The Structures and Functions of Parvovirus Capsids and Missing Pieces: the Viral DNA and Its Packaging, Asymmetrical Features, Nonprotein Components, and Receptor or Antibody Binding and Interactions.

Parvoviruses are among the smallest and superficially simplest animal viruses, infecting a broad range of hosts, including humans, and causing some deadly infections. In 1990, the first atomic structure of the canine parvovirus (CPV) capsid revealed a 26-nm-diameter T=1 particle made up of two or three versions of a single protein, and packaging about 5,100 nucleotides of single-stranded DNA. Our structural and functional understanding of parvovirus capsids and their ligands has increased as imaging and molecular techniques have advanced, and capsid structures for most groups within the Parvoviridae family have now been determined. Despite those advances, significant questions remain unanswered about the functioning of those viral capsids and their roles in release, transmission, or cellular infection. In addition, the interactions of capsids with host receptors, antibodies, or other biological components are also still incompletely understood. The parvovirus capsid's apparent simplicity likely conceals important functions carried out by small, transient, or asymmetric structures. Here, we highlight some remaining open questions that may need to be answered to provide a more thorough understanding of how these viruses carry out their various functions. The many different members of the family Parvoviridae share a capsid architecture, and while many functions are likely similar, others may differ in detail. Many of those parvoviruses have not been experimentally examined in detail (or at all in some cases), so we, therefore, focus this minireview on the widely studied protoparvoviruses, as well as the most thoroughly investigated examples of adeno-associated viruses.

Antiviral alternatives against important members of the subfamily Parvovirinae: a review.

Parvoviruses are responsible for multiple diseases, and there is a critical need for effective antiviral therapies. Specific antiviral treatments for parvovirus infections are currently lacking, and the available options are mostly supportive and symptomatic. In recent years, significant research efforts have been directed toward understanding the molecular mechanisms of parvovirus replication and identifying potential targets for antiviral interventions. This review highlights the structure, pathogenesis, and treatment options for major viruses of the subfamily Parvovirinae, such as parvovirus B19 (B19V), canine parvovirus type 2 (CPV-2), and porcine parvovirus (PPV) and also describes different approaches in the development of antiviral alternatives against parvovirus, including drug repurposing, serendipity, and computational tools (molecular docking and artificial intelligence) in drug discovery. These advances greatly increase the likelihood of discoveries that will lead to potent antiviral strategies against different parvovirus infections.

Inhibition of canine parvovirus 2 (CPV-2) replication by TAT-scFv through targeting of the viral structural protein VP2 of CPV-2.

Canine parvovirus (CPV) causes severe infectious disease with a high mortality rate in dogs. CPV is still a major health issue of dogs in the clinic. Therefore, there is an urgent need to develop effective drugs to treat the disease. In this study, we fused the transactivating transcriptional activator peptide (TAT) with scFv. TAT-scFv was identified by Western blot. CCK8 kit was used to detect the toxicity of TAT-scFv to cells. The binding activity of TAT-scFv to CPV-2-VP2 was detected by DAS ELISA. The cell uptake rate of TAT-scFv was assessed by IFA. After infection with CPV-2, F81 cells were incubated by TAT-scFv. The replication of virus was measured to determine the neutralization effect of TAT-scFv on intracellular and extracellular viruses. Protein docking was used to predict the amino acid (AA) sites of VP2 binding to TAT-scFv. TAT-scFv was expressed in Escherichia coli and purified. The DAS ELISA showed that TAT-scFv could bind with CPV-2-VP2. We demonstrated that TAT-scFv entered cells in a dose-dependent and time-dependent manner and effectively inhibited the replication of CPV-2. Using protein docking, we determined the interaction pattern and found that the N-terminal region (AA 41-49) and the C-terminal region (AA 558) of VP2 interacted with the TAT-scFv. Taken together, these results suggest that, TAT-scFv may be a potential antiviral drug for inhibiting CPV-2 replication and controlling disease caused by CPV-2.

First isolation and molecular characterization of canine parvovirus-type 2b (CPV-2b) from red foxes (Vulpes vulpes) living in the wild habitat of Turkey.

