Detection of persistent Cytauxzoon felis infection by polymerase chain reaction in three asymptomatic domestic cats

Repeated polymerase chain reaction (PCR) testing of 3 asymptomatic domestic cats were positive for Cytauxzoon felis DNA, suggesting persistent infection. Two cats initially presented with clinical signs consistent with acute cytauxzoonosis and, in both cases, signs of illness resolved after treatment. Parasitemia was detected in peripheral blood smears from these cats upon presentation with illness and, at subsequent follow-up appointments, in the absence of clinical illness. Polymerase chain reaction analysis was positive for C. felis from blood sampled at each time point. A third cat, a housemate of a cat fatally infected with C. felis, was preventatively treated for infection at the time of the housemate cat's death. This contact cat, having never shown signs of clinical illness consistent with cytauxzoonosis infection, had no detectable parasitemia but was positive for C. felis on repeated PCR testing. Detection of asymptomatically infected cats allows for the possibility of a yet unrecognized population of infected domestic cats that may have the capacity to serve as an additional reservoir host for C. felis, altering the currently accepted paradigm of C. felis transmission to domestic cats through bobcats as the reservoir host. In cases of very low parasitemia, more sensitive means of parasite detection, such as PCR testing, may be necessary to detect infected cats. Increased detection of asymptomatically infected cats will aid in understanding the epidemiology of C. felis infection and enhance the ability to prevent this highly fatal infectious disease of domestic cats.     

Use of enrofloxacin for treatment of large-form Haemobartonella felis in experimentally infected cats

OBJECTIVE: To compare treatment with enrofloxacin and doxycycline with no treatment in cats experimentally infected with Haemobartonella felis. DESIGN: Prospective case-control study. ANIMALS: 16 cats. PROCEDURE: Cats were inoculated with large-form H. felis from a chronically infected donor. Cats were assigned to 1 of 4 treatment groups: doxycycline (5 mg/kg [2.3 mg/lb], p.o., q 12 h), low-dose enrofloxacin (5 mg/kg, p.o., q 24 h), high-dose enrofloxacin (10 mg/kg [4.5 mg/lb], p.o., q 24 h), and an untreated control group. Clinical signs, Hct, blood smears, and a polymerase chain reaction (PCR) assay were used to monitor progression of the infection. RESULTS: All cats were confirmed to be infected with H. felis via blood smear evaluations and PCR assay results. Treatment had no effect on Hct during the intratreatment period, but Hct values were significantly greater in the low-dose enrofloxacin group, compared with the control group, during the posttreatment period. During the intratreatment period, H. felis organism counts per 1,000 RBC in the doxycycline treatment and the high-dose enrofloxacin treatment groups decreased at a significantly faster rate than those in the control group. In the posttreatment period, organism counts in the doxycycline treatment group and the low- and high-dose enrofloxacin groups decreased at significantly faster rates than counts in the control group. There was no significant effect of treatment on the number of positive PCR assay results. Two cats treated with enrofloxacin and 1 cat treated with doxycycline completely cleared the H. fe is organism despite presumed immunosuppression caused by glucocorticoids. CONCLUSIONS AND CLINICAL RELEVANCE: Results support the hypothesis that enrofloxacin has anti-H. felis effects.     

Attempted transmission of Candidatus Mycoplasma haemominutum and Mycoplasma haemofelis by feeding cats infected Ctenocephalides felis

OBJECTIVE: To determine whether Mycoplasma haemofelis (Mhf) and Candidatus Mycoplasma haemominutum (Mhm) can be transmitted by ingestion of Mycoplasma-infected Ctenocephalides felis and by-products (feces, larvae, and eggs). ANIMALS: 10 cats. PROCEDURE: 3 cats were carriers of Mhf, and 1 was a carrier of Mhm. Six cats had negative results of PCR assay for Mhf and Mhm DNA. A chamber containing 100 C felis was bandaged to 2 Mhf carrier cats. Five days later, fleas and by-products were analyzed for Mycoplasma spp DNA. The remaining fleas and a sample of by-products were fed to 2 Mycoplasma-na?ve cats. A chamber containing 200 C felis was bandaged to the Mhm carrier cat. Five days later, fleas and by-products were analyzed for Mycoplasma spp DNA. The remaining fleas and a sample of by-products were fed to 2 Mycoplasma-na?ve cats. A chamber containing 200 C felis was bandaged to an Mhf carrier cat and Mhm-carrier cat. Three days later, fleas and by-products were analyzed for Mycoplasma spp DNA. The remaining fleas and a random sample of by products were fed to 4 Mycoplasma-na?ve cats. All cats were monitored for infection for >or=7 weeks. RESULTS: Uptake of Mhf and Mhm DNA into fleas and by-products was detected. None of the na?ve cats became infected. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that ingestion of Mycoplasma-infected C felis or by-products is not an important means of transmission for Mhf or Mhm.     

