A fairly common problem seen among dogs along the West Coast, extending from northern California to British Columbia, is Salmon Poisoning Disease. The name Salmon Poisoning is a bit misleading, though, since dogs can get this disease from not only any species of salmon, but also from trout, steelhead, and the Pacific Giant Salamander.
Salmon Poisoning Life Cycle
Here’s how it all happens. Refer to the diagram above. To start, eggs from a trematode (a fluke) called Nanophyetus salmincola are passed in the stool of canids or birds. The eggs hatch and the next lifestage of the fluke, called a miracidia, infects a particular snail that lives in fresh or brackish water throughout the Pacific Northwest and down the west coast into northern California. The miracidia mature, then exit the snail as larvae. These larvae then live in the water for a short period until they come into contact with a fish or salamander, at which time they penetrate the body of this host. The larvae then mature into the next life stage, called a metacercaria, which can live anywhere in the host animal (including the slime on the fish’s skin!) but tends to prefer to live in the blood-rich environment of the kidney. Next, a dog (hopefully not your dog!) eats or licks the slime, blood, or flesh (raw or partially cooked) of the fish or salamander. Voila! The dog is infected. The parasite matures to the final lifestage, the adult trematode or fluke, and it establishes residence in the cells that line the intestines. As if this were not enough, the fluke then inoculates a second parasite, a bacteria-like organism (a rickettsia) called Neorickettsia helminthoeca, into the intestinal lining. This organism reproduces tremendously, causing severe inflammation of the intestines, resulting in diarrhea. It also finds its way into the bloodstream, where it spreads to the spleen, lymph nodes, tonsils, thymus, liver, lungs and brain of the infected dog!
How it Affects Your Dog
So, what does all of this do to the infected dog? A lot. To start, it usually takes from 5-7 days after coming into contact with the fish or salamander for the dog to show clinical signs. Then, the dog can develop a fever, loss of appetite, lethargy, vomiting, diarrhea, bloody stool, abdominal pain, enlarged lymph nodes, and even neurologic signs. Left untreated, salmon poisoning can often be fatal.
How do We Diagnose Salmon Poisoning Disease?
Diagnosis of salmon poisoning is made by taking into account three main things. First, is the dog showing the clinical signs (fever, enlarged lymph nodes, diarrhea, etc.) that are consistent with salmon poisoning? Second, has there been potential or known exposure to raw or undercooked fish or salamander? And finally, we use laboratory testing to complete the diagnosis. This usually comes in the form of a fecal analysis, where we often, but not always, find the egg of the fluke. Additionally, a complete blood count and serum chemistries and lymph node aspirates can give us indications of infection.
How is Salmon Poisoning Treated?
To effectively treat salmon poisoning, both infectious agents – the intestinal fluke and the bacteria-like organism, the rickettsia – must be eliminated. Tetracycline antibiotics will kill the rickettsia and a common dewormer called praziquantal will kill the fluke. As important for these patients, however, is supportive care. Most dogs diagnosed with this disease are running high fevers, have severe diarrhea and vomiting, are notably dehydrated and can be in metabolic crisis. We usually recommend hospitalizing these patients so they can receive one or more days of IV fluids and electrolyte replacement, anti-emetics and, initially, injectable antibiotics and an injectable form of the dewormer. Once they are stable, patients are sent home with an oral course of antibiotics and the dewormer to complete the treatment. As we noted above, dogs that do not receive appropriate treatment for this disease will often die of infection, dehydration, or shock.
To prevent this disease from infecting your dog, you must keep him or her from coming into contact with raw or undercooked salmon, trout, steelhead or the Pacific Giant Salamander. If you witness your dog eating or licking any of these tasties, you can prevent full-blown salmon poisoning by calling us and getting him or her in to the hospital right away. After performing an exam, the doctor can prescribe the same medications that are used to treat the actual infection and thereby prevent your canine friend from developing this serious illness. Also, if your dog develops diarrhea that lasts for more than one day, we always recommend getting him or her into the hospital for assessment. There’s a lot more that can be done (often for significantly less cost to you) if we catch a problem early in it’s course as opposed to treating a patient suffering from a full-blown or prolonged illness.
As always, if you have questions regarding this article or any topic regarding any of your furry family members, don’t hesitate to call!
The Doctors and Staff of Orchard Hills Animal Hospital