Myocarditis Associated with Foot-and-Mouth Disease Virus Type O in Lambs

Foot-and-mouth disease-associated myocarditis is age dependent in suckling calves

Myocarditis is considered a fatal form of foot-and-mouth disease (FMD) in suckling calves. In the present study, a total of 17 calves under 4 months of age and suspected clinically for FMD were examined for clinical lesions, respiratory rate, heart rate, and heart rhythm. Lesion samples, saliva, nasal swabs, and whole blood were collected from suspected calves and subjected to Sandwich ELISA and reverse transcription multiplex polymerase chain reaction (RT-mPCR) for detection and serotyping of FMD virus (FMDV). The samples were found to be positive for FMDV serotype "O". Myocarditis was suspected in 6 calves based on tachypnoea, tachycardia, and gallop rhythm. Serum aspartate aminotransferase (AST), creatinine kinase myocardial band (CK-MB) and lactate dehydrogenase (LDH), and cardiac troponins (cTnI) were measured. Mean serum AST, cTn-I and LDH were significantly higher (P < 0.001) in < 2 months old FMD-infected calves showing clinical signs suggestive of myocarditis (264.833 ± 4.16; 11.650 ± 0.34 and 1213.33 ± 29.06) than those without myocarditis (< 2 months old: 110.00 ± 0.00, 0.06 ± 0.00, 1050.00 ± 0.00; > 2 months < 4 months: 83.00 ± 3.00, 0.05 ± 0.02, 1159.00 ± 27.63) and healthy control groups (< 2 months old: 67.50 ± 3.10, 0.047 ± 0.01, 1120.00 ± 31.62; > 2 months < 4 months: 72.83 ± 2.09, 0.47 ± 0.00, 1160.00 ± 18.44). However, mean serum CK-MB did not differ significantly amongst the groups. Four calves under 2 months old died and a necropsy revealed the presence of a pathognomic gross lesion of the myocardial form of FMD known as "tigroid heart". Histopathology confirmed myocarditis. This study also reports the relevance of clinical and histopathological findings and biochemical markers in diagnosing FMD-related myocarditis in suckling calves.

Novel pathologic findings and viral antigen distribution in cattle and buffalo calves naturally infected with Foot-and-Mouth disease virus

The Foot-and-Mouth disease is highly contagious acute viral disease of livestock inflicting huge economic loss to the farmers. The limited knowledge regarding the pathological lesions vis-a-vis distribution of the FMDV in lesser explored endocrine glands and important vital organs other than the target organs of infected calves prompted us to take the present investigation to have detailed insight into the pathogenesis. The systematic necropsy of 37 dead calves (cattle-28 and buffalo-9) was conducted, and thin representative tissue pieces from the affected organs were collected in 10% neutral buffered formalin (NBF) for pathological and immunohistochemical investigations. The genomic detection and its serotyping were done by RT-PCR and multiplex-PCR, respectively. Necropsy examination in all cases showed myocardial lesions resembling 'tigroid heart appearance'. Other organ specific lesions include vesiculo-ulcerative stomatitis, edema of the lungs, petechial hemorrhages, edema of the endocrines, and gastroenteritis. Histopathological examination showed varying sizes of vesicles and ulcerations in stratified squamous epithelium of the tongue, acute necrotizing myocarditis, lymphoid depletion in lymphoid tissues, hepatitis, pancreatitis, thymic hyperplasia, thyroiditis, adrenitis, and enteritis. Positive immunolabeling for viral antigens was observed in endocrine glands, lymphoid organs, lungs, liver, kidneys, and intestine, in addition to other typical locations. The thyroid, adrenal glands, and pancreas, in addition to the tongue and heart, are the tissue of choice for sampling in the field during epidemics. Further, the viral genome and serotype A was confirmed in the affected tissues. This study provides insights into novel tissue tropism and pathogenesis in young calves naturally infected with FMDV.

Experimental infection of foot and mouth disease virus (FMDV) upregulates the expression of Coxsackie and adenovirus receptor (CAR) in the myocardium of suckling mice

The relative overexpression of Coxsackie and adenoviral receptor (CAR) predisposes children to viral myocarditis. As the foot and mouth disease virus (FMDV) causes fatal myocarditis in calves, lambs, and piglets and belongs to the same family as the Coxsackie virus, we investigated the role of CAR in FMDV induced myocarditis in the suckling mice model. Swiss albino suckling mice of 5 days (n = 24) were divided into two equal groups. One group was inoculated with suckling mice adapted FMDV serotype O at 10 LD50, while the other group served as uninfected control. In addition, adult mice (n = 12) served as the control for age related CAR expression and lack of pathogenicity to FMDV. The establishment of myocarditis was confirmed by histopathological changes typical of myocarditis along with immunolocalization of FMDV antigens in the heart of suckling mice. The FMDV inoculated suckling mice group showed a significant upregulation of CAR transcripts by 2.5 folds, overexpression of CAR protein by densitometric analysis of immunoblots, and intense immunolocalization of CAR in the sarcolemma and intercalated discs of cardiomyocytes as compared to the uninfected suckling mice group and adult mice. It was concluded that FMDV infection induced overexpression of CAR in the myocardium of suckling mice.

