Complement Deficiency in Dogs

Dogs can be affected by complement deficiency, they can be not affected but be carriers or they can be not affected and not carriers. If they are affected or are not affected but carriers, they can pass this trait onto their offspring. Therefore, dogs with this condition or carry the trait for this condition should never be bred. 

There is a genetic test that can be performed to determine if your dog is affected or a carrier of complement-3 deficiency. The test results will be classified as clear, carrier or at-risk. Clear means that your dog does not have the complement deficiency trait and will not pass it to their offspring. Carrier means that your dog does not have the trait but can pass it to their offspring. An at-risk test result means that your dog does have the trait and will pass it to their offspring.

Complement deficiency or better known as complement-3 deficiency (C3) is an autosomal recessive genetic immune deficiency that affects Brittany Spaniels. It occurs when there is a lack of the protein complement component 3. Generally, C3 is characterized by an increased vulnerability to renal disease and infection. Dogs that are affected with complement deficiency are also predisposed to the development of familial juvenile glomerulonephropathy and hereditary canine spinal muscular atrophy.

If you notice that your dog is experiencing recurring bacterial infections or is experiencing any of the symptoms below, contact your veterinarian for an appointment. Early detection of complement deficiency could help improve your dog’s quality of life and keep them from developing severe bacterial infections that can cause death.

• Recurring pneumonia
• Recurring urinary tract infections
• Uterine infections
• Kidney disease and/or failure
• Lethargy
• Diarrhea
• Death

Complement deficiency in dogs is an inherited disease in an autosomal recessive manner. This means that in order for your dog to be affected with C3, they must have received two copies of the mutated gene, one from each parent.

Dogs that are carries of the complement deficiency trait do not have the disease but if bred to another dog that also has the trait, they can produce puppies that are affected with complement deficiency. When a carrier is bred to a carrier, there is a 25% chance that their offspring will inherit the disease. There is a 50% chance that they will inherit one copy of the mutation and will then be carriers themselves.

This is why genetic testing for the C3 gene mutation is very important to breeders. Dogs that are clear are not carriers and do not have the trait to pass on to their offspring. Ideally, breeders should strive to breed only dogs that are genetically tested clear for the C3 gene mutation to eventually eradicate this problem from the breed.

Your veterinarian will most likely suspect complement deficiency if your dog develops recurring bacterial infections, if they are familiar with the Brittany spaniel breed. 

A bacterial infection can occur for a number of reasons so complement deficiency may not be diagnosed right away. But when your dog begins to experience a chronic bacterial infection that is when your veterinarian will begin to look for a genetic link. At this point, your veterinarian will recommend performing the genetic test to determine if your dog is affected with C3.

Your veterinarian will also perform a complete blood count to determine the best course of treatment for your dog’s bacterial infection. Blood tests will also show a decrease in C3.

While there are no specific treatment plans for complement deficiencies, your veterinarian will be able to treat the symptoms of the secondary illnesses that are associated with complement deficiency. 

Vaccinations will be essential in keeping your dog’s immune system healthy and able to fight the infections that will occur. Antibiotics will be prescribed as bacterial infections occur. Be sure to watch for signs that your dog may be developing an infection and seek treatments immediately. 

Your dog will also need to have their kidney functions closely monitored. Kidney disease can develop as a result of complement deficiency. Kidney failure can also occur. When this happens, usually euthanasia will be recommended.

Complement deficiency is an inherited disease and there is no cure. Your veterinarian will discuss with you how to manage it and what to watch for when an infection or other serious health problems occur because of C3. 

Your dog will require specialized care to ensure that their quality of life does not suffer from complement deficiency. Be sure to follow your veterinarian’s instructions on care and medications. If you have any questions about your dog’s care or the medications that have been prescribed, direct those to your veterinarian.