Identification of Cytauxzoon felis antigens via protein microarray and assessment of expression library immunization against cytauxzoonosis.

BACKGROUND: Cytauxzoonosis is a disease of felids in North America caused by the tick-transmitted apicomplexan parasite Cytauxzoon felis. Cytauxzoonosis is particularly virulent for domestic cats, but no vaccine currently exists. The parasite cannot be cultivated in vitro, presenting a significant limitation for vaccine development. METHODS: Recent sequencing of the C. felis genome has identified over 4300 putative protein-encoding genes. From this pool we constructed a protein microarray containing 673 putative C. felis proteins. This microarray was probed with sera from C. felis-infected and naïve cats to identify differentially reactive antigens which were incorporated into two expression library vaccines, one polyvalent and one monovalent. We assessed the efficacy of these vaccines to prevent of infection and/or disease in a tick-challenge model. RESULTS: Probing of the protein microarray resulted in identification of 30 differentially reactive C. felis antigens that were incorporated into the two expression library vaccines. However, expression library immunization failed to prevent infection or disease in cats challenged with C. felis. CONCLUSIONS: Protein microarray facilitated high-throughput identification of novel antigens, substantially increasing the pool of characterized C. felis antigens. These antigens should be considered for development of C. felis vaccines, diagnostics, and therapeutics.

Cytauxzoonosis: Diagnosis and treatment of an emerging disease.

PRACTICAL RELEVANCE: Cytauxzoonosis is a life-threatening hematoprotozoal disease with a rapidly progressive clinical course. Once considered a rare disease only relevant to a small geographic area, it is now recognized in more than about a third of the United States. The geographic range seems likely to increase with expansion of the range of the vector tick. CLINICAL CHALLENGES: Both disease diagnosis and treatment offer challenges. The acute illness is often recognized by characteristic parasitic cellular inclusions, but illness may occur before parasites can be identified, and parasitic inclusions may persist long after illness has resolved. Also, while infection was once considered nearly uniformly fatal, subclinical infections are now recognized. Disease prognosis has improved for many cats through implementation of new therapies, but some pathogens are resistant to these therapies and death from disease is still common. Currently, prevention strategies are limited to ectoparasite control. GLOBAL IMPORTANCE: Cytauxzoonosis caused by Cytauxzoon felis is limited to the Americas, and is especially problematic in southeastern and south central USA. However, other Cytauxzoon species have been recognized in Europe and Asia. AUDIENCE: This review is aimed at veterinary practitioners and focuses on the diagnosis and treatment of cytauxzoonosis. Disease management is of crucial importance in endemic regions. Furthermore, the expanding geographic range of infection, and the possibility of parasite identification in chronically infected cats with a travel history, make understanding cytauxzoonosis relevant in non-endemic regions as well. EVIDENCE BASE: The authors draw on evidence from prospective clinical trials, experimental infections, retrospective clinical studies and case reports, as well as their own personal experience with the diagnosis and treatment of cytauxzoonosis.