One-step protocol for amplification of near full-length cDNA of the rabies virus genome

Comparison of 4 laboratory tests for the detection of bovine rabies viral infection in Paraguay: fluorescent antibody test, rapid detection test, histologic lesions, and RT-PCR

Rabies virus (RABV; Lyssavirus rabies) is a neurotropic virus that can be transmitted to mammals by the hematophagous bat Desmodus rotundus. An accurate, accessible method for the detection of RABV in cattle is necessary in Paraguay; thus, we evaluated the detection of RABV using 4 techniques: fluorescent antibody test (FAT), immunochromatography rapid detection test (RDT; Anigen Rapid Rabies Ag test kit; Bionote), a reverse-transcription PCR (RT-PCR) assay, and histologic lesions in different portions of the CNS of 49 Paraguayan cattle to determine the most sensitive and specific technique. By FAT and RDT, 15 of 49 (31%) samples were positive. By RT-PCR amplification of N and G genes, 13 of 49 (27%) and 12 of 49 (25%) were positive, respectively. RDT had high agreement with FAT (kappa = 1); sensitivity was 100% (95% CI: 97-100%) and specificity was 100% (95% CI: 99-100%). The amplification of the N and G genes resulted in substantial agreement (kappa of 0.9 and 0.8, respectively) compared with FAT, and the sensitivity and specificity of the N gene were 87% (95% CI: 66-100%) and 100% (95% CI: 98-100%), respectively, and those of the G gene were 80% (95% CI: 56-100%) and 100% (95% CI: 98-100%), respectively. Histologic lesions observed were lymphoplasmacytic meningoencephalitis, gliosis, and neuronophagia. The agreement observed between the FAT and RDT tests suggests that RDT is an accurate tool for the detection of RABV. Histopathology can be used to confirm lesions caused by RABV and to rule out other conditions; the RT-PCR assay is useful for molecular epidemiology studies.

Evaluation of LN34 Pan-Lyssavirus RT-qPCR assay for rabies diagnosis in Brazil

Rabies, a fatal zoonotic viral disease affecting mammals, including humans, remains a significant global health concern, particularly in low-income countries. The disease, primarily transmitted through infected animal saliva, prompts urgent diagnosis for timely post-exposure prophylaxis (PEP). The gold standard diagnostic test, direct fluorescent antibody test (dFAT), while sensitive, suffers from limitations such as subjective interpretation and high costs. As a confirmatory technique, the LN34 Pan-Lyssavirus RT-qPCR assay has emerged as a promising tool for universal Lyssavirus detection. This study evaluated its performance using 130 rabies virus isolates representing eleven Brazilian variants and 303 clinical samples from surveillance operations. The LN34 assay demonstrated 100% sensitivity and 98% specificity compared to dFAT. Additionally, it detected all samples, including those missed by dFAT, indicating superior sensitivity. The assay's specificity was confirmed through Sanger nucleotide sequencing, with only a minimal false-positive rate. Comparative analysis revealed higher accuracy and concordance with dFAT than traditional rabies tissue culture infection tests (RTCIT). False-negative RTCIT results were attributed to low viral load or suboptimal sampling. These findings underscore the LN34 assay's utility as a confirmatory technique, enhancing rabies surveillance and control in Brazil. Its widespread adoption could significantly improve diagnostic sensitivity, crucial for effective PEP and public health interventions.

No Evidence of Rabies Exposure in Wild Marmosets (Callithrix jacchus) of Northeast Brazil

Rabies transmitted by wildlife is the main source of human rabies mortality in Latin America and considered an emerging disease. The common marmoset Callithrix jacchus of Brazil is the only known primate reservoir of rabies worldwide. We tested whether alive free-ranging C. jacchus were exposed to rabies in four northeast states that have previously reported rabies-positive dead C. jacchus (Pernambuco and Bahia) or not (Paraíba and Rio Grande do Norte). Our results show no evidence of rabies antibodies or infection in the sampled C. jacchus, suggesting that apparently healthy marmosets are not widely exposed to rabies over their natural range.

Rabies virus diversification in aerial and terrestrial mammals

Rabies is a fatal zoonotic infection of the central nervous system of mammals and has been known to humans for millennia. The etiological agent, is a neurotropic RNA virus in the order Mononegavirales, family Rhabdoviridae, genus Lyssavirus. There are currently accepted to be two cycles for rabies transmission: the urban cycle and the sylvatic cycle. The fact that both cycles originated from a common RABV or lyssavirus ancestor and the adaptive divergence that occurred since then as this ancestor virus adapted to a wide range of fitness landscapes represented by reservoir species in the orders Carnivora and Chiroptera led to the emergence of the diverse RABV lineages currently found in the sylvatic and urban cycles. Here we study full genome phylogenies and the time to the most recent common ancestor (TMRCA) of the RABVs in the sylvatic and urban cycles. Results show that there were differences between the nucleotide substitution rates per site per year for the same RABV genes maintained independently in the urban and sylvatic cycles. The results identify the most suitable gene for phylogenetic analysis, heterotachy among RABV genes and the TMRCA for the two cycles.