BACKGROUND: The canine parvovirus, with its many variants, is responsible for a pivotal and common viral infection affecting millions of dogs and other carnivore species worldwide, particularly the wild ones, which are considered as the main reservoir hosts. To that end, this study investigated the presence of canine parvovirus (CPV) in red foxes (Vulpes vulpes) living in wild habitats of several regions of Turkey. METHODS: We randomly collected 630 archival fox stool specimens from rural areas of 22 provinces and used real-time PCR to detect CPV. RESULTS: Two of the 630 (0.3%) stool samples were positive for CPV-DNA, named Tr-Fox/128(Aydin) and Tr-Fox/159(Manisa). We attempted to isolate the virus in a MDCK cell line, and cytopathic effects were observed four days post-inoculation. Three regions corresponding to the CPV capsid protein VP2 gene from extracted DNA of positive samples were amplified by conventional PCR, and the products were visualised, purified, and Sanger sequenced. Three overlapping DNA raw sequence fragments, were read, assembled, and aligned to obtain approximately 1.5 kb-long regions that cover most of the VP2 gene, then deposited in GenBank. After comparing the isolates with parvovirus sequences data of domestic and wild carnivores by BLAST processing, our isolates' similarity rate with each other was 99.40%, with base differences in 9 nucleotide positions. They were classified as 2b variant closely related to isolates from dogs in Turkey, Egypt, Iraq, Italy, Thailand, and China. CONCLUSION: This study presents evidence of interspecies transmission of CPV, of which there are no reports on prevalence in wildlife carnivores of our country. Identification of CPV in red foxes threatens local and hunting dogs, which may contract the infection or disseminate it to other wild animal species or vice-versa.

Colloidal gold and fluorescent immunochromatographic test strips for canine parvovirus detection.

Canine parvovirus (CPV) is an acute and highly infectious virus causing disease in puppies and, thus, affecting the global dog industry. The current CPV detection methods are limited by their sensitivity and specificity. Hence, the current study sought to develop a rapid, sensitive, simple, and accurate immunochromatographic (ICS) test to detect and control the spread and prevalence of CPV infection. More specifically, 6A8, a monoclonal antibody (mAb) with high specificity and sensitivity, was obtained by preliminary screening. The 6A8 antibody was labelled with colloidal gold particles. Subsequently, 6A8 and goat anti-mouse antibodies were coated onto a nitrocellulose membrane (NC) as the test and control lines, respectively. Furthermore, 6A8 and rabbit IgG antibodies were labelled with fluorescent microspheres and evenly sprayed onto a glass fibre membrane. Both strips could be prepared in 15 min with no noticeable cross-reactivity with other common canine intestinal pathogens. The strips were simultaneously used to detect CPV in 60 clinical samples using real-time quantitative PCR, hemagglutination, and hemagglutination inhibition assays. The colloidal gold (fluorescent) ICS test strip was stable for 6 (7) and 4 (5) months at 4 °C and room temperature (18-25 °C). Both test strips were easy to prepare and rapidly detected CPV with high sensitivity and specificity. Moreover, the results were easily interpretable. This study establishes a simple method for two CPV diseases, colloidal gold and fluorescent immunochromatographic (ICS) test strips. KEY POINTS: • CPV test strips do not exhibit cross-reactivity with other canine intestinal pathogens. • The strips are stable for months at 4 °C and at room temperature (18-25 °C). • These strips are a promising approach for the timely diagnosis and treatment of CPV.

Spillover of Canine Parvovirus Type 2 to Pigs, South Dakota, USA, 2020.

In 1978, canine parvovirus type 2 originated from spillover of a feline panleukopenia-like virus, causing a worldwide pandemic of enteritis and myocarditis among canids. In 2020, the virus was identified in pigs in South Dakota, USA, by PCR, sequencing, in situ hybridization, and serology. Genetic analysis suggests spillover from wildlife.

The first evaluation of the effectiveness of canine vaccination schedule by two commercial vaccines in Iran.