Pathological and genetic characterization of foot and mouth disease viruses collected from cattle and water buffalo in Egypt

Foot-and-mouth disease (FMD), a highly contagious viral disease caused by FMD virus (FMDV) that threatens Egypt's livestock industry. FMDV causes severe economic losses in the livestock, with restriction of international trade from endemic regions. Surveillance for FMDV serotypes circulating in Egypt is urgently needed to assess the epidemiological situation in the country. FMD outbreaks reported in Egypt in between December 2016 and January-March 2017. A cross-sectional study was conducted to identify the FMDV serotypes responsible for the outbreaks and to collect information on the virus's morphopathological effects. Postmortem tissue and clinical samples (oral swabs, vesicular fluids from ruptured vesicles, and blood) were collected from recently deceased and infected animals. Pathological examination revealed classical FMD lesions as vesicular and erosive lesions on epithelial tissues with non-suppurative lymphoplasmacytic myocarditis. Phylogenetic and sequencing analyses demonstrated that FMDV serotype O, EA-3 topotype, VP1 is the prevalent serotype responsible for the pathological alterations and the high mortality in young calves, adult cattle, and water buffalo. The outcomes indicate continuous mutations in the circulating FMDV, which result in the occasional failure of vaccination. Based on these findings, extensive continuous monitoring and serotyping of the existing circulating FMDV isolates and regular vaccination with reevaluation of the currently used vaccine in Egypt are recommended to prevent the recurrence of such outbreaks.

Characterization of arrhythmias, evaluation of cardiac biomarkers and their association with survival in calves suffering from foot-and-mouth disease

INTRODUCTION

Foot-and-mouth disease (FMD) causes mortality in calves due to myocarditis; however, the effects of FMD virus on cardiac arrhythmogenesis and Purkinje cells are unknown. Identifying diagnostic and prognostic markers in FMD-affected calves may be useful in disease management in the endemic countries.

MATERIALS AND METHODS

A total of 81 FMD-affected calves were prospectively monitored till death or recovery. Foot-and-mouth disease was diagnosed by serology and reverse transcriptase-polymerase chain reaction (RT-PCR). Electrocardiography was recorded and serum cardiac biomarkers were measured. Histopathological examination of the ventricular myocardium was carried out in the calves that died of FMD (n = 33). Apparently healthy calves (n = 15) served as control.

RESULTS

Serology and RT-PCR consistently revealed that the FMD was caused by serotype O virus. Arrhythmias occurred in 62 of 81 (76.5%) FMD-affected calves, of which, ventricular premature complexes (VPCs) were the most common type (22%). The combined mortality rate due to ventricular tachycardia, polymorphic VPCs, and atrial fibrillation was 27.6%. Receiver operating characteristic curve analysis revealed that cardiac troponin I (cTnI) concentrations of ≥1.3 ng/mL were diagnostic of myocarditis with a sensitivity and specificity of 90% and 100%, respectively. Similarly, serum cTnI concentrations of <6.4 ng/mL were a good predictor of survival [odds ratio of 263; 95% confidence interval: 29-2371]. Histopathology of the myocardium revealed hyaline degeneration, necrosis, edema, mononuclear cell infiltration, and disruption by fibroblasts. Atrophy of the Purkinje cells was also present.

CONCLUSIONS

FMD induces cardiac arrhythmias and Purkinje cell pathology in the calf. Portable ECG coupled with assay of serum cTnI would help in predicting survival in FMD-affected calves.

Virus-Host Interactions in Foot-and-Mouth Disease Virus Infection

Foot-and-mouth disease (FMD) is a highly contagious disease of cloven-hoofed animals, which has been regarded as a persistent challenge for the livestock industry in many countries. Foot-and-mouth disease virus (FMDV) is the etiological agent of FMD that can spread rapidly by direct and indirect transmission. FMDV is internalized into host cell by the interaction between FMDV capsid proteins and cellular receptors. When the virus invades into the cells, the host antiviral system is quickly activated to suppress the replication of the virus and remove the virus. To retain fitness and host adaptation, various viruses have evolved multiple elegant strategies to manipulate host machine and circumvent the host antiviral responses. Therefore, identification of virus-host interactions is critical for understanding the host defense against virus infections and the pathogenesis of the viral infectious diseases. This review elaborates on the virus-host interactions during FMDV infection to summarize the pathogenic mechanisms of FMD, and we hope it can provide insights for designing effective vaccines or drugs to prevent and control the spread of FMD and other diseases caused by picornaviruses.

