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Molecular Assessment of North American Vector-Borne Hemoparasites and In Vitro Studies
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The hemoparasite Cytauxzoon felis causes cytauxzoonosis, an emerging infectious disease of cats in the United States. Its life cycle involves sexual reproduction in the tick vector and asexual reproduction (schizogonous and erythrocyctic stages) in the felid. Cytauxzoon felis studies involve the use of infected cats, and in vitro cultivation would obviate this use as well as provide a continuous parasite source. Modeled after the microaerophilous stationary phase system used in cultures of Babesia bovis, a similar hemoparasite, 332 C. felis cultures were initiated to optimize the in vitro cultivation of the erythrocytic stage. Although no continuous cultivation was achieved, parasites were maintained short-term at a percentage of parasitized erythrocytes ranging from undetectable to 1.1% for two days to 140 days, with an average of 32 days. Five cultures underwent subculture four times, the maximum level achieved. Cytauxzoonosis can manifest itself as a recovered, chronic, or fatal infection. Historically, nearly all infected cats died, but as years passed, the number of cats that did survive increased, which may be attributed to different strains of Cytauxzoon felis. Internal transcribed spacer regions 1 and 2 (ITS1 and ITS2) were assessed for genetic variation and used for determining clinical outcome and spatial correlations. Even though the ITS1 and ITS2 regions are genetically diverse, they do not aid in understanding differences in C. felis strains, as there was no association with clinical outcome or geography. A potential C. felis coinfection with a hemoplasma was assessed for difference in clinical outcome. Polymerase chain reaction (PCR) and subsequent cloning showed clones of 11 of 41 C. felis-infected cats as positive for Candidatus Mycoplasma haemominutum with at least 99% identity and two other cats as positive for Rhodococcus spp. with at least a 97% identity. Clones of one of these two cats also matched Candidatus Mycoplasma kahanei with 99% identity. Based on prior molecular evidence of B. bovis and the sylvatic component of the C. felis life cycle, 161 ticks removed from white-tailed deer in south Texas were molecularly surveyed for hemoparasites. No ticks were positive for species of Babesia, Cytauxzoon, or Theileria.
Pollard, Dana Alicia (2017). Molecular Assessment of North American Vector-Borne Hemoparasites and In Vitro Studies. Doctoral dissertation, Texas A & M University. Available electronically from