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.”

AnimalBacteriaNumber of Drugs Resisted
Harp sealChryseobacterium indologenes13
Harbor porpoiseSphingomonas multivorium12
Minke whaleVibrio alginolyticus10
Hooded sealPseudomonas sp.8
Common dolphinPseudomonas sp.8
Thresher sharkPseudomonas sp.8
Pygmy sperm whaleProvidencia rettgeri7
Mako sharkPseudomonas aeruginosa6
Pygmy sperm whaleSphingomonas paucimobili5
Grey sealEdwardsiella tarda3
Striped dolphinStaphlycoccus2


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