LEPTOSPIROSIS IN PINNIPEDS
- kradiganscience24
- Jan 17
- 4 min read
Tavishi
This is Vincent, a harbor seal (Phoca vitulina) pup admitted to the Marine Mammal Center in March 2023 for leptospirosis and maternal abandonment. Vincent weighed about the size of two small adult cats, and as you can see, was a tiny cute little baby.
From this image alone, you can tell that Vincent was very young upon being admitted, as he not only has the lanugo characteristic of pups, but his lanugo is still yellowed with amniotic fluid.
Vincent is one of many Marine Mammal Center patients admitted for leptospirosis. Leptospirosis is a bacterial infection caused by members of the genus Leptospira. Leptospira bacteria are spiral in shape and gram-negative.
Leptospirosis is a zoonotic disease commonly found in mammals after contacting infected water. Leptospira bacteria form biofilms, and are much of the reason people are warned not to go near undisturbed, still water.
Leptospirosis can't quite be prevented in humans. In domestic animals, leptospirosis vaccines are generally recommended for animals that encounter water a lot. At the veterinarian I intern at, we offer leptospirosis for puppies as a "lifestyle vaccine". In wild animals like pinnipeds, vaccinations are seldom an option- only in the very limited case of very endangered animals like the Hawaiian monk seal (See https://www.kradigan.org/post/hawaiian-monk-seal-genetics) Leptospirosis has primarily been a risk for California sea lions like Cavalry (pictured below), and sometimes, for harbor seals and elephant seals.
The primary region of leptospirosis infection is the kidneys, and as a result, the primary indicator of leptospirosis within pinnipeds is dehydration leading to the drinking of water.
A normal, healthy sea lion, does NOT seek out water for consumption. Pinnipeds hydrate while swimming, and if a pinniped is drinking water, it's almost an automatic indicator of leptospirosis.
Leptospirosis takes about 8-20 days to incubate and settle into the body after initial entrance. Afterwards, the little bacteria circulate the blood and mark their territory by replicating in a variety of tissue, including gastrointestinal, renal, and nervous.
However, in both short-term and long-term patients, leptospirosis infection remains the most in the urinary system, around the nephrons and the genital tract.
The nephrons are the individual units that do the actual filtration within the kidney, and leptospirosis within the kidney prevents reabsorption of certain solutes.
Different parts of the nephron function to reabsorb different portions of the filtrate that will eventually become the urine. We want to maintain certain parts of the blood, and get rid of stuff that we don't want. For example, we want just the right amount of water, and just the right amount of potassium in the blood.
Above is a diagram of the nephron. After a TON of solute is filtered out in Bowman's capsule, we have to go through and make sure we're keeping some stuff. Think of it like cleaning out a particularly cluttered drawer. It's much easier to clean out if we take everything in the drawer out first, and then add back what we want to keep.
After the filtrate leaves Bowman's capsule, the proximal convoluted tubule takes out select ions and water, and makes the filtrate (I'm going to call this proto-urine from now on. Not sure if this is the proper science word.) much more acidic. In the descending limb of the Loop of Henle, a lot of water leaves the proto-urine, and goes back in the metaphorical drawer, or the blood. Then, in the ascending limb of the Loop of Henle, sodium and chloride ions are reabsorbed from the filtrate, allowed by the influx of water into the interstitial fluid prior. Finally, in the distal convoluted tubule, lots of last adjustments, including to pH, are made to the proto-urine.
Now, leptospira bacteria primarily colonize the proximal tubule and the glomerular capillaries within Bowman's capsule, which, as you might expect, causes a lot of issues with dehydration.
If you take this in combination with what they do within the liver, leptospirosis pretty much seals your fate.
Leptospira bacteria also wreak havoc within the liver, where they incite apoptosis by proliferating in between the hepatocyte cells. (I guess you could say that they make the liver cells not quite good at live-ing). Hepatocytic apoptosis also produces jaundice because of the release of bilirubin. Bilirubin is a byproduct of the breakdown of hemoglobin, and is what gives feces its distinct brown color.
When bilirubin is circulating in the blood, it turns the skin yellow. For pinnipeds, you can't quite see that through all the fur- but rather, you can see in the eyes. A jaundiced seal will have yellow eyes, which I can't quite find a photo of. When the leptospira have found their way to the liver, they also begin to inevitably release a medley of toxins, of which those that induce hemorrhage cause the most problems. The hemorrhage-inducing toxins unique to leptospirosis prevent the activation of platelets, by preventing them from binding to the von Willebrand factors necessary for blood clotting.
When attempting to diagnose leptospirosis, although water consumption is fairly telling, blood tests and urine tests can adequately detect leptospirosis. Because leptospira proliferate within the renal tubules, they also show up in the urine- which is one of many routes of spread of infection for leptospirosis. This is also why dogs who go out a lot are recommended to get a leptospirosis vaccine- a dog at the beach could easily encounter leptospira bacteria in the urine of an infected sea lion, take a whiff, and end up with kidneys not having a fun time.
To treat leptospirosis, antibiotics like doxycycline and amoxycillin and administration of fluid is used. Fluid administration helps with the dehydration earlier discussed. However, it is important to note that about 2/3rds of sea lions that present with symptoms of leptospirosis ultimately don't end up surviving.
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