Valley Fever (Coccidioidomycosis) - Posted 01/04/2013
Welcome to the first episode of the Ina Road Animal Hospital blog. This month's Ask the Vet topic is Valley Fever. Our presenter today is Dr. Liane Lunetta.
Where is VF found? - The areas where this disease can be found include So. Cal, all of Arizona, So. NV,SW UT, most of NM, and SW to central TX.
What is VF? – Fungal infection of the desert southwest, with the Phoenix-Tucson corridor being a hotspot of this disease. Coccidioides immitus is the name of the fungus involved in causing the disease commonly known as Valley Fever. It lives in our desert soil in what is known as a saprophytic phase (non-parasitic form) and will break apart into smaller pieces known as arthrospores when the soil is disturbed (digging, construction, wind, etc).
How does a dog become infected with VF? – These arthrospores from the soil can be inhaled in varying numbers by dogs. Once in the moist environment of the lungs, these spores transform into the parasitic phase in which spherules form. These then grow and eventually release endospores which can each create a new spherule and hence more endospores. As the infection spreads through the lungs, the immune system works to destroy the spherules and endospores. If the pet’s immune system is unable to stop the spread and eventually resolve the infection, then the spherules and endospores can spread throughout the lungs and possibly other organs in the body. It is estimated that 70% of dogs that inhale the spores will become infected, but remain asymptomatic and clear the infection on their own. The remaining 30% of infected dogs will exhibit varying degrees of severity of the disease. Cases of VF can range from mild to severe and in some cases, it may even be fatal.
What are the symptoms of VF? – In the pulmonary (lung) phase of this disease, symptoms can include coughing, lethargy, loss of appetite, fever, and weight loss. Dogs can develop a pneumonia associated with this phase which can often be seen on radiographs (x-rays). They can also develop enlargement of the lymph nodes at the base of the heart. These can press upon the trachea causing irritation and leading to the dry, hacking cough often associated with VF.
What other areas of the body can be affected? – If VF is able to spread outside of the lungs, it becomes known as disseminated VF. In this phase, nearly any organ can be affected with the bones being the second site most commonly infected. Symptoms of disseminated VF are associated with the organ system infected. Lameness, bony swellings, back pain, seizures, ocular abnormalities/pain, swelling of the lymph nodes, swollen testicles in intact male dogs, heart failure (that is unexpected in a young patient), chronically oozing skin lesions or abscesses that don’t respond to antibiotics are all symptoms which can be associated with this form of the disease. It is possible for a dog to never show symptoms of the pulmonary phase and for the first symptoms noticed to be associated with the disseminated form.
Is VF contagious? – No, this disease is not contagious, though several members of a household can be infected as it is possible their common environment is a hot spot for the arthrospores. If there is a skin lesion with fluid draining, it is recommended to keep these areas bandaged with frequent bandage changes. Care should be taken to discard the soiled bandage material in outside waste containers. This is done to minimize environmental contamination. However, if there is an immunocompromised individual in the household of a pet with a draining lesion, they should consult their healthcare professional for further recommendations in how to handle soiled materials from VF skin lesions.
How is VF diagnosed? – When there is suspicion of a possible VF infection, veterinarians will likely recommend multiple diagnostic tests. These can include general organ chemistries, blood cell counts, radiographs of suspected affected areas (such as lungs, bones, joints), a VF screen and titer, cultures of fluids or tissues from lesions, biopsies of tissues, and possible more advanced diagnostics such as CT scans or MRI in suspected CNS cases.
Is the VF screen and titer always positive if my pet has VF? – Unfortunately, this is not a fool-proof test and false negatives can occur, especially early in the disease. In some of these cases, the VF screen and titer needs to be repeated several weeks after the initial test has been performed. It has even been noted that some animals that have had VF confirmed through other diagnostic tests, never develop a positive titer results.
How is the titer result interpreted? – When exposed to VF, the pet’s immune system creates antibodies to the fungus. The amount of antibodies being produced is measured in the blood and reported as a titer. The titer is performed by doubling the dilutions (1:2, 1:4, 1:16, etc up to 1:256) until the test becomes negative. The titer value reported is the last positive dilution. In general, the higher the titer, the more severe the disease, though this does not hold true for all cases. There are some cases in which the patient has a low positive or even a negative titer, but is clinically experiencing severe disease. These are the cases in which additional diagnostics are necessary to come to either a working diagnosis or hopefully eventually a definitive diagnosis of VF. As a pet is being treated for VF, the titer is monitored as it typically will decrease as the pet responds positively to treatment. Asymptomatic pets can also have a positive titer, but it is usually 1:16 or less and will often be referred to as an “exposure titer” as the pet has been exposed to VF, but has been able to overcome the infection while still having circulating antibodies against the disease in their bloodstream. Even with treatment, some pets never develop a negative titer. Some of these pets will require long-term or lifelong monitoring and possibly lifelong treatment.