BACKGROUND: Canine Parvovirus type 2 (CPV-2) is a member of the Parvoviridae family with a global distribution and causes pathogenicity in puppies aged from 6 weeks to 6 months. It should be noted that Maternally Derived Antibodies (MDA) have protection against CPV-2 in the first weeks of puppies' life. However, MDA declines with age. The most important influential factor is timely vaccination against CPV-2. METHODS: In this study, 24 healthy 8-week-old terrier puppies were selected and divided into three identical groups based on a randomized, double-blind comparative trial. One of which was called the control group that was injected with the physiological serum. The second group was the group A that was vaccinated by the vaccine provided by Biocan DHPPi+L (Bioveta, Czech). The third group was group B that was vaccinated by the vaccine of Duramune Max 5 + LCI / GP (Fort Dodge Animal Health, USA) from 8 to 16 weeks of their life at every 4 weeks. Then serum samples were analyzed with HI and ELISA tests. RESULTS: The MDA titer was protective in some puppies until 18 weeks of age. Also, after the first vaccination, all puppies had a protective titer against CPV-2, and Duramune vaccine had seroconverted after the first injection and Biocan had seroconverted after the second injection. CONCLUSIONS: It is recommended that to reduce the risk of vaccine failure: such as the MDA titer should be measured in puppies before designing a vaccination schedule.

Molecular characteristics and genetic evolutionary analyses of circulating parvoviruses derived from cats in Beijing.

BACKGROUND: Feline parvovirus (FPV) is a member of the family Parvoviridae, which is a major enteric pathogen of cats worldwide. This study aimed to investigate the prevalence of feline parvovirus in Beijing of China and analyze the genetic features of detected viruses. RESULTS: In this study, a total of 60 (8.5%) parvovirus-positive samples were detected from 702 cat fecal samples using parvovirus-specific PCR. The complete VP2 genes were amplified from all these samples. Among them, 55 (91.7%) sequences were characterized as FPV, and the other five (8.3%) were typed as canine parvovirus type 2 (CPV-2) variants, comprised of four CPV-2c and a new CPV-2b strain. In order to investigate the origin of CPV-2 variants in cats, we amplified full-length VP2 genes from seven fecal samples of dogs infected with CPV-2, which were further classified as CPV-2c. The sequences of new CPV-2b/MT270586 and CPV-2c/MT270587 detected from feline samples shared 100% identity with previous canine isolates KT156833 and MF467242 respectively, suggesting the CPV-2 variants circulating in cats might be derived from dogs. Sequence analysis indicated new mutations, Ala91Ser and Ser192Phe, in the FPV sequences, while obtained CPV-2c carried mutations reported in Asian CPV variants, showing they share a common evolutionary pattern with the Asian 2c strains. Interestingly, the FPV sequence (MT270571), displaying four CPV-specific residues, was found to be a putative recombinant sequence between CPV-2c and FPV. Phylogenetic analysis of the VP2 gene showed that amino acid and nucleotide mutations promoted the evolution of FPV and CPV lineages. CONCLUSIONS: Our findings will be helpful to further understand the circulation and evolution of feline and canine parvovirus in Beijing.

The Changes in Canine Parvovirus Variants over the Years.

Canine parvovirus (CPV-2) is one of the most important pathogens in dogs, and despite the continual development of vaccines against CPV-2, CPV-2 is still circulating in the canine population. The CPV-2a/2b/2c variant has replaced the original CPV-2 virus and seems to exhibit accelerated transmission. Although CPV-2 infection has been frequently reported, no studies have summarized information of CPV-2 variants currently circulating worldwide. To track the evolution of CPV-2, we downloaded and analyzed all VP2 sequences from the NCBI database (from 1978 to 2022). We found that CPV-2c shows a tendency to replace CPV-2a as the new dominant variant in Asia, South America, North America and Africa. Additionally, CPV-2c, which is prevalent in most regions of Asia, carries two special mutations in VP2, A5G and Q370R, and has become a dominant mutation with spillover already occurring. In conclusion, this summary of the types of global epidemic variants provides new insight into the evolution of CPV-2 and raises awareness for blocking the spread of this virus. The spread of Asian-derived CPV-2c urgently needs to be further under surveillance.

Canine Circovirus Suppresses the Type I Interferon Response and Protein Expression but Promotes CPV-2 Replication.