ID1 inhibits foot-and-mouth disease virus replication via targeting of interferon pathways

Inhibitor of DNA-binding 1 (ID1) protein has been studied intensively for its functions in tumorigenesis and maintenance of stem cell-like properties, but its roles in virus infection are less understood. In the present study, we have clearly shown that the foot-and-mouth disease virus (FMDV) promotes ID1 degradation via Cdh1-mediated ubiquitination to facilitate its replication. Mechanistic investigations reveal Forkhead Box O1 (FOXO1) as an ID1 partner, which suppresses interferon regulatory factors 3 expression and interferon (IFN) production. Further investigation identified that ID1 suppresses FOXO1 transcription activity through HDAC4-mediated deacetylation, promoting IFN production and antiviral immune response. These studies establish a prominent role for ID1 in suppressing FDMV replication, which may be extended to other viruses.

Pathogenesis of non-epithelial foot-and-mouth disease in neonatal animals

Foot-and-mouth disease virus (FMDV), which causes a highly contagious viral disease of cloven-hoofed animals, is notable for epithelial cell tropism, resulting in the appearance of vesicles on the feet and in and around the mouth in infected animals, while FMDV infection in neonatal animals is also associated with not only epithelial lesions, but also muscle-associated lesions, which leads to myocarditis, resulting in high-mortality. However, critical knowledge about the non-epithelial tropism of FMDV is still lacking. In this paper, the current progress of the FMDV non-epithelial tropisms is summarized and the possible role of the key viral and cellular components involved is discussed.

The Carrier Conundrum; A Review of Recent Advances and Persistent Gaps Regarding the Carrier State of Foot-and-Mouth Disease Virus

The existence of a prolonged, subclinical phase of foot-and-mouth disease virus (FMDV) infection in cattle was first recognized in the 1950s. Since then, the FMDV carrier state has been a subject of controversy amongst scientists and policymakers. A fundamental conundrum remains in the discordance between the detection of infectious FMDV in carriers and the apparent lack of contagiousness to in-contact animals. Although substantial progress has been made in elucidating the causal mechanisms of persistent FMDV infection, there are still critical knowledge gaps that need to be addressed in order to elucidate, predict, prevent, and model the risks associated with the carrier state. This is further complicated by the occurrence of a distinct form of neoteric subclinical infection, which is indistinguishable from the carrier state in field scenarios, but may have substantially different epidemiological properties. This review summarizes the current state of knowledge of the FMDV carrier state and identifies specific areas of research in need of further attention. Findings from experimental investigations of FMDV pathogenesis are discussed in relation to experience gained from field studies of foot-and-mouth disease.

Foot-and-Mouth Disease Virus Capsid Protein VP1 Interacts with Host Ribosomal Protein SA To Maintain Activation of the MAPK Signal Pathway and Promote Virus Replication

Foot-and-mouth disease virus (FMDV) is the causative agent of foot-and-mouth disease, a highly contagious, economically important viral disease. The structural protein VP1 plays significant roles during FMDV infection. Here, we identified that VP1 interacted with host ribosomal protein SA (RPSA). RPSA is a viral receptor for dengue virus and classical swine fever virus infections. However, the incubation of susceptible cells using the anti-RPSA antibodies did not block the infection of FMDV. Overexpression of porcine RPSA in the insusceptible cells could not trigger FMDV infection, suggesting that RPSA was not responsible for FMDV entry and infection. On the contrary, we found that overexpression of RPSA suppressed FMDV replication, and knockdown of RPSA enhanced FMDV replication. We further determined that FMDV infection activated the mitogen-activated protein kinase (MAPK) pathway and demonstrated that MAPK pathway activation was critically important for FMDV replication. RPSA negatively regulated MAPK pathway activation during FMDV infection and displayed an antiviral function. FMDV VP1 interacted with RPSA to abrogate the RPSA-mediated suppressive role in MAPK pathway activation. Together, our study indicated that MAPK pathway activation was required for FMDV replication and that host RPSA played a negatively regulatory role on MAPK pathway activation to suppress FMDV replication. FMDV VP1 bound to RPSA to promote viral replication by repressing RPSA-mediated function and maintaining the activation of MAPK signal pathway.IMPORTANCE Identification of virus-cell interactions is essential for making strategies to limit virus replication and refine the models of virus replication. This study demonstrated that FMDV utilized the MAPK pathway for viral replication. The host RPSA protein inhibited FMDV replication by suppressing the activation of the MAPK pathway during FMDV infection. FMDV VP1 bound to RPSA to repress the RPSA-mediated regulatory effect on MAPK pathway activation. This study revealed an important implication of the MAPK pathway for FMDV infection and identified a novel mechanism by which FMDV VP1 has evolved to interact with RPSA and maintain the activation of the MAPK pathway, elucidating new information regarding the signal reprogramming of host cells by FMDV.