How is VF treated? – The current mainstay of treatment is the use of oral antifungal medications. The medications commonly used include Ketoconazole (Nizoral), Itraconazole (Sporanox), and Flucoazole (Diflucan). In severe cases, an IV medication known as Amphotericin B can be administered in a veterinary hospital setting. Ketoconazole, Itraconazole, and Fluconazole are all fungi static medications which means they slow or inhibit the growth of the fungal organisms, but don’t directly kill them. Amphotericin B is a fungicidal medication in which it directly kills the fungal organisms, but it can be toxic to the kidneys and is reserved for the critically ill patient who is not responding well to oral antifungal medication. The fungicidal medications may all act similarly (ketoconazole, itraconazole and fluconazole), but they differ in how they are metabolized and how they are chemically structured. All of these medications can cause gastrointestinal upset/side effects, elevations in liver enzymes and birth defects. Ketoconazole
and Itraconazole are metabolized primarily by the liver, while the liver is only responsible for
approximately 10-20% of the metabolism of fluconazole. Although fluconazole is not extensively
metabolized by the liver, it is still possible for a pet being treated with this medication to have a negative reaction by the liver to this drug. Organ chemistry monitoring is recommended for pets that need to be on any of these medications. Fluconazole appears to be tolerated more readily as an oral antifungal than the other two medications previously mentioned and is well absorbed from the intestinal tract even when the pet is not eating well. It is also able to cross into the brain and eye tissues and is the drug of choice for infections of these sites.
Other supportive treatments for VF? – Additional medications may be prescribed to help with the secondary effects of the VF infection. This may include cough suppressants, pain control medications, nutritional support and sometimes hospitalization for a brief period to provide supportive care as the antifungal medication begins help treat the infection.
What is the fatality rate? – Thankfully, most cases, if found and treated early in the course of the disease, have a positive outcome. Many pets will require long-term treatment with oral antifungals (12-18 months) in uncomplicated cases of the pulmonary (lung) form of the disease, though some of these patients will require longer courses of therapy and it may extend to lifelong therapy. Those with bone involvement may require even longer courses of treatment, which can be also be lifelong. CNS cases are usually on antifungal therapy lifelong. It is possible, even with appropriate antifungal therapy, for this disease to be fatal.
When to stop treatment? – This decision is based on the pet’s response to therapy, the titer results on follow-up tests and the location of the infection. If a patient has been on an appropriate course of therapy, has been responding well and symptoms have resolved, we may discuss a trial cessation of the antifungal medication. If this is done, we will want to perform a recheck examination and repeat VF titer usually 2-3 months after stopping the medications. If symptoms return, or the titer begins to rise again, oral medication is restarted. If a pet experiences multiple relapses after trying to cease the use of the antifungal medication, then the pet is likely to need to be on this medication for the remainder of his/her life. It is extremely important not to stop the medication without first consulting your pet’s veterinarian!
Can VF be prevented? – Unfortunately, there is no way to currently prevent this disease. Pet owners can try to minimize their pet’s chances of coming in contact with the spores by discouraging digging behaviors, avoid allowing them to sniff rodent burrows/holes and using dust reducing ground covers such as large gravel and grass. Treating the yard is not effective as the spores can live up to a foot deep in the soil. It is possible that one day a vaccine may be developed to help prevent this disease, but one is not currently available.
OK, so you’ve talked a lot about dogs, but can my cat also become infected with VF? – Cats can come down with VF infections, though they are not as common as they are in dogs. However, when a cat is infected with VF, their symptoms can often be more severe as cats are great at hiding illness. They symptoms in cats vary a bit from dogs. Cats do not experience the coughing or lameness as often as dogs when infected with VF. On the other hand, the chronically draining skin lesions or vague symptoms of weight loss, behavioral changes, and inappetance are what are often noticed by feline owners. Blood testing can be done in cats, but often fluid samples or biopsies of skin lesions and radiographs of the chest are used to aid in the diagnosis of VF in the feline. Most cats respond well with the use of the same medications used to treat VF in dogs.
Thank you Dr. Lunetta!
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