Genetic variability of cloned Cytauxzoon felis ribosomal RNA ITS1 and ITS2 genomic regions from domestic cats with varied clinical outcomes from five states

CLINICAL AND SUBCLINICAL CYTAUXZOON FELIS INFECTIONS IN DOMESTIC CATS FROM A RECENTLY IDENTIFIED ENDEMIC REGION

Cytauxzoon felis is a tick-transmitted intraerythrocytic apicomplexan infecting felids in the southeastern and midwestern United States. Bobcats (Lynx rufus) are the natural wildlife reservoir of C. felis, where in enzootic areas prevalence can reach 100%. Domestic cats can be subclinically infected with C. felis or can develop cytauxzoonosis. Two studies have documented the presence of C. felis in domestic cats in Illinois; these studies have shown a limited number of cases submitted to specialty labs. During 2014-2018, we obtained blood samples collected by veterinary staff from 514 cats that were apparently healthy and 74 cats that were suspected of cytauxzoonosis. These samples were screened using a sensitive, nested PCR to detect the presence of C. felis DNA. We herein document frequent occurrences of cytauxzoonosis (8-15 cases/year from 4 veterinary clinics) and 12.5% prevalence of subclinical infections in southern Illinois, a locality showing a sharp increase in cases of cytauxzoonosis. Our results suggest a high risk of cytauxzoonosis in southern Illinois, despite only recently being recognized in the area. We found no specific risk factors for cytauxzoonosis or subclinical infections in this location. In addition, cases of cytauxzoonosis occur every month of the year (with the highest frequency in summer) and therefore tick prevention should be used in domestic cats in enzootic regions throughout the year.

Serum biochemical changes in cats with naturally acquired feline cytauxzoonosis

OBJECTIVE

The geographical distribution of feline cytauxzoonosis is expanding in the US. Clinical signs of feline cytauxzoonosis, including lethargy, anorexia, and icterus, are similar to hepatic lipidosis and cholangiohepatitis. Hematologic and serum biochemical abnormality patterns may assist practitioners in prioritizing feline cytauxzoonosis as a differential diagnosis over hepatic lipidosis and cholangiohepatitis.

SAMPLE

Hematology and serum biochemical profiles of cats with naturally acquired feline cytauxzoonosis, hepatic lipidosis, or cholangiohepatitis.

PROCEDURES

Retrospective search and analysis of the Kansas State Veterinary Diagnostic Laboratory or Kansas State University Veterinary Health Center records between January 2007 and June 2018 for cats with cytauxzoonosis, hepatic lipidosis, or cholangiohepatitis.

RESULTS

Patients with acute feline cytauxzoonosis presented with frequent nonregenerative anemia (20/28 [71%]), leukopenia (23/28 [82%]), thrombocytopenia (23/23 [100%]), hyperbilirubinemia (27/28 [97%]), hypoalbuminemia (26/28 [93%]), reduced (18/28 [64%]) or low normal (10/28 [36%]) serum ALP activity, and hyponatremia (23/28 [82%]). Reduced ALP activity was unique to cats with feline cytauxzoonosis relative to hepatic lipidosis and cholangiohepatitis. No correlation between the severity of anemia and the magnitude of hyperbilirubinemia was identified in feline cytauxzoonosis patients.

CLINICAL RELEVANCE

The combination of nonregenerative anemia, leukopenia, thrombocytopenia, hyperbilirubinemia, and reduced serum ALP activity in icteric cats may increase the clinical suspicion, but is not pathognomonic, for acute feline cytauxzoonosis. Hematologic and serum biochemical abnormalities of naturally acquired feline cytauxzoonosis are like those reported with feline bacterial sepsis. Blood smear evaluation for intraerythrocytic Cytauxzoon felis piroplasms, tissue aspirates for schizont-laden macrophages, and/or molecular testing are required to diagnose feline cytauxzoonosis.