Virulence beneath the fleece; a tale of foot-and-mouth disease virus pathogenesis in sheep

Foot-and-mouth disease virus (FMDV) is capable of infecting all cloven-hoofed domestic livestock species, including cattle, pigs, goats, and sheep. However, in contrast to cattle and pigs, the pathogenesis of FMDV in small ruminants has been incompletely elucidated. The objective of the current investigation was to characterize tissue- and cellular tropism of early and late stages of FMDV infection in sheep following three different routes of simulated natural virus exposure. Extensive post-mortem harvest of tissue samples at pre-determined time points during early infection (24 and 48 hours post infection) demonstrated that tissues specifically susceptible to primary FMDV infection included the paraepiglottic- and palatine tonsils, as well as the nasopharyngeal mucosa. Additionally, experimental aerosol inoculation of sheep led to substantial virus replication in the lungs at 24-48 hours post-inoculation. During persistent infection (35 days post infection), the paraepiglottic- and palatine tonsils were the only tissues from which infectious FMDV was recovered. This is strikingly different from cattle, in which persistent FMDV infection has consistently been located to the nasopharyngeal mucosa. Analysis of tissue sections by immunomicroscopy revealed a strict epithelial tropism during both early and late phases of infection as FMDV was consistently localized to cytokeratin-expressing epithelial cells. This study expands upon previous knowledge of FMDV pathogenesis in sheep by providing detailed information on the temporo-anatomic distribution of FMDV in ovine tissues. Findings are discussed in relation to similar investigations previously performed in cattle and pigs, highlighting similarities and differences in FMDV pathogenesis across natural host species.

Foot-and-mouth disease virus O/ME-SA/Ind 2001 lineage outbreak in vaccinated Holstein Friesian cattle in Saudi Arabia in 2016

Background: Foot-and-mouth disease virus (FMDV) is a highly contagious viral infection of large ruminants. Despite the massive application of vaccines against FMDV, several outbreaks are still being reported in Africa and Asia.

Aim: To perform molecular characterization of FMDV in an outbreak among a cattle herd Saudi Arabia in 2016. This herd had been vaccinated with a polyvalent FMDV vaccine.

Methods: To investigate this outbreak, we collected specimens from 77 animals showing typical clinical signs of FMDV. Specimens including sera, nasal swabs, and tissues (tongue, coronary bands, hooves, and hearts) were collected. We tested the collected cattle sera for the presence of FMDV antibodies with commercial ELISA kits. In addition, we tested the swabs for the presence of the most common FMDV strains (O, A, Asia-1 and SAT-2) with RT-PCR using serotype-specific oligonucleotides.

Results: Serology showed that 22% of the tested sera were positive. Molecular testing of the examined swabs confirmed that 24% of the tested animals were positive. Our sequencing analysis confirmed that the circulating strains of FMDV belonged to FMDV serotype O. The phylogenetic tree based on the FMDV-VP-1 gene revealed high nucleotide identity between the circulating strains and the Bangladesh strain (99%). These strains were distinct (shared 89% nucleotide identity) from the FMDV-O strains used for the preparation of the vaccine administered to the animals in this herd. Moreover, they had 7% nucleotide difference between the FMDV-O strains reported in Saudi Arabian in 2013.

Conclusion: More in-depth molecular characterization of these FMDV strains is warranted.

Pathogenesis of the attenuated foot-and-mouth disease virus O/JPN/2000 in experimentally infected pigs

We examined the pathogenesis of the attenuated foot-and-mouth disease virus (FMDV) O/JPN/2000 in pigs. The virus used in this study was passaged three times in primary bovine kidney (BK) cells and once in baby hamster kidney-21 (BHK-21) cells after isolation. A plaque assay demonstrated that this virus exhibited the small plaque (SP) phenotype. There was no clinical or histological evidence of vesicular lesions in pigs intraorally inoculated with 10⁶ 50% tissue culture infectious dose (TCID₅₀)/ml of the SP virus (SPV) of FMDV O/JPN/2000. Although fever was detected from 2 or 3 days post inoculation (dpi), there was no other prominent clinical sign up to 6 dpi. Virus shedding from saliva and nasal swab samples was not observed in any pigs inoculated with the SPV of FMDV O/JPN/2000. In the foot, mild lamellar degeneration of prickle cells in the upper layer of the stratum spinosum was histologically observed without development into vesicular or necrotic lesions. Immunohistochemical virus antigen- and terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL)-positive reactions observed in the foot at 1 dpi seemed to disappear after 3 and 6 dpi. Our findings suggest that the SPV of FMDV O/JPN/2000 had low pathogenicity against pigs by intraoral inoculation.

Systemic antibodies administered by passive immunization prevent generalization of the infection by foot-and-mouth disease virus in cattle after oronasal challenge

The role of passively transferred sera in the protection against aerogenous foot-and-mouth disease (FMD) virus infection in cattle was evaluated using vaccine-induced immune serum preparations obtained at 7 and 26 days post-vaccination (dpv). We showed that circulating antibodies were sufficient to prevent disease generalization after oronasal infection in animals passively transferred with 26-dpv serum but not with the 7-dpv serum. Conversely, conventional FMD vaccination provided clinical protection at 7 dpv, promoting fast and robust antibody responses upon challenge and even though antibody titers were similar to those found in animals passively immunized with 7-dpv serum. These results demonstrate that presence of antigen-specific antibodies is critical to prevent the dissemination of the virus within the animal. Conventional FMD vaccination additionally promoted the deployment of rapid, high titer and isotype-switched antibody responses at systemic and mucosal levels after infection, thus conferring protection even in the presence of low pre-challenge antibody titers.