Canine circovirus (CanineCV) is an emerging virus in canines. Since the first strain of CanineCV was reported in 2012, CanineCV infection has shown a trend toward becoming a global epidemic. CanineCV infection often occurs with coinfection with other pathogens that may aggravate the symptoms of disease in affected dogs. Currently, CanineCV has not been successfully isolated by laboratories, resulting in a lack of clarity regarding its physicochemical properties, replication process, and pathogenic characteristics. To address this knowledge gap, the following results were obtained in this study. First, a CanineCV strain was rescued in F81 cells using infectious clone plasmids. Second, the Rep protein produced by the viral packaging rescue process was found to be associated with cytopathic effects. Additionally, the Rep protein and CanineCV inhibited the activation of the type I interferon (IFN-I) promoter, blocking subsequent expression of interferon-stimulated genes (ISGs). Furthermore, Rep was found to broadly inhibit host protein expression. We speculate that in CanineCV and canine parvovirus type 2 (CPV-2) coinfection cases, CanineCV promotes CPV-2 replication by inducing immunosuppression, which may increase the severity of clinical symptoms.

Generation and evaluation of IgY-scFv based mimetics against canine parvovirus.

Antibody mimetics may be used for various biomedical applications, especially those for which conventional antibodies are ineffective. In this study, we developed a smaller molecular chicken IgY mimetic peptide (IgY-peptide) based on the complementarity-determining regions (CDRs) of the anti-canine parvovirus (CPV) IgY-scFv prepared previously. The mimetic peptide showed no cross-reactivity with canine distemper virus (CDV) and canine coronavirus (CCV) and showed excellent protective properties for Crandell-Rees Feline Kidney (CRFK) cells against CPV. This study is the first attempt to develop a mimetic IgY-peptide and demonstrates the ease and feasibility in generating such a novel antibody-like functional molecule for biomedical purposes.

The detection of canine parvovirus type 2c of Asian origin in dogs in Romania evidenced its progressive worldwide diffusion.

BACKGROUND: Canine parvovirus (CPV) is one of the most important pathogens of dogs. Despite vaccination, CPV infections are still ubiquitous in dogs, and the three antigenic variants 2a, 2b and 2c are variously distributed in the canine population worldwide. To date, no information is available on CPV variants circulating in some European countries. The aim of this study was to genetically characterise the CPV detected in ten dogs with clinical signs of acute gastroenteritis in Romania. The presence of Carnivore protoparvovirus 1 DNA was investigated in faecal samples using an end-point PCR targeting the complete VP2 gene and positive amplicons were sequenced and analysed. RESULTS: All ten dogs with acute gastroenteritis tested positive to Carnivore protoparvovirus 1 DNA in faecal samples. The identified viruses belonged to CPV-2c type, showed identical sequences of the VP2 gene and were characterised by distinctive amino acid residues in the deduced VP2 protein: 5-glicine (5Gly), 267-tirosine (267Tyr), 324-isoleucine (324Ile) and 370-arginine (370Arg). These distinctive amino acid residues have already been reported in CPV-2c widespread in Asia and occasionally detected in Italy and Nigeria. CONCLUSIONS: Since CPV-2c with VP2 amino acid residues 5Gly, 267Tyr, 324Ile and 370Arg were never reported before 2013, it can be assumed that this virus is progressively expanding its spread in the world dog population. This study adds new data about the presence of this new virus in Europe and underline worrying questions about its potential impact on the health of the canine population.

Canine Parvovirus Infections in Taiwanese Pangolins (Manis pentadactyla pentadactyla).

