Control and elimination of rabies in Croatia

Is golden jackal (Canis aureus) the most important indicator species of Trichinella infection in Croatia?

Epidemiologic monitoring of wild animals is always an important step in defining potential zoonoses that can threaten humans. Particular emphasis should be given to those zoonotic agents permanently cycling within wild animal populations and represent a permanent reservoir for other wild or domesticated animals that can be direct sources of disease for humans. In Croatia, there are two European jackal populations: the Dalmatian population (DP) that has been inhabiting the islands and coastal area along the Adriatic Sea since medieval times, and the South East European population (SEEP) that is found in continental Croatia. Research on Trichinella infections in jackal populations in Croatia was conducted from 2008 to 2022. During this 15-year period, we tested 186 jackal samples and confirmed infection in 47 individuals (25.3 %). The dominant species was T. spiralis, identified in 28 samples (60 %), T. britovi was found in 13 samples (28 %), while for six samples (12 %) the PCR test was unsuccessful. In both populations, the Trichinella species of the domestic cycle (T. spiralis) was found, though in varying ratios: in DP the ratio of identified species was 10:6 in favour of T. britovi, as opposed to 22:3 in favour of T. spiralis in SEEP. The frequency of infection with parasites from the genus Trichinella was significantly different in DP (22.9 %) than in SEEP (26.7 %) (p<0.001), while the larval count in analysed tissue did not differ by type of Trichinella species (p=0.1028). Infected jackals were found in nine of ten tested counties. The results were analysed statistically and the origin of tested and positive samples shown on a map of Croatia. Based on these findings, both jackal populations can be considered to represent an exceptionally important indicators of parasites from the genus Trichinella in Croatia, both for the sylvatic and domestic cycles. There is an evident need for epidemiological monitoring for members of both populations.

Bat Bites and Rabies PEP in the Croatian Reference Centre for Rabies 1995-2020

Seroprevalence of lyssaviruses in certain bat species has been proven in the Republic of Croatia, but there have been no confirmed positive bat brain isolates or human fatalities associated with bat injuries/bites. The study included a retrospective analysis of bat injuries/bites, post-exposure prophylaxis (PEP) and geographic distribution of bat injuries in persons examined at the Zagreb Antirabies Clinic, the Croatian Reference Centre for Rabies. In the period 1995-2020, we examined a total of 21,910 patients due to animal injuries, of which 71 cases were bat-related (0.32%). Of the above number of patients, 4574 received rabies PEP (20.87%). However, for bat injuries, the proportion of patients receiving PEP was significantly higher: 66 out of 71 patients (92.95%). Of these, 33 received only the rabies vaccine, while the other 33 patients received the vaccine with human rabies immunoglobulin (HRIG). In five cases, PEP was not administered, as there was no indication for treatment. Thirty-five of the injured patients were biologists or biology students (49.29%). The bat species was confirmed in only one of the exposure cases. This was a serotine bat (Eptesicus serotinus), a known carrier of Lyssavirus hamburg. The results showed that the bat bites were rather sporadic compared to other human injuries caused by animal bites. All bat injuries should be treated as if they were caused by a rabid animal, and according to WHO recommendations. People who come into contact with bats should be strongly advised to be vaccinated against rabies. Entering bat habitats should be done with caution and in accordance with current recommendations, and nationwide surveillance should be carried out by competent institutions and in close collaboration between bat experts, epidemiologists and rabies experts.

Retrospective phylogenetic analysis of rabies virus G and N genes from Serbia

Rabies is a viral disease of the central nervous system of all warm-blooded animals and one of the oldest and most important zoonoses. In the Republic of Serbia, rabies is controlled by compulsory vaccination of dogs and cats and oral vaccination of wild carnivores, which has been implemented since 2010. In the period 2009-2018, 367 rabies cases were recorded. The last rabies case in Serbia was recorded in 2018 in a red fox (Vulpes vulpes), while the last case in dogs was diagnosed in 2011. This study aimed to perform a retrospective phylogenetic analysis of G and N genes of the rabies virus from Serbia from 2009 to 2018 to understand sources and pathways of infection better and to enable molecular virus tracing in the future based on the association of rabies virus genetic lineages with the geographic distribution. For the phylogenetic analysis of the rabies virus, 14 historically positive brain samples of red foxes from 2009 to 2018, collected in central Serbia, were used. All field strains from Serbia were identified as classic rabies virus and grouped within the Cosmopolitan lineage. Phylogenetic analysis of N gene sequences revealed that 13 rabies virus strains (92.9%) from Serbia belonged to the EE sub-lineage of isolates, while one virus (7.1%) ON988027 from 2011 clustered together with isolates from the WE sub-lineage.