Early pathogenesis of the foot-and-mouth disease virus O/JPN/2010 in experimentally infected pigs

We examined the histological distribution of the lesions and the viral antigen associated with the virus and virus RNA in multisystemic organs in the early stages of foot-and-mouth disease virus (FMDV) O/JPN/2010 infection in pigs. Characteristic lesions commonly observed in pigs with FMD arise following inoculation with 10⁶ tissue culture infectious dose (TCID)₅₀/ml of FMDV O/JPN/2010 in pigs at 3 days post inoculation (dpi) by a natural infectious route. However, none of the six pigs inoculated with 10³ TCID₅₀/ml of FMDV O/JPN/2010 showed any evidence of infection up to 6 dpi. Immunohistochemical detection for the FMDV antigen and terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) showed that FMDV predominantly infected prickle cells in the stratum spinosum in the tongue, coronet and bulb of the heel, and caused these infected cells to undergo cell death by apoptosis. However, there was no evidence that FMDV O/JPN/2010 infected epithelial/epidermal basal cells in the basal layer. Epithelial lesions with viral antigen in the tongue were distributed in the dorsal surface but not in the papillae, corpus linguae or inferior surface of the tongue. Non-suppurative myocarditis and epithelial lesions in the esophagus with FMDV antigen were observed in all three pigs examined at 3 dpi.

Outbreaks of foot and mouth disease in Egypt: Molecular epidemiology, evolution and cardiac biomarkers prognostic significance

Foot and mouth disease virus (FMDV) was isolated from sloughed tongue epithelium of Egyptian cattle presenting with mouth lesions and ropy salivation in two Egyptian governorates (El-Fayoum and Dakahlia). The virus was isolated in Madin-Darby bovine kidney (MDBK) cells and identified by reverse transcription-polymerase chain reaction (RT-PCR). The complete genome was obtained by next generation sequencing. The strains isolated from El-Fayoum and Dakahlia were serotype A and O, respectively and both isolates had identity with the previously reported Egyptian strains. This study reports successive outbreaks of FMDV that occurred in Egypt during 2015–2016 and describes the dynamics of two outbreaks in addition to the use of cardiac biomarkers in the diagnosis of FMD-related myocarditis in calves and its clinical relevance. Serum cardiac troponin1 (cTn I) and creatinine kinase myocardial band (CK-MB) were measured. Mean serum cardiac troponin1 (cTn I) showed significant increase (P < 0.001) in FMDV-infected calves. The increase in fatal and recovered cases was (2.794 ± 0.502 ng/mL) and (1.196 ± 0.443 ng/mL), respectively, compared to the healthy control cases (0.014 ± 0.002 ng/mL). Thus, the serum cTn-I successfully diagnosed FMD-associated myocarditis in calves but not prognostic for the fatal cases. The FMDV sequences described in this study should further help in studying FMDV endemicity in Egypt, tracking the source of infection, selection of control strategies and vaccine updates. The study also determines the clinical relevance of cardiac biomarkers in diagnosis of FMDV-related myocarditis in infected calves.

Foot-and-mouth disease virus infection inhibits LGP2 protein expression to exaggerate inflammatory response and promote viral replication

The role of the innate immune protein LGP2 (laboratory of genetics and physiology 2) in FMDV-infected cells remains unknown. Here, we demonstrate the antiviral role of LGP2 during FMDV infection. FMDV infection triggered LGP2 mRNA expression but reduced protein expression. Overexpression of LGP2 suppressed FMDV replication, and the inflammatory response was significantly inhibited by LGP2 in virus-infected cells. The N-terminal DExDc and the C-terminal regulatory domain regions of LGP2 were essential for LGP2-mediated antiviral activity against FMDV. Disruption of RNA recognition by LGP2 is suggested to abolish completely LGP2-mediated antiviral activity against FMDV. FMDV leader protein (L^pro), as well as the 3C^pro and 2B proteins were determined to possess the ability to induce reduction of LGP2 protein expression. 2B-induced reduction of LGP2 was independent of cleavage of eukaryotic translation initiation factor 4 gamma; and the proteasomes, lysosomes or caspase-dependent pathways were not involved in this process. The C-terminal amino acids of 101–154 were essential for 2B-induced reduction of LGP2 and upregulation of inflammatory response. Direct interaction was demonstrated between LGP2 and 2B. Our results describe the antiviral role of LGP2 against FMDV and a novel antagonistic mechanism of FMDV that is mediated by 2B protein.

