Reassessing the risk from rabies: a continuing threat to the UK?

Proficiency test for rabies serology: A design complying with international standards for a reliable assessment of participating laboratories

BACKGROUND

Domestic carnivores can introduce rabies into disease-free countries or areas if they are incubating the disease and transported during the pre-symptomatic period. For pets moved into the European Union, the European Commission decided to establish a system of community approval of laboratories willing to carry out the rabies serological controls to guarantee an effective control system. As the specific institute to coordinate the approval of the laboratories, designated by the European Commission in 2000, our laboratory organizes annual proficiency tests (PT) for laboratories already agreed or willing to be agreed to perform rabies serological controls (by detecting rabies virus neutralizing antibodies only) in the frame of international trade.

METHODOLOGY/PRINCIPAL FINDINGS

The assessment criteria of this PT rely on the analysis of the specificity and the intra-laboratory consistency. The approach used to evaluate the degree of laboratory consistency is based on the use of compiled data obtained from previous PT campaigns, and is measured by the quality of a regression model. By using historical data for calculating assigned values and associated standard deviations, instead of values obtained from only one campaign, they became robust without any additional statistical treatment. In the present paper, more than 800 historical values were compiled for each of the regression parameters.

CONCLUSIONS/SIGNIFICANCE

Since the beginning of these PT schemes in 1999, the overall percentage of failing laboratories remained stable over the years (4.1%) while the number of participants increased to 79 in 2018. This highlighted the robustness and the consistency of the statistical analyses used to assess the laboratory's performance over the years. The improvements carried out and the consistency of our statistical analyses have resulted in the compliance of the rabies serology PT with the ISO/IEC 17043 and ISO 13528:2015 International Standards.

The impact of novel lyssavirus discovery

The global discovery of novel lyssaviruses is of continued scientific interest through its importance to both public and animal health. Lyssaviruses cause an invariably fatal encephalitis that is more commonly known as rabies. The term rabies has a long history in human society, as rabies virus (RABV) is the only pathogen that is associated with 100% fatality once the onset of clinical disease has started. Although predominantly associated across the globe with domestic and feral dog populations, the association of bats is clear. Whilst evolutionarily associated with bats, RABV is most commonly transmitted to human populations through the bite of an infected dog and dogs are considered the primary reservoir of disease. Indeed, RABV does cause more than an estimated 70000 deaths every year globally in human populations and whilst this is largely in areas where the disease is endemic, areas that remain free of rabies must remain vigilant to the risk of re-incursion of disease. Characterisation of novel lyssaviruses is of importance on several levels. Not least to investigate the pathogenesis and potential transmission routes of different lyssavirus species but also to assess the potential effect of post-exposure treatments and vaccination should human exposure occur. Bat lyssaviruses and the problems associated with novel discoveries and the potential impact they have on both human and animal populations are discussed.

Demography and health of Pugs under primary veterinary care in England

Background

The Pug is an ancient dog breed and was the fifth most commonly registered UK pedigree breed in 2014. However, the breed has been reported to be predisposed to several disorders including ocular, respiratory and dermatological problems. The VetCompass Programme collates de-identified clinical data from primary-care veterinary practices in the UK for epidemiological research. Using VetCompass clinical data, this study aimed to characterise the demography and common disorders of the general population of Pugs under veterinary care in England.

Results

Pugs comprised 2709 (1.03 %) of 264,260 study dogs under veterinary care from September 1^st, 2009 to 30^th April, 2015. Annual proportional birth rates showed that Pugs rose from less than 1 % of annual birth cohorts before 2008 to comprise 2.8 % of the 2013 annual birth cohort. The most common colours of Pugs were fawn (63.1 %), black (27.7 %), apricot (7.6 %) and silver (2.1 %).

Of the 1009 pugs under veterinary care in the study during 2013, 688 (68.19 %) had at least one disorder recorded. The most prevalent disorders recorded overall were overweight/obesity (number of events: 133, prevalence: 13.18 %, 95 % CI: 11.12–15.43), corneal disorder (88, 8.72 %, 95 % CI: 7.05–10.63) and otitis externa (76, 7.53 %, 95 % CI: 5.98–9.34). The most prevalent disorder groups were ophthalmological (n = 164, prevalence: 16.25 %, 95 % CI: 14.03–18.68), dermatological (157, 15.60 %, 95 % CI: 13.38–17.95) and aural (152, 15.06 %, 95 % CI: 12.91–17.42). The most prevalent body locations affected were the head-and-neck (n = 439, prevalence = 43.51 %, 95 % CI: 40.42–46.63) and abdomen (195, 19.33 %, 95 % CI: 16.93–21.90). The most prevalent organ systems affected were the integument (321, 31.81 %, 95 % CI: 28.15–35.72) and digestive (257, 25.47 %, 95 % CI: 22.54–28.65). The most prevalent pathophysiologic processes recorded were inflammation (386, 38.26 %, 95 % CI: 34.39–42.27) and congenital/developmental (153, 15.16 %, 95 % CI: 12.61–18.13).