Canine Distemper Virus Infection in the Free-Living Wild Canines, the Red Fox (Vulpes vulpes) and Jackal (Canis aureus moreoticus), in Croatia

The canine distemper virus (CDV), a paramyxovirus that is closely related to the human measles virus and rinderpest virus of cattle, is a highly contagious viral disease in dogs and wild carnivores worldwide. CDV represents a serious threat to domestic and wild animals, especially to the conservation of endangered wild carnivores. Our study aims to investigate the occurrence of CDV in free-living wild canines in Croatia. For this purpose, 176 red foxes and 24 jackal brain samples collected in the frame of the active surveillance of rabies during winter 2021/2022 were tested. This study provided the first comprehensive overview of the prevalence and spatial distribution of CDV in the wildlife of Croatia, including the molecular phylogenetic analysis of the H gene sequence of field CDV strains circulating in red fox and jackal populations of Croatia. The molecular characterization of hemagglutinin gene genomic regions confirmed the phylogenetic clustering of obtained sequences into the Europa 1 genotype. The obtained CDV red fox sequences were mutually very similar (97.60%). This study indicates the high genetic similarity of Croatian CDV red fox sequences and CDV red fox sequences from Italy and Germany, badger sequences from Germany, polecat sequences from Hungary, and dog sequences from Hungary and Germany.

Current Status of Rabies and Its Eradication in Eastern and Southeastern Europe

The objective of this paper is to provide an overview of the current status of rabies in Europe, with special emphasis on Croatia and Southeast and East Europe. Due to the systematic implementation of a rabies eradication program by oral vaccination of wild animals, by the end of the 20th century, most West and Central European countries were rabies-free. The EU goal was to eradicate rabies in wildlife and domestic animals by 2020. No matter how achievable the goal seemed to be, the disease is still present in the eastern part of the EU, as was notified in 2020 by two member states—Poland and Romania. Croatia has been rabies-free for the last seven years but given that it borders a non-EU country in which a case of rabies was confirmed in 2020, it will continue to contribute to the maintenance of the rabies-free region. A rabies-free EU can only be achieved by continuous oral vaccination, coordination and a regional approach. The prevention of reintroductions from bordering countries in which rabies has not been eradicated yet, and the support for the eradication efforts made by these countries, are goals still pending.

The Successful Elimination of Sylvatic Rabies Using Oral Vaccination of Foxes in Slovenia

Sylvatic rabies was present in Slovenia between 1973 and 2013, with the red fox as the main reservoir of the rabies virus. The first oral rabies vaccination (ORV) control program in foxes started in 1988, using the manual distribution of baits. Significant improvement of fox vaccination was achieved with the aerial distribution of baits, starting in 1995 and successfully finished with the final, fifty-ninth vaccination campaign in 2019. Between 1979 and 2019, a total of 86,471 samples were tested, and 10,975 (12.69%) rabies-positive animals were identified. Within the ORV, two different vaccines were used, containing modified live virus strain Street Alabama Dufferin (SAD) B19 and SAD Bern, while the last ORV campaigns were completed in 2019, with a vaccine containing a genetically modified strain of SPBN GASGAS. Molecular epidemiological studies of 95 rabies-positive samples, originating from red foxes, badgers, cattle, dogs, martens, cats, and horses, revealed a low genetic diversity of circulating strains and high similarity to strains from neighboring countries. During the elimination program, few vaccine-induced rabies cases were detected: three in red foxes and one case in a marten, with no epidemiological relevance. Slovenia has been officially declared a country free of rabies since 2016.

Emerging and Neglected Viruses of Zoonotic Importance in Croatia

Several arboviruses have emerged in Croatia in recent years. Tick-borne encephalitis is endemic in continental counties; however, new natural micro-foci have been detected. Two autochthonous dengue cases were reported in 2010. West Nile virus emerged in 2012, followed by emergence of Usutu virus in 2013. Although high seroprevalence rates of Toscana virus have been detected among residents of Croatian littoral, the virus remains neglected, with only a few clinical cases of neuroinvasive infections reported. Lymphocytic choriomeningitis virus is a neglected neuroinvasive rodent-borne virus. So far, there are no reports on human clinical cases; however, the seroprevalence studies indicate the virus presence in the Croatian mainland. Puumala and Dobrava hantaviruses are widely distributing rodent-borne viruses with sporadic and epidemic occurrence. Hepatitis E virus is an emerging food-borne virus in Croatia. After the emergence in 2012, cases were regularly recorded. Seropositivity varies greatly by region and population group. Rotaviruses represent a significant healthcare burden since rotavirus vaccination is not included in the Croatian national immunization program. Additionally, rotaviruses are widely distributed in the Croatian ecosystem. A novel coronavirus, SARS-CoV-2, emerged in February 2020 and spread rapidly throughout the country. This review focuses on emerging and neglected viruses of zoonotic importance detected in Croatia.