Foot-and-Mouth Disease Virus-Associated Abortion and Vertical Transmission following Acute Infection in Cattle under Natural Conditions

Foot-and-mouth disease (FMD) is a highly contagious and economically important viral disease of cloven-hoofed animals, including domestic and wild host species. During recent FMD outbreaks in India, spontaneous abortions were reported amongst FMD-affected and asymptomatic cows. The current study was an opportunistic investigation of these naturally occurring bovine abortions to assess causality of abortion and vertical transmission of FMDV from infected cows to fetuses. For this purpose, fetal tissue samples of eight abortuses (heart, liver, kidney, spleen, palatine tonsil, umbilical cord, soft palate, tongue, lungs, and submandibular lymph node) were collected and screened by various detection methods, including viral genome detection, virus isolation, and immunomicroscopy. Amongst these cases, gross pathological changes were observed in 3 abortuses. Gross pathological findings included blood-tinged peritoneal and pleural effusions and myocarditis. Hearts of infected calves had mild to moderate degeneration and necrosis of the myocardium with moderate infiltration by mixed inflammatory cells. Localization of FMDV antigen was demonstrated in lungs and soft palate by immunomicroscopy. FMDV serotype O viral genome was recovered from 7 of 8 cases. Infectious FMDV serotype O was rescued by chemical transfection of the total RNA extracted from three soft palate samples and was sequenced to confirm 100% identity of the VP1 (capsid) coding region with isolates collected from infected cattle during the acute phase of infection. Based upon these findings, it may be concluded that FMDV-associated abortion occurred among the infected pregnant cows included within this study and FMDV was subsequently transmitted vertically to fetuses. This is the first documentation of FMDV-associated abortions in cattle.

The Pathogenesis of Foot-and-Mouth Disease in Pigs

The greatest proportion of foot-and-mouth disease (FMD) clinical research has been dedicated to elucidating pathogenesis and enhancing vaccine protection in cattle with less efforts invested in studies specific to pigs. However, accumulated evidence from FMD outbreaks and experimental investigations suggest that critical components of FMD pathogenesis, immunology, and vaccinology cannot be extrapolated from investigations performed in cattle to explain or to predict outcomes of infection or vaccination in pigs. Furthermore, it has been shown that failure to account for these differences may have substantial consequences when FMD outbreaks occur in areas with dense pig populations. Recent experimental studies have confirmed some aspects of conventional wisdom by demonstrating that pigs are more susceptible to FMD virus (FMDV) infection via exposure of the upper gastrointestinal tract (oropharynx) than through inhalation of virus. The infection spreads rapidly within groups of pigs that are housed together, although efficiency of transmission may vary depending on virus strain and exposure intensity. Multiple investigations have demonstrated that physical separation of pigs is sufficient to prevent virus transmission under experimental conditions. Detailed pathogenesis studies have recently demonstrated that specialized epithelium within porcine oropharyngeal tonsils constitute the primary infection sites following simulated natural virus exposure. Furthermore, epithelium of the tonsil of the soft palate supports substantial virus replication during the clinical phase of infection, thus providing large amounts of virus that can be shed into the environment. Due to massive amplification and shedding of virus, acutely infected pigs constitute a considerable source of contagion. FMDV infection results in modulation of several components of the host immune response. The infection is ultimately cleared in association with a strong humoral response and, in contrast to ruminants, there is no subclinical persistence of FMDV in pigs. The aim of this review is to provide an overview of knowledge gained from experimental investigations of FMD pathogenesis, transmission, and host response in pigs. Details of the temporo-anatomic progression of infection are discussed in relation to specific pathogenesis events and the likelihood of transmission. Additionally, relevant aspects of the host immune response are discussed within contexts of conventional and novel intervention strategies of vaccination and immunomodulation.

Comparative transcriptome analyses indicate enhanced cellular protection against FMDV in PK15 cells pretreated with IFN-γ

Interferon gamma (IFN-γ) can induce a host antiviral response to foot and mouth disease virus (FMDV) in vivo and in vitro. To elucidate the mechanism of IFN-γ anti FMDV infection in host cells, high-throughput RNA sequencing was analyzed for systemic changes in gene expression profiles in PK15 cells infected by FMDV with or without IFN-γ pretreatment. More than 25 million reads, covering 1.2-1.5 Gb, were analyzed from each experiment panel. FMDV challenge altered the transcription of genes involved in positively and negatively regulating cell death or apoptosis; however, the expected immune suppression response was not obvious. IFN-γ pretreatment combined with FMDV infection normalized the increase in apoptosis. Furthermore, the transcription factors required for IFN-γ functioning, STAT1 and IRF1 were up-regulated by IFN-γ pretreatment and stimulated downstream IFN-stimulated genes (ISGs). These induced ISGs are mainly responsible for antigen processing, antigen presentation or antiviral defense. Interestingly, a synergistic effect on some ISGs, including OAS1, OAS2, MX1, MX2, RIG-I and IFIT1, was observed in the combined treatment compared to the IFN-γ treatment alone. The suggested effects identified by RNA sequencing were consistent with cellular morphology changes and confirmed by related protein markers. This is the first report exploring transcriptome alterations introduced by FMDV infection with or without IFN-γ pretreatment. The identified key host genes that control cell survival in vitro broaden our comprehensive understanding of how IFN-γ inhibits FMDV infection and may shed light on developing improved FMD control approaches.

