Tuberculosis and Seals: Sea Mammals as Harbingers of Disease

By Chris Healey

Seals introduced one of the deadliest illnesses in history to the Western Hemisphere centuries before Europeans carried it over. Researchers at the University of Tubingen in Germany published findings in the research journal Nature describing the role seals played in introducing tuberculosis to the Americas.

Before these findings, the presence of tuberculosis in North and South America prior to European exploration was unexplained. Tuberculosis spread across Africa, Europe, and Asia, but there was no evidence demonstrating tuberculosis concurrently existed in the Americas. The bacteria made its first appearance in Peruvian skeletal remains dating back to approximately A.D. 700 – centuries before the arrival of European explorers.

Research findings indicate approximately 2500 years ago, seals contracted a Mycobacterium strain from Africa and carried it across the ocean to the shores of Peru and Northern Chile. Possibly through seal predation, costal humans contracted a version of the seal Mycobacterium which had adapted to humans. Tuberculosis has been found in skeletal remains in North America dating back to approximately A.D. 900, indicating the seal-derived strain spread person-to-person from South America.

One limitation of this study was the inability to rule out humans passing the agent to seals. The researchers deemed that alternative a distant possibility; humans did not treat seals as livestock. A close relationship, such as between farmer and animal, is required to pass a pathogen from human to animal.

The seal-derived strain did not last long in the Western Hemisphere. Following European settlement, European tuberculosis strains outcompeted and eliminated those from seals. Today, viable seal-derived strains do not exist.

Tuberculosis is a condition caused by Mycobacterium tuberculosis, a slow-growing bacterium adept at evading host immune response. The illness is one of the greatest threats to public health worldwide. According to the World Health Organization, tuberculosis kills more people than any other infectious agent except HIV/AIDS.

Despite advancements in therapeutic techniques, there has been a resurgence of tuberculosis fueled by the emergence of HIV/AIDS in the late 20th century. As an opportunistic pathogen, tuberculosis kills more AIDS patients than any other illness.

Tuberculosis is not the first human illness associated with seals. They are susceptible to certain subtypes of influenza, including H7N7, H4N5, and H3N2. Influenza subtypes maintained in seal populations could be re-assorted in other animals, such as fowl or swine, to produce subtypes which are highly virulent in humans.


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