Fox rabies outbreaks in the republic of Buryatia: Connections with neighbouring areas of Russia, Mongolia and China

The Republic of Buryatia (RB) is located southeast of Lake Baikal and shares a long border with Mongolia. This region of Russia was rabies-free from 1982 to 2010. The first outbreak of fox rabies in RB was identified in 2011, about 30 km from the Russian-Mongolian border. We assessed the possible pathways to further spread the 'steppe' phylogenetic lineage of the rabies virus near the northeastern limits of its known distribution. All rabies cases were located 30-210 km north of the Russia-Mongolia border, with a distance of up to 320 km from each other. Rabies has spread to the north across steppe landscapes and river valleys, with foxes being the main natural hosts of the infection. All RABV isolates from RB belong to the 'steppe' phylogenetic lineage, and three major phylogenic groups could be separated. Group 1 contains sequences from RB, Mongolia, China (Inner Mongolia), and bordering regions of Russia. Group 2 is formed by isolates from other regions of Eastern Siberia, which have no borders with RB and foreign countries. Group 3 contains samples from Western Siberia with endemic fox rabies since the 1950s. The most probable cause of fox rabies epizooty in the RB was multiple drift of the RABV across the Russian-Mongolian border. Our data show that after 2010, fox rabies affected new areas in Central Asia and extended to the north and northeast. Affected areas are similar to the Mongolian-type steppes in their zoogeographical aspect. Closely related genetic lineages of RABV are circulating in RB, Mongolia and the nearest areas of China. International cooperation is necessary to prevent the spread of rabies in the bordering territories of these countries.

Phylogenetic analysis of near full-length sequences of the Desmodus rotundus genetic lineage of rabies virus

The World Health Organization (WHO), reports that rabies causes tens of thousands of deaths every year killing humans, non-human primates and other animals. Rabies continues to be a public health issue, despite the existence of effective vaccines. The dogs remain the primary reservoir and transmitter of rabies to humans globally. In the Americas, bats are regarded as the second most common source of rabies virus to humans. The vampire bat Desmodus rotundus has been identified as a natural reservoir of rabies virus (RABV) in this region. The complete genome of the RABV variant maintained by populations of vampire bats D. rotundus has rarely been reported. In this study, we sequenced and analyzed the genome of a RABV variant detected in D. rotundus. The sample, collected from an endemic area in São Paulo State, was phylogenetically compared with the genome of the standard sample for species Rabies virus as well as other samples belonging to terrestrial and bat-associated cycles of rabies transmission, available in GenBank. Distinct patterns linked to the genetic lineage were identified. These data can aid in the understanding of the molecular epidemiology of this virus and the epidemiological importance of this species in the transmission of the RABV.

Re-emergence of rabies virus maintained by canid populations in Paraguay

Paraguay has registered no human cases of rabies since 2004, and the last case in dogs, reported in 2009, was due to a variant maintained in the common vampire bat "Desmodus rotundus". In 2014, a dog was diagnosed as positive for rabies with aggression towards a boy and all required measures of control were successfully adopted. Epidemiological investigation revealed that the dog was not vaccinated and had been attacked by a crab-eating fox, "zorro" (Cerdocyon thous). The sample was diagnosed by the Official Veterinary Service of the Country and sent to the Center on Rabies Research from the University of São Paulo, Brazil, for antigenic and genetic characterization. A second sample from a dog positive for rabies in the same region in 2015 and 11 samples from a rabies outbreak from Asuncion in 1996 were also characterized. The antigenic profile of the samples, AgV2, was compatible with one of the variants maintained by dogs in Latin America. In genetic characterization, the samples segregated in the canine (domestic and wild species)-related group in an independent subgroup that also included samples from Argentina. These results and the epidemiology of the case indicate that even with the control of rabies in domestic animals, the virus can still circulate in wildlife and may be transmitted to domestic animals and humans, demonstrating the importance of continuous and improved surveillance and control of rabies, including in wild species, to prevent outbreaks in controlled areas.

Molecular and mathematical modeling analyses of inter-island transmission of rabies into a previously rabies-free island in the Philippines

Rabies is endemic in the Philippines and dog bites are a major cause of rabies cases in humans. The rabies control program has not been successful in eliminating rabies because of low vaccination coverage among dogs. Therefore, more effective and feasible strategies for rabies control are urgently required in the country. To control rabies, it is very important to know if inter-island transmission can occur because rabies can become endemic once the virus is introduced in areas that previously had no reported cases. Our molecular epidemiological study suggests that inter-island transmission events can occur; therefore, we further investigated these inter-island transmission using phylogenetic and modeling approaches. We investigate inter-island transmission between Luzon and Tablas Islands in the Philippines. Phylogenetic analysis and mathematical modeling demonstrate that there was a time lag of several months to a year from rabies introduction to initial case detection, indicating the difficulties in recognizing the initial rabies introductory event. There had been no rabies cases reported in Tablas Island; however, transmission chain was sustained on this island after the introduction of rabies virus because of low vaccination coverage among dogs. Across the islands, a rabies control program should include control of inter-island dog transportation and rabies vaccination to avoid viral introduction from the outside and to break transmission chains after viral introduction. However, this program has not yet been completely implemented and transmission chains following inter-island virus transmission are still observed. Local government units try to control dog transport; however, it should be more strictly controlled, and a continuous rabies control program should be implemented to prevent rabies spread even in rabies-free areas.