Laboratory animal models to study foot-and-mouth disease: a review with emphasis on natural and vaccine-induced immunity

Laboratory animal models have provided valuable insight into foot-and-mouth disease virus (FMDV) pathogenesis in epidemiologically important target species. While not perfect, these models have delivered an accelerated time frame to characterize the immune responses in natural hosts and a platform to evaluate therapeutics and vaccine candidates at a reduced cost. Further expansion of these models in mice has allowed access to genetic mutations not available for target species, providing a powerful and versatile experimental system to interrogate the immune response to FMDV and to target more expensive studies in natural hosts. The purpose of this review is to describe commonly used FMDV infection models in laboratory animals and to cite examples of when these models have failed or successfully provided insight relevant for target species, with an emphasis on natural and vaccine-induced immunity.

Morphologic and phenotypic characteristics of myocarditis in two pigs infected by foot-and mouth disease virus strains of serotypes O or A

Myocarditis is often cited as the cause of fatalities associated with foot-and-mouth disease virus (FMDV) infection. However, the pathogenesis of FMDV-associated myocarditis has not been described in detail. The current report describes substantial quantities of FMDV in association with a marked mononuclear inflammatory reaction, interstitial edema and cardiomyocyte degeneration in the myocardium of two pigs that died during acute infection with either of two different strains of FMDV. Despite similar clinical progression, there was a marked variation in morphological characteristics of myocarditis with a significant difference in intensity of myocardial inflammation between the two cases. Phenotypic characterization of leukocyte populations revealed that in both cases, the inflammatory infiltrate consisted mainly of combinations of CD172a+, CD163+ and CD44+ cells, with a distinct subset of CD8+ cells, but with consistent lack of detection of CD3+ and CD21+ cells. This suggests that the FMDV-associated acute myocardial inflammation in the two observed cases consisted mainly of leukocytes of monocyte lineage, with a distinct population of CD8+ cells which, based on lack of CD3 detection in serial sections, are likely to represent NK cells.

Increased plasma cardiac troponin I concentration in lambs with myocarditis

BACKGROUND

Cardiac troponin I (cTnI) is a blood biomarker of myocardial injury. A human cTnI assay may be useful for measuring cTnI concentrations in lambs with naturally occurring myocarditis.

OBJECTIVE

The aims of this study were to evaluate the utility of a commercially available human chemiluminescent microparticle cTnI immunoassay for measuring plasma cTnI concentrations in lambs with naturally occurring myocarditis from infection with foot and mouth disease virus (FMDV), and to determine cTnI expression in cardiac muscle of affected lambs.

METHODS

Ten lambs with myocarditis and 10 clinically healthy lambs (control group) were included. Clinical signs, gross and histologic necropsy findings, and immunoreactivity for cTnI in cardiac tissue were evaluated. Plasma cTnI concentration was determined using the commercial human immunoassay system.

RESULTS

All lambs with myocarditis died within 1 day of clinical signs. Infection with FMDV was confirmed by PCR analysis. Gross cardiac lesions were evident and histologic examination revealed myocarditis. Immunoreactivity for cTnI was absent in cardiac myocytes that were degenerative or necrotic, but was strong in cardiac myocytes from unaffected areas of the myocardium and in all cardiac myocytes of healthy lambs. The geometric mean plasma concentrations of cTnI for lambs in the myocarditis and control groups were 146.78 μg/L (95% confidence interval [CI], 61.90-348.06) and 0.013 μg/L (95% CI, 0.010-0.017), respectively (t-value 19.27; P < .0001).

CONCLUSIONS

A commercial human cTnI assay may be used to detect plasma cTnI concentrations in sheep, and cTnI may be used as a blood-based biomarker of myocarditis in this species.

The expressions of HSP70 and αB-crystallin in myocarditis associated with foot-and-mouth disease virus in lambs

This study describes the expression of heat shock protein70 (HSP70) and alpha-basic-crystallin (α-BC) and their association with apoptosis and some related adaptor proteins in the pathogenesis of foot-and-mouth disease virus (FMDV)-induced myocarditis in lambs. HSP70 was generally overexpressed in the myocardial tissues and inflammatory cells of FMDV-induced myocarditis with differential accumulation and localization in same hearts when compared to non-foot-and-mouth disease control hearts. α-BC immunolabeling showed coarse aggregations in the Z line of the cardiomyocytes in FMDV-infected hearts in contrast to control hearts. Overall, the results of this study show that the anti-apoptotic proteins, HSP70 and α-BC, were overexpressed with increased apoptosis in FMDV-infected heart tissues. Both proteins failed to protect the cardiomyocytes from apoptosis as defense mechanisms to the FMDV during the infection, suggesting that the virus is able to increase apoptosis via both downregulation and/or upregulation of these anti-apoptotic proteins.

