Efficacy of rabies vaccines in dogs and cats and protection in a mouse model against European bat lyssavirus type 2

Identification of risk factors on rabies vaccine efficacy from censored data: Pre-travel tests for dogs and cats from Yaoundé (2005-2015)

Little research is available on acquired immunity to rabies in dogs and cats from Central Africa, particularly regarding the legal movements of pets. Movement of domestic animals from rabies-endemic countries like Cameroon to rabies free areas poses one of the main risks for rabies introduction into rabies-free areas. Thus, the aim of this study was to assess the effect of various risk factors on rabies vaccine efficacy in Cameroonian. Since the dependent variable, rabies neutralizing titres, were censored from above (right-censoring), Generalized Additive Model for Location, Scale and Shape (GAMLSS) was used in the analysis. Overall, 85.7% of dogs and 100% of cats had titres greater than or equal to 0.5 IU/mL, which is considered protective. Additionally, compared to cats, the value of the rabies-neutralizing serum titres in dogs was on average smaller by 2.3 IU/mL. For each additional year of age, the value of the rabies-neutralizing serum titre, on average, increased by approximately 0.14 IU/mL. Finally, for each 30 additional days between the date of the last rabies vaccination and the date of the sampling, the value the rabies neutralizing titre, on average, decreased by approximately 0.10 IU/mL, given the species and age at sampling were equivalent. These results are useful for assessing risk and improving surveillance to prevent the introduction of rabies into a country via the international movement of animals.

Bayesian modeling of post-vaccination serological data suggests that yearly vaccination of dog aged <2 years old is efficient to stop rabies circulation in Cambodia

Rabies control remains challenging in low and middle-income countries, mostly due to lack of financial resources, rapid turnover of dog populations and poor accessibility to dogs. Rabies is endemic in Cambodia, where no national rabies vaccination program is implemented. The objective of this study was to assess the short and long-term vaccination-induced immunity in Cambodian dogs under field conditions, and to propose optimized vaccination strategies. A cohort of 351 dogs was followed at regular time points following primary vaccination only (PV) or PV plus single booster (BV). Fluorescent antibody virus neutralization test (FAVNT) was implemented to determine the neutralizing antibody titer against rabies and an individual titer ≥0·5 IU/mL indicated protection. Bayesian modeling was used to evaluate the individual duration of protection against rabies and the efficacy of two different vaccination strategies. Overall, 61% of dogs had a protective immunity one year after PV. In dogs receiving a BV, this protective immunity remained for up to one year after the BV in 95% of dogs. According to the best Bayesian model, a PV conferred a protective immunity in 82% of dogs (95% CI: 75-91%) for a mean duration of 4.7 years, and BV induced a lifelong protective immunity. Annual PV of dogs less than one year old and systematic BV solely of dogs vaccinated the year before would allow to achieve the 70% World Health Organization recommended threshold to control rabies circulation in a dog population in three to five years of implementation depending on dog population dynamics. This vaccination strategy would save up to about a third of vaccine doses, reducing cost and time efforts of mass dog vaccination campaigns. These results can contribute to optimize rabies control measures in Cambodia moving towards the global goal of ending human death from dog-mediated rabies by 2030.

Tracking lethal threat: in-depth review of rabies

An infectious disease known as rabies (family Rhabdoviridae, genus Lyssavirus) causes severe damage to mammals' central nervous systems (CNS). This illness has been around for a very long time. The majority of human cases of rabies take place in underdeveloped regions of Africa and Asia. Following viral transmission, the Rhabdovirus enters the peripheral nervous system and proceeds to the CNS, where it targets the encephalon and produces encephalomyelitis. Postbite prophylaxis requires laboratory confirmation of rabies in both people and animals. All warm-blooded animals can transmit the Lyssavirus infection, while the virus can also develop in the cells of cold-blooded animals. In the 21st century, more than 3 billion people are in danger of contracting the rabies virus in more than 100 different nations, resulting in an annual death toll of 50,000-59,000. There are three important elements in handling rabies disease in post exposure prophylaxis (PEP), namely wound care, administration of anti-rabies serum, and anti-rabies vaccine. Social costs include death, lost productivity as a result of early death, illness as a result of vaccination side effects, and the psychological toll that exposure to these deadly diseases has on people. Humans are most frequently exposed to canine rabies, especially youngsters and the poor, and there are few resources available to treat or prevent exposure, making prevention of human rabies challenging.

