2. Outline
Summary of the Current Outbreak
Morbillivirus Overview
Pollution Implications
Past Study
Future action and possible solutions
3. Current Outbreak
NOAA declared a
Unusual Mortality
Event (UME) for
bottlenose dolphins
(Turnsiops truncatus) in
the Northeast United
States in July 2013
An epizootic
6. Morbillivirus spp.
Genus Morbillivirus is a group of single-stranded RNA
viruses
Highly contagious, even between species
Symptoms
Skin lesions
Pnuemonia
Brain Infections
Secondary infections
7. Persistent Organic Pollutants
(POPs)
Chemicals used in agriculture for pest control,
disease control, and increased crop production
Polychlorinated biphenyls (PCBs)
Dichlorodiphenyl trichloroethane (DDT)
Cause variety of adverse effects
Accumulate and persist in environment
Readily travel long distances
8. POP Biomagnification
"Biomagnification is the sequence of processes in an
ecosystem by which higher concentrations of a particular
chemical are reached in organisms higher up the food chain,
generally through a series of prey-predator relationships.“
- Oxford Dictionary, 2008
http://toxics.usgs.gov/
9. POPs as Immunosuppressants
Aguilar and Borrel (1994)
Studied
Morbillivirus
epizootic in striped
dolphins (Stenella
coeruleoalba) the
Mediterranean Sea
from 1990-1992
Discovered that concentrations of PCBs were
significantly higher during a Morbillivirus
outbreak
http://www.yourchildlearns.com/online-atlas/mediterranean-map.htm
10. Methods:
Dolphins were classified as ‘infected’ or
‘healthy’
Tissue samples taken
PCB concentrations measured
Compared infected dolphins to healthy
dolphins
POPs as Immunosuppressants
Aguilar and Borrel (1994)
11. Variation of Polychlorinated Biphenyl Concentrations
in Dorsal Blubber in Mediterranean Striped Dolphins
Aguilar and Borrel 1994
Results:
13. Conclusions
Virus susceptibility is complex
Cetaceans be negatively impacted by high levels of
ocean pollutants
More studies need to be done researching the
implications of POPs as immunosuppressants in
marine mammals
14. Future Goals
Establish more conclusive causes of susceptibility
Continue to lower POP emissions
Use current outbreak to uncover more data
Eradicate disease
Good afternoon everyone, my name is Kayla Boyes and today I will be discussing the relationship between ocean pollution and the susceptibility of cetaceans to the morbillivirus infection. Cetaceans include whales, dolphins, and porpoises, but for this presentation I will mainly be talking mostly about bottlenose and striped dolphins.
First, I am going to get you guys up to date on the current morbillivirus outbreak on the East Coast. Second I’ll briefly go over the disease itself. Third we’ll look at how pollution could be linked to the high mortality rates of the virus. Then we’ll check out a few studies that have researched this relationship. Last I’ll touch on what can be done to prevent future outbreaks.
Now, I don’t know if you’ve heard about this recent die off on the news, but a news article is what really got me interested in this topic. As of November 1st, more than 700 dead or dying dolphins have washed ashore along the United States East Coast. The National Oceanic and Atmospheric Administration declared the outbreak an Unusual Mortality Event, or UME in July 2013. The culprit was determined to be a strain of Morbillivirus. A viral outbreak of this magnitude that is still contained to a certain area is also classified as an epizootic, which is just the zoological equivalent of an epidemic in humans.
This graph, provided by the NOAA, shows the bottlenose dolphin strandings by state in November from the past 6 years. A stranding is classified as an animal washing up on the shore, either alive or dead. The year is shown on the x axis and the total number of strandings for the month is shown here on the y axis. Different states on the East Coast are represented by the different colored bars. As you can see, states like New Jersey, Delaware, and Maryland have not witnessed a single bottlenose dolphin stranding in November in years past. Even states that have had some strandings in the past are reporting notably higher numbers of stranding incidents. And this is just November.
This graph is similar to the last graph, but it shows annual bottlenose dolphin strandings on the East Coast from 2007-2012. In previous years, the average number of strandings has hovered around 200 animals per year. The 2013 average as of November 10th was more than 900. Since July only, 700 bottlenose dolphins have been stranded on the East Coast. Also, these estimates don’t include infected animals that are not stranded, so it is very difficult to accurately gauge the true magnitude of the outbreak. However, just recently there have also been reports of the virus further south. This indicates that the infection is spreading toward Floridian waters. So far, we’ve seen some pretty convincing evidence that this is an unusual mortality event. So what is it that is causing all this damage?
Meet the morbillivirus virion. The Morbillivirus genus is a group of single stranded RNA viruses. Other morbillivirus infections include measles in humans, canine distemper virus in canines, phocine distemper virus in seals, and of course cetacean morbillivirus in dolphins, porpoises and whales. These infections are highly contagious, and are spread by close contact, so it is easily spread between social species. It has been suggested that bottlenose dolphins may have been catching cetacean morbillivirus from migrating infected pilot whales. Skin lesions have been present in almost all strandings, and other complications found in confirmed cases include pneumonia, brain infections, or other secondary or latent infections. The disease is identified by the presence of morbilliviral antigens and nucleic acids in tissue samples. Morbilliviruses are not always lethal, but there have been some factors shown to increase the risk of catching or dying from the infection. Susceptibility can be influenced by factors like personal immunity, herd immunity, and potentially environmental conditions like climate change or water pollution.
