Spherusol Skin Testing
Skin tests were once widely used as a means of assessing infection with the fungus that causes Valley Fever in people. The benefit of a skin test is that it is easier and more cost-effective than running blood tests on a large population. This makes it particularly useful when trying to study the epidemiology, or distribution, of the disease. Spherusol is a new skin test reagent that has shown good efficacy in people. We wanted to know if the reagent is similarly effective in dogs.
We enrolled dogs that had been diagnosed with Valley Fever within the last five years. Dogs did not need to be currently treated for Valley Fever to be eligible for participation in the study. Enrolled dogs received two intradermal skin tests, one on each flank, which were then read 48 hours later.
Utility of Skin Testing for Epidemiological Survey of Coccidioides Infection in Dogs
Our primary goal was to evaluate the usefulness of Spherusol, a commercially available skin test reagent, in the identification of a delayed type hypersensitivity reaction in dogs known to have been diagnosed with Valley Fever. Twenty-two dogs were tested with both Spherusol and coccidioidin, a historically used skin test reagent. We combined this data with previously unpublished work evaluating coccidioidin.
We found that the sensitivity of coccidioidin and Spherusol in the detection of dogs infected with the Coccidioides spp. was 49.1% and 18.2%, respectively. Coccidioidin was highly specific, but our small study could not determine the specificity for Spherusol. We conclude that skin tests are not a sensitive marker of infection in the dog.
Incidence and Risk Factors Study
In order to better understand the number of dogs that become infected with Valley Fever, blood was sampled from dogs in Pima and Maricopa counties. One group of dogs was enrolled between 4 and 6 months of age and received a blood test every six months. The other group of dogs was enrolled between 4 and 18 months of age and received a single blood test for Valley Fever. All owners were questioned about the health status of their dog and were asked to complete a questionnaire about potential risk factors for infection by the fungus.
We found that dogs in Pima and Maricopa counties had a 28% chance of becoming infected with Valley Fever in the first two years of life. During that time, the chance of a dog becoming ill was 6%. The results of the Valley Fever test were reported as a titer, or dilution of the sample that still tested positive for the presence of antibodies to the fungus. Dogs that were infected but not sick had titers ranging from <1:2 to 1:16, while dogs that were ill at the time of the blood sample had titers ranging from <1:2 to 1:32, indicating an overlap in titers between sick and healthy dogs.
The risk of infection was 4.9 times greater for dogs that spent more than 80% of their time outdoors as compared to predominantly indoor dogs. Dogs with more than an acre of land to roam were found to have a risk of infection 6.2 times greater than dogs with a smaller roaming area. No relationship was found between infection and breed, age of home, yard cover, digging behavior, or proximity to construction. Details of this study can be found here.
Nikkomycin Z is chitin synthase inhibitor, meaning that it works by disrupting the fungal cell wall. A study of the effectiveness of nikkomycin Z was completed using twelve dogs. All of the dogs enrolled in the study had been diagnosed with respiratory Valley Fever. Study dogs were treated with nikkomycin Z for 60 days, and clinical signs, blood results, and Xrays were compared from the start and end of the study period. Nine of the dogs finished the entire course of the medication. Of those 9, 7 dogs showed improvement in their clinical signs and Xrays. No dogs exhibited any adverse effects to the medication.
Nikkomycin Z appears to have good potential as a new therapeutic for the treatment of Valley Fever in dogs. It is currently in clinical trials in humans and is unavailable for commercial use at this time. More detailed information about this study is available: here
VT-1161 is a new antifungal medication designed to interfere with the fungal cell membrane. It has demonstrated a low number of drug interactions while being non-toxic to mammals. Twenty-four dogs with respiratory Valley Fever were enrolled into this study and randomized to receive either a high or low dose of VT-1161. Twenty-two dogs completed the full 60 day course of the medication. Clinical signs, Xrays, and bloodwork were compared from the start to the end of the study. Most dogs showed improvement, with only a couple of dogs exhibiting mild adverse effects. Further analysis of the data from this study is ongoing.
VT-1161 has demonstrated efficacy against Valley Fever but is not currently commercially available.
Valley Fever Vaccine
Work on an effective vaccine for the prevention of Valley Fever in dogs has been ongoing for decades. Currently, we have a vaccine candidate that shows excellent efficacy in mice. We are proceeding through the steps of working with regulatory agencies in order to bring this vaccine to market for our canine patients, and then, ultimately, to humans residing in endemic regions.