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Cetacean Infectious Diseases

Infectious diseases are illnesses caused by organisms such as bacteria, viruses, fungi or parasites.  In cetaceans (whales and dolphins), infectious agents have been identified in both wild and captive populations.  While some infectious diseases may cause mild or insignificant illness in animals, others have lead to the death of individuals and in some cases, large die-offs of groups of animals in the wild. 

Some of the most notable marine mammal die-offs have been attributed, at least in part to viral infections.  Specifically, morbillivirus has been implicated in the largest and most well-known events occurring in the Mediterranean Sea, Atlantic Ocean, Gulf of Mexico, and Indian Ocean. 

Some infectious diseases are contagious, meaning that they can be transmitted from one animal to another through contaminated breath, bodily fluids, bite wounds, or from mother to fetus/newborn.  Infectious organisms can also be contracted through the ingestion of contaminated food, infection with affected parasites, or from the environment.  The signs of illness vary depending on the part of the body that the disease affects.  Some diseases impact particular organ systems, such as the respiratory system (causing for instance, pneumonia) or the gastrointestinal system (causing diarrhoea, for example), while other infections cause cetaceans to have more general signs of illness such as fever, decreased appetite and lethargy.   Respiratory infections are one of the more commonly reported types of disease in cetaceans.  Some infectious diseases that impact cetaceans have also been shown to infect humans as well.

Most infectious diseases have been recognized through opportunistic examinations of dead animals that wash ashore, but live animal diagnostics and research efforts have also provided important contributions to the knowledge base.  Reports of infectious diseases in cetaceans are on the rise, which may be due to recent advances in diagnostic capabilities, more intensive surveillance efforts, or an actual increase in the rate of infectious disease in these animals. 

While great strides have been made in the last 50 years to improve our understanding of these diseases in whales and dolphins, this is still a new field of study with many unanswered questions.  Basic information about the way that diseases are transmitted and the degree of illness they cause is lacking in many cases.  Increasing pressures on cetacean populations, including rising ocean temperatures and ocean acidification, may change disease dynamics as well, further complicating research efforts. 

There has also been evidence suggesting that humans may play a role in cetacean disease, with the discoveries of an unexpected number of antibiotic resistant bacteria present in wild populations, and of the bioaccumulation of contaminants in blubber that may have a suppressant effect on these animals’ immune systems.  Research efforts are currently underway around the world to better understand infectious diseases in cetaceans, with a focus on the role these diseases play in population health and conservation.