Some diseases seem like they should have always been with us. It has long been thought that measles was one of those with a pedigree stretching back into the depths of Antiquity, as soon as people were living in a high enough concentration to maintain a virus that needs a constant supply of human hosts. A recent study by Yuki Furuse, Akira Suzuki, and Hitoshi Oshitani shows us that this is not the case.
All circulating strains of measles (MeV) have a common ancestor from the early 20th century. This says a lot about the global spread and need for constant naive human hosts of measles. Furuse, Suzuki and Oshitani went in search of measles previous last common ancestor with its most closely related virus Rinderpest (RPV), a cattle virus. Rinderpest was once a catastrophic disease wiping out cattle herds and causing human famines. The economic and human costs were so great that countries around the world successfully united to drive it into extinction. In 2010, the United Nations officially declared Rinderpest extinct in global livestock herds. What does it say about our priorities that Rinderpest is extinct and measles outbreaks are still occurring in the US? While measles cases are dropping globally it is far from gone. In 2009, about 400 children were dying per day from measles, according to the World Health Organization.
Furuse, Suzuki and Oshitani (2010) collected DNA sequences for the hemagglutinin (H) and nucleocapsid (N) genes of the measles virus (MeV), and rinderpest (RPV) with the sequence for peste des pestitis rumninants virus being used to define the divergence point. I’m not an expert in the molecular clock models used so I can’t critique that aspect. Their molecular clock setting predicted 1916 (H gene)/1921 (N gene) as the last common ancestor point for MeV, close to previous estimates, and 1171 (N gene) / 1074 (H gene) for the divergence point with Rinderpest (RPV). Furuse, Suzuki and Oshitani (2010) therefore place the emergence of the Measles virus to between the 11th and 12th century.
Measles evolved in a context where humans and cattle were closely associated. Models predict that the measles virus requires a naive (non-immune) human population of 250,000-500,000. These conditions were possible since prehistory in the Middle East. According to Furuse, Suzuki and Oshitani, the earliest “measles-like syndrome” was described in the 9th century by Abu Becr, also called Rhazes, and identifiable measles epidemics began to be recorded in the 11th to 12th century. They note that the ancestral virus before the divergence probably could infect both humans and cattle, though its symptoms may have been significantly different. The modifications that finally made measles a human-only virus should have given it significant boost in virulence. Measles is highly contagious with a Ro of 15 (meaning each person with measles infects on average 15 others). Malnourished children are known to have fatality rates around 40% (Crawford, 2007) If an early medieval emergence holds up, then measles would have been a primary emerging infectious disease between the two major plague pandemics (5th-8th century and 14th century onwards).
Furuse Y, Suzuki A, & Oshitani H (2010). Origin of measles virus: divergence from rinderpest virus between the 11th and 12th centuries. Virology journal, 7 PMID: 20202190
Crawford, DH. (2007) Deadly Companions: How Microbes Shaped Our History. Oxford University Press.