Ever wonder what’s inside of the brain of a harbor seal?

As promised I am here to provide some new information about marine mammals. I know you’ve waited too long. This time I will be telling you about my very own research that was just published in PLOS ONE!!! This is my first, first author publication so there was a steep learning curve on data analysis, graphing, and the publication process. In future post I plan on taking the reader on the journey of my first publication. Especially the struggles, since the public often doesn’t hear about that side of science.

For this blog I will  give a quick synopsis of my paper for those who just really want to know what I found inside the brains of Pacific harbor seals.  Although, before I get to the nitty gritty of my story I like to tell you a bit about my study subjects, the harbor seals. I mostly worked with pups (< 1 month) and weaned (1 -12 months) harbor seals, which tend to be born between February and April. Their mothers wean them for about 3-4 weeks and soon after they begin to catch small fish and shrimp. During these early stages of life, they encounter many dangerous situations for example, being preyed, starvation, and disease.

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Popeye a Pacific harbor seal not related to this study. Photo by me

I am particularly interested in the diseases of young harbor seals, since understanding this may increase their survival rates during this fragile stage of their lives. About 44% of marine mammal diseases remain a mystery. That means that many harbor seals die and we have no idea what’s killing them. So, I wanted to help discover possible culprits that cause marine mammal diseases.

I started my search with the brain tissue of 14 harbor seals that were found sick on the California coast. I first looked into the viral world and I found viruses in four of the animals from the family Herpesviridae, which have previously been found in harbor seal brains in European and North American waters. A virus from this family (Phocine herpesvirus-1,  PhV-1) are particularly harmful for young seals since they have an undeveloped immune system.

However, the bacteria side of the story proved to be a bit more interesting. One of our significant discoveries was the presence of Burkholderia along with a high amount of Burkholderia genes that are known to cause disease. Burkholderia is an interesting genus of bacteria that can be zoonotic (passed from animals to humans), but it is also ubiquitous and can be harmless. While this is not the first time someone has looked for bacteria in the brains of marine mammals and found Burkholderia, it is the first time that this bacteria was found in harbor seals in the USA. So where else were Burkholderia found in the brains of marine mammals? Well in Southeast Asia, this bacteria was found in an aquarium, which caused the death of marine mammals.

Our other interesting finding on bacteria comes from Coxiella burnetiiSimilar to Burkholderia, it was found at a high abundance with high amounts of disease causing genes. Unlike, Burkholderia it was not found in all our harbor seals, but only in three of our animals. Meaning this pathogen may be less common in harbor seal populations compared to Burkholderia. 

C. burnetii is a known pathogen that needs to replicate within a cell (obligate intracellular pathogen). It is best known for causing Q fever, but in marine mammals it causes inflammation of the placenta (placentitis) and it has never been found in the brain of harbor seals. We think since these harbor seals were young animalsthe placenta may be a source of C. burnetii infection for pups, but this is just a hypothesis that needs some testing!

So what exactly did we learn from all this? Well our study adds to our knowledge about the distribution of Burkholderia in marine mammals and like in Southeast Asia it may also be causing the death of harbor seals in the USA. Also, now we know that C.burnetii  can infect the brains of harbor seals and we should investigate the source of this infection. Finally, we can now begin to monitor for these bacteria in the brains of these animals as possible sources of infections.

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