Canine parvovirus type 2 (CPV-2) is among the most important and highly contagious pathogens that cause enteric or systemic infections in domestic and nondomestic carnivores. However, the spillover of CPV-2 to noncarnivores is rarely mentioned. Taiwanese pangolins (Manis pentadactyla pentadactyla) are threatened due to habitat fragmentation and prevalent animal trafficking. Interactions between Taiwanese pangolins, humans, and domestic animals have become more frequent in recent years. However, information about the susceptibility of pangolins to common infectious agents of domestic animals has been lacking. From October 2017 to June 2019, 4 pangolins that were rescued and treated in wildlife rescue centers in central and northern Taiwan presented with gastrointestinal signs. Gross and histopathological examination revealed the main pathologic changes to be necrotic enteritis with involvement of the crypts in all intestinal segments in 2 pangolins. By immunohistochemistry for CPV-2, there was positive labeling of cryptal epithelium throughout the intestine, and immunolabeling was also present in epidermal cells adjacent to a surgical amputation site, and in mononuclear cells in lymphoid tissue. The other 2 pangolins had mild enteritis without crypt involvement, and no immunolabeling was detected. The nucleic acid sequences of polymerase chain reaction (PCR) amplicons from these 4 pangolins were identical to a Chinese CPV-2c strain from domestic dogs. Quantitative PCR revealed a higher ratio of CPV-2 nucleic acid to internal control gene in the 2 pangolins with severe intestinal lesions and positive immunoreactivity. Herein, we present evidence of CPV-2 infections in pangolins.

Limited Intrahost Diversity and Background Evolution Accompany 40 Years of Canine Parvovirus Host Adaptation and Spread.

Canine parvovirus (CPV) is a highly successful pathogen that has sustained pandemic circulation in dogs for more than 40 years. Here, integrating full-genome and deep-sequencing analyses, structural information, and in vitro experimentation, we describe the macro- and microscale features that accompany CPV's evolutionary success. Despite 40 years of viral evolution, all CPV variants are more than ∼99% identical in nucleotide sequence, with only a limited number (<40) of substitutions becoming fixed or widespread during this time. Notably, most substitutions in the major capsid protein (VP2) gene are nonsynonymous, altering amino acid residues that fall within, or adjacent to, the overlapping receptor footprint or antigenic regions, suggesting that natural selection has channeled much of CPV evolution. Among the limited number of variable sites, CPV genomes exhibit complex patterns of variation that include parallel evolution, reversion, and recombination, compromising phylogenetic inference. At the intrahost level, deep sequencing of viral DNA in original clinical samples from dogs and other host species sampled between 1978 and 2018 revealed few subconsensus single nucleotide variants (SNVs) above ∼0.5%, and experimental passages demonstrate that substantial preexisting genetic variation is not necessarily required for rapid host receptor-driven adaptation. Together, these findings suggest that although CPV is capable of rapid host adaptation, a relatively low mutation rate, pleiotropy, and/or a lack of selective challenges since its initial emergence have inhibited the long-term accumulation of genetic diversity. Hence, continuously high levels of inter- and intrahost diversity are not necessarily required for virus host adaptation.IMPORTANCE Rapid mutation rates and correspondingly high levels of intra- and interhost diversity are often cited as key features of viruses with the capacity for emergence and sustained transmission in a new host species. However, most of this information comes from studies of RNA viruses, with relatively little known about evolutionary processes in viruses with single-stranded DNA (ssDNA) genomes. Here, we provide a unique model of virus evolution, integrating both long-term global-scale and short-term intrahost evolutionary processes of an ssDNA virus that emerged to cause a pandemic in a new host animal. Our analysis reveals that successful host jumping and sustained transmission does not necessarily depend on a high level of intrahost diversity nor result in the continued accumulation of high levels of long-term evolution change. These findings indicate that all aspects of the biology and ecology of a virus are relevant when considering their adaptability.

Development of a monoclonal antibody against canine parvovirus NS1 protein and investigation of NS1 dynamics and localization in CPV-infected cells.

Canine parvovirus (CPV) non-structural protein-1 (NS1) plays crucial roles in CPV replication and transcription, as well as pathogenic effects to the host. However, the mechanism was not fully understood. Lack of NS1 antibody is one of the restricting factors for NS1 function investigation. To prepare NS1 monoclonal antibody (mAb), the NS1 epitope (AA461 ~ AA650) gene was amplified by PCR, and inserted into pGEX-4T-1vector to construct the prokaryotic expression vector of GST-tag-fused NS1 epitope gene. The NS1 fusion protein was expressed in E. coli, and purified with GSH-magnetic beads, and then used to immunize BALB/c mice. The mouse splenic lymphocytes were isolated and fused with myeloma cells (SP 2/0) to generate hybridoma cells. After several rounds of screening by ELISA, a hybridoma cell clone (1B8) stably expressing NS1 mAb was developed. A large amount of NS1 mAb was prepared from mouse ascites fluid. The isotype of NS1 mAb was identified as IgG1, which can specifically bind NS1 protein in either CPV-infected cells or NS1 vector-transfected cells, indicating the NS1 mAb is effective in detecting NS1 protein. Meanwhile, we used the NS1 mAb to investigate NS1 dynamic changes by qRT-PCR and location by confocal imaging in CPV-infected host cells and showed that NS1 began to appear in the cells at 12 h after CPV infection and reached the highest level at 42 h, NS1 protein was mainly located in nucleus of the cells. This study provided a necessary condition for further investigation on molecular mechanism of NS1 function and pathogenicity.