Molecular detection and characterization of Haemobartonella felis in domestic cats in Japan employing sequence-specific polymerase chain reaction (SS-PCR)

A novel PCR assay was developed in order to examine the prevalence of Haemobartonella felis (H. felis) in Japanese domestic cats and which was able to differentiate of the Ohio strain and the California strain of H. felis. Blood samples from a total of 21 cats suspected of having haemobartonellosis were examined employing a novel PCR assay and demonstrated positive results in 18 cats which was confirmed by cytological examination of blood smears. Four out of 18 positive cats (22%) were infected with the California strain, whilst the other 12 cats (67%) were infected with the Ohio strain and two animals (11%) were infected with both strains. As most of the cats with moderate to severe anemia were infected with the Ohio strain, it is suggested that the most prevalent strain of H. felis in Japanese domestic cats might be the Ohio strain. In the present study, it was thought that molecular detection and characterization of H. felis may provide valuable information regarding the severity and prognosis of this illness.     

Experimental infection of domestic cats (Felis domesticus) with Cytauxzoon manul from Pallas' cats (Otocolobus manul)

In a random, blind study, six domestic cats were assigned to two treatment groups that received either sterile water or dexamethasone by subcutaneous injection prior to intravenous inoculation with Pallas' cat (Otocolobus manul) blood infected with Cytauxzoon manul. A seventh domestic cat served as a control and was inoculated only with sterile water. Cats were monitored for clinical signs consistent with cytauxzoonosis, and periodically screened for hemoparasitemia. All domestic cats (6/6) that received Pallas' cat blood infected with C. manul developed a low but detectible parasitemia by 9 days post-inoculation, yet remained clinically healthy. All domestic cats (7/7) were subsequently challenged with Cytauxzoon felis and developed clinical signs typical of cytauxzoonosis within 5 days post-challenge. Affected animals were euthanized and cytauxzoonosis was confirmed by histopathology. While inoculation of domestic cats with Pallas' cat blood infected with C. manul induced a parasitemia, it did not cause disease or provide protection against challenge with C. felis. Further studies are warranted to determine the potential for interspecies transmission and disease with C. manul.     

The detection of Cytauxzoon felis in apparently healthy free-roaming cats in the USA

Cytauxzoon felis typically causes fatal disease in domestic cats. Survival after infection and persistent parasitemia without clinical illness has been documented in a few cases. To our knowledge there are no prevalence studies of C. felis in domestic cats. The purpose of this study was to estimate the prevalence of C. felis infected cats that were presented to trap-neuter-return programs in Florida, North Carolina and Tennessee. Cats that were presented to trap-neuter-return programs were tested using a C. felis-specific PCR assay. A total of 961 domestic cats were tested (494 from Florida; 392 from North Carolina; 75 from Tennessee). Prevalence of C. felis infection in this population was 0.3%. Two cats from Florida and one cat from Tennessee tested positive for the presence of C. felis DNA. These amplicons were sequenced and confirmed to be C. felis. The cat from Tennessee was alive without evidence of illness 2 months post-surgery. The other two cats were alive 24 h post-surgery, but were then lost to follow-up. This is the first report documenting C. felis infections in free-roaming cats. Despite the low prevalence rate, the presence of apparently healthy infected free-roaming cats suggests that they may have the capacity to serve as an additional reservoir host for C. felis. Further investigations should evaluate the potential vector competence of domestic cats as well as the role of chronically infected cats in areas in which cytauxzoonosis appears hyperendemic.     

Prevalence of Rickettsia felis DNA in the blood of cats and their fleas in the United States

Rickettsia felis is associated with fever, headache, myalgia, and macular rash in some infected humans and has been detected in the cat flea (Ctenocephalides felis) in many countries around the world. While some naturally exposed cats have been assessed for antibodies against R felis, to our knowledge, no one has reported use of polymerase chain reaction (PCR) to attempt to amplify R felis DNA from client-owned cats and the fleas collected from them. In this study, we assayed 92 pairs of cat blood and flea extracts from Alabama, Maryland and Texas, using PCR assays that amplify a region of the citrate synthase gene (gltA) and the outer membrane protein B gene (ompB). Of the 92 pairs, 62 of 92 (67.4%) flea extracts and none of the cat blood samples were positive for R felis DNA.     