Dog Population Rabies Immunity before a Mass Vaccination Campaign in Lima, Peru: Vulnerabilities for Virus Reestablishment

Lima, Peru, has not had a case of canine rabies since 1999. However, Lima remains at risk of rabies reintroduction due to the free movement of dogs from nearby rabies-endemic areas. In Latin America, rabies vaccination campaigns must reach 80% of dogs to halt transmission, but estimates of vaccine coverage are often unavailable, unreliable, or inaccurate. Quantifying virus neutralizing antibodies (VNA) allows monitoring of the immunological status of the canine population, evaluation of the degree of humoral protection to the virus, and assessing, partially, the population response to vaccination. We evaluated the dog population's immunity level against the rabies virus before a mass vaccination campaign in Lima. We collected 141 canine blood samples in the district of Surquillo and quantified rabies virus neutralizing antibody titers using the fluorescent antibody virus neutralization test). We surveyed dogs owners to reconstruct canine vaccination histories. Among dogs previously vaccinated, 73.9% exceeded the seroconversion threshold of > 0.5 IU/mL. Among all dogs, only 58.2% reached the titer limit for seroconversion. Dogs ≤ 1 year old constituted 26.2% of the total canine population and had lower levels of VNA than dogs > 1 year old (χ2 = 9.071; P = 0.028). Importantly, dogs vaccinated with single-pathogen vaccines had higher levels of VNA than those who received combined-pathogen vaccines (χ2 = 7.721; P = 0.005). We provide an important and timely glimpse to the immunity status of the dog population in urban areas of Lima, a metropolis near a dog rabies-endemic region.

Novel Bat Lyssaviruses Identified by Nationwide Passive Surveillance in Taiwan, 2018–2021

Bat lyssaviruses were identified in Taiwan’s bat population during 2016–2017. The lyssavirus surveillance system was continuously conducted to understand the epidemiology. Through this system, the found dead bats were collected for lyssavirus detection by direct fluorescent antibody test and reverse transcription polymerase chain reaction. Three bats were identified as positive during 2018–2021. A novel lyssavirus, designated as Taiwan bat lyssavirus 2, was detected in a Nyctalus plancyi velutinus. This lyssavirus had less than 80% nucleotide identity in the nucleoprotein (N) gene with other lyssavirus species, forming a separate branch in the phylogenetic analysis. The other two cases were identified in Pipistrellus abramus (Japanese pipistrelles); they were identified to be similar to the former lyssavirus identified in 2016–2017, which was renominated as Taiwan bat lyssavirus 1 (TWBLV-1) in this study. Even though one of the TWBLV-1 isolates showed high genetic diversity in the N gene compared with other TWBLV-1 isolates, it may be a TWBLV-1 variant but not a new species based on its high amino acid identities in the nucleoprotein, same host species, and same geographic location as the other TWBLV-1.

Robust humoral immune response against rabies virus in rabbits and guinea pigs immunized with plasmid DNA vectors encoding rabies virus glycoproteins - An approach to the production of polyclonal antibody reagents

DNA-based immunization has been previously shown to be an efficient approach to induce robust immunity against infectious diseases in animals and humans. The advantages of DNA vaccines are simplicity of their construction and production, low cost, high stability, and ability to elicit a full spectrum of immune responses to target antigens. The goals of this study were (i) to assess the antibody immune response to rabies virus glycoproteins (rGPs) in rabbits and guinea pigs after intramuscular immunization with pTargeT and pVAC2-mcs mammalian expression vectors encoding either the wild-type (WT) or codon-optimized (cOPT) rGP genes; and (ii) to prepare in-house rabbit anti-rGP polyclonal antibody reagents suitable for in Single Radial Immunodiffusion (SRID) and Indirect Fluorescent Antibody (IFA) assays. The maximum antibody responses against rabies virus in rabbits and guinea pigs were observed after immunization series with 500 μg/dose of pVAC2-mcs vector encoding either the WT or cOPT rGP genes adjuvanted with Emulsigen-D. No significant difference in the anti-rabies virus neutralizing antibody titers was observed in rabbits immunized with the WT and cOPT rGPs. The in-house rabbit anti-rGP polyclonal antibody reagents reacted comparable to the current reference reagents in SRID and IFA assays. The results of the study demonstrated that the DNA immunization of animals with the WT or cOPT rGPs is a promising approach to either induction of high anti-rabies virus neutralizing antibody titers in vivo or for production of polyclonal antibody reagents against rabies.

