The invisible "chain of transmission" of rubella virus has been broken in the United States. With it disappears a disease that a little more than a generation ago struck fear in the heart of every pregnant woman.
Fewer than 10 people a year in this country now contract the infection known popularly as German measles. Since 2002, all cases have been traceable to foreigners who carried the virus in from abroad.
Between those rare events, however, no rubella virus has circulated in the United States because the bug simply cannot find enough susceptible hosts. After years of assiduous vaccination, virtually the entire U.S. population is immune.
Mild and often entirely unnoticed in children, rubella infection can be devastating to developing fetuses. A woman infected with the virus in the first three months of pregnancy will probably suffer miscarriage, or deliver a stillborn or permanently disabled child. In the last great U.S. epidemic of rubella -- 40 years ago, before there was a vaccine against the disease -- about 12,000 babies were born deaf or deaf and blind.
The outbreak so swelled the number of congenitally deaf Americans that Gallaudet University, the District's educational institution for the hearing-impaired, eventually acquired a second campus to accommodate them.
"This is a milestone," said Julie L. Gerberding, director of the Centers for Disease Control and Prevention. "It is a major step forward in our ability to eliminate this problem in the Western Hemisphere, and then in the world." She will announce rubella's disappearance from the United States at the opening this morning of the National Immunization Conference here.
The disease's decline began after the introduction of rubella vaccine in 1969. The infection's virtual disappearance, however, required more than high levels of immunization in the United States. The disease also needed to become less common in the Caribbean and Latin America, the source of most imported cases. Mass rubella vaccination began in those regions in the late 1990s, although some countries (notably Cuba and Uruguay) had moved against rubella decades earlier.
The recent campaigns reduced the number of cases coming across the border, and to some extent also reduced the number of susceptible immigrants living here -- a segment of the population in which an unusual number of the last decade's cases occurred.
Lacking both spark and fuel, rubella burned itself out.
Keeping rubella at bay depends entirely on keeping immunity high. According to the CDC, more than 93 percent of children younger than 3 have been vaccinated, usually with the measles-mumps-rubella (MMR) shot, although rubella vaccine can be given by itself. The Pan American Health Organization's recent resolution to eliminate rubella from all of the Americas by 2010 will also help.
"Eliminated" means the disease is no longer endemic -- all new cases arise from imports. "Eradicated" means there are no cases from any source. Global eradication of rubella, while conceivable, is a distant goal.
Rubella vaccine is not yet part of the standard package of childhood immunizations in many developing countries. The annual number of cases globally is unknown. However, the World Health Organization estimates that 100,000 babies are born with "congenital rubella syndrome" -- the constellation of birth defects the virus causes.
In the United States, there was a single case of the syndrome in 2003, none in 2002 and three in 2001. The total number of U.S. rubella infections was nine in 2004, seven in 2003 and nine in 2002, said Susan Reef, an epidemiologist at the CDC who tracks the disease.
The infection, whose name means "little red," was thought to be a variant of measles until 1814, when German researchers described it as a distinct illness (hence its popular name). It causes a short-lived red rash, low-grade fever and, in adult women, often pain in the joints. If a woman is pregnant, however, the virus crosses the placenta and infects the fetus 50 to 85 percent of the time. There, it spreads widely, causing cells to die or stop dividing.