When it comes to diseases that can infect animals, I’m always fascinated by those having the potential to transmit among species (see Could Your Pet Get SARS). These conditions, termed zoonotic diseases, are those that can pass from animals to humans (and vice versa, called reverse zoonosis).
This potential to be exposed to zoonotic disease has significant relevance in my career as a clinical practice veterinarian. The frequency with which I have close contact with my patients certainly increases the likelihood that I could be an unwitting victim of zoonotic disease transmission (hence my frequent hand washing and rubber glove wearing).
The news that has captivated my attention as of late is the rash of dolphin deaths occurring on East coast shores this summer. According to the Philly.com article, With more dolphins dying, necropsy results awaited: “Twenty-five bottlenose dolphins have been found dead or dying in New Jersey since July 9. Forty-four have also washed up in Virginia this summer, with five discovered Thursday. Delaware and Maryland are also reporting higher-than-normal dolphin deaths.”
Dolphins aren’t the only species dying, as there have been over 120 deceased animals found stranded since June according to the National Oceanic and Atmospheric Administration's Fisheries (NOAAF) Service. Maggie Mooney-Seus, a representative of NOAAF, indicates that the large number and circumstance of the deaths is considered an "unusual mortality event".
Dolphins don’t simply strand themselves on beaches on a voluntary basis. Such an unfortunate event (stranding) can be caused by trauma (hit by boat, shark attack, etc.), contact with algal blooms, poisoning by man-made chemicals, or succumbing to infectious organisms (virus, bacteria, parasite, etc.)
The exact cause (or causes) of death has not yet been determined, but suspicions run high for a virus known to infect multiple species. The Morbillivirus is the prime suspect. Deceased dolphins are being sent for necropsy (the animal form of autopsy) at the University of Pennsylvania School of Veterinary Medicine (my alma mater).
What is Morbillivirus?
Morbillivirus belongs to the Paramyxoviridae family and is a single-stranded RNA virus. Diseases such as measles, rinderpest, and canine distemper are also in this family and considered highly infectious.
According to the 1998 Journal of Comparative Pathology article Morbillivirus infections in aquatic mammals: “Morbillivirus infections, which were not documented in aquatic mammals until 1988, have caused at least five epizootics in these species during the last 10 years. An epizootic is an outbreak of disease in a particular population over a defined period that is considered uncharacteristic by a sharp increase in numbers of cases.”
The last time the U.S. experienced such a significant dolphin die-off was 1987, when 740 animals died of morbillivirus-related complications in coastal communities from New Jersey to Florida.
How is the Morbillivirus Transmitted?
Morbillivirus is transmitted through the respiratory tract. Secretions from the lungs, trachea, nose, and mouth can be aerosolized by sneezing, coughing, and direct contact with orifices. When a dolphin expels air through its blowhole, the virus will be transmitted into the surrounding air and enter the respiratory tracts of other dolphins.
The virus readily replicates in respiratory tract tissues, enters the lymph system and organs (thymus, spleen, etc.), and ultimately causes a blood-borne infection (viremia).
Can Dogs, Cats, or Humans Be Infected with Morbillivirus?
Yes, dogs, cats, and even humans can be infected by Morbillivirus. Canine distemper virus commonly infects unvaccinated dogs residing in densely packed quarters like shelters, kennels, or even veterinary medical facilities.
Feline Morbillivirus (FmoPV) was found to infect 12 percent of stray cats tested in a 2012 study performed by Hong Kong University.
In humans, measles sickened and killed thousands until the MMR (Measles, Mumps, Rubella) vaccination “led to a greater than 99 percent reduction in measles cases in the United States compared with the pre-vaccine era” according to the Center for Disease Control.
Since multiple species can be infected with Morbillivirus, the potential exists for humans and other species to become infected via contact with stranded dolphins and other animals.
Can Morbillivirus Infection Be Stopped?
As Morbillivirus infection is occurring naturally in the dolphins’ shared environment, there’s really nothing that we humans can do to directly stop transmission among dolphins.
We can do our part to prevent the spread of Morbillivirus by avoiding any contact with stranded wildlife. If you’re in the Northeast part of the U.S. and discover a deceased or stranded aquatic mammal, please contact NOAA's marine mammal stranding network at 1-866-755-6622.
Dr. Patrick Mahaney