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Dogs and Valley Fever


Dogs and Valley Fever

What you need to know


Dogs primarily contract Valley Fever (
Coccidioidomycosis) in the low desert regions of Arizona, New Mexico, southwestern Texas and the central deserts of California. Dogs accompanying people traveling through these areas or wintering in these warm climates have about the same chance as their owners of being infected.

With the Monsoon season approaching, doctors say there will likely be increased cases of Valley Fever in people as well as in our pets.

Valley Fever is caused by a fungus that lives in the desert soil. As part of its life cycle the fungus grows in the soil and matures, drying into fragile strands of cells. 
The strands are very delicate and when the soil is disturbed; by digging, walking, construction, high winds-(Monsoons) the strands break apart in to tiny individual spores called arthroconidia or arthrospores. 
We get Valley Fever by inhaling the fungal spores living in the dust when it's blown around by disturbance. The dog may inhale only a few spores or many hundreds. 

Once inhaled the spores grow into spherules (parasitic cycle) which continue to enlarge until they burst, releasing hundreds of endospores. 
Each endospore can grow into a new spherule, spreading the infection in the lungs until the dog's immune system surrounds and destroys it. The sickness occurs when the immune system does not kill the spherules and endospores quickly and they continue to spread in the lungs and sometimes throughout the animal's body.


About 70% of dogs who inhale Valley Fever spores control the infection and do not become sick. These dogs are asymptomatic. The remainders develop disease which can range from very mild to severe and occasionally fatal.

The most common early symptoms of primary pulmonary Valley Fever in dogs are:
  • Coughing 
  • Fever 
  • Weight loss 
  • Lack of appetite 
  • Lack of energy 

As the infection progresses, dogs can develop pneumonia. Sometimes the coughing is caused by pressure of swollen lymph nodes near the heart pressing on the dog's windpipe. These dogs often have a dry, hacking or honking cough and the swollen lymph nodes can be seen on x-rays.

When the infection spreads outside the lungs it causes disseminated disease. The most common symptom of disseminated disease in dogs is lameness. The fungus has a predilection for infecting bones of the legs in dogs. However, Valley Fever can occur in almost any organ of dogs. 

Signs of disseminated Valley Fever can include:
  • Lameness or swelling of the limbs 
  • Back or neck pain, with or without weakness/paralysis 
  • Seizures and other manifestations of brain swelling 
  • Soft abscess-like swellings under the skin 
  • Swollen lymph nodes under the chin, in front of the shoulder blades, or behind the stifles 
  • Non-healing skin ulcerations or draining tracts that ooze fluid 
  • Eye inflammation with pain or cloudiness 
  • Unexpected heart failure in a young dog 
  • Swollen testicles 
Sometimes a dog wont have signs of a primary infection such as in the lungs causing coughing; but will develop symptoms of disseminated disease, e.g., lameness, seizures. Very few of the signs of Valley Fever are specific to this disease alone therefore your veterinarian will do tests to determine that your dog's illness is Valley Fever and to rule out other causes.
Is Valley Fever contagious from animal to animal or animal to human? Valley Fever is considered a noncontagious disease. Even if multiple animals or humans are affected in a household each infection was acquired by inhaling spores from the soil individually.

Coughing cannot spread Valley Fever between animals or people. In a case of draining lesions; the form of the organism in the fluid is not considered to be infectious to people or animals. Nevertheless, such lesions are best handled by wearing protective gloves and bandaging. Bandages should be changed daily or every other day and discarded in an outside waste container to minimize risk of contaminating the environment. Do this only once your veterinarian has confirmed the disease and instructed you to bandage, otherwise you could be making a different disease worse.

For immunocompromised persons living in a household with a pet that has a draining lesion it is best to consult your physician regarding this issue. There are cases of immunocompromised
people that developed illnesses when living with a pet who had a draining lesion. 

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:
  • General blood tests and blood cell counts 
  • Chest x-rays 
  • Bone and joint x-rays 
  • Valley Fever blood test (Also called cocci test, cocci serology,  or cocci titer) 
When does my dog need a Valley Fever test?
If your dog lives in a region where Valley Fever is common, your dog could need a test for any illness that manifests the common clinical signs - coughing, fever, weight loss, limping, etc. Or illnesses with vague signs that will not go away.

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 coccidioidomycosis
 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 reports 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 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.

Titers usually reduce over time as the animal's disease regresses. Dogs that start with low titers (1:4 or less than 1:4) may undergo little change in the titer. This is probably not to be interpreted that your dog is not getting well. 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 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.

Will My Dog Recover From Valley Fever? 

The good news is that most dogs with adequate anti-fungal therapy, do recover from this disease, especially with early diagnosis and intervention. Dogs with infection only in the lungs have the best prognosis for recovery and usually respond the quickest to treatment. However, dogs can have extensive lung disease that is so severe and progressive that they require hospitalization or surgery to remove the diseased lung, or they may die.

Dogs with disseminated infection almost always have a more guarded prognosis than dogs with uncomplicated lung disease. As with lung infections, it seems that the majority respond well to medication and lead normal lives, though they often require prolonged drug treatment (12-18 months). A small proportion of animals must take medication for life and another small number, unfortunately, die of Valley Fever in spite of drug treatment.

Dogs with Valley Fever in the brain (seizures, etc.) also carry a guarded prognosis. Among those that respond to medication about 80%, most will remain well with fluconazole, but treatment may be required for life.

For dogs that are seriously ill, requiring hospitalization and supportive therapy, the prognosis can be grave. With aggressive treatment, possibly including intravenous anti-fungal medication, some dogs will get well.

Some dogs do not recover in spite of everyones best efforts, either due to the severity of illness at the time of diagnosis or because of long-standing, poorly responsive disease. Fortunately, these animals represent a minority of dogs with Valley Fever.

Stopping Treatment

Treatment of the Valley Fever in your dog is monitored by progress exams with your veterinarian. Your veterinarian will examine your dog to look for improvement as well as perform blood tests and follow up x-rays to monitor progress and to make sure the medication is not harming your dog in any way. If your dog is very ill, progress exams may be frequent at first. As the disease stabilizes and recovery becomes apparent, your veterinarian will probably only need to evaluate your dog every 2-4 months, maybe even yearly.

It is very important to continue medicating your dog as directed until the veterinarian confirms that the blood tests are negative and tells you to stop medication. If you stop treating too soon, symptoms may recur. If symptoms recur after your dog is taken off medication your veterinarian will probably recommend resuming treatment and may suggest the dog remain on medication for life.

Can Valley Fever relapse and can dogs be reinfected? Valley Fever is well known to relapse in both humans and dogs. In particular, cases of disseminated infection have a 30-50% rate of relapse in humans, no matter how well the initial infection was treated. It is not known how many canine cases of Valley Fever relapse, but relapses are not uncommon.

In the case of a relapse, a return to medication is usually enough to make symptoms subside; but the dog may require several additional months of treatment. Dogs that experience more than one relapse or get very sick with the relapse should probably have lifetime treatment with medication considered.
Reinfections in humans are documented only rarely. 

Parts of this article were shared by The Valley Fever Center for Excellence, located at the University of Arizona in Tucson.


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Kim MacCrone is the author of this Blog and is also a freelance and copywriter for hire. If you are interested in Kim writing an article or articles for your business please email her at kimimacc@gmail.com. 


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