Canine parvovirus: a predicting canine model for sepsis.

BACKGROUND: Sepsis is a severe condition associated with high prevalence and mortality rates. Parvovirus enteritis is a predisposing factor for sepsis, as it promotes intestinal bacterial translocation and severe immunosuppression. This makes dogs infected by parvovirus a suitable study population as far as sepsis is concerned. The main objective of the present study was to evaluate the differences between two sets of SIRS (Systemic Inflammatory Response Syndrome) criteria in outcome prediction: SIRS 1991 and SIRS 2001. The possibility of stratifying and classifying septic dogs was assessed using a proposed animal adapted PIRO (Predisposition, Infection, Response and Organ dysfunction) scoring system. RESULTS: The 72 dogs enrolled in this study were scored for each of the PIRO elements, except for Infection, as all were considered to have the same infection score, and subjected to two sets of SIRS criteria, in order to measure their correlation with the outcome. Concerning SIRS criteria, it was found that the proposed alterations on SIRS 2001 (capillary refill time or mucous membrane colour alteration) were significantly associated with the outcome (OR = 4.09, p < 0.05), contrasting with the 1991 SIRS criteria (p = 0.352) that did not correlate with the outcome. No significant statistical association was found between Predisposition (p = 1), Response (p = 0.1135), Organ dysfunction (p = 0.1135), total PIRO score (p = 0.093) and outcome. To explore the possibility of using the SIRS criteria as a fast decision-making tool, a Fast-and-Frugal tree (FFT) was created with a sensitivity of 92% and a specificity of 29%. CONCLUSION: These results suggest that increasing the SIRS criteria specificity may improve their prognostic value and their clinical usefulness. In order to improve the proposed PIRO scoring system outcome prediction ability, more specific criteria should be added, mainly inflammatory and organ dysfunction biomarkers.

Study of the immunogenicity of the VP2 protein of canine parvovirus produced using an improved Baculovirus expression system.

BACKGROUND: Canine parvovirus (CPV) is now recognized as a serious threat to the dog breeding industry worldwide. Currently used CPV vaccines all have their specific drawbacks, prompting a search for alternative safe and effective vaccination strategies such as subunit vaccine. VP2 protein is the major antigen targeted for developing CPV subunit vaccine, however, its production in baculovirus expression system remains challenging due to the insufficient yield. Therefore, our study aims to increase the VP2 protein production by using an improved baculovirus expression system and to evaluate the immunogenicity of the purified VP2 protein in mice. RESULTS: The results showed that high-level expression of the full length VP2 protein was achieved using our modified baculovirus expression system. The recombinant virus carrying two copies of VP2 gene showed the highest expression level, with a productivity of 186 mg/L, which is about 1.4-1.6 fold that of the recombinant viruses carrying only one copy. The purified protein reacted with Mouse anti-His tag monoclonal antibody and Rabbit anti-VP2 polyclonal antibody. BALB/c mice were intramuscularly immunized with purified VP2 protein twice at 2 week intervals. After vaccination, VP2 protein could induce the mice produce high level of hemagglutination inhibition antibodies. CONCLUSIONS: Full length CPV VP2 protein was expressed at high level and purified efficiently. Moreover, it stimulated mice to produce high level of antibodies with hemmaglutination inhibition properties. The VP2 protein expressed in this study could be used as a putative economic and efficient subunit vaccine against CPV infection.

Detection of canine parvovirus types 2b and 2c in canine faecal samples contaminating urban thoroughfares in Brazil.

