Marmoset distemper virus mutations enhance use of primate SLAM receptors

Researchers examined the hemagglutinin (HA) protein of a canine distemper virus (CDV) strain isolated from a marmoset during a 2018 outbreak in Brazil, comparing it with a dog-derived strain. Using engineered Vero cells expressing canine, marmoset, macaque or human SLAM receptors, they assessed receptor-mediated cell fusion with HA variants carrying selected amino acid substitutions. The work used cell-expression systems and did not involve experiments in humans or animals.

The marmoset-derived strain used marmoset SLAM, unlike the conventional dog-derived strain. In the dog-strain background, the R519I substitution increased marmoset and human SLAM use, with a further increase when combined with G530S. Reversing either substitution in the marmoset-strain HA reduced receptor use. The adapted HA retained canine SLAM use, with no apparent trade-off in these assays.

The findings indicate that CDV can acquire mutations naturally associated with increased use of primate SLAM receptors, including human SLAM. They do not show that CDV infects or spreads among people: the clinical consequences of human infection remain unknown, and SLAM use alone is insufficient for host switching. The article is an early-release report, and the authors call for continued surveillance.