Kidney parasites in dogs may be something you have never heard about. You are more familiar though with intestinal parasites since your vet requires annual stool checks to ensure your dog has none of these. It's unfortunate, but there are many types of pesky parasites in dogs and some of them can live in vital internal organs like the kidneys. Fortunately though, these are rather rare. Dr. Ivana discusses kidney parasites in dogs, what they are and the symptoms they may cause in affected dogs.
Kidney Parasites in Dogs
Dioctophyma renale, or more popularly known as the giant kidney worm, is a parasite from the roundworms family. In infected animals, Dioctophyma renale causes a disease known as dioctophymiasis.
Although more common among cats, minks, otters and other carnivores regularly feeding on freshwater fish, Dioctophyma renale can be found in dogs too. Dioctophyma renale can be found worldwide but is relatively rare in certain parts of Asia and in Oceania.
As stated, the incidence of Dioctophyma renale in dogs is particularly rare, even in endemic areas (less than 1 percent). However, this parasitic infestation is worth mentioning because if it does develop, its consequences can be lethal.
As the name suggests, Dioctophyma renale is a parasitic worm that lives in the kidneys. Listed among the largest known helminths, adult females can reach lengths of as much as 1 meter. Males are significantly smaller – usually 20 to 40 centimeters long. They have pink to reddish, flexible bodies covered with a protective cuticle. They have simple digestive and nervous systems, but lack excretory organs, heart and blood vessels. On the other hand, their reproductive systems are well developed. The eggs are embryonated and oval in shape with thick, shell capsules.
Dioctophyma renale has a so-called indirect life cycle. This means, it needs a final host (carnivore), an intermediate host (aquatic worm) and a transport host (fish, frog, crab). Simply put, infected dogs pass Dioctophyma renale eggs through their urine. These eggs are not infectious. To become infectious they must develop in fresh waters where eventually they get eaten by the intermediate host – the aquatic worms.
In the intermediate host the eggs mature into infectious larvae. Fish, crabs and frogs feeding on aquatic worms serve as transport hosts. Namely, dogs can become infected by eating aquatic worms or some transport host (fish, carbs or frogs).
Once ingested by the dog, the larva inhabits the stomach where it stays for about 2 weeks. Then, it migrates to the liver and feeds on liver tissue. Usually, the larvae stay in the liver for a month and then enter the abdominal cavity. At this point, they may either remain in the abdominal cavity or go in the kidney where they mature into adults and reproduce. Feeding on kidney tissue and blood, adult worms can live in the final host for as up to 5 years.
Dioctophyma renale prefers infecting the right kidney because it is closer to the stomach and liver. If there is a massive infection though, both kidneys will be affected.
Signs of Kidney Parasites in Dogs
The activities and movements of this parasite cause massive damages to the kidney tissue. At first, that damage manifests as nephritis (inflammation of the kidney). Over time, as the condition progresses, the severely damaged and inflamed kidney tissue is replaced by connective tissue (a process known as fibrosis).
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Logically, the newly formed connective tissue does not have the same properties as the kidney tissue (it cannot filtrate blood and eliminate waste products) which leads to impaired kidney functioning.
Fortunately, in most dogs, the parasite affects only one kidney. In such cases, the healthy kidney takes over and compensates. That is why most cases go unnoticed. In cases where both kidneys are affected, the consequences can be fatal – the dog may die due to renal failure.
In such cases, the infected dog will experience abdominal pain, back pain, fever, bloody urine, anorexia and weight loss. If instead of invading the kidneys, the worms decide to stay in the abdomen, over time they cause peritonitis (inflammation of the peritoneum), hepatitis (inflammation of the liver) and ascites (fluid accumulation in the abdomen).
At The Vet's Office
The diagnosis of Dioctophyma renale is usually done during post-mortem examinations or as accidental finding during non-related surgeries. When there are suspicions for renal worms, the diagnosis can be set through the following tests:
Urine sediment analysis – typically there will be eggs in the urine sediment. However, it should be noted that false negatives are quite common with this test. This is because the egg shedding is intermittent (happens in certain intervals). Another possible reason for false negative result is infestation with only female worms (if there are no male worms, the females will not be able to lay eggs).
Kidney ultrasound – this is the more reliable form of diagnosing. If present, the adult worms in the kidneys will be visible on the echography image. Even if the worms are not visible, there will be significant kidney enlargement. The kidney enlargement can also be confirmed by an abdominal x-ray.
The treatment of choice for kidney parasites in dogs is surgical removal of the parasites. If only one kidney is affected and is too damaged, it is best advised to have it removed. Although medical treatments are available, there are not always 100 percent efficient. For example, the anthelmintic fenbendazole kills the larvae, while ivermectin kills the adult worms inside the kidneys. However, officially, commonly used de-wormers are not approved for treating this kidney parasite.
Preventing Kidney Parasites in Dogs
In endemic regions, where freshwater fishing is commonly practiced, the best way of preventing infections is by limiting dogs from scavenging on fish waste and drinking contaminated water. It goes without saying that dogs must never be fed raw or undercooked fish, crabs and frogs.
Can Humans Get Kidney Parasites From Their Dogs?
Luckily, the answer is no. Dioctophyma renale cannot be transmitted from dog to humans neither through contact nor through feces and vomit. Humans can get infected by this parasite, but the eggs shed by infected dogs are not directly infective. For the eggs to become infective they need to spend some time in the environment and be eaten by an intermediate host. Usually people become infected with Dioctophyma renale by eating raw or undercooked fish, crabs or frogs or by drinking contaminated water.
About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.