Baylor College of Medicine and Texas Children's Hospital in Houston -- The study is the first to provide hard evidence that mumps was the underlying cause of EFE, says Towbin, and the first to "strongly infer" that use of a vaccination has had an impact on any type of heart disease.
Scientists have speculated for decades that viruses are involved in some forms of heart disease. Towbin says the medical literature is full of arguments about whether mumps infections during pregnancy could cause EFE in unborn and newborn infants.
Until the development of a technique called polymerase chain reaction, or PCR, searching for viruses in the heart during an autopsy was like looking for a needle in a haystack. But now scientists need only a small piece of a virus' genetic material in order to "amplify" it with PCR and then identify it.
With heart tissue samples obtained during autopsies of 29 infants who died between 1955 and 1992, Towbin and his colleagues used PCR to search for several viruses -- enterovirus, adenovirus, mumps, cytomegalovirus, parvovirus, influenza and herpes simplex virus.
EFE had been documented in all 29 autopsies. PCR testing uncovered at least one virus type in all but three of the infants. Twenty-one of them (72 percent) were "positive" for the mumps virus, reports Towbin's team. "The most striking result was the number of EFE patient samples that were PCR positive for mumps," the researchers write in Circulation.
"EFE was previously considered a significant cause of infant mortality," they continue. "In recent years, however, the incidence of this disease has declined dramatically, probably because of the availability of the mumps vaccine."
"Almost all the heart samples we looked at that were collected before 1980 had mumps," says Towbin, "while none of them had it after 1980."
Their finding has more than just historical significance. The next step is to determine what viruses are causing heart muscle infections nowadays, he says. "It may be worthwhile investing in vaccinations against those viruses, too, if it saves young children's hearts."
In an earlier paper published in Circulation, (V. 90, pp. 330-339, 1994), Towbin's team found adenoviruses now are the most common cause of acute heart-muscle inflammation in children. Adenoviruses are a group known to cause eye and upper respiratory infections, as well as viral pneumonia.
A vaccine against adenoviruses already is being produced, Towbin says, but currently it's available only to some U.S. military personnel.
Towbin's laboratory has performed PCR tests on hundreds of samples of heart muscle. These samples can be obtained from living individuals by using a long, thin tube (a catheter called a bioptome) that slides through the circulatory system until one end reaches the heart.
In heart muscle samples from cases after 1980, investigators usually find adenoviruses, he says. How do viruses that normally infect the eye, nose and throat end up in the heart?
At some point during a viral infection, "you have a brief period of so-called viremia, when the virus is in the bloodstream," Towbin explains. Certain viruses, including adenoviruses, have affinity for heart muscle -- "they enjoy the heart," he says.
As the virus-laden blood flows through the heart, some heart muscle cells become infected and eventually lose their ability to contract normally.
When echocardiography shows a child's heart is enlarged and dysfunctional, a viral infection often is the cause, says Towbin. "We believe adenovirus is the most common cause, at least in kids," The second most commonly found virus is Coxsackie virus, he adds.
But children aren't the only ones who are susceptible. The death certificate for Reggie Lewis, the Boston Celtics basketball player who collapsed on the court, states that he died of inflammation of the heart caused by adenovirus, Towbin says.
"Nobody really knows" the incidence or prevalence of heart muscle diseases caused by viral infections, the researcher says. Towbin is a principal investigator on a new federally funded registry of children with heart muscle disease, in collaboration with scientists at Boston's Children Hospital. Pediatric centers such as Towbin's and the one in Boston see about 10 to 12 cases of this type each year, he says.
Towbin's co-authors are Jiyuan Ni, M.D.; Neil E. Bowles, Ph.D.; Young-Hwue Kim, M.D.; Gail Demmler, M.D.; Debra Kearney, M.D.; and J. Timothy Bricker, M.D.
Circulation is one of five scientific journals published by the Dallas-based AHA.
Media advisory: Dr. Towbin's office phone number in Houston is (713) 798-7342. Reporters may call (214) 706-1173 for a copy of the journal report. (Please do not publish numbers.)