Epidemiology and molecular characterization of Feline panleukopenia virus from suspected domestic cats in selected Bangladesh regions

Feline Panleukopenia Virus ZZ202303 Strain: Molecular Characterization and Structural Implications of the VP2 Gene Phylogenetic Divergence

Feline panleukopenia virus (FPV), the etiological agent of a highly contagious multispecies disease, demonstrates concerning phylogenetic divergence that compromises vaccine cross-protection. This study aimed to characterize a novel FPV strain through integrated virological and molecular analyses to assess epidemiological implications. From seven clinical specimens obtained from feline hosts with panleukopenia in Henan Province, China, we isolated FPV ZZ202303 using an F81 cell culture coupled with PCR verification, demonstrating potent cytopathic effects (TCID50: 10-5.72/0.1 mL) and rapid replication kinetics (viral peak at 12-24 h post-infection). Comparative virulence assessments revealed a 1.8- to 2.3-fold greater pathogenicity versus contemporary field strains (2021-2023). Phylogenetic reconstruction based on complete VP2 gene sequences positioned FPV ZZ202303 within an emerging clade sharing 97.5-98.2% identity with canine parvovirus strains versus 98.8-99.7% with FPV references, forming a distinct cluster (bootstrap = 94%) diverging from vaccine lineages. Critical structural analysis identified a prevalent I101T mutation (89.13% prevalence) in the VP2 capsid protein's antigenic determinant region, with molecular modeling predicting altered surface charge distribution potentially affecting host receptor binding. Our findings substantiate FPV ZZ202303 as an evolutionarily divergent strain exhibiting enhanced virulence and unique genetic signatures that may underlie vaccine evasion mechanisms, providing critical data for updating prophylactic strategies against this economically impactful pathogen.

Development and utilization of a multiplex PCR assay for detecting three feline enteroviruses

BACKGROUND

Feline diarrhea is a common digestive tract disease in clinical practice, with watery feces as the main clinical manifestation. There are numerous pathogenic factors causing feline diarrhea, among which viral infections are prevalent, and feline panleukopenia virus (FPV) is the most common pathogen. In recent years, a variety of novel viruses have been detected in the intestines of cats with diarrhea. For example, feline kobuvirus (FKoV) and feline norovirus (FNoV) have been identified. These viruses may have a direct relationship with feline diarrhea or the connection has yet to be discovered. However, with the continuous emergence of these novel viruses and the frequent contact between pet cats and humans, it is prone to large-scale epidemics and outbreaks of viruses. Therefore, developing an accurate, rapid, and simple method to detect novel enteric viruses is of great significance for the early warning of emerging feline enteric viral infectious diseases.

METHODS AND RESULTS

A detailed comparison of the genome sequences of the three aforementioned feline enteroviruses was conducted. Subsequently, three pairs of specific primers were designed by selecting the conserved gene regions, and the single and multiplex PCR amplification reaction systems as well as reaction conditions were repeatedly optimized. The target fragment sizes detected by the multiplex PCR method were 650 bp for FPV, 500 bp for FKoV, and 340 bp for FNoV. Sensitivity tests demonstrated that the lower detection limit was one-tenth of that of single PCR. Meanwhile, the detection results for feline calicivirus (FCV), feline herpesvirus (FHV), and feline coronavirus (FCoV) were all negative. Testing of a total of 209 clinical samples from various regions in Shandong Province revealed that the detection rates of the three viruses were 13.4%, 4.8%, and 3.8%, respectively, and mixed infections were present.

CONCLUSIONS

In this study, an epidemiological investigation of the three feline enteroviruses was performed, and a sensitive, specific, and reproducible multiplex PCR assay was developed, which can be utilized for the detection of clinical samples.

Epidemiology of canine ehrlichiosis and molecular characterization of Erhlichia canis in Bangladeshi pet dogs

BACKGROUND

Ehrlichia canis, a rickettsial organism, is responsible for causing ehrlichiosis, a tick-borne disease affecting dogs.

OBJECTIVES

This study aimed to estimate ehrlichiosis prevalence and identify associated risk factors in pet dogs.