Rabies in Europe in 2010-2019

The paper presents the epizootic and epidemiological situation of rabies in European countries during the last decade. The presented results indicate that the oral immunisation of fox anti-rabies (ORV), used in many European countries, significantly reduced the number of rabies cases found in ground mammals, but did not eliminate the virus at all. Currently, the largest reservoir of the virus are Eastern European countries where there are no immunisation activities or their effectiveness is low. Due to the absence of geographical barriers, the virus reappears in countries that have been described as free from rabies. As a rule, it is dragged into these areas along with the movement of companion animals and by people travelling to countries where the prevalence of the virus is common. It should be emphasised that due to the significant elimination of the virus in wild and domestic animals, it found quite quickly found a new reservoir in a specific group of mammals, having the ability to fly, like bats. Currently there is no possibility of carrying out any preventive measures in bats, so all the virus strains found in this group of animals are dangerous to humans, raising possibilities of epidemiological threat. It should be noted that despite the significant elimination of rabies in many European countries, given the almost unlimited possibilities of virus transmission to new areas, it still poses a serious threat to public health. Thus, it is necessary to constantly monitor the occurrence of the virus and possibly take preventive actions in terms of its elimination from the environment.

Seasonal variation in bait uptake and seropositivity during a multi-year biannual oral rabies fox vaccination programme in Kosovo (2010-2015)

The European Union supported programmes for rabies control in Kosovo between 2010 and 2015, including spring and autumn biannual oral vaccination campaigns targeting foxes. Throughout the programmes foxes were obtained to provide samples for monitoring the campaigns. This paper explores the seasonal pattern of bait uptake and seropositivity in the fox population. Bait uptake varied by season and by the phase of the project supporting the programme (the main differences between phases being the number of baits distributed and flight line separation). Seropositivity varied by season and by titre of the vaccine used in the preceding campaign. The analyses also suggested a negative effect of higher daytime temperature on bait uptake, and possible association between geographic location of sampling and concordance between bait uptake and seropositivity, but the dataset was too unbalanced to support robust conclusions on these detailed aspects. Descriptive summaries of the data and the multilevel analyses showed that the proportion of sampled foxes that were positive for bait uptake and the proportion seropositive were both high through winter, following the autumn campaigns, and declined through spring and summer, with a low point in samples collected during the time when juvenile foxes are typically dispersing from their birth dens. The percentage of foxes positive for bait uptake was below 30 % (first project phase) and 40 % (second project phase) from mid-July to mid-October following a spring campaign, compared with around 70 % (first project phase) and 80 % (second project phase) in the periods between autumn and the following spring campaigns. As could be expected, the percent of samples that were seropositive followed a similar seasonal pattern, with some additional variation associated with the titre of vaccine used. This seasonal pattern is likely because the population sampled in the late summer months includes increasing numbers of young foxes that could not have been effectively exposed to the spring vaccination campaign, and would have lost any possible maternal immunity by late summer. The main finding of high levels of bait uptake and seroprevalence through winter, following the autumn campaigns, declining through summer despite the implementation of spring campaigns, supports advice that countries lacking financial resources to support biannual campaigns should focus resources on once per year vaccination in late autumn or early winter. This pattern also indicates that a fox population may rapidly become naïve after cessation of vaccination programmes, therefore strongly coordinated regional programmes and good surveillance will be needed.

Zero Endemic Cases of Wildlife Rabies (Classical Rabies Virus, RABV) in the European Union by 2020: An Achievable Goal

The elimination of rabies transmitted by Classical Rabies Virus (RABV) in the European Union (EU) is now in sight. Scientific advances have made it possible to develop oral vaccination for wildlife by incorporating rabies vaccines in baits for foxes. At the start of the 1980s, aerial distribution of vaccine baits was tested and found to be a promising tool. The EU identified rabies elimination as a priority, and provided considerable financial and technical resources to the infected EU Member States, allowing regular and large-scale rabies eradication programs based on aerial vaccination. The EU also provides support to non-EU countries in its eastern and south eastern borders. The key elements of the rabies eradication programs are oral rabies vaccination (ORV), quality control of vaccines and control of their distribution, rabies surveillance and monitoring of the vaccination effectiveness. EU Member States and non-EU countries with EU funded eradication programs counted on the technical support of the rabies subgroup of the Task Force for monitoring disease eradication and of the EU Reference Laboratory (EURL) for rabies. In 2018, eight rabies cases induced by classical rabies virus RABV (six in wild animals and two in domestic animals) were detected in three EU Member States, representing a sharp decrease compared to the situation in 2010, where there were more than 1500 cases in nine EU Member States. The goal is to reach zero cases in wildlife and domestic animals in the EU by 2020, a target that now seems achievable.