[Anti-rabies vaccines applied in the Russian Federation and perspectives for their improvement]

Rabies is almost ubiquitous (except in certain areas) and poses a significant danger to both animals and humans. Every year around 55,000 people die from this disease worldwide. In the Russian Federation alone 400,000- 450,000 patients annually apply for anti-rabies treatment. In the absolute majority of cases human infection is caused by contact with infected animals. In RF, a number of cultured inactivated anti-rabies vaccines for medical and veterinary purposes have been developed, registered and used for specific prevention of rabies. These vaccine preparations have shown high effectiveness in preventing infection in domestic and farm animals. At the same time, the main reservoir of the rabies virus (Mononegavirales: Rhabdoviridae: Lyssavirus) (RV) are wild carnivores (Mammalia: Carnivora). For the purpose of their oral immunization, live virus vaccines from attenuated (fixed) strains of RV that are little resistant in the external environment are used. In Western Europe and North America there is successful experience with recombinant anti-rabies vaccine preparations containing a viral glycoprotein gene (G-protein). Such vaccines are safe for humans and animals. In Russia also had been developed a vector anti-rabies vaccine based on adenovirus (Adenoviridae), which can be used to combat this infection. Currently, in addition to classical rabies, diseases caused by new, previously unknown lyssaviruses (Lyssavirus) are becoming increasingly important. Bats (Mammalia: Microchiroptera) are their vectors. Cases of illness and death after contact with these animals have been described. In the near future, we should expect the development of new vaccines that will provide protection not only against RV, but also against other lyssaviruses.

Evaluation of dog vaccination schemes against rabies in Kinshasa, Democratic Republic of the Congo

The traditional rabies control strategy based on annual mass vaccination of dogs appears to be costly and cumbersome. Given the existence of different risk zones for rabies transmission, the present study aimed at proposing risk-based vaccination schemes by considering canine population dynamics as well as vaccine efficacy and duration of immunity (DOI). The capital of the Democratic Republic of the Congo (RDC), Kinshasa, was chosen as study site. The turnover rate of dogs was used to assess their population dynamics in two low-roaming (<25 % of dogs are roaming) and in two high-roaming zones (>75 % of dogs are roaming). The sero-conversion rate was assessed in response to primo-vaccination in three age groups: 24 puppies (≤3months), 37 juveniles (4-12 months) and 22 adult dogs. The DOI was evaluated serologically by revaccinating dogs previously vaccinated since 1-2 years (n = 31), 2-3 years (n = 12) or 3-7.5 years (n = 4). Rapid Fluorescent Focus Inhibition Test was used to quantify antibodies. These data were used to implement vaccination outcome models.The turnover rate was twice as high in high-roaming zones (36 %) as that in lowroaming zones (17 %). Irrespective of roaming level, 75 % of dogs were less than 3 years old. The vaccine was equally effective in puppies (96 %), juvenile (97 %) and adult dogs (100 %, p = 0.24). The vaccine was effective in 93 % (11/12) of puppies without pre-vaccinal protective titers (≥0.5 IU/mL). The anamnestic response was strong within 5-8 days upon the booster vaccination, in 96 % (45/47) of dogs reported vaccinated 1-7.5 years before. This suggests that the vaccine provided a long-term protection (≥3 years) which is likely to occur in 75 % of dogs in Kinshasa.Hypothesizing a vaccination stop, the vaccination outcome model allowed to estimate the time point after which vaccination coverage would drop below 40 % in function of dog population turnover rate. The systematic vaccination of puppies as well as annual vaccination of dogs aged between 3 and 15 months or annual vaccination of all unvaccinated dogs aged more than 3 months of age appeared as valuable alternative to systematic annual mass vaccination.In conclusion, this study developed a vaccination outcome model pointing out the impact of dog population dynamics and of effective duration of immunity. It appears as a promising tool for designing cost-effective rabies vaccination campaigns.

[Optimization of rabies (Rhabdoviridae: Lyssavirus) dog vaccination schedule using a mathematical model]

INTRODUCTION

Most cases of human rabies are caused by dog (Canis lupus familiaris) bites. Therefore, the implementation of vaccination programs of these animals is one of the urgent tasks.The work aims to identify the factors influencing the production of antirabies virus-neutralizing antibodies (VNAs) in vaccinated dogs, and to formulate recommendations for adjusting the vaccination schedule using mathematical modeling (MM).

MATERIAL AND METHODS

We used a fixed-effects modeling procedure to estimate the two-compartment model parameters using log-transformed data (obtained by RFFIT, rapid fluorescent focus inhibition test; and FAVN, fluorescent antibody virus-neutralization test) on the VNAs levels in the serum of vaccinated dogs.

