Bacteria, viruses and parasites from land animals such as cats, cows and humans are sickening and killing sea mammals. Scientists have been finding a daunting number of land-based pathogens in seals, dolphins, sharks and other ocean dwellers that wash ashore dead or dying, according to an article by Christopher Solomon in the May 2013 issue of Scientific American, entitled “How Kitty is Killing the Dolphins.”

The “pollutagens” could pose a threat to people, too. Researchers are finding strains of bacteria that commonly infect people and are resistant to drugs. One harp seal had bacteria that were resistant to 13 of the 16 drugs tested by a team from Woods Hole Oceanographic Institution on Cape Cod. In recent years researchers have tested numerous sea mammals from various parts of the oceans to see which bacteria they harbor and the antibiotics those bacteria are immune to. A sample from the northwestern Atlantic is below.

The discoveries are worrisome for several reasons, Solomon writes: “A surfer or fisher with an open wound, or someone who gulps water while swimming, could get an infection that is hard to treat.” Of course people also eat seafood that could harbor the germs. Solomon also notes that sea mammals “could serve as swimming Petri dishes, nurturing and transforming diseases until they re-emerge among humans as something new and more difficult to defeat.”

Animal Bacteria Number of Drugs Resisted
Harp seal Chryseobacterium indologenes 13
Harbor porpoise Sphingomonas multivorium 12
Minke whale Vibrio alginolyticus 10
Hooded seal Pseudomonas sp. 8
Common dolphin Pseudomonas sp. 8
Thresher shark Pseudomonas sp. 8
Pygmy sperm whale Providencia rettgeri 7
Mako shark Pseudomonas aeruginosa 6
Pygmy sperm whale Sphingomonas paucimobili 5
Grey seal Edwardsiella tarda 3
Striped dolphin Staphlycoccus 2


Sources: Occurrence and Patterns of Antibiotic Resistance In Vertebrates off the Northeastern United States Coast. Julie M. Rose et al. in FEMS Microbiol Ecol 67, 421–431, 2009. Victims or Vectors: A Survey of Marine Vertebrate Zoonoses from Coastal Waters of the Northwest Atlantic. Andrea L. Bogomolni et al. in Diseases of Aquatic Organisms, Vol. 81: 13–38, Aug. 19, 2008.

Photo of harp seals courtesy of courosa on Flickr