Feline panleukopenia virus (FPV) infection leads to severe leukopenia and gastrointestinal signs in cats, with mortality rate of up to 70%. Besides supportive therapy, information regarding specific treatments is yet very limited in affected cats. Class A CpG oligodeoxynucleotides (CpG-A) are short single-stranded DNA molecules containing unmethylated cytosine-phosphate-guanosine motifs that stimulate production of type I interferons. Studies in cats showed the ability of CpG-A to induce an antiviral state in vivo and to inhibit replication of FPV in vitro. Therefore, aims of this study were to investigate the effects of CpG-A on survival and clinical score, white blood cell (WBC), red blood cell (RBC) and platelet counts, as well as viremia and fecal viral shedding in cats naturally infected with FPV. Cats with positive fecal parvovirus antigen test were prospectively enrolled if presenting clinical or laboratory signs of FPV, had body weight >500 gr, were unvaccinated and not previously treated. Cats were randomly allocated to receive 100 µg/kg of CpG-A or placebo subcutaneously, at admission and after 48 hours; all cases were treated with supportive therapy. A clinical score derived from attitude, appetite, vomiting, diarrhea and temperature was assigned daily until death or during 7 days. Blood and fecal samples were collected at admission and at 1, 2, 7 days; complete blood counts were obtained and real-time PCR was performed to quantify FPV DNA in blood and fecal samples. Chi-square test and mixed ANOVA were used to compare treatment groups. Forty-two cats were included: 22 received CpG-A and 20 placebo. Survival rate did not differ between cats treated with CpG-A and placebo [11 of 22 (50%) vs. 8 of 20 (40%), respectively; p=0.516]. Differences between groups were not observed for clinical score, RBC, platelets, viremia and fecal viral shedding at any time point. Mean WBC count was higher in cats treated with CpG-A than with placebo at 7 days (25800±13800/µl vs. 14900±8400/µl, respectively; p=0.017) but not at the other time points. All cats showed discomfort during CpG-A injections.

In conclusion, treatment with CpG-A did not improve survival or clinical score and did not reduce viral shedding, suggesting that the drug or the treatment regimen used in this study is not beneficial in cats affected with FPV. The lack of favorable response to CpG-A might be due to the delayed improvement of WBC counts. Of note, the administration of CpG-A may be painful in cats.

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