RESULTS

More vigorous immune response after a two-dose primary vaccination is formed in juvenile dogs at the age of 3 months to 1 year compared to the adult dogs. Following the primary vaccination and revaccination 1 year after, VNAs were produced more intensively in adult stray dogs than in domestic dogs.

DISCUSSION

The short-term immune response observed in dogs aged up to 3 months is due to the presence of colostral antibodies and the active growth of the organism at this age. The results of our study confirm that most of the dogs have a level of antirabies VNAs of ≥0.5 IU/ml up to two or more years following immunization. However, only regular annual revaccination ensures the protective VNAs level in animals that responded poorly to vaccination due to various factors.

CONCLUSION

The following antirabies vaccination schedule is recommended: primary vaccination of the dog at the age of 3 months up to 1 year with 1-2 month intervals, then revaccination annually. This work also demonstrates the possibility of a wider application of MM methods for solving problems of vaccine prevention.

Immunogenicity of an inactivated rabies vaccine for animals derived from the recombinant ERAGS strain

Purpose

The aims of the present study were to evaluate the immunogenicity of an inactivated rabies vaccine based on the ERAGS strain

Materials and Methods

The ERAGS virus propagated in Vero cells was inactivated with 3 mM binary ethylenimine for 8 hours. Three types of inactivated rabies vaccines were prepared to determine the minimum vaccine virus titers. Four further types of inactivated rabies vaccines were prepared by blending inactivated ERAGS with four different adjuvants; each vaccine was injected into mice, guinea pigs, and dogs to identify the optimal adjuvant. The immunogenicity of a Montanide (IMS) gel-adjuvanted vaccine was evaluated in cats, dogs, and cattle. Humoral immune responses were measured via a fluorescent antibody virus neutralization method and a blocking enzyme-linked immunosorbent assay.

Results

The minimum virus titer of the inactivated rabies vaccine was over 10^7.0 50% tissue culture infectious doses (TCID₅₀ values)/mL. Of the four kinds of adjuvants, the IMS gel-adjuvanted vaccine induced the highest mean viral neutralizing antibody (VNA) titers of 6.24 and 2.36 IU/mL in guinea pigs and dogs, respectively, and was thus selected as the vaccine for the target animals. Cats, dogs, and cattle inoculated with the IMS gel-adjuvanted vaccine developed protective VNA titers ranging from 3.5 to 1.2 IU/mL at 4 weeks post-inoculation (WPI).

Conclusion

Our data indicate that cats, dogs, and cattle inoculated with an inactivated rabies vaccine derived from the ERAGS strain developed protective immune responses that were maintained to 12 WPI.

Genome-based local dynamics of canine rabies virus epidemiology, transmission, and evolution in Davao City, Philippines, 2018-2019

Rabies is a fatal zoonotic and neglected tropical disease caused by the rabies virus (RABV) and is associated with neuronal dysfunction and death, with dogs as the predominant carrier. The Philippines plans to eradicate rabies by 2022, but this is challenged with sub-optimal coverage of vaccination programs coupled with sustained transmission chains, making it unable to eradicate the disease. We investigated the dynamics of canine rabies in the highly urbanized Davao City of the Philippines and its neighboring localities by assessing genetic relationships, transmission patterns, selection pressure, and recombination events using the whole genome sequence of 49 RABV cases from June 2018 to May 2019, majority of which (46%) were from the district of Talomo, Davao City. Although phylogeographic clustering was observed, local variants also exhibited genetic sub-lineages. Phylogenetic and spatial transmission analysis provided evidence for intra- and inter-city transmission predominantly through the Talomo district of Davao City. Around 84% of the cases were owned dogs, but the genetic similiarity of RABVs from stray and owned dogs further alluded to the role of the former as transmission vectors. The high rate of improper vaccination among the affected dogs (80%) was also a likely contributor to transmission. The RABV population under Investigation is generally under strong purifying selection with no evidence of vaccine evasion due to the genetic homogeneity of viruses from vaccinated and improperly vaccinated dogs. However, some homologous recombination (HR) events were identified along the G and L genes, also predominantly associated with viruses from Talomo. The complementary findings on epidemiology, transmission, and recombination for Talomo suggest that high incidence areas can be seeds for virus dispersal and evolution. We recommend further Investigations on the possibility of HR in future large-scale genome studies. Finally, districts associated with these phenomena can be targeted for evidence-based local strategies that can help break RABV transmission chains and prevent emergence of novel strains in Davao City.