An etiological investigation of domestic cats with conjunctivitis and upper respiratory tract disease in Japan

Chlamydophila felis (C. felis), feline herpesvirus-1 (FHV-1) and feline calicivirus (FCV) were detected in 39 (59.1%), 11 (16.7%) and 14 (21.2%) cats respectively, from 66 domestic cats presented with conjunctivitis and upper respiratory tract disease (URTD) in 9 prefectures of Japan. Dual and multiple infections were found in 7 (10.6%) cats with both C. felis and FHV-1, 10 (15.2%) cats with both C. felis and FCV, and 1 (1.5%) cat with all three agents. C. felis was isolated from 11 (28.2%) of 39 PCR positive cats. Antigenic difference was found in a 96 kDa protein of our isolates and Fe/145 strain isolated in USA. In conclusion, C. felis is the most common agent of feline conjunctivitis and URTD, and the coinfection with C. felis, FHV-1 and FCV are also common in cats in Japan.     

Development and evaluation of a PCR assay for the detection of Cytauxzoon felis DNA in feline blood samples

Cytauxzoonosis is an emerging tick borne infectious disease of domestic cats in the United States, caused by the organism Cytauxzoon felis (C. felis). In naturally infected domestic cats the disease is almost always fatal. Currently there are no commercially available molecular or serologic tests to facilitate the antemortem diagnosis of C. felis infection. Clinical and pathological diagnosis of cytauxzoonosis is based on microscopic identification of parasites in tissues or on blood smears. We have developed and evaluated the sensitivity and specificity of a polymerase chain reaction (PCR) based assay for the diagnosis of C. felis infections in feline blood samples. The assay is sensitive enough to detect one copy of a cloned fragment of the C. felis 18S rRNA gene. This PCR assay can be used for the rapid clinical diagnosis of cytauxzoonosis and for epidemiological studies that will better define the geographic distribution of C. felis infection in cats.     

Evaluation of experimental transmission of Candidatus Mycoplasma haemominutum and Mycoplasma haemofelis by Ctenocephalides felis to cats

OBJECTIVE: To determine whether Ctenocephalides felis can transmit Mycoplasma haemofelis (Mhf) and Candidatus Mycoplasma haemominutum (Mhm) through hematophagous activity between cats. ANIMALS: 11 cats. PROCEDURE: 2 cats were carriers of either Mhf or Mhm. Nine cats had negative results via polymerase chain reaction (PCR) assay for Mhf and Mhm DNA; 3 of those cats were infected from the chronic carriers via i.v. inoculation of blood. At the time of maximum organism count for each of the Mycoplasma spp, 1 chamber containing 100 C felis was bandaged to the amplifier cats. Five days later, fleas, feces, larvae, or eggs from each chamber were analyzed for Mycoplasma spp DNA. Viable fleas from the chambers were allocated into new chambers (3 Mhm and 6 Mhf) and attached to na?ve cats for 5 days. Cats were monitored daily for clinical signs and weekly via CBC and PCR assay for infection with Mhf or Mhm for a minimum of 8 weeks. RESULTS: Uptake of Mhf and Mhm DNA into fleas, feces, and, potentially, eggs and larvae was detected. Of the na?ve cats fed on by Mhf-infected fleas, 1 cat transiently yielded positive PCR assay results for Mhf on 1 sampling date without clinical or hematologic changes consistent with Mhf infection. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that hematophagous transfer of Mhm and Mhf into fleas occurred and that C felis is a possible vector for Mhf via hematophagous activity.     

Use of a polymerase chain reaction assay to detect and differentiate two strains of Haemobartonella felis in naturally infected cats

