Public health scientists verified that a common virus -- a coronavirus -- that has become more severe as the likely cause of severe acute respiratory syndrome (SARS). Many people wonder just how scientists know that the cause is a virus and, more importantly, this particular virus.
In 1890, Robert Koch described the basis rules that scientists use to determine if an infectious organism causes a specific disease. These four rules are called "Koch's postulates."
The organism must be found in...
Paragonimiasis is caused by infection with a trematode. That's a parasitic worm also called a fluke or lung fluke because it commonly infects the lungs. Usually, infection comes after eating undercooked crab or crayfish that carry immature flukes.
Once swallowed by a person, the worms mature and grow inside the body. Over months, the worms spread through the intestines and belly (abdomen). They penetrate the diaphragm muscle to enter the lungs. Once inside the lungs, the worms lay eggs and can survive for years, causing chronic (long-term) paragonimiasis.
Paragonimiasis is rare in the U.S. Most cases occur in Asia, West Africa, and South and Central America.
Paragonimiasis causes no symptoms during initial infection. Many people with paragonimiasis never experience any symptoms. When paragonimiasis symptoms do occur, they result from the worms’ location and activity in the body, which change over time.
In the first month or so after someone is infected, paragonimiasis worms spread through the abdomen, sometimes causing symptoms that can include:
Worms then travel from the belly into the chest. There they can cause respiratory symptoms, such as:
Shortness of breath
Chest pain (made worse by deep breathing or coughing)
Without treatment, paragonimiasis becomes chronic. It can continue for decades.
The most common long-term paragonimiasis symptom is a cough with bloody sputum (hemoptysis) that comes and goes. Other chronic paragonimiasis symptoms may include:
Lumps or bumps on the skin of the belly or legs that come and go over time
Some people with chronic paragonimiasis have no noticeable symptoms.
In less than 1% of people with paragonimiasis, the worms infect the brain. Symptoms can include:
Diagnosing paragonimiasis can be difficult or delayed. That's because its symptoms are often mild and overlap with more common conditions.
Most often, a person with symptoms has multiple tests before a doctor makes the diagnosis of paragonimiasis. Exams and tests used to make a diagnosis include:
Patient History. Your doctor will get clues about possible paragonimiasis by looking at the pattern in which your symptoms appeared. Your doctor will ask about your past eating of undercooked crab or crayfish.
Physical examination. Abnormal breath sounds or belly tenderness observed with a doctor’s examination of the chest or belly can suggest a problem and direct further testing.
Blood tests. A high number of a specific type of white blood cells can suggest parasitic infection. Antibodies against flukes may be present in the blood.