The virus that causes a fatal illness that was first reported among Navajos in New Mexico and was later found in other parts of the Western United States has been isolated and grown in a laboratory for the first time by two teams of federal researchers.
The development improves prospects for eventually developing a simple diagnostic test to detect infection, drug therapy and possibly even a vaccine. In the six months since the first cases were reported, the virus has produced flulike symptoms in at least 45 people in 12 states. In 27 of those cases it was fatal. The virus struck many previously healthy young adults.The ability to grow the entire virus in the laboratory is expected to improve ways to detect its presence in humans and in the deer mice that spread it. Detection, in turn, would help determine how prevalent the virus is and what circumstances allow it to spread.
Scientists from the Centers for Disease Control and Prevention in Atlanta and the Army Medical Research Institute in Fort Detrick, Md., reported the advance Saturday in separate papers at a scientific meeting in Albuquerque.
The Centers for Disease Control found evidence of success in isolating and growing the virus only last week, days before the scheduled meeting on hantavirus, and the Army's findings were made public shortly before that, the scientists, Dr. Clarence J. Peters of the CDC and Dr. Connie Schmal-john of the Army, said in interviews.
Donna Shalala, secretary of health and human services, said in a news release, "This is a major step forward in our efforts to prevent this devastating disease."
The newly isolated virus belongs to the hantavirus group, which takes its name from the Hantaan River in Korea. A different hantavirus caused thousands of cases among U.N. troops during the Korean War in the 1950s. It took scientists until the late 1970s to isolate that virus.
The newly isolated virus often produces a respiratory illness that can be difficult to distinguish from influenza. Those infected may suffer fever, muscle aches and pains, coughs and other respiratory symptoms for a few days. But then the illness leads to a condition known as acute respiratory distress syndrome. Breathing becomes labored as fluid accumulates in the lungs.
This condition, known as pulmonary edema, is usually caused by heart disease. But those infected with the hantavirus "literally drown to death in blood plasma," said Dr. Clarence J. Peters, the scientist who delivered CDC's report. "I have never seen anything like it."
The Centers for Disease Control and the Army conducted their research independently but exchanged information. The investigations began immediately after doctors first recognized a mysterious respiratory illness in the Four Corners area of Colorado, Arizona, New Mexico and Utah.
At first doctors suspected that the cases were caused by influenza or pneumonic plague. But these illnesses were quickly ruled out by laboratory tests and epidemiologic investigations by the Indian Health Service, New Mexico Health Department and University of New Mexico.
The Centers for Disease Control was consulted. "Over the Memorial Day weekend, a bunch of us got together, and the feeling around the table was that this was something new," Peters said. "Nobody had any idea what it was, there was nothing that anybody could think of that fit the epidemiology, the clinical picture. And later, as we added the pathology data, it did not fit the pathology of any known disease."
Researchers also had reason to worry about their own safety.
"The mortality rate was around 75 percent, and we had no idea what the organism was," Peters said. "So we were pretty careful around the lab and we took a lot of precautions."
On June 4, the fourth day of the laboratory investigation at the Centers for Disease Control, "we got a hint that it was a hantavirus," Peters said.
The finding was a surprise because the four known hanta-vi-ruses, which produce widespread bleeding, attack the kidneys, not the lungs.
The case for hantavirus soon strengthened when Dr. Sherif Zaki, a pathologist at the centers, found evidence of it in tissues from autopsies of victims.
Using newer genetic and other scientific methods, researchers were able to detect a portion of a hantavirus in the tissue samples. They also determined that it was not a previously known hanta-vi-rus.
The scientists knew that rodents carried other hantaviruses, so they developed blood tests to determine whether they could detect the new virus among the exploding population of deer mice in the region. Next, they had not yet isolated the virus or grown it in cells in the laboratory. So, using the tissues of a deer mouse that had been trapped in the house of a fatal case, they repeatedly inoculated several new generations of cells in the laboratory over the course of weeks. The scientists eventually isolated the virus in test tubes. The molecular pattern in the virus from the mouse was virtually the same as in other samples from the fatal case.
Scientists believe deer mice spread the virus through contaminated urine, feces and saliva. But the virus is not believed to spread from person to person.
"We don't fully understand how the deer mice pass the virus from one to another," Peters said. "And by having the virus, we can infect animals in the laboratory to study such patterns and to learn how the virus makes you sick."