Cross-Protection of Inactivated Rabies Vaccines for Veterinary Use against Bat Lyssaviruses Occurring in Europe

Human rabies vaccines have been shown to induce partial protection against members of phylogroup I bat lyssaviruses. Here, we investigated the capacity of a widely used rabies inactivated vaccine (Rabisin, Boehringer-Ingelheim) for veterinary use to cross-protect mice experimentally infected with European bat lyssavirus 1 (EBLV-1b), European bat lyssavirus 2 (EBLV-2), and Bokeloh bat lyssavirus (BBLV) occurring in Europe. For each lyssavirus, we investigated the efficacy of two different doses of vaccine against two viral doses administrated by either central or peripheral routes. In parallel, seroconversion following pre-exposure vaccination was investigated. In this study, we demonstrated that the three investigated bat isolates were pathogenic, even at low dose, when inoculated by the central route but were not/less pathogenic when administrated peripherally. The Rabisin vaccine was capable of significantly cross-protecting mice inoculated intramuscularly with EBLV-1b and EBLV-2 and intracerebrally with BBLV. The level of rabies neutralizing antibodies induced by the Rabisin was quite high against the bat lyssaviruses, but with no significant differences between immunization with 1 and 5 IU/dose. The study emphasizes that the quality of rabies-inactivated vaccines for veterinary use is of utmost importance to optimize the cross-protection of pets against phylogroup I bat lyssaviruses occurring in Europe.

Risk assessment on rabies entry through hunting dog movement with semi-quantitative approach to Sumatera Island, Indonesia

Objective:

The objective of this study was to assess the risk of rabies entry through the movement of hunting dog from Garut District to Sumatera Island with a semi-quantitative approach.

Materials and Methods:

Rabies entry assessment used the standard risk analysis according to the World Organization for Animal Health, with a semi-quantitative approach referring to Australian Biosecurity. Risk estimation calculation used Microsoft Excel and probabilities were estimated using Monte Carlo stochastic simulation modeling with @Risk (Palisade Corporation).

Results:

Risk estimation were considered as “very low” with a 0.02 (90%; 0.01–0.03) probability. The probability of undetected rabies-infected dog during Veterinary Certificate issuance [node probability (NP4)] was considered as the highest, with “moderate” likelihood and 0.63 (90%; 0.51–0.75) of probability value. The number of dog movement to Sumatera reached 27,000 heads per year which 5,050 heads of them come from Garut District. There were 2 of 100 dogs from Garut District entered to Sumatera possibly infected by rabies. The five highest parameters most determinant of the risk were dog vaccination before transported (0.66), dog obtained from other District (0.41), vaccination program (0.32), serologically test (0.27), and history of vaccination (0.23).

Conclusion:

Risk estimation from assessing on rabies entry to Sumatera through hunting dogs movement from Garut District was considered “very low.” Risk mitigation is focused on the highest parameters that contribute the most to risk based on the results of the sensitivity analysis. Semi-quantitative likelihood evaluations can consider the volume of dog traffic which is an important issue in risk analysis which is not easy to get with a simpler qualitative approach.

Comparative study of rabies antibody titers of dogs vaccinated in Finland and imported street dogs vaccinated abroad

Seventy-two canine serum samples were analyzed for post-vaccination serum titers of rabies antibodies. The samples were divided into two groups: Group 1 dogs (n = 36) were imported dogs from the Russian Federation (n = 31) or Romania (n = 5), with a mean serum antibody titer value of 1.54 IU/mL. Group 2 dogs (n = 36) were Finnish dogs vaccinated in Finland, with a mean titer of 4.19 IU/mL. Altogether, 14 (39%) dogs (CI 95% 23-56) were without detectable antibodies (≤ 0.1 IU/mL) in Group 1, whereas in Group 2, all dogs had an antibody titer greater than 0.1 IU/mL. A statistically significant difference was observed between these groups when comparing the proportions of dogs with antibody levels less than or exceeding 0.5 IU/mL. In Group 1, 19 out of the 36 dogs (CI 95% 36-70) had serum titer values < 0.5 IU/mL, while in Group 2, only 2 dogs had serum titer values < 0.5 IU/mL. Despite the small sample size, this raises concern over the imported dogs having insufficient antibody levels required for international travel and implies that these dogs had perhaps not been vaccinated, even though they had documentation of vaccination upon arrival.