: A disease that suddenly has begun infecting increasing numbers of people or other organisms and could increase dramatically, more so in the near future.

epidemiologist: Like health detectives, these researchers look to link a particular illness to what might have caused it and/or allowed it to spread.

epinephrine: A type of stress hormone, commonly called adrenaline, that is secreted by the adrenal glands. It constricts blood vessels. It also increases the force and rate at which the heart contracts.

gelatin: A substance made from animal collagen, usually bones and cow or pig hides. It starts out as a pale colored, tasteless powder. It contains proteins and amino acids. It can make jiggly desserts (like those known as Jell-O). But this substance also is used in yogurt, soups, candies and more. It can even be used as the basis of the clear capsules used to hold single-serving amounts of dry medicines.

gluten: A pair of proteins — gliadin and glutenin — joined together and found in wheat, rye, spelt and barley. The bound proteins give bread, cake and cookie doughs their elasticity and chewiness. Some people may not be able to comfortably tolerate gluten, however, because they have an allergy to it or suffer from celiac disease.

hives: Also known urticaria, this condition produces an itchy, raised skin rash. It’s often caused by an allergy to various foods or drugs. It can also accompany some infections or be brought on by emotional stress.

immune system: The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

infectious: An adjective that describes a type of microbe or virus that can be transmitted to people, animals or other living things.

Lyme disease: A disease caused by the bacterium Borrelia burgdorferi. It can be carried by blacklegged ticks and can be spread to people through their bite. Symptoms can include headache, fever, a bullseye-shaped skin rash and being very tired. If it is not treated early with antibiotics, the infection can move into heart, joints and nervous system.

molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types.

range: The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

red meat: A term used to describe beef, lamb or other meats that appear red when uncooked — and not light colored (as chicken breast is) when cooked.

species: A group of similar organisms capable of producing offspring that can survive and reproduce.

steroid: (in biology) A chemical that serves as a signaling molecule in living things. Steroids are usually hormones — which means they are released in the bloodstream to have effects throughout the body.

survey: (with people) To ask questions that glean data on the opinions, practices (such as dining or sleeping habits), knowledge or skills of a broad range of people. Researchers select the number and types of people questioned in hopes that the answers these individuals give will be representative of others who are their age, belong to the same ethnic group or live in the same region. (n.) The list of questions that will be offered to glean those data.

symptom: A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

syndrome: Two or more symptoms that together characterize a particular disease, disorder or social condition.

system: A network of parts that together work to achieve some function. For instance, the blood, vessels and heart are primary components of the human body’s circulatory system.

tick: A small eight-legged blood-sucking arthropod, related to spiders and mites. Although they look like bugs, these are not insects. They attach themselves to the skin of their host and feed on their blood. But in the process, they may spread any germs that could have been present in the blood of an earlier host.

transmit: (n. transmission) To send or pass along.