Conclusions

Ownership of Pugs in England is rising steeply. Overweight/obesity, corneal disorder and otitis externa are the most common disorders in Pugs. Identification of health priorities based on VetComapss data can support evidence–based reforms to improve health and welfare within the breed.

Electronic supplementary material

The online version of this article (doi:10.1186/s40575-016-0035-z) contains supplementary material, which is available to authorized users.

Lyssavirus infection: 'low dose, multiple exposure' in the mouse model

The European bat lyssaviruses (EBLV-1 and EBLV-2) are zoonotic pathogens present within bat populations across Europe. The maintenance and transmission of lyssaviruses within bat colonies is poorly understood. Cases of repeated isolation of lyssaviruses from bat roosts have raised questions regarding the maintenance and intraspecies transmissibility of these viruses within colonies. Furthermore, the significance of seropositive bats in colonies remains unclear. Due to the protected nature of European bat species, and hence restrictions to working with the natural host for lyssaviruses, this study analysed the outcome following repeat inoculation of low doses of lyssaviruses in a murine model. A standardized dose of virus, EBLV-1, EBLV-2 or a 'street strain' of rabies (RABV), was administered via a peripheral route to attempt to mimic what is hypothesized as natural infection. Each mouse (n=10/virus/group/dilution) received four inoculations, two doses in each footpad over a period of four months, alternating footpad with each inoculation. Mice were tail bled between inoculations to evaluate antibody responses to infection. Mice succumbed to infection after each inoculation with 26.6% of mice developing clinical disease following the initial exposure across all dilutions (RABV, 32.5% (n=13/40); EBLV-1, 35% (n=13/40); EBLV-2, 12.5% (n=5/40)). Interestingly, the lowest dose caused clinical disease in some mice upon first exposure ((RABV, 20% (n=2/10) after first inoculation; RABV, 12.5% (n=1/8) after second inoculation; EBLV-2, 10% (n=1/10) after primary inoculation). Furthermore, five mice developed clinical disease following the second exposure to live virus (RABV, n=1; EBLV-1, n=1; EBLV-2, n=3) although histopathological examination indicated that the primary inoculation was the most probably cause of death due to levels of inflammation and virus antigen distribution observed. All the remaining mice (RABV, n=26; EBLV-1, n=26; EBLV-2, n=29) survived the tertiary and quaternary inoculations although the serological response did not necessarily reflect the repeated exposure. We conclude that despite repeated exposure, neither clinical disease nor serological response can be predicted and that further studies are required to understand the mechanisms behind survival following multiple exposures to lyssaviruses.

Bat Rabies

The lyssaviruses are a diverse group of viruses capable of causing rabies, which is an invariably fatal encephalitic disease in both humans and animals. Currently, the lyssavirus genus consists of 12 species with 11 of these distinct species having been isolated from bats. The basis for the apparent geographical segregation of bat lyssavirus infection between the Old and New World is poorly understood. In the New World species of insectivorous, frugivorous, and hematophagous bats, all represent important reservoirs of rabies virus. In contrast, rabies virus has never been detected in Old World bat populations, despite being endemic in terrestrial mammals. Instead, both insectivorous and frugivorous bat species across the Old World appear to act as reservoirs for the non-rabies lyssaviruses. In this chapter, we describe the association of the different lyssaviruses with different bat species across the world, classifying bat species by their feeding behavior.