Evaluation of infectivity and transmission of different Asian foot-and-mouth disease viruses in swine

Most isolates of foot-and-mouth disease virus (FMDV) display a broad host range. Since the late 1990s, the genetic lineage of PanAsia topotype FMDV serotype O has caused epidemics in the Far East, Africa, the United Kingdom, France, the Netherlands, and numerous other countries throughout Europe and Asia. In contrast, there are several FMDV isolates that exhibit a more restricted host range. A Cathay topotype isolate of FMDV serotype O from the 1997 epizootic in Taiwan (O/TAW/97) demonstrated restricted host specificity, only infecting swine. Methods used to evaluate infectivity and pathogenicity of FMDV isolates in cattle are well-documented, but there has been less progress studying transmission and pathogenicity of FMDV isolates in pigs. In previous studies designed to examine pathogenicity, various chimeric viruses derived from O/TAW/97 were intradermally inoculated in the heel bulb of pigs. Subsequent quantitative scoring of disease and evaluation of virus released into nasal secretions and blood was assessed. Here we prove the usefulness of this method in direct and contact inoculated pigs to evaluate infectivity, pathogenicity and transmission of different Asian FMDV isolates. Virus strains within the Cathay topotype were highly virulent in swine producing a synchronous disease in inoculated animals and were efficiently spread to in-contact naive pigs, while virus strains from the PanAsia topotype displayed more heterogeneous properties.

Understanding the molecular epidemiology of foot-and-mouth-disease virus

The use of molecular epidemiology is an important tool in understanding and consequently controlling FMDV. In this review I will present basic information about the disease, needed to perform molecular epidemiology. I will give a short introduction to the history and impact of foot-and-mouth disease, clinical picture, infection route, subclinical and persistent infections, general aspects of the transmission of FMDV, serotype-specific epidemiological characteristics, field epidemiology of FMDV, evolution and molecular epidemiology of FMDV. This is followed by two chapters describing the molecular epidemiology of foot-and-mouth disease in global surveillance and molecular epidemiology of foot-and-mouth disease in outbreak investigation.

Differences in the susceptibility of dromedary and Bactrian camels to foot-and-mouth disease virus

In this study, two sheep, eight dromedary camels and two Bactrian camels were inoculated with foot-and-mouth disease virus (FMDV) type A SAU 22/92. Five naive dromedary camels and four sheep were kept in direct or indirect contact with the inoculated camels. The inoculated sheep, which served as positive controls, displayed typical moderate clinical signs of FMD and developed viraemia and high antibody titres. The presence of the virus was also detected in probang and mouth-swab samples for several days after inoculation. In contrast, the inoculated dromedary camels were not susceptible to FMDV type A infection. None of them showed clinical signs of FMD or developed viraemia or specific anti-FMDV antibodies despite the high dose of virus inoculated. All the contact sheep and contact dromedaries that were kept together with the inoculated camels remained virus-negative and did not seroconvert when tested up to 28 days post-inoculation (p.i.). In comparison with the non-susceptible dromedaries, the two inoculated Bactrian camels showed moderate to severe clinical signs of FMD; however, the clinical signs of FMD appeared rather late, between 8 and 14 days p.i., compared to the inoculated sheep. Characteristic FMD lesions in the Bactrian camels, accompanied with severe lameness, were only observed on the hind feet. The presence of the virus in the serum samples of both Bactrian camels was detected by real-time RT–PCR in one of the animals on days 3 and 7 p.i. and in the second animal from days 1 to 3 p.i. and subsequently again on day 21 p.i. The Bactrian camels developed high titres of antibodies to the inoculated FMDV which appeared at 7–10 days p.i. and lasted up to 130 days p.i. Only low and transient amounts of FMDV were detected in the mouth-swab and probang samples collected from both Bactrian camels.

Evading the host immune response: how foot-and-mouth disease virus has become an effective pathogen

Foot-and-mouth disease virus (FMDV) causes an economically devastating disease of cloven-hoofed animals. In this review, we discuss the mechanisms FMDV has evolved to counteract the host innate and adaptive immune responses and the role of viral proteins in this process. The viral leader proteinase, L pro, limits the host innate response by inhibiting the induction of interferon beta (IFN beta) mRNA and blocking host cell translation. A second viral proteinase, 3C pro, may affect host cell transcription because it cleaves histone H3. Viral protein 2B in conjunction with 2C or their precursor 2BC inhibits protein trafficking through the endoplasmic reticulum and Golgi apparatus. A decrease in surface expression of major histocompatibility class I molecules during FMDV infection suggests that 2B, 2C and/or 2BC may be involved in delaying the initiation of the host adaptive immune response and also adversely affect the secretion of induced signaling molecules. FMDV also causes a transient lymphopenia in swine, but the mechanism involved is not understood nor have any viral protein(s) been implicated. Furthermore, the interaction of FMDV with various cells in the immune system including lymphocytes and dendritic cells and the possible role of apoptosis and autophagy in these interactions are discussed.