“Social distancing” during an outbreak of a contagious disease is difficult for dolphins as well as for humans. Researchers are now investigating how dolphin social interactions may help spread the virus that has resulted in significant dolphin strandings and die-offs in recent years. 

Cetacean morbillivirus is a lethal and highly contagious virus that infects marine mammals including dolphins, porpoises, and whales. First discovered in Virginia and Maryland waters in 1987, the virus is related to measles in humans. It can spread rapidly among dolphins, as it did from 2013 to 2015 in populations along the Atlantic Coast. 

Delmarva Now reports that during that outbreak, more than 1,600 dolphins washed ashore on beaches from New York to Florida, according to the National Oceanic and Atmospheric Administration. Altogether, an estimated 20,000 dolphins died from the virus, and the region’s population of coastal dolphins shrank by about 50%.

“It’s much like COVID — it’s respiratory” in how it spreads, said Janet Mann, a dolphin researcher from Georgetown University. “When dolphins breathe together at the surface, they’re sharing respiratory droplets just like we do when we’re talking or coughing on each other.”

Mann and other researchers have observed social behaviors typical of bottlenosed dolphins, including synchronized jumping and breathing, which may tend to spread the virus.

A briefing paper by Access Science explains that bottlenose dolphins can contract the morbillivirus disease through the inhalation of aerosolized particles containing the virus. They also can be infected via direct contact with other infected dolphins. The virus can enter a dolphin through its eyes, mouth, urogenital tract, or skin wounds, in addition to the respiratory tract. The lungs and brain of infected dolphins are the major organs of the body that are affected. Infected dolphins appear thin and display numerous skin lesions. They are stressed by breathing difficulties, which are often related to pneumonia, and act abnormally. Moreover, these dolphins become prone to other illnesses because the morbillivirus infection weakens their immune systems. 

Initially, the cetacean morbillivirus outbreak was limited to bottlenose dolphins in the northern Atlantic Ocean. In recent years, however, lethal outbreaks have been observed worldwide including off Brazil, Hawaii, and Australia. The virus represents one of the greatest infectious disease threats to cetaceans.

Fortunately, the dolphin-killing pathogen is not a threat to humans. Unfortunately, there is no vaccine or effective treatment for marine mammals suffering from the infection.