Molecular epidemiology of bat lyssaviruses in Europe

Bat rabies cases in Europe are principally attributed to two lyssaviruses, namely European bat lyssavirus type 1 (EBLV-1) and European bat lyssavirus type 2 (EBLV-2). Between 1977 and 2011, 961 cases of bat rabies were reported to Rabies Bulletin Europe, with the vast majority (>97%) being attributed to EBLV-1. There have been 25 suspected cases of EBLV-2, of which 22 have been confirmed. In addition, two single isolations of unique lyssaviruses from European insectivorous bats were reported in south-west Russia in 2002 (West Caucasian bat virus) and in Germany in 2010 (Bokeloh bat lyssavirus). In this review, we present phylogenetic analyses of the EBLV-1 and EBLV-2 using partial nucleoprotein (N) gene sequences. In particular, we have analysed all EBLV-2 cases for which viral sequences (N gene, 400 nucleotides) are available (n = 21). Oropharyngeal swabs collected from two healthy Myotis daubentonii during active surveillance programmes in Scotland and Switzerland also yielded viral RNA (EBLV-2). Despite the relatively low number of EBLV-2 cases, a surprisingly large amount of anomalous data has been published in the scientific literature and Genbank, which we have collated and clarified. For both viruses, geographical relationships are clearly defined on the phylogenetic analysis. Whilst there is no clear chronological clustering for either virus, there is some evidence for host specific relationships, particularly for EBLV-1 where more host variation has been observed. Further genomic regions must be studied, in particular for EBLV-1 isolates from Spain and the EBLV-2 isolates to provide support for the existence of sublineages.

Canine Rabies: A Looming Threat to Public Health

Rabies is an acute, fatal viral disease that infects domestic and wild animals and is transmissible to humans. Worldwide, rabies kills over 55,000 people every year. The domestic dog plays a pivotal role in rabies transmission. Domestic dogs are not only part of our daily lives but also of our immediate surroundings, and this is reflected in the rise in pet dog ownership in developed and developing countries. This is important given that more frequent exposures and interactions at the animal-human interface increases the likelihood of contracting zoonotic diseases of companion animals. Despite existing vaccines and post-exposure prophylactic treatment, rabies remains a neglected disease that is poorly controlled throughout much of the developing world, particularly Africa and Asia, where most human rabies deaths occur. It is believed that with sustained international commitments, global elimination of rabies from domestic dog populations, the most dangerous vector to humans, is a realistic goal.

Bats and lyssaviruses

Numerous bat species have been identified as important reservoirs of zoonotic viral pathogens. Rabies and rabies-related viruses constitute one of the most important viral zoonoses and pose a significant threat to public health across the globe. Whereas rabies virus (RABV) appears to be restricted to bats of the New World, related lyssavirus species have not been detected in the Americas and have only been detected in bat populations across Africa, Eurasia, and Australia. Currently, 11 distinct species of lyssavirus have been identified, 10 of which have been isolated from bat species and all of which appear to be able to cause encephalitis consistent with that seen with RABV infection of humans. In contrast, whereas lyssaviruses are apparently able to cause clinical disease in bats, it appears that these lyssaviruses may also be able to circulate within bat populations in the absence of clinical disease. This feature of these highly encephalitic viruses, alongside many other aspects of lyssavirus infection in bats, is poorly understood. Here, we review what is known of the complex relationship between bats and lyssaviruses, detailing both natural and experimental infections of these viruses in both chiropteran and nonchiropteran models. We also discuss potential mechanisms of virus excretion, transmission both to conspecifics and spill-over of virus into nonvolant species, and mechanisms of maintenance within bat populations. Importantly, we review the significance of neutralizing antibodies reported within bat populations and discuss the potential mechanisms by which highly neurovirulent viruses such as the lyssaviruses are able to infect bat species in the absence of clinical disease.

Virus neutralising activity of African fruit bat (Eidolon helvum) sera against emerging lyssaviruses

It is likely that phylogroup 2 lyssaviruses circulate within bat reservoirs. We adapted a pseudotype (pt) neutralisation assay (PNA) to a multiplex format enabling serosurveillance for Lagos bat virus (LBV), Mokola virus (MOKV) and West Caucasian bat virus (WCBV) in a potential reservoir, the African straw-coloured fruit bat, Eidolon helvum. Highly correlated titres were observed between single and multiplex PNAs using ptLBV and ptMOKV (r=0.97, p<0.0001), validating its use for bat serosurveillance. Of the bat serum samples screened 56% neutralised ptLBV, 27% ptMOKV and 1% ptWCBV. Mean VNAb titres were 1:266, 1:35 and 1:7 against ptLBV, ptMOKV and ptWCBV respectively. The high seroprevalence estimates suggest that the infection rate of LBV in E. helvum remains high enough to persist in this species. This supports the hypothesis that LBV is endemic in Ghanaian E. helvum and we speculate that LBV may have co-evolved with African megachiroptera.