OBJECTIVE: To develop a polymerase chain reaction (PCR) assay that detects and differentiates the Ohio strain of Haemobartonella felis (H. felis-OH) and the California strain of H. felis (H. felis-CA) and to apply the assay to blood samples from cats with and without suspected haemobartonellosis (suspect and control cats, respectively). SAMPLE POPULATION: 220 blood samples were examined; 82 were from suspect cats, and 138 were from control cats. PROCEDURE: A PCR assay was designed to detect and differentiate H. felis-OH and H. felis-CA. RESULTS: On the basis of PCR assay results, the overall prevalence of H. felis infection was 19.5% (43/220). Suspect cats (28.0%; 23/82) were significantly more likely than control cats (14.5%; 20/138) to be H. felis infected. Significantly greater numbers of suspect cats were H. felis-OH infected (12.2%, 9/82) or H. felis-OH and H. felis-CA infected (4.9%, 4/82) than control cats (0% [0/138] and 0.7% [1/138], respectively). Significantly more anemic cats were H. felis-OH infected (14.3%; 4/28) or H. felis-OH and H. felis-CA infected (7.1%; 2/28) than nonanemic cats (2.3% [3/128] and 0.8% [1/128], respectively). The PCR assay was more accurate than cytologic examination for detection of H. felis. CONCLUSIONS AND CLINICAL RELEVANCE: Haemobartonella felis infections are more common in cats than previously recognized. Haemobartonella felis-OH is apparently more pathogenic than H. felis-CA. The PCR assay is more accurate than cytologic examination for detection of H. felis infection and is an effective clinical tool for the detection and differentiation of both H. felis strains known to infect cats.     

Blood smear from a pregnant cat that died shortly after partial abortion

A 1-year-old, 5- to 6-week pregnant cat was presented with a history of aborting 3 kittens the previous night. During the examination, the cat began to seizure and died. At necropsy, formalin-fixed tissues and blood smears prepared from an EDTA blood sample collected via cardiac puncture were submitted to a diagnostic laboratory. Examination of the blood smears revealed numerous large (15-75 microm) clumped macrophages containing dark blue intracytoplasmic organisms consistent with Cytauxzoon merozoites. Scattered erythrophagocytic macrophages were also observed. Within several erythrocytes, 1-2 small, round, ring-like piroplasms consistent with Cytauxzoon were observed. Histologic examination revealed numerous large, schizont-laden macrophages filling the blood vessels of multiple organs. The cytologic and histologic findings were diagnostic for Cytaxuzoon felis infection. This case was of particular interest because of the unusually large number of organism-laden macrophages in the cardiac blood sample, an uncommon finding in peripheral blood. Although the cat was presented for complications of abortion, it remains uncertain whether C felis organisms crossed the placenta and infected the fetuses or lead to the abortions.     

Cytauxzoon felis infections are present in bobcats (Lynx rufus) in a region where cytauxzoonosis is not recognized in domestic cats

This study was performed to determine the prevalence of Cytauxzoon felis (C. felis) infections in bobcats (Lynx rufus) from a region where C. felis is recognized in domestic cats, North Carolina (NC), and a region where C. felis is not recognized in domestic cats, Pennsylvania (PA). Samples from NC (n=32) were obtained post-mortem via cardiac puncture from legally trapped bobcats. Samples from PA (n=70) were collected post-mortem onto Nobuto blood collecting strips by the PA Game Commission. Each sample was tested using a C. felis specific PCR assay as well as a PCR assay targeting host DNA to rule out the presence of PCR inhibitors. Three samples were excluded due to the presence of PCR inhibitors. Thirty-three percent (10/30) of the samples from NC and 7% (5/69) of the samples from PA tested positive for the presence of C. felis. The proportion of C. felis positive bobcats from NC was significantly different than that from PA (P<0.005). Despite the lower prevalence of C. felis infections in bobcats from PA this finding is unique and indicates the potential for C. felis infections in domestic cats in the northeastern USA if the appropriate tick vectors are present. Veterinary practitioners in PA should be on alert for cytauxzoonosis in domestic cats. Further studies about the epidemiology and transmission of C. felis infections among both domestic cats and bobcats are needed.     

Experimental transmission of Cytauxzoon felis from bobcats (Lynx rufus) to domestic cats (Felis domesticus)

Freshly collected blood and/or spleen homogenate from an experimentally infected Florida bobcat (Lynx rufus floridanus), which had died of feline cytauxzoonosis, was inoculated into domestic cats. All inoculated cats had clinical signs of feline cytauxzoonosis and died within 2 weeks after they were inoculated. Similar material collected from an eastern bobcat (Lynx rufus rufus) carrying an experimentally infected Cytauxzoon felis parasitemia was inoculated into domestic cats. All inoculated cats developed a parasitemia, but none developed clinical signs of disease and none died of the disease. Cats subinoculated with parasitemic cat blood also developed parasitemias and they too did not develop clinical signs of infection nor died. After carrying the blood phase of Cytauxzoon felis for various periods, the domestic cats were then challenge exposed with proven lethal Cytauxzoon inoculum of domestic cat origin. All cats died of cytauxzoonosis.     

