The virus that causes rubella, or German measles, finally has company. Scientists had never identified close relatives of the virus, leaving it as the only member of its genus, Rubivirus. But with a report in this week’s issue of Nature, rubella has gained a family. One of its two newfound relatives infects bats in Uganda; the other killed animals from three different species in a German zoo and was found in wild mice living nearby as well.
The findings strongly suggest that at some point in the past, a similar virus jumped from animals to humans, giving rise to today’s rubella virus, the researchers say. Although neither of the new viruses is known to infect humans, the fact that a related virus jumped species raises concerns that the two viruses or other, as-yet-unknown relatives could cause human outbreaks. “We would be remiss not to be concerned, given what’s going on in the world today,” says epidemiologist Tony Goldberg of the University of Wisconsin, Madison, a senior author of the study.
Highly infectious, the rubella virus usually causes rashes and fever, but in pregnant women it can lead to miscarriages, stillbirth, and babies born with congenital rubella syndrome, which includes deafness and eye, heart, and brain problems. An estimated 100,000 newborns are affected by the syndrome annually, mostly in Africa, the western Pacific, and the eastern Mediterranean; in many other countries the measles, mumps, and rubella (MMR) vaccine has made it a rarity.
Goldberg and his former graduate student Andrew Bennett discovered one of the new viruses in apparently healthy cyclops leaf-nosed bats, netted at night in Kibale National Park in Uganda. They named it ruhugu virus, after the Ruteete region of Uganda and the local word for bat. The architecture of ruhugu’s genome is identical to that of the rubella virus, and 56% of the amino acids in its eight proteins matched those in rubella. The protein that interacts with the host’s immune cells was almost identical in both viruses.
As they were getting ready to publish, the researchers learned that a team led by Martin Beer at the Friedrich-Loeffler Institute had detected another rubella relative in brain tissue from a donkey, a kangaroo, and a capybara—a giant rodent native to South America—that all died from encephalitis, an inflammation of the brain, at an unnamed zoo. They found the same virus in wild yellow-necked field mice caught in the zoo or within a 10-kilometer radius. The mice appeared to be fine, suggesting they were a natural reservoir from which the virus spilled over to the zoo animals. Comparing their data, the teams realized their viruses were related, although ruhugu was closer to rubella than the second relative, rustrela virus, named after a lagoon in the Baltic Sea. The teams decided to publish jointly.
Two other viruses that primarily affect children, measles and mumps, also came from animals, Goldberg notes. “Now we know that every disease in the letters of the MMR vaccine has a zoonotic origin,” he says. Given the genetic distance between rubella and the ruhugu and rustrela viruses, the researchers don’t think either of them made the jump to humans—but they suspect they’ll find other Rubiviruses if they look closely.
The paper is “really important because there’s very little understanding of where rubella came from,” says molecular anthropologist Anne Stone of Arizona State University, Tempe. “It was all by itself without any close relative.” The finding underscores the importance of the One Health approach, which recognizes that the health of people is closely connected to that of animals and the environment, she says.
Both viruses bear close watching, researchers say. It’s “really interesting” that rustrela was able to infect both placental and marsupial mammals, and “was actively jumping between species,” says evolutionary virologist Edward Holmes of the University of Sydney. That flexibility could spell trouble, says vaccinologist Gregory Poland of the Mayo Clinic. “Who knows, if it could move from mice to other mammals, could it move to humans?” he asks. “In the end, the bugs win.”