From 2007 to 2009, a devastating yellow fever virus outbreak nearly decimated brown and black and gold howler monkey populations at El Parque El Piñalito in northeastern Argentina. An international research team tested if howlers who survived the outbreak had any genetic variations that may have kept them alive. In brown howlers, they found two mutations on immune genes that resulted in amino acid changes in the part of the protein that detects the disease.
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Source: ScienceDaily