An outbreak of pig rabies in Hunan province, China

Diversity of rabies virus detected in Inner Mongolia, China, 2019-2021

Rabies is a serious public health issue in China, with over 95% of human infections transmitted by dogs. As part of a routine surveillance carried out in the Inner Mongolia Autonomous Region (IMAR) between 2019 and 2021, 80 of 95 suspected rabies cases in domestic animals (dogs, livestock) and wild carnivores (foxes, badgers, a raccoon dog) were confirmed as rabies virus (RABV) positive. Phylogenetic analysis of RABVs of the 80 cases based on complete N genes showed that 97.5% (78/80) of the virus strains belonged to the Cosmopolitan (steppe-type) clade, with one in each of Arctic-related (AL2) and Asian (SEA1) clades. The data show that infected foxes have become a major transmission source of rabies in China, second only to dogs, and play a pivotal role in animal rabies epizootics in the north and northwest of the country. The recent spread of fox rabies to other animal species presents an increasing threat to public health and emphasizes the importance of animal rabies surveillance.

Zoonotic and reverse zoonotic transmission of viruses between humans and pigs

Humans and pigs share a close contact relationship, similar biological traits, and one of the highest estimated number of viruses compared to other mammalian species. The contribution and directionality of viral exchange between humans and pigs remain unclear for some of these viruses, but their transmission routes are important to characterize in order to prevent outbreaks of disease in both host species. This review collects and assesses the evidence to determine the likely transmission route of 27 viruses between humans and pigs.

Early diagnosis of rabies virus infection by RPA-CRISPR techniques in a rat model

Rabies, which is caused by rabies virus (RABV), poses an ever-present threat to public health in most countries of the world. Once clinical signs appear, the mortality of rabies approaches 100%. To date, no effective method for early rabies diagnosis has been developed. In this study, an RPA-CRISPR nucleic-acid-based assay was developed for early rabies diagnosis by detecting viral RNA shedding in the cerebrospinal fluid (CSF) of rats. This method can detect a single copy of RABV genomic RNA in 1 μL of liquid. RABV genomic RNA released from viral particles in the CSF could be detected via RPA-CRISPR as early as 3 days postinfection in a rat model. This study provides an RPA-CRISPR technique for early detection of RABV with potential application in the clinical diagnosis of human rabies.

Different rabies outbreaks on two beef cattle farms in the same province of China: Diagnosis, virus characterization and epidemiological analysis

Eliminating rabies is challenging in many developing countries, especially in rural areas. In contrast to the annual decline of human cases in China in last decade, the incidence of rabies in livestock has been increasingly reported. This paper reports the rabies outbreaks in beef cattle (Angus) in Shaanxi Province, China, which caused 31 and 5 deaths at an attack rate of 19.4% (95% CI: 13.6%-26.4%) and 0.25% (95% CI: 0.1%-0.6%) in a satellite cow farm (farm A) and a core intensive farm (farm B), respectively. The rabies infection was confirmed by several laboratory tests, and rabies virus (RABV) strains SXBJ15 and SXYL15 were isolated and characterized from farm A and B, respectively. The two strains were found to have a high genomic sequence similarity to the dog-associated China clade I strains previously identified in the neighbouring area. SXBJ15 was shown to have a higher mouse pathogenicity (1.07) than SXYL15 (0.45). RABV was also detected in the saliva and salivary glands from the affected cattle. The potential causes were investigated on the farm, and the biosecurity scores were 20 and 64 (a full score of 82) for farms A and B, respectively. The rabies infection is likely to result from rabid free-roaming dogs (FRDs). On farm A with more cow deaths, the rabies transmission between animals can be attributed to the improper disposal of aborted foetuses and placental materials as a food source for rabid FRDs, high stocking density and drinking water sharing. Additionally, vaccinating cattle with a canine vaccine was shown to help stop the spread of rabies in herds. These results indicate that the occurrence of RABV on cattle farms can be prevented by improving biosecurity measures to control the entry of rural FRDs on the farm and immunizing farm cattle against rabies.

Rabies viruses in specific wild fur animals in northern China, 2017-2019

In recent years, rabies virus (RABV) has been detected in numerous specific wild fur animals in northern China. Therefore, we performed an epidemiologic investigation of RABV in the main fur animal farming provinces during 2017-2019. The results showed that brain tissue samples from eight animals that presented with central nervous symptoms were positive for rabies virus according to direct fluorescent antibody assays and RT-PCR. The phylogenetic relationships and distributions of the viruses were determined, and the results indicated that they belonged to Cosmopolitan and Arctic-related lineages. Serological investigations revealed a RABV positivity rate of 2.78% (34/1,222) in fur animals. A total of 79 unimmunized breeders were negative for serum antibodies, and 9.62% of 52 immunized breeders (5/52) were not seroconverted. The results emphasize that specific wild fur animals are potential sources of RABV and that the current vaccination programme for animals and breeders is deficient, indicating the need for mandatory rabies vaccination to eliminate rabies transmission from dogs to farmed fur animals.

