For owners living outside of the endemic area, diagnosis of Valley Fever requires suspicion of the disease from the dog's history, its symptoms, and the results of examinations and tests performed by your veterinarian.
If your dog has recently visited an area where the fungus can be acquired, telling your veterinarian about your dog's travel history can be very helpful in deriving the diagnosis.
In addition to examining your dog, your veterinarian is very likely to order diagnostic tests to help identify the Valley Fever infection.
Common tests include:
- Valley Fever blood test (also called cocci test, cocci serology, or cocci titer)
- general blood tests and blood cell counts
- chest x-rays
- bone and joint x-rays
Sometimes tests are negative early in the infection, especially the Valley Fever blood test, and they may need to be repeated in 3-4 weeks to establish the diagnosis.
In difficult cases, the routine tests are not very helpful in the diagnosis. Your veterinarian may recommend other tests to find out what is making your dog sick.
These tests are often more definitive:
- Culture of fluid or tissue samples from your dog to isolate and identify the fungus; this is highly specific
- Biopsies or aspirates with microscopic examination of cell, fluid, or tissue samples to visualize fungal organisms and inflammation in your dog
- For paralysis or seizures, a CT or MRI scan of the brain or spinal cord
Does my dog need a Valley Fever test?
If your dog lives in a region where Valley Fever is typical,
your dog could need a Valley Fever test for any illness that manifests the common clinical signs - coughing, fever, weight loss, etc. - or illnesses with vague signs that will not go away. In addition, your dog will need some serum chemistries and white blood cell counts and sometimes x-rays to aid in diagnosing the illness. A positive test in and of itself is often not enough to diagnose Valley Fever.
For dogs that do not live in regions with Valley Fever but have traveled through or spent time in one,
a Valley Fever test may be indicated for undiagnosed, unresolving illnesses. If your dog becomes ill outside the typical locations for Valley Fever, it is important to tell your veterinarian of your dog's travel history.
What is a Valley Fever test/titer and what does it mean?
A Valley Fever test, Cocci test, or Cocci titer checks the blood to see if your dog is making antibodies against the Valley Fever fungus. If the test is positive, it means your dog has been infected with the fungus.
If the Valley Fever test is positive, the laboratory then performs a titer.
The titer measures how much antibody your dog is making against the fungus. A titer is obtained by doubling dilutions of the positive blood (1:4, 1:8, 1:16, 1:32 . . .) until the test becomes negative. The titer that is reported to your veterinarian is the last positive dilution. The laboratories typically stop the titer at 1:256 and report the result as >1:256 if the dog's blood is still positive.
In broad terms, a higher titer is equated with more severe disease.
However, some very sick animals have low titers, or even negative Valley Fever tests. For these dogs, other diagnostic tests are necessary for diagnosing the illness. X-rays, blood cell counts, biopsies, and microscopic examination of cellular specimens are a few of the tests your veterinarian may need to run.
Asymptomatic dogs (infected but not showing any illness)
may also have low titers, such as 1:4 or 1:8, sometimes 1:16. The titer is helpful in diagnosing Valley Fever in sick dogs, but other tests are usually needed to confirm the diagnosis.
Titers usually reduce over time as the animal's disease heals.
Dogs that start with low titers (1:4 or less than 1:4) may undergo little change in the titer. Monitoring your dog's symptoms and other tests, such as blood counts and x-rays, will be better determinants of improvement in cases with low titers.
Some dogs will remain Valley Fever positive with a low titer for life.
Continued treatment and monitoring of these animals needs to be determined by your veterinarian on a case by case basis.