Cytauxzoon felis: An Overview

Cytauxzoon felis is a tick-transmitted, obligate, hemoprotozoal, piroplasmid pathogen of felids and the causative agent of cytauxzoonosis. It has a complex life cycle which includes a tick as its definitive host and a felid as its intermediate host. Since its first description in 1976, C. felis infections of felids have been reported in several southeastern and south-central U.S. states, overlapping with the ranges of its two known biological vectors, Amblyomma americanum (Lone star tick) and Dermacentor variabilis (American dog tick). Infected felids demonstrate disease as either an acute, often-fatal, infection, or a subclinical carrier infection. To develop effective C. felis transmission control strategies, the incidence of acute cytauxzoonosis, patient risk factors, the role of domestic cat carriers, and ecological variabilities need to be investigated further. Of equal importance is communicating these strategies for high-risk cat populations, including recommending year-round use of an acaricide product for all cats that spend any time outdoors. More studies are needed to further identify factors affecting C. felis and other Cytauxzoon spp. infection, transmission, disease progression, and treatment options and outcomes within the U.S. and globally. Here we provide an overview of C. felis highlighting its lifecycle within its definitive host, transmission to its intermediate host, symptoms and signs providing evidence of transmission, definitive diagnosis, current treatment and prevention strategies, and future considerations regarding this condition.

Description of a novel Babesia sp. genotype from a naturally infected Eurasian lynx (Lynx lynx) in Anatolia, Turkey, with remarks on its morphology and phylogenetic relation to other piroplasmid species

There are very limited data on Babesia species infecting lynx species worldwide, and almost nothing is known about babesias in the Eurasian lynx, the most widely distributed wild feline species in the Palearctic geography. This study describes a novel Babesia sp. genotype in a free-living Eurasian lynx in Turkey, named tentatively as 'Babesia sp. lynx', and its integrated genetic and morphological features. Phylogenetic analyses of piroplasmids with the novel Babesia sp. genotype in the current study indicated that this genotype falls into the 'carnivore clade A' of Babesia sensu stricto (true babesias), at the level of different genes (mainly 18S rRNA, ITS1, ITS2, and cyt b) and is monophyletic with the Babesia sp. Ankara genotype, previously observed in Turkey. Additionally, the constructed phylogenetic trees showed that the Babesia sp. lynx genotype infecting the Eurasian lynx is closely related to certain domestic and wild carnivore babesias, mainly Babesia rossi, Babesia presentii, and Babesia pisicii, at the level of different genes. This study also genetically barcoded the lynx infected with the Babesia sp. lynx and Haemaphysalis erinacei, and specimens collected from the animal revealed significant genetic variations between the sample Ha. erinacei and Babesia sp. Ankara-related Ha. erinacei that persists with sympatric populations in Central Anatolia. The lynx infected with the Babesia sp. lynx genotype was also found to be coinfected with Hepatozoon felis, an adeleorinid tick-borne protozoan parasite infecting wild and domestic felids, confirming for the first time its presence in a lynx species. Therefore, this study is the first to describe a potential novel Babesia sp. using its both morphological and phylogenetic characteristics in a lynx species. Adding the Babesia sp. lynx genotype to the phylogeny of feline piroplasmids significantly expands our knowledge of feline babesias in the Palearctic geography and their putative coevolution with their vertebrate hosts.

Cytauxzoonosis in North America

Cytauxzoonosis is an emerging tick-borne disease of domestic and wild felids produced by infection of Cytauxzoon felis, an apicomplexan protozoan similar to Theileria spp. Transmitted by Amblyomma americanum, lone star tick, and Dermacentor variabilis, American dog tick, infection of C. felis in cats is severe, characterized by depression, lethargy, fever, hemolytic crisis, icterus, and possibly death. Cytauxzoonosis occurs mainly in the southern, south-central, and mid-Atlantic United States in North America, in close association with the distribution and activity of tick vectors. Infection of C. felis, although severe, is no longer considered uniformly fatal, and unless moribund, every attempt to treat cytauxzoonosis cats should be made. Herein we review cytauxzoonosis, including its etiology, affected species, its life cycle and pathogenesis, clinical signs, diagnosis, and epidemiology, emphasizing clinical pathology findings in cats infected with this important emerging tick-borne disease in North and South America.