METHODS

A total of 246 peripheral blood samples were purposively collected from pet dogs in Dhaka, Mymensingh, and Rajshahi districts between December 2018 and December 2020. Risk factor data were obtained through face-to-face interviews with dog owners using a pre-structured questionnaire. Multivariable logistic regression analysis identified risk factors. Polymerase chain reaction targeting the 16S rRNA gene confirmed Ehrlichia spp. PCR results were further validated by sequencing.

RESULTS

The prevalence and case fatality of ehrlichiosis were 6.9% and 47.1%, respectively. Dogs in rural areas had 5.8 times higher odds of ehrlichiosis (odd ratio, OR: 5.84; 95% CI: 1.72-19.89) compared to urban areas. Dogs with access to other dogs had 5.14 times higher odds of ehrlichiosis (OR: 5.14; 95% CI: 1.63-16.27) than those without such access. Similarly, irregularly treated dogs with ectoparasitic drugs had 4.01 times higher odds of ehrlichiosis (OR: 4.01; 95% CI: 1.17-14.14) compared to regularly treated dogs. The presence of ticks on dogs increased ehrlichiosis odds nearly by 3 times (OR: 3.02; 95% CI: 1.02-8.97). Phylogenetic analysis, based on 17 commercially sequenced isolates, showed different clusters of aggregation, however, BAUMAH-13 (PP321265) perfectly settled with a China isolate (OK667945), similarly, BAUMAH-05 (PP321257) with Greece isolate (MN922610), BAUMAH-16 (PP321268) with Italian isolate (KX180945), and BAUMAH-07 (PP321259) with Thailand isolate (OP164610).

CONCLUSIONS

Pet owners and veterinarians in rural areas should be vigilant in monitoring dogs for ticks and ensuring proper preventive care. Limiting access to other dogs in high-risk areas can help mitigate disease spread. Tick prevention measures and regular treatment with ectoparasitic drugs will reduce the risk of ehrlichiosis in dogs. The observed genetic similarity of the Bangladeshi Ehrlichia canis strain highlights the need for ongoing surveillance and research to develop effective control and prevention strategies, both within Bangladesh and globally.

Development and Application of an RPA-Based Rapid Point-of-Care Testing (POCT) Method for the Detection of Feline Panleukopenia Virus

Feline panleukopenia (FP) is a highly prevalent and consequential disease that poses a substantial threat to both adult and juvenile cats across all geographical regions. The causative agent responsible for this disease is the feline panleukopenia virus (FPV). Therefore, it is imperative to develop a facile, efficient, and accurate detection method for FPV. Hence, a recombinase polymerase amplification-lateral flow dipstick assay (RPA-LFDA) method was specifically designed for the detection of FPV. The amplification process was optimized. This investigation focused on evaluating the expansion temperature detection system and revealed an optimal reaction temperature of 39°C. Then, primer combination screening involving nine groups identified F3R2 as the most effective primer set, while dilution ratio experiments determined that a 10-fold dilution yielded the best amplification products. Our findings demonstrated that the RPA-LFDA assay had an analytical sensitivity that was capable of detecting as low as 10 target copies per reaction. Furthermore, cross-reactivity tests demonstrated no interference between feline herpesvirus-1 (FHV-1) and feline calicivirus (FCV). To validate our newly developed method against existing techniques in clinical samples from three common sources on the market, we observed superior sensitivity and specificity compared to those of the colloidal gold method (CGM), with a higher positive detection rate using our nucleic acid detection system than CGM. Compared to qPCR as a reference standard, RPA-LFDA detected 39 out of 44 positive samples (including one false positive), whereas CGM detected 26 out of 44 positive samples. Based on the RPA-LFDA, the sensitivity was calculated to be 100%, the specificity was 83.33%, the mistake diagnostic rate was 16.67%, the omission diagnostic rate was 0%, and the overall accuracy reached 97.73%. Moreover, the positive coincidence rate was 97.44%, while the negative coincidence rate reached 100%. The agreement κ value was 0.8962. In conclusion, this approach exhibits greater sensitivity than CGM and offers greater convenience and cost-effectiveness than the qPCR methodology, making it a viable option for the clinical detection of FPV.