http://viralzone.expasy.org/viralzone/all_by_species/86.html
After large morbillivirus outbreaks in the U.S. in 1987-88 and in the Mediterranean in 1990-1992, scientists began to question how much environmental factors were facilitating the susceptibility of these top predators to these deadly infections. Researchers began to speculate that the high levels of persistent organic pollutants, or POPs may be suppressing the immune system of marine mammals. But before we get too far into that, we need a little background on POPs. Persistent Organic Pollutants, sometimes referred to as persistent organochlorides are chemicals that were introduced after World War II and were used mainly in agriculture for pest and disease control, and to increase crop production. The two main POPs that I am going to refer to are polychlorinated bipheynls, or PCBs, which were widely used in industrial processes (like electrical transformers and in plastics), and dichlorodiphenyl trichloroethane, understandably shortened to DDT, which is still used in some places as an insecticide. POPs have negative effects that can accumulate in species and persist for long periods of time in the environment. POPs can travel through the water cycle as rain, snow, or mist, and therefore ends up in our rivers, lakes and eventually oceans. Due to these harmful effects, the United States and 90 other countries signed a treaty in 2001 known as the Stockholm Convention to reduce POP production and use.
http://www.epa.gov/oia/toxics/pop.html#pops
So we know now that POPs can get into the ocean, but how do they get into our friends the bottlenose dolphins? POPs are lipophilic, or fat loving. They move through the food chain in the fat tissue of living organisms, becoming more concentrated as the move through the trophic levels. This phenomenon is called biomagnification. So our pollutant here attaches to the phytoplankton, and is then ingested by small fish. The small fish are eaten by subsequent predators and are eventually consumed by our top predator, the dolphin, all the while accumulating higher and higher concentrations of the pollutant. They are then stored in the fat tissue, or blubber of the dolphin or other marine mammal. Let’s look at a study done examining how these high concentrations of POPs could be acting as immunosuppresants.
http://toxics.usgs.gov/definitions/biomagnification.html
Since not much pollutant data was collected from the past outbreak in the United States, we’re going to look at a study done on a similar species, the striped dolphin, in the Mediterranean Sea in 1990-1992.
http://www.yourchildlearns.com/online-atlas/mediterranean-map.htm
Two treatment groups were used, generally labeled ‘infected’ if they tested positive for morbillivirus, or ‘healthy’. Infected samples were gathered from the stranded dolphins in the year 1990, and healthy dolphin tissue samples were taken using a biopsy dart from living, apparently healthy dolphin populations. Biopsy darts were fired from a boat into bowriding dolphins with a cross bow or spear gun.
This graph shows… The years is shown on the X axis and the PCB concentration in ppm on the Y axis. The solid horizontal line represents the median, the boundaries of the boxes represent the upper and lower quartiles, and the extensions represent the smallest and largest observations made. Aguilar and Borrel found that in years before and after the epizootic, years 1987, 1988,1989, and 1991, there was no significant difference between the amounts of PCBs found in the fat tissue of the Mediterranean striped dolphin population. However, in 1990, the year the outbreak began, a Kruskal-Wallis test determined there was a significant difference in PCB levels between dolphins affected by the outbreak and those considered healthy. Not only was the average significantly higher than in past years, but the highest concentration observed was more than twice the concentration observed in any other year. Liver lesions were also found in the infected treatment that did not appear to be related to the morbillivirus infection. PCB and DDT exposure have been known to produce various liver lesions in mammals, but it is not known whether these lesions were caused by organochloride exposure, or even if they are present in the whole population. So, there is good evidence for a positive correlation between dolphins being infected with the morbillivirus infection and having high levels of PCBs in their systems, but which is the cause and which is the effect?
So we have two theories here that suggest high PCB levels are the reason mortality is higher in polluted individuals. The first theory suggests the high PCB levels depress the animal’s immune system. Immunity suppression and antibody inhibition would then lead to greater virus susceptibility and increased mortality. This theory has been supported by other studies as well, and in my opinion is the strongest of the three hypotheses. The second theory suggests that the high PCB levels when mobilized from fat reserves causes liver lesions which are in turn causing the increased susceptibility and high mortality rates. The third theory suggests that the high PCB concentrations are not even causing the mortality, but are actually an effect. According to this third theory, the liver lesions are causing the liver to shut down which decreases the ability of the mammal to filter PCBs from the body while also making them more susceptible to disease. However, this possibility is less likely due to the presence of enzymes in the dolphins that indicated healthy liver function.
In conclusion, we have very few conclusions. We have learned that viral susceptibility is very complex, and it is hard to differentiate the causes of an infection from an effect of it.
There are a few things we can do in the future to help control future cetacean morbillivirus epizootics. First of all, more conclusive evidence needs to be obtained determining what factors make cetaceans more susceptible to the morbillivirus. Second, we need to continue to try to lower our persistent organic pollutant emissions, because although the relationship has not been able to be completely explained, there is a correlation between high POP concentrations and high infection susceptibility. Another goal that can be accomplished is to use the current morbillivirus epizootic to collect data that can be used in future studies. Perhaps comparing this outbreak to past outbreaks will help more clearly explain the role of POPs in cetacean susceptibility. Last but certainly not least, a major goal of marine biologists would be to eliminate this disease. Only 2 viruses have ever been declared as completely eradicated; smallpox and rinderpest. This is reassuring because rinderpest is also in the Genus Morbillivirus. If we can find practical ways to immunize wild cetacean populations like cattle were immunized, there may be a way to reduce or even eradicate the cetacean morbillivirus.
I would like to thank Dr. Paladino for being my mentor for the duration of this project. I would also like to thank the staff at Helmke Library for helping me find my research materials. And of course I owe a big thank you to all the IPFW Biology Staff members who have contributed to my biology education.