Experimental infection of the bat tick Carios fonsecai (Acari: Ixodidae) with the rabies virus

INTRODUCTION

This study assessed the viability of the rabies virus in the argasid tick Carios fonsecai following experimental infection.

METHODS

The mouse inoculation test (MIT), fluorescent antibody test (FAT) and polymerase chain reaction (PCR) were used. The rabies virus was administered to ticks via the intra-coelomic route, and the ticks were sacrificed at different time points.

RESULTS

The inoculated ticks were negative for rabies according to the MIT. Ticks macerated with rabies virus were positive according to the MIT and FAT. All of the tick lots tested by PCR were positive. CONCLUSIONS The rabies virus became unviable shortly after its inoculation into tick bodies. Ticks are not likely to play an important role in the epidemiology of rabies.

Enzootic and epizootic rabies associated with vampire bats, peru

During the past decade, incidence of human infection with rabies virus (RABV) spread by the common vampire bat (Desmodus rotundus) increased considerably in South America, especially in remote areas of the Amazon rainforest, where these bats commonly feed on humans. To better understand the epizootiology of rabies associated with vampire bats, we used complete sequences of the nucleoprotein gene to infer phylogenetic relationships among 157 RABV isolates collected from humans, domestic animals, and wildlife, including bats, in Peru during 2002-2007. This analysis revealed distinct geographic structuring that indicates that RABVs spread gradually and involve different vampire bat subpopulations with different transmission cycles. Three putative new RABV lineages were found in 3 non-vampire bat species that may represent new virus reservoirs. Detection of novel RABV variants and accurate identification of reservoir hosts are critically important for the prevention and control of potential virus transmission, especially to humans.

Enzootic and epizootic rabies associated with vampire bats, peru

During the past decade, incidence of human infection with rabies virus (RABV) spread by the common vampire bat (Desmodus rotundus) increased considerably in South America, especially in remote areas of the Amazon rainforest, where these bats commonly feed on humans. To better understand the epizootiology of rabies associated with vampire bats, we used complete sequences of the nucleoprotein gene to infer phylogenetic relationships among 157 RABV isolates collected from humans, domestic animals, and wildlife, including bats, in Peru during 2002-2007. This analysis revealed distinct geographic structuring that indicates that RABVs spread gradually and involve different vampire bat subpopulations with different transmission cycles. Three putative new RABV lineages were found in 3 non-vampire bat species that may represent new virus reservoirs. Detection of novel RABV variants and accurate identification of reservoir hosts are critically important for the prevention and control of potential virus transmission, especially to humans.

Biotechnology advances: a perspective on the diagnosis and research of Rabies Virus

Rabies is a widespread zoonotic disease responsible for approximately 55,000 human deaths/year. The direct fluorescent antibody test (DFAT) and the mouse inoculation test (MIT) used for rabies diagnosis, have high sensitivity and specificity, but are expensive and time-consuming. These disadvantages and the identification of new strains of the virus encourage the use of new techniques that are rapid, sensitive, specific and economical for the detection and research of the Rabies Virus (RABV). Real-time RT-PCR, phylogeographic analysis, proteomic assays and DNA recombinant technology have been used in research laboratories. Together, these techniques are effective on samples with low virus titers in the study of molecular epidemiology or in the identification of new disease markers, thus improving the performance of biological assays. In this context, modern advances in molecular technology are now beginning to complement more traditional approaches and promise to revolutionize the diagnosis of rabies. This brief review presents some of the recent molecular tools used for RABV analysis, with emphasis on rabies diagnosis and research.

Molecular characterization of rabies virus isolated from non-haematophagous bats in Brazil

INTRODUCTION

Rabies is an important zoonosis that causes thousands of deaths worldwide each year. Although the terrestrial cycle, mainly transmitted by dogs, is controlled in Brazil, the aerial cycle remains a serious public health issue, besides the economic problem. In the aerial cycle, the haematophagous bat Desmodus rotundus is the main source of infection, where several different species of non-haematophagous bats can be infected and can transmit the virus.

METHODS

The aim of this work was to study the epidemiological pattern of rabies using antigenic characterization with monoclonal antibodies and genetic characterization by reverse-transcriptase polymerase chain reaction followed by sequencing and phylogenetic analysis of non-haematophagous bats' and herbivorous animals' central nervous system samples from the western region of the State of São Paulo, Brazil.

RESULTS

From 27 samples, 3 antigenic variants were identified: AgV-3, AgV-4, and AgV-6; and from 29 samples, 5 different clusters were identified, all belonging to the rabies virus species.

CONCLUSIONS

Although only non-haematophagous bats were evaluated in the studied region, the majority of samples were from antigenic and genetic variants related to haematophagous bats Desmodus rotundus. Samples from the same antigenic variant were segregated in more than one genetic cluster. This study demonstrated the diversity of rabies virus genetic lineages presented and circulating in non-haematophagous bats in the studied region.