Canine parvovirus type 2 (CPV-2) is a highly contagious virus that causes acute gastroenteritis in dogs all over the world. Because of its stability in the environment, CPV-2 can remain infective for a long time, especially if protected in organic matter. To demonstrate CPV-2's potential as an environmental hazard for nonimmunized susceptible hosts, we investigated 50 faecal samples collected from public areas in a municipality of Paraná state, Brazil. Seven samples tested positive for CPV by a PCR assay targeting the partial VP2 gene, with three strains being confirmed as CPV-2b variant and one as CPV-2c variant by sequence analysis. These findings were supported by phylogenetic analysis, and the species identity of faecal samples source was confirmed by canine mitochondrial DNA amplification and sequencing. Our results demonstrate the presence of CPV in canine faeces contaminating urban thoroughfares and reinforce the importance of environmental control to reduce the potential exposure risks to susceptible hosts.

CARNIVORE PROTOPARVOVIRUS 1 (PARVOVIRUSES) AT THE DOMESTIC-WILD CARNIVORE INTERFACE IN INDIA.

Carnivore protoparvovirus 1 (CP1, earlier called Feline panleukopenia virus) variants such as canine parvovirus (CPV) and feline parvovirus (FPV) are significant, emerging, multihost pathogens of domestic and wild carnivores. The diversity of CP1 variants was studied between 2008 and 2014 in Wayanad, India, where flagship wildlife species such as tigers (Panthera tigris) and leopards (Panthera pardus) coexist alongside domestic carnivores, including dogs (Canis lupus familiaris) and cats (Felis catus). Using polymerase chain reaction, FPV and CPV sequences were obtained from the heart blood of a necropsied leopard individual for the first time in the world and from rectal swabs of three sympatric and clinically ill domestic dogs. CP1 amplicons were also detected in a tiger. Cross-species transmission possibilities were identified, as the closest relatives to the leopard FPV sequence were found in domestic cats from a neighboring state.

Complex and Dynamic Interactions between Parvovirus Capsids, Transferrin Receptors, and Antibodies Control Cell Infection and Host Range.

Antibody and receptor binding are key virus-host interactions that control host range and determine the success of infection. Canine and feline parvovirus capsids bind the transferrin receptor type 1 (TfR) to enter host cells, and specific structural interactions appear necessary to prepare the stable capsids for infection. Here, we define the details of binding, competition, and occupancy of wild-type and mutant parvovirus capsids with purified receptors and antibodies. TfR-capsid binding interactions depended on the TfR species and varied widely, with no direct relationship between binding affinity and infection. Capsids bound feline, raccoon, and black-backed jackal TfRs at high affinity but barely bound canine TfRs, which mediated infection efficiently. TfRs from different species also occupied capsids to different levels, with an estimated 1 to 2 feline TfRs but 12 black-backed jackal TfRs binding each capsid. Multiple alanine substitutions within loop 1 on the capsid surface reduced TfR binding but substitutions within loop 3 did not, suggesting that loop 1 directly engaged the TfR and loop 3 sterically affected that interaction. Binding and competition between different TfRs and/or antibodies showed complex relationships. Both antibodies 14 and E competed capsids off TfRs, but antibody E could also compete capsids off itself and antibody 14, likely by inducing capsid structural changes. In some cases, the initial TfR or antibody binding event affected subsequent TfR binding, suggesting that capsid structure changes occur after TfR or antibody binding and may impact infection. This shows that precise, host-specific TfR-capsid interactions, beyond simple attachment, are important for successful infection.IMPORTANCE Host receptor binding is a key step during viral infection and may control both infection and host range. In addition to binding, some viruses require specific interactions with host receptors in order to infect, and anti-capsid antibodies can potentially disrupt these interactions, leading to neutralization. Here, we examine the interactions between parvovirus capsids, the receptors from different hosts, and anti-capsid antibodies. We show that interactions between parvovirus capsids and host-specific TfRs vary in both affinity and in the numbers of receptors bound, with complex effects on infection. In addition, antibodies binding to two sites on the capsids had different effects on TfR-capsid binding. These experiments confirm that receptor and antibody binding to parvovirus capsids are complex processes, and the infection outcome is not determined simply by the affinity of attachment.