Prevalence of Cytauxzoon felis Infection-Carriers in Eastern Kansas Domestic Cats

Cytauxzoon felis is a hemoprotozoal tick-transmitted pathogen of felids. Felids that survive acute disease often remain infected and serve as reservoirs for subsequent tick transmission to other susceptible felines. States adjacent to Kansas have identified C. felis-domestic cat carriers while statewide awareness and concern of cytauxzoonosis have increased. The objective of this study was to determine the prevalence of C. felis-carriers in the eastern Kansas domestic cat population using a sensitive quantitative PCR assay targeting the C. felis Cox3 mitochondrial gene. An overall C. felis infection prevalence of 25.8% was determined for asymptomatic domestic cats in eastern Kansas. Significantly more C. felis-carrier cats were identified in spring and fall, suggesting a seasonal fluctuation of survivors. Additionally, a greater percentage of feral and owned cats were positive for C. felis compared to rescue/rescinded cats. This study demonstrates that C. felis-domestic cat carriers are common among cats that spend at least a portion of time outdoors in eastern Kansas, and that more cats likely survive cytauxzoonosis than expected. Understanding the role of domestic cat carriers of C. felis is essential in developing cytauxzoonosis mitigation strategies, including recommending year-round use of acaricide products for all cats that spend any time outdoors.

Genetic diversity of Hepatozoon (Apicomplexa) from domestic cats in South Africa, with a global reassessment of Hepatozoon felis diversity

Genetic diversity within partial 18S rRNA sequences from Hepatozoon protozoan parasites from domestic cats in South Africa was assessed and compared against published data to assess global biogeographic patterns. Multiple distinct haplotypes of Hepatozoon felis were identified, as well as an unrelated Hepatozoon lineage. Hepatozoon felis genetic diversity globally is very high, indicating a likely complex of species. The recently described Hepatozoon apri from wild boars is closely related to some lineages of H. felis. Sarcocystis and Babesia parasites were also detected. Since Hepatozoon felis is apparently a species complex, potential differences between genetically distinct forms need to be assessed. The finding of an unrelated Hepatozoon indicates that felids can be infected by more species of Hepatozoon than currently known, and that trophic interactions may increase the number of Hepatozoon species found in carnivores. Genetic screening again is demonstrated to identify previously unrecognised parasites from vertebrate hosts.

Limited genetic variability of Cytauxzoon felis apical membrane antigen-1 (ama1) from domestic cats and bobcats

Background

Cytauxzoon felis is a tick-transmitted apicomplexan that causes cytauxzoonosis in domestic cats (Felis catus). Even with intensive care, the mortality rate of acute cytauxzoonosis approaches 40% in domestic cats, while bobcats (Lynx rufus), the natural intermediate host of C. felis, remain clinically asymptomatic. However, multiple reports of domestic cats surviving acute disease without any treatment exist. One hypothesis for survival of these cats is infection with unique C. felis genotypes of lower pathogenicity. Prior studies have identified genetically distinct C. felis isolates containing polymorphisms within internal transcribed spacer regions (ITS) of the rRNA operon. However, these polymorphisms do not correlate with the clinical outcome of cytauxzoonosis, and so additional genetic markers are needed to test this hypothesis. We selected C. felis apical membrane antigen-1 (ama1) as a potential genetic marker of differential pathogenicity. AMA1 is a vaccine candidate for relatives of C. felis within Plasmodium spp.; however its historically high level of genetic polymorphism has resulted in escape from vaccine-induced immunity. While such diversity has hindered vaccine development, the expected polymorphism within the ama1 gene may be useful to evaluate population genetics.

Results

A 677 bp sequence of the C. felis ama1 gene was PCR-amplified from 84 domestic cats and 9 bobcats and demonstrated 99.9% sequence identity across all samples. A single nucleotide polymorphism (SNP) was identified in domestic cats and bobcats with evidence for co-infection with both genotypes identified in two domestic cats. The prevalence of the two genotypes varied with geographical distribution in domestic cats. Nucleotide diversity (π) and haplotype diversity (H) were calculated for C. felis ama1 and ama1 of related apicomplexans to assess genetic diversity. Based on these values (π = 0.00067 and H = 0.457), the diversity of the C. felis ama1 gene region analyzed is considerably lower than what is documented in related apicomplexans.

Conclusions

In surprising contrast to related apicomplexans, our results support that the sequence of the C. felis ama1 gene is highly conserved. While lack of genetic diversity limits utility of C. felis AMA1 as a genetic marker for clinical outcome, it supports further investigation as a vaccine candidate for cytauxzoonosis.

Efficacy of a topical formulation of selamectin plus sarolaner against induced infestations of Amblyomma americanum on cats and prevention of Cytauxzoon felis transmission

Cytauxzoonosis, caused by infection with Cytauxzoon felis, is the most severe tick-borne disease of cats. The purpose of our study was to determine the efficacy of selamectin (6.0 mg/kg) plus sarolaner (1.0 mg/kg) formulated in combination (Revolution® Plus / Stronghold^® Plus, Zoetis) applied topically once a month on cats for three months against induced infestations of Amblyomma americanum adults and to evaluate the effectiveness of the product in preventing the transmission of C. felis. This study was conducted in two phases. Sixteen cats were dosed with selamectin/sarolaner or a placebo (vehicle control) on Days 0, 28, and 56. In phase 1, each cat was infested with 50 (±5) unfed adult A. americanum on Day 4 and tick counts were conducted on Day 6 (48 h post infestation) and Day 7 (72 h post infestation) to evaluate acaricidal efficacy. In phase 2, to confirm acaricidal efficacy and evaluate prevention of C. felis transmission, each cat was infested on Day 60 with 50 (±5) adult A. americanum acquisition fed as nymphs on two C. felis-infected donor cats. Tick counts were conducted on Day 62 (48 h post infestation) and Day 63 (72 h post infestation). Blood samples were collected on Days -9, 60, 70, 76, and 90 and tested for infection with C. felis. Placebo cats were adequately infested on all count days, with least squares (geometric) mean live tick counts ranging from 34.0 (28.8) to 46.1 (46.0). Treatment reduced the least squares (geometric) mean counts compared to placebo by 27.1 (32.1)% and 90.4 (96.8)% on Days 6 and 7, respectively. The corresponding percent reductions were 56.4 (60.6)% and 94.7 (97.3)% on Days 62 and 63, respectively. Least squares mean counts were significantly lower in the treated group compared with the placebo group on all count days (P ≤ 0.0286). All cats were negative for C. felis by PCR prior to study start. In phase 2, seven cats in the control group and no cats in the selamectin/sarolaner group became infected with C. felis (P = 0.0017). Topical treatment with selamectin/sarolaner was >90% effective in reducing A. americanum tick counts 72 h after infestation and prevented the transmission of C. felis from infected ticks following the third of three monthly treatments. Revolution^® Plus / Stronghold^® Plus offers an option for the control of A. americanum infestations on cats and for preventing the transmission of C. felis to cats.

Chronic Cytauxzoon felis infections in wild-caught bobcats (Lynx rufus)

Cytauxzoon felis, and the resulting disease, cytauxzoonosis, is an emerging threat to domestic cats in the Midwest and Southeastern United States. Domestic cats that survive cytauxzoonosis (or are subclinically infected) are chronically infected with C. felis, yet to date, there is no information relative to chronic infections in bobcats, the natural reservoir. Over a period of 3.5 years (2014-2017), we captured and re-captured 5 bobcats in southern Illinois. One bobcat was captured each year of trapping, 1 was caught in the first and third year and 3 were recaptured approximately 1 year apart. We screened bobcats for the presence of C. felis using a nested PCR that amplified the nuclear small subunit (SSU) 18S rRNA. In addition, we amplified and sequenced the internal transcribed spacers 1 and 2 (ITS1 and ITS2) to detect if the strains of C. felis in each bobcat were consistent over time. All bobcats were positive for C. felis at the initial and subsequent capture(s). Bobcats that were PCR-positive for C. felis had blood smears screened for the presence of C. felis; all PCR-positive bobcats had detectable parasites in blood smears. The strains of C. felis present were consistent each year in 4 of 5 bobcats indicating these bobcats remained infected during this period. One bobcat appeared to be infected with a different strain based on a polymorphism at a nucleotide in ITS1. Our study provides important details of the epizootiology of C. felis: bobcats are chronically infected and are not immune to reinfection with new strains of C. felis.