Dual Role of Toll-Like Receptor 7 in the Pathogenesis of Rabies Virus in a Mouse Model

Rabies, caused by rabies virus (RABV), is a fatal encephalitis in humans and other mammals, which continues to present a public health threat in most parts of the world. Our previous study demonstrated that Toll-like receptor 7 (TLR7) is essential in the induction of anti-RABV antibodies via the facilitation of germinal center formation. In the present study, we investigated the role of TLR7 in the pathogenicity of RABV in a mouse model. Using isolated plasmacytoid dendritic cells (pDCs), we demonstrated that TLR7 is an innate recognition receptor for RABV. When RABV invaded from the periphery, TLR7 detected viral single-stranded RNA and triggered immune responses that limited the virus's entry into the central nervous system (CNS). When RABV had invaded the CNS, its detection by TLR7 led to the production of cytokines and chemokines and an increase the permeability of the blood-brain barrier. Consequently, peripheral immune cells, including pDCs, macrophages, neutrophils, and B cells infiltrated the CNS. While this immune response, triggered by TLR7, helped to clear viruses, it also increased neuroinflammation and caused immunopathology in the mouse brain. Our results demonstrate that TLR7 is an innate recognition receptor for RABV, which restricts RABV invasion into the CNS in the early stage of viral infection but also contributes to immunopathology by inducing neuroinflammation.IMPORTANCE Developing targeted treatment for RABV requires understanding the innate immune response to the virus because early virus clearance is essential for preventing the fatality when the infection has progressed to the CNS. Previous studies have revealed that TLR7 is involved in the immune response to RABV. Here, we establish that TLR7 recognizes RABV and facilitates the production of some interferon-stimulated genes. We also demonstrated that when RABV invades into the CNS, TLR7 enhances the production of inflammatory cytokines which contribute to immunopathology in the mouse brain. Taken together, our findings suggest that treatments for RABV must consider the balance between the beneficial and harmful effects of TLR7-triggered immune responses.

Neuropathology and diagnostic features of rabies in a litter of piglets, with a brief review of the literature

Porcine rabies is exceedingly rare worldwide. We describe herein the neuropathology and the diagnostic features of an outbreak of rabies in a litter of piglets attacked by a skunk in Georgia, United States. Rabies viral infection was confirmed in 2 of 3 piglets submitted for testing. Inflammatory and degenerative changes were more prominent in the brainstem and consisted of lymphoplasmacytic meningoencephalitis with glial nodules, neuronal necrosis, and neuronophagia. No viral inclusions (Negri bodies) were observed in multiple sections of brain. A fluorescent antibody test on fresh samples of brainstem and cerebellum was confirmatory for the eastern United States raccoon rabies virus variant. Immunoreactivity for rabies virus was detected across all brain sections in both cases but was more prominent in the thalamic and brainstem nuclei, as well as in the medial lemniscus. Rabies is an important differential diagnosis in pigs with neurologic disease.

Toll-Like Receptor 7 Enhances Rabies Virus-Induced Humoral Immunity by Facilitating the Formation of Germinal Centers

Rabies virus (RABV) causes fatal encephalitis in mammals and poses a public health threat in many parts of the world. Vaccination remains the most effective means for prevention and control of rabies. Studies focusing on the mechanism of RABV immunogenicity are necessary for improvement of rabies vaccines. Toll-like receptor 7 (TLR7), an innate receptor sensing single-stranded viral RNA, is important for the induction of innate and adaptive immunity. Our studies revealed that the absence of TLR7 led to a lower antibody production in mice immunized with RABV. It is further found that TLR7 deficiency affected the recruitment of germinal center (GC) B cells and led to lessened GCs formation. Consistently, there were less plasma cells (PCs) and antibody secreting cells (ASC) in TLR7^-/- mice than those in wild type (WT) mice, resulting in impaired production of RABV-neutralizing antibodies (VNA). TLR7 deficiency also impaired the generation of memory B cells (MBCs) and the induction of secondary immune responses. Moreover, TLR7 deficiency down-regulated the induction of some cytokines/chemokines, especially IFN-γ, resulting in a Th2-biased antibody production. Overall, our results suggest that TLR7 facilitates the induction of the humoral immunity in response to RABV.

A recombinant rabies virus (ERAGS) for use in a bait vaccine for swine

Purpose

Rabies viruses (RABV) circulating worldwide in various carnivores occasionally cause fatal encephalitis in swine. In this study, the safety and immunogenicity of a recombinant rabies virus, the ERAGS strain constructed with a reverse genetics system, was evaluated in domestic pigs.

Materials and Methods

Growing pigs were administered 1 mL (10^8.0 FAID₅₀/mL) of the ERAGS strain via intramuscular (IM) or oral routes and were observed for 4 weeks' post-inoculation. Three sows were also inoculated with 1 mL of the ERAGS strain via the IM route. The safety and immunogenicity in swine were evaluated using daily observation and a virus-neutralizing assay (VNA). Fluorescent antibody tests (FAT) for the RABV antigen and reverse transcriptase-polymerase chain reaction (RT-PCR) assays for the detection of the nucleocapsid (N) gene of RABV were conducted with brain tissues from the sows after necropsy.

