Investigating Cytochrome b Allelic Mutations Associated with Atovaquone Resistance in Bobcats and Domestic Cats

Abstract

Cytauxzoonosis is a highly fatal disease of domestic cats and other felids caused by the apicomplexan Cytauxzoon felis and is treated with atovaquone and azithromycin (A&A) with around a 60% survival rate. Atovaquone, a structural analog of a protozoan mitochondrial protein called ubiquinone, inhibits binding of ubiquinone to cytochrome bc1 in the electron transport chain. Atovaquone resistance has recently been associated with M128 cytochrome b mutations in C. felis, however its prevalence and relationship to clinical disease in natural populations remain poorly defined. This study evaluated cytochrome b mutations at M128 to determine the prevalence of each mutation in two felid populations, bobcats (Lynx rufus), and domestic cats (Felis catus). I also evaluated if these mutations were associated with clinical outcomes in domestic cats (clinically ill or subclinical infections). Domestic cat samples included subclinical infections (n=19) and clinical cytauxzoonosis cases (n=26), while the bobcat samples were all subclinical. I found several point mutations in the M128 position of cytochrome b in both domestic cat and bobcats. This mutation resulted in amino acid changes in the protein. The wild-type, (as identified in literature and susceptible to atovaquone was ATG), the mutations were GTG, ATA and ATT. GTG resulted in Valine instead of methionine while ATA and ATT resulted in Isoleucine. In domestic cats, 84% of subclinical cats and 85% of clinical cats were associated with M128 Valine (M128V) mutations. Likewise, M128 Isoleucine (M128I) mutation was associated with 16% subclinical and 35% clinical cats with ATA(Isoleucine) point mutations, and 11% subclinical and 38% clinical cats with ATT (Isoleucine) point mutations. In bobcats (n=69), T was rare (10%), while A (64%) and G (78%) were common with all 3 documenting heteroplasmy. Overall T mutation was observed in 10% subclinical and 38% in clinical infections. Statistical analysis indicated that cats with cytauxzoonosis are five times more likely to have mutation T with genotype “ATT” coding for isoleucine. These outcomes establish enrichment of T mutation in clinical domestic infections and demonstrate a foundational cytochrome b variant distribution in untreated populations. This supports the need to continue molecular surveillance of C. felis for probable resistance associated variants and potentially pathology associated with variants.

Date of Award	2026
Original language	American English
Awarding Institution	Eastern Illinois University
Supervisor	Elliott A. Zieman (Supervisor)