Dissertation/Thesis Abstract

A New Niche for “The Itch”: Characterization of an Emerging Sarcoptic Mange Epidemic in the San Joaquin Kit Fox
by Rudd, Jaime Leanne, Ph.D., University of California, Davis, 2019, 71; 22621835
Abstract (Summary)

The San Joaquin kit fox (Vulpes macrotis mutica) is the only subspecies of kit fox endemic to California and is federally endangered. Although this small fox exhibits incredible adaptability, its geographic distribution is limited and contracting due to profound habitat destruction. Only twelve populations persist, including a unique urbanized satellite population which, until recently, thrived in the city of Bakersfield. This urban population had been considered a potential source population for reintroductions into remaining natural lands in the event of catastrophic kit fox population declines. In spring 2013, sarcoptic mange was first detected in the Bakersfield population. Preliminary data demonstrate that most or all infested kit foxes die if not treated, and therefore individual-based citywide treatment and rehabilitation are underway. Yet this individual-based approach to sarcoptic mange treatment has done little to slow the progression of disease through the population and there have been over 460 documented cases as of October 2018, demonstrating a need for a population-level intervention strategy. Therefore, the objectives of my dissertation were to: 1) determine whether sarcoptic mange in kit foxes and other sympatric canids is due to a shared vs. multiple diverse mite strains, 2) evaluate the effectiveness of a long-lasting acaricidal collar that might be used for a population-level intervention, and 3) identify additional health problems associated with mange to optimize medical management of mange-infested individuals in rehabilitation. The overarching goal was to conduct applied conservation research to inform future disease mitigation efforts.

In Chapter 1, I used microsatellite genotypes of 351 Sarcoptes mites collected from kit foxes, red foxes (Vulpes vulpes), domestic dogs (Canis lupus familiaris), and coyotes (Canis latrans) to determine whether a kit fox variant of Sarcoptes scabiei mite was circulating only among kit foxes or if it was shared with these other sympatric canids. Bakersfield mites from kit foxes and red foxes showed the least loci polymorphism compared to coyotes and domestic dogs from the same area. The closest genetic relationship was between Bakersfield kit fox mites and Bakersfield red fox mites (FST = 0.060). In contrast, Bakersfield kit fox mites and Bakersfield coyote mites (FST = 0.509), and Bakersfield kit fox mites and Bakersfield dog mites (FST = 0.742) were much less closely related genetically. Further, only a single private allele (frequency of 0.005) was detected in kit fox mites; otherwise they shared alleles with coyotes and domestic dogs. These results demonstrate that the Sarcoptes mites are relatively host-specific and, although a spill-over event occurred initially, the primary route of mite transmission appears to be fox-to-fox. Therefore, future planning for a citywide intervention should focus on treating kit foxes.

Accordingly, in Chapter 2, I evaluated a pilot intervention strategy that could reduce mite-infestation risk by deploying long-acting acaricidal collars on at-risk kit foxes. Traditional Sarcoptes treatments last anywhere from 10 days (ivermectin) to 28 days (selamectin), but S. scabiei infested individuals can live for up to 100 days before death and remain infectious during that time. The short duration of protection from standard treatment is not a feasible means to achieve herd immunity because individuals would need to be captured and treated every month. Flumethrin collars reportedly prevent sarcoptic mange infestation for up to 8 months, which make this an appealing alternative, but there was a need to test the claims of long-term protection and the true efficacy at the population level in reducing disease risk before a citywide intervention could be planned. Therefore, I performed a 2-year field trial with 35 kit foxes to study flumethrin’s safety, longevity, and efficaciousness. All kit foxes were treated with a single dose of selamectin (6mg/kg) and then assigned to the flumethrin treatment group (n = 17) and to the control group (n = 18). A Cox Proportional Hazards model was used to compare the duration of time it took for an individual to develop mange in the treated and control groups. There was no overall significant difference in the number of days before a kit fox in the treatment group developed mange (176 days) compared to the control group (171 days). Further, most mange transmission was observed within social groups, which could have serious consequences for mange transmission and spread if the entire family group is not synchronously treated. Like numerous drugs available on the market, flumethrin showed promise as being safe, long-lasting, and efficacious. However, its extra-label use in the field was not as effective as it is for treatment of mange in domestic animals.

Finally, to better understand this debilitating, multisystemic disease process, in Chapter 3, I analyzed serum biochemistry and hematology values of kit foxes with mange and compared them to healthy kit foxes. Several serum chemistry and CBC parameters in mange-infested foxes were consistent with chronic disease and inflammation, starvation, and dehydration – a similar pathogenesis that has been observed in other canids and bobcats (Lynx rufus). The alterations in blood values observed indicate that kit foxes must be properly hydrated and their protein requirement supported while antibiotics and antiparasitic medications are administered in order to improve their chance of survival in rehabilitation.

This dissertation focused on various aspects of a recent sarcoptic mange outbreak in San Joaquin kit foxes living in an urban city in California. Using molecular epidemiology, I was able to show that the current transmission dynamics of sarcoptic mange and thus intervention efforts should focus on kit foxes. While flumethrin was safe, its extra-label use in the field was not as efficacious for the treatment and prevention of sarcoptic mange as it is for domestic animals. Further, these results identified various health parameters that should be addressed for mange-infested kit foxes presented for rehabilitation to increase their chances of survival during treatment. Additional studies focusing on mange transmission, novel medications, and kit fox sociology should be conducted to determine what refinements could improve individual animal protection and reduce the impacts of this disease in kit foxes.

Indexing (document details)
Advisor: Foley, Janet E
Commitee: Clifford, Deana L, Cypher, Brian L, Hull, Josh M
School: University of California, Davis
Department: Animal Biology
School Location: United States -- California
Source: DAI-B 81/4(E), Dissertation Abstracts International
Subjects: Epidemiology, Wildlife Conservation, Veterinary services
Keywords: Bakersfield, endangered species, free-ranging wildlife, intervention, mites, Sarcoptes scabiei
Publication Number: 22621835
ISBN: 9781392581186
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