Results

The growing pigs and sows administered the ERAGS strain did not exhibit any clinical sign of rabies during the test period test and did develop VNA titers. The growing pigs inoculated with the ERAGS strain via the IM route showed higher VNA titers than did those receiving oral administration. FAT and RT-PCR assays were unable to detect RABV in several tissues, including brain samples from the sows.

Conclusion

Our results suggest that the ERAGS strain was safe in growing pigs and sows and induced moderate VNA titers in pigs.

Disease outbreaks caused by steppe-type rabies viruses in China

While rabies is a significant public health concern in China, the epidemiology of animal rabies in the north and northwest border provinces remains unknown. From February 2013 to March 2014, seven outbreaks of domestic animal rabies caused by wild carnivores in Xinjiang (XJ) and Inner Mongolia (IM) Autonomous Regions, China were reported and diagnosed in brain samples of infected animals by the fluorescent antibody test (FAT) and RT-PCR. Ten field rabies viruses were obtained. Sequence comparison and phylogenetic analysis based on the complete N gene (1353 bp) amplified directly from the original brain tissues showed that these ten strains were steppe-type viruses, closely related to strains reported in Russia and Mongolia. None had been identified previously in China. The viruses from XJ and IM clustered separately into two lineages showing their different geographical distribution. This study emphasizes the importance of wildlife surveillance and of cross-departmental cooperation in the control of transboundary rabies transmission.

Characterization of a wild rabies virus isolate of porcine origin in China

Rabies virus (RABV) that circulates worldwide in a variety of mammals can cause fatal encephalomyelitis. GD-SH-01, a street rabies virus, was isolated from a rabid pig in China. We investigated the pathogenicity of GD-SH-01 in suckling and adult mice, and compared the susceptibility of NA and BHK-21 cells in the culture to infection by GD-SH-01 and CVS-24. The complete GD-SH-01 genome sequence was determined and compared with known RABV wild strains to understand the mutations and genetic diversity that allow RABV to spread and adapt in new hosts, such as pigs. Our results suggest that GD-SH-01 possesses the characteristics of a virulent strain in Southern China and shows higher pathogenicity index than that of CVS-24 regardless of its lower level of replication in mouse brain. Up to 47 unique nucleotide substitutions were found in the genome, including five missense mutations. These data provide useful information for further understanding the transmission mechanism and the genetic variation of RABV in dissimilar hosts.

Complete genome sequence of a highly virulent rabies virus isolated from a rabid pig in south China

A virulent rabies virus (RABV) strain, GD-SH-01, was isolated from brain tissue of a rabid pig in China. This report describes the first complete genome sequence of a swine-origin RABV strain, and this information will provide important insights into the transmission cycle and genetic diversity of RABV from different hosts in China.

An outbreak of sheep rabies in Shanxi province, China

This study describes an outbreak of rabies in a flock of 110 sheep in Yangqu county, Shanxi province, China, in 2010. The flock, housed in a cave being used as a sheepfold, was attacked by a rabid dog, which resulted in 36 deaths over the following 2 days from the crushing and trampling caused by panic, and some 15 further deaths from rabies 2 weeks later. Rabies in the sheep was confirmed by the fluorescent antibody test (FAT) and RT-PCR. Rabies virus was isolated from the index dog brain and its N gene was partially sequenced (nucleotides 77-880). Results showed that the canine isolate (SXTYD01) was rabies virus with the N gene fragment 100% identical to that of the virus isolated from rabid sheep. This is the first confirmed sheep rabies outbreak in China. The clinical presentation of the disease is also described.

Diagnosis and molecular characterization of rabies virus from a buffalo in China: a case report

Background

Rabies virus (RABV) can infect many different species of warm-blooded animals. Glycoprotein G plays a key role in viral pathogenicity and neurotropism, and includes antigenic domains that are responsible for membrane fusion and host cell receptor recognition.

Case presentation

A case of buffalo rabies in China was diagnosed by direct fluorescent antibody test, G gene reverse-transcriptase polymerase chain reaction, and RABV mouse inoculation test. Molecular characterization of the RABV was performed using DNA sequencing, phylogenetic analysis and amino acid sequence comparison based on the G gene from different species of animals.

Conclusion

The results confirmed that the buffalo with suspected rabies was infected by RABV, which was genetically closely related to HNC (FJ602451) that was isolated from cattle in China in 2007. Comparison of the G gene among different species of animal showed that there were almost no amino acid changes among RABVs isolated from the same species of animals that distributed in a near region. However, there were many changes among RABVs that were isolated from different species of animal, or the same species from different geographic regions. This is believed to be the first case report of buffalo rabies in China, and the results may provide further information to understand the mechanism by which RABV breaks through the species barrier.

Rabies in China: an update

Human rabies cases in China have continued to increase in recent years, reaching a new peak in 2007. Parallel with an increase in human rabies deaths, a number of animal species with rabies have been reported in the majority of rabies-endemic areas. In this report, the occurrence, status, and control of rabies in both humans and animals are reviewed. Vaccines and immunoglobulin for human and animal use and postexposure prophylaxis for human are also summarized. The current strategies for rabies elimination in China are presented.