One-step triplex TaqMan quantitative reverse transcription polymerase chain reaction for the detection of feline coronavirus, feline panleukopenia virus, and feline leukemia virus

Background and Aim

Feline coronavirus (FCoV), feline panleukopenia virus (FPV), and feline leukemia virus (FeLV) are prevalent throughout China and significantly threaten cat health. These viruses cause similar manifestations and pathological damage. Rapid and accurate diagnosis depends on detection in the laboratory. This study aimed to establish a reliable and rapid method for accurate detection of FCoV, FPV, and FeLV so that a definite diagnosis can be made and effective measures can be taken to prevent and control viral infection.

Materials and Methods

We designed three pairs of specific primers and probes for the detection of FCoV 5' untranslated region, FPV viral protein 2, and FeLV pol genes. Recombinant plasmid constructs were generated for use as standard plasmid constructs. Optimal reaction conditions, including primer and probe concentrations, reaction cycles, and annealing temperatures, were obtained on the basis of optimization tests. One-step triplex real-time reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was successfully established to simultaneously detect FCoV, FPV, and FeLV. The specificity, sensitivity, and repeatability of the assay were analyzed, and its applicability was validated by testing 1175 clinical samples.

Results

One-step triplex RT-qPCR had a high degree of specificity only for the detection of FCoV, FPV, and FeLV; it had high sensitivity with limits of detection of 139.904, 143.099, and 152.079 copies/reaction for p-FCoV, p-FPV, and p-FeLV standard plasmid constructs, respectively, and it had reliable repeatability with 0.06%-0.87% intra-assay coefficients of variations. A total of 1175 clinical samples were examined for FCoV, FPV, and FeLV using triplex RT-qPCR, and the FCoV, FPV, and FeLV positivity rates were 18.47%, 19.91%, and 47.57%, respectively. The clinical sensitivity and specificity of one-step triplex RT-qPCR were 93.07% and 97.99%, respectively.

Conclusion

We developed a rapid and reliable one-step triplex RT-qPCR method for the detection of FCoV, FPV, and FeLV, which could be used as a diagnostic tool for clinical monitoring and diagnosis.

A potential dual protection vaccine: Recombinant feline herpesvirus-1 expressing feline parvovirus VP2 antigen

Recently, herpesvirus viral vectors that stimulate strong humoral and cellular immunity have been demonstrated to be the most promising platforms for the development of multivalent vaccines, because they contain various nonessential genes and exhibit long-life latency characteristics. Previously, we showed that the feline herpesvirus-1 (FHV-1) mutant WH2020-ΔTK/gI/gE, which was safe for felines and provided efficacious protection against FHV-1 challenge, can be used as a vaccine vector. Moreover, previous studies have shown that the major neutralizing epitope VP2 protein of feline parvovirus (FPV) can elicit high levels of neutralizing antibodies. Therefore, to develop a bivalent vaccine against FPV and FHV-1, we first generated a novel recombinant virus by CRISPR/Cas9-mediated homologous recombination, WH2020-ΔTK/gI/gE-VP2, which expresses the VP2 protein of FPV. The growth characteristics of WH2020-ΔTK/gI/gE-VP2 were similar to those of WH2020-ΔTK/gI/gE, and WH2020-ΔTK/gI/gE-VP2 was stable for at least 30 generations in CRFK cells. As expected, we found that the felines immunized with WH2020-ΔTK/gI/gE-VP2 produced FPV-neutralizing antibody titers (27.5) above the positive cutoff (26) on day 14 after single inoculation. More importantly, recombinant WH2020-ΔTK/gI/gE-VP2 exhibited severely impaired pathogenicity in inoculated and cohabiting cats. The kittens immunized with WH2020-ΔTK/gI/gE and WH2020-ΔTK/gI/gE-VP2 produced similar levels of FHV-specific antibodies and IFN-β. Furthermore, felines immunized with WH2020-ΔTK/gI/gE-VP2 were protected against challenge with FPV and FHV-1. These data showed that WH2020-ΔTK/gI/gE-VP2 appears to be a potentially safe, effective, and economical bivalent vaccine against FPV and FHV-1 and that WH2020-ΔTK/gI/gE can be used as a viral vector to develop feline multivalent vaccines.