Prevalence of ectoparasites in a population of feral cats from north central Florida during the summer

Ectoparasites are a common and important cause of skin disorders in cats. Ectoparasites are capable of disease transmission and can cause life-threatening anemia in young or debilitated animals. The objective of this study was to determine the potential feline ectoparasites in domestic cats by using a cohort of feral cats from north central Florida that have not received veterinary care and have no known exposure to insecticide application. A total of 200 feral cats were randomly selected for this study. Four monthly sessions were scheduled for feral cat ectoparasite examination and sample collection. Five minutes flea combing revealed that 185/200 (92.5%) of the cats were infested with fleas. The cat flea, Ctenocephalides felis was the most common flea infesting 92.5% feral cats (mean = 13.6; standard deviation +/- 16.4 fleas per cat). Pulex simulans was identified on 9/200 (4.5%) (mean = 1 +/- 0.50 fleas per cat). Echidnophaga gallinacea was found on 11/200 (5.5%) of cats (mean = 14.8 +/- 9.63 fleas per cat). There was a significant difference (P = 0.0005) in the average number of C. felis counted per cat between months. Mean counts in June (18.3 +/- 2.4) and July (16.6 +/- 2.1) were significantly (P < 0.01) higher than in August (8.4 +/- 2.5) and September (7.7 +/- 2.0). Only 15/200 cats had skin disease. Flea infestation may potentially be the underlying cause in 10/15. Otoscopic examination of both ears revealed mite movement and black ceruminous exudate typically indicative of the presence of Otodectes cynotis in 45/200 (22.5%) cats. Examination of a swab specimen from both ear canals of all cats revealed O. cynotis in 74/200 (37%) cats. Of 74 cats positive on ear swab, 8 (10.8%) showed a normal ear canal appearance (no or mild ceruminous exudate) in both ears upon otoscopic examination. A total of nine ticks were recovered from five cats. The number and species of ticks recovered were: one adult female Rhipicephalus sanguineus; one adult female Amblyomma americanum; one adult male A. americanum; five adult female Dermacentor variabilis; and one adult female Ixodes scapularis. All superficial skin scrapes were negative. Hair clippings from the abdomen of all cats revealed 2/200 (1%) of the cats were infested with Felicola subrostratus.     

Cytauxzoon felis infection in cats in the mid-Atlantic states: 34 cases (1998-2004)

OBJECTIVE: To describe the demographic and clinical characteristics of feline cytauxzoonosis in the mid-Atlantic states and compare the Cytauxzoon felis 18S rRNA gene sequences from affected cats with sequences reported from affected cats in other regions. DESIGN: Retrospective case series. ANIMALS: 34 cats with C. felis infection. PROCEDURE: Medical records of cats in which C. felis infection was diagnosed from May 1998 through June 2004 were reviewed; data collected included signalment, month of diagnosis, geographic location, clinicopathologic abnormalities, medical treatments, outcome, and necropsy findings when applicable. Cytauxzoon felis DNA was amplified, cloned, and sequenced from 4 of these cats and compared with previously reported C. felis DNA sequences. RESULTS: Of 34 C. felis-infected cats, 28 resided in North Carolina, 3 resided in South Carolina, and 3 resided in Virginia; in 32 cats, a diagnosis of C. felis infection was made in April through September. Pancytopenia and icterus were the most common clinicopathologic abnormalities. Thirty-two cats either died or were euthanatized, and 2 cats survived. At 5 veterinary hospitals, multiple cases were identified, and 4 multicat households had > 1 cat infected with C. felis. The 18S rRNA gene sequences characterized in organisms obtained from 4 cats were nearly identical to C. felis DNA sequences reported from other US regions. CONCLUSIONS AND CLINICAL RELEVANCE: Data indicate that veterinarians in the mid-Atlantic region of the United States should consider C. felis infection in cats that become ill with fever, icterus, and pancytopenia or bicytopenia, especially in the spring and summer months.     

Evaluation of different sampling methods and results of real-time PCR for detection of feline herpes virus-1, Chlamydophila felis and Mycoplasma felis in cats

Objective To investigate how different sampling techniques affect detection of DNA from feline herpes virus Type 1 (FHV-1), Chlamydophila felis and Mycoplasma felis and to study the correlation between positive test results and clinical signs in cats. Animals Fifty-one cats; 24 with ocular signs and 27 healthy control cats. Procedures Samples were collected from all cats using cotton swabs, conjunctival and corneal biopsies, and corneal scrapings. Samples were analyzed for presence of FHV-1, C. felis, M. felis, and feline DNA, defined by 28S rDNA, by using real-time PCR. Results In affected cats, FHV-1 was detected in only one cat; C. felis and M. felis were not detected in any affected cats. None of the three organisms was detected in any control cats. Feline DNA was demonstrated in all conjunctival samples, in 82% of corneal swabs, 92% of corneal scrapings, and 100% of keratectomy samples. Conclusions Because of the generally low detection rate for FHV-1, C. felis, and M. felis DNA in this study, differences regarding sampling technique could not be determined and correlation between positive test results and degree of clinical signs could not be made. Detection of feline DNA in most samples irrespective of sampling technique, suggests a low prevalence of FHV-1, C. felis and M. felis in this population of cats.     

Cytauxzoonosis in domestic cats: report of two cases in Oklahoma, with a review and discussion of the disease

In 2 cases of cytauxzoonosis in domestic cats in Oklahoma, the clinical features, gross lesions, and microscopic findings were of similar nature and degree to those previously reported by others, both in the naturally occurring and experimentally induced disease. Intraerythrocytic forms of Cytauxzoon felis organisms were demonstrated in stained blood smears from one cat. Blood from the other cat was not examined. The diagnosis was established by the finding of schizonts in endothelial-associated macrophages within vascular channels in tissues from both cats.     

Comparison of the activity of selamectin, imidacloprid and fipronil for the treatment of cats infested experimentally with Ctenocephalides felis felis and Ctenocephalides felis strongylus

Twenty adult, domestic short hair cats were randomly allocated into four groups of five cats and housed in separated cages. Each cat was infested with 25 fleas Ctenocephalides felis felis and 25 Ctenocephalides felis strongylus and 2 days later (day 0) the cats in group 1, 2 and 3 received a spot on application of selamectin, imidacloprid or fipronil, respectively, while the cats in group four were not treated. The cats were combed 48 h later, the fleas were removed, counted and their subspecies were determined. All the cats were reinfested with the same number of the two subspecies of fleas on days 7, 14, 21, 29 and 35. The efficacy of each treatment was calculated 48 h after each infestation. The mean number of fleas on the control cats was 16.4 C. f. felis and 13.4 C. f. strongylus. The three treatments were effective for the first 31 days for C. f. felis and for the full 37 days for C. f. strongylus. Over the first 31 days, the efficacy of selamectin ranged from 89 to 100% and 85 to 100% against C. f. felis and C. f. strongylus, respectively, the efficacy of imidacloprid ranged from 76 to 100% and 92 to 100% and the efficacy of fipronil ranged from 98 to 100% and 97 to 100% against C. f. felis and C. f. strongylus. There were no significant differences between the control of C. f. felis and C. f. strongylus by the three products.     

Efficacy of pradofloxacin in cats with feline upper respiratory tract disease due to Chlamydophila felis or Mycoplasma infections

BACKGROUND: Upper respiratory tract disease (URTD) of cats is caused by a number of pathogens, including Chlamydophila felis and Mycoplasma spp. For effective treatment of both infections, doxycycline and enrofloxacin are recommended, but adverse effects limit their use in cats. HYPOTHESIS: That the fluoroquinolone pradofloxacin is effective against C. felis and Mycoplasma infection in cats with URTD or conjunctivitis. ANIMALS: Thirty-nine cats with signs of URTD or conjunctivitis. METHODS: Placebo-controlled, double-blind clinical trial. Cats were randomly entered into 1 of 2 treatment groups: treated PO with either 5 mg/kg pradofloxacin q24h or 5 mg/kg doxycycline q12h for 42 consecutive days. Changes in health status and clinical scores were evaluated. The presence of C. felis and Mycoplasma spp. was determined by quantitative polymerase chain reaction (PCR) and nested PCR of conjunctival swabs, respectively. RESULTS: At the beginning of the study, C. felis and Mycoplasma spp. were detected in 23 and 20 cats, respectively. Cats of both groups responded rapidly with a marked improvement in clinical signs within the 1st week. During treatment with either drug, C. felis DNA copy number declined quickly. Complete elimination of Mycoplasma spp. was achieved in both groups; however, whereas all cats receiving doxycycline eliminated C. felis, 4 cats treated with pradofloxacin remained PCR-positive. CONCLUSION AND CLINICAL IMPORTANCE: This study demonstrates that both pradofloxacin and doxycycline have good efficacy against C. felis and Mycoplasma spp., resulting in a marked improvement of clinical signs. However, C. felis DNA remained in some cats after treatment with pradofloxacin, suggesting that infection might not have been eliminated.