Epidemiological studies

Epidemiological studies investigating disease dynamics and measures of disease frequency

Data collected through systematic literature review are presented in the right panel, mapped separately according to the study context eligible:

Studies not meeting the inclusion criteria for the literature review, but which contribute to understanding of the disease geographical distribution, were sometimes flagged and listed for the reader's reference (see dedicated sections further below), but they were not subjected to detailed data collection. These are the types in parenthesis.

A summary of all epidemiological study references reviewed for this agent is shown to the right. More detailed information for each of those is presented in individual sections below when data is available. All references are listed in a dedicated section following further.

It is important to note that studies targetting humans were NOT systematically included in the literature reviews.

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

The review was last updated in November 2023. The complete list of references is available for download here. If important references to primary studies are missing, contact animal-diseases@efsa.europa.eu. The full review protocol can be downloaded here.

The table on the right lists the main features of case-control or cohort studies. It has one row per study group from all studies reviewed. This means that the same reference may appear in several rows if several target species or years were reported.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Country: where the investigation was conducted.
Year: year when the study was conducted (start year when multiple years are reported).
Target species
Lab target: target of the test for laboratorial confirmation. It specifies whether the agent or antibodies were detected.
Sample size: number of units tested.
Prevalence: the reported prevalence found (which can be apparent prevalence or seroprevalence, according to the "Lab target").
Incidence: documented when studies specifically reported investigating incidence.
Sampling point: where in the animal production chain samples were taken, for example farms, abattoirs, etc.

The table on the right lists the main features of eligible studies reporting active testing of animals and search for cases. It has one row per study group from all studies reviewed. This means that the same reference may appear in several rows if several target species or different tests were reported.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Country: where the investigation was conducted.
Year: year when the study was conducted (start year when multiple years are reported).
Target species
Reason for sampling: the reported trigger for animals being tested, when reported.
Sampling strategy: how sampling was designed.
Lab target: target of the test for laboratorial confirmation. It specifies whether the agent or antibodies were detected.
Sample size: number of units tested.
N Pos: number of units tested which were found positive. This was only reported as prevalence when there was a specific sampling strategy used, and the article reported the result as a prevalence estimation.
Prevalence: documented only when reported in the reviewed references as a prevalence estimation.
Sampling point: where in the animal production chain samples were taken, for example farms, abattoirs, etc.

The table on the right lists the main features of eligible studies reporting designed sampling and testing of animals. It has one row per study group from all studies reviewed. This means that the same reference may appear in several rows if several target species or different tests were reported.

When multiple seroprevalence studies were available from the same country, we have made an effort to collect data from the most recent and most comprehensive (geographically) ones. Studies which reported serological testing, but which were not designed to allow prevalence estimation were generally excluded.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Country: where the investigation was conducted.
Year: year when the study was conducted (start year when multiple years are reported).
Target species
Lab target: target of the test for laboratorial confirmation. It specifies whether the agent or antibodies were detected.
Sample size: number of units tested.
Prevalence: documented only when reported in the reviewed references as a prevalence estimation.
Sampling strategy: how sampling was designed.
Sampling point: where in the animal production chain samples were taken, for example farms, abattoirs, etc.

The table on the right lists the main features of eligible studies reporting results from passive surveillance activities.

Case reported and reports of specific surveillance activities following reported cases were included in the literature review in cases of diseases not reportable to WOAH, or when additional information on disease burden and impact on animal health were reported on the study.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Country: where the investigation was conducted.
Year: year when the study was conducted (start year when multiple years are reported).
Target species
Lab target: target of the test for laboratorial confirmation. It specifies whether the agent or antibodies were detected.
Sample size: number of units tested. Sampling designs can vary a lot, and are usually in two-stages for disease freedom. Visit the reference or the full dataset for details.
N Pos: number of units tested which were found positive. This was only reported as prevalence when there was a specific sampling strategy used, and the article reported the result as a prevalence estimation.
Reason for sampling: the reported trigger for animals being tested, when reported.
Sampling point: where in the animal production chain samples were taken, for example farms, abattoirs, etc.

The table on the right lists the main features of eligible studies reporting results from outbreak investigations.

Data from papers reported as outbreak investigations was only collected for (i) diseases not reportable to WOAH, or (ii) when the paper contained additional information regarding measures of disease frequency or burden, that is, when it was not simply a case or outbreak report.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Country: where the investigation was conducted.
Year: year when the study was conducted (start year when multiple years are reported).
Target species : Species investigated in the study.
Prevalence: the reported prevalence found (which can be apparent prevalence or seroprevalence, according to the "Lab target").
Incidence: documented when studies specifically reported investigating incidence.
Epi unit: the epidemiological unit reported (for example herd or individual animals).
Outcome reported: when the study reported any additional measure of disease burden, this was recorded during data collection unting the 3 next fields - data collectors documented what was the outcome (for instance mortality rate), the value reported , and the unit of measurement used. For example mortality rate, 30%; or number of deaths, 5 animals.

The panel to the right lists all the information reported by any of the epidemiological studies in this section regarding investigated risk factors for detection of the pathogen.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Country: where the investigation was conducted.
Year: year when the study was conducted (start year when multiple years are reported).
Target species : Species investigated in the study.
Risk factors: text copied directly from the reported results when risk factors where investigated.

The table to the right shows references for all the studies included in the epidemiological studies section. You can find specific papers by their RefID.

Disease

Animal Health Impact

A summary of the disease in animal hosts is given in the WOAH Technical disease card.

The panel to the right summarizes evidence collected from published studies describing natural infections with this agent (as opposed to experimental infections, summarised in dedicated section).

EFSA conducts regular systematic literature reviews covering studies investigating natural infections with this agent, and published in peer-reviewed literature in English since 1970.

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

*The review was last updated in November 2023. The complete list of references is available for download here. If important references to primary studies are missing, contact animal-diseases@efsa.europa.eu. The full review protocol can be downloaded here.

The table to the right summarises the clinical signs or severity described in epidemiological studies on field occurrence of this pathogen.

When reviewing eligible articles for the epidemiological studies section, if descriptions of the clinical signs observed were provided those were copied (as free-text) and compiled in the table to the right.

RefID: the paper unique ID, which can be used to get full bibliographical details in the References table for this section, further below.
Target species
Clinical signs: text copied as reported in the articles reviewed.
Severity: if a specific severity score or categorization was reported, this was also documented (but no attempt to categorize severity was made by those collecting data from the literature).

This table shows references for all the studies included in this section. You can find specific papers by their RefID.

Experimental infections

EFSA conducts regular systematic literature reviews covering all experimental infections published in peer-reviewed literature in English since 1970.

A summary of the disease in animal hosts is given in the WOAH Technical disease card.

The panel to the right summarizes all evidence collected by EFSA from published experimental infection studies describing the health effects of Tick-Borne Encephalitis Virus in host animal species.

Summaries of available scientific evidence are provided concerning:

Host species
Duration of clinical signs
Clinical signs observed
Case fatality
Meta-analysis of reported duration of observed clinical signs, accounting for censoring in the experimental infection study groups

The panel to the right shows the animal species in which experimental infection has been demonstrated.

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

Agent

Virus taxonomy

Family: Flaviviridae

Genus: Flavivirus

Species: Tick-borne encephalitis virus

Agent characteristics

Refer to the WOAH Technical disease card for a key summary of the virus characteristics.

Agent survival outside living hosts

The panel to the right summarizes all evidence collected by EFSA from published experiments on pathogen survival.

Summaries of available scientific evidence are provided concerning:

Survival plots indicating the maximum number of days the virus was detected in different matrices under different conditions (temperature)
Half-life studies which documented virus viability decay over time under different temperatures
Meta-analysis of the reported virus survival period for matrices in which a sufficient number of studies were found

EFSA conducts regular systematic literature reviews covering pathogen survival experiments published in peer-reviewed literature in English since 1970.

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

Transmission

Refer to the WOAH Technical disease card for a key summary of the disease transmission and epidemiological parameters.

The panel to the right summarizes all evidence collected by EFSA from published experimental infection studies describing host infectiousness. Scroll down through the content.

Summaries of available scientific evidence are provided concerning:

Evidence of Host-host transmission
Evidence of transplacentary transmission
Meta-analysis of the reported duration of the infectious period, accounting for censoring in the experimental infection study groups
Data for all animal matrices in which agent presence was demonstrated.

Please note that experimental infections are generally conducted in animal groups.

Species listed are those for which evidence was available in peer-reviewed literature (in English).

Plots are interactive, hover to see more information, drag to zoom.

Infectious period cannot be measured directly unless transmission experiments are also conducted. Infection experiments reviewed in the literature actually measured the period of time during which the pathogen/genetic material could be detected in specific body matrices.
All data were recorded per ANIMAL GROUP, not individually. As a result, the periods were recorded in the form of minimum and maximum values (in days) observed in the group. The values therefore do not reflect a distribution of infectivity in a single animal, but the earliest and latest day in which the pathogen/genetic material could possibly be detected in specific body matrices.
Animals could still be infectious on the last day of the experiment. Data in this case is censored - the maximum represents the maximum observed, not the true maximum.

Data collected from matrices other than blood, and calculations of the infectious period accounting for censoring (lack of information about true maximum when experiments ended while virus was still detectable) are available further below.

EFSA conducts regular systematic literature reviews covering all experimental infections published in peer-reviewed literature in English since 1970.

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

Diagnosis

There are no WOAH-recommended standard tests for Tick-Borne Encephalitis Virus.

EFSA conducts regular systematic literature reviews covering peer-reviewed literature in English since 1970, covering diagnostic tests approved for use in the European Union (EU).

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

Vector

Known vectors

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