Phocine Distemper Virus (PDV) is a morbillivirus of pinnipeds that was first identified in 1988. As an enveloped RNA virus, it shares several similarities with influenza, including possible clinical presentation of respiratory distress. Also like influenze, PDV appears to cause significantly more morbidity and mortality in harbor seals than it does in grey seals, though both are susceptible to infection. There have only been a handful of documented PDV outbreaks, with both the 1988 and 2002 epidemics in Northern Europe each resulting in the death of approximately 20,000 harbor seals. A smaller epidemic occurred in harbor seals in the Northeastern United States in 2006, and an additional Unusual Mortality Event in the same region has been underway since the summer of 2018. Given the similarities between morbillivirus and influenza, we seek to determine if similar internal and external factors play a role in susceptibility, maintenance, and evolution of the virus, while also investigating the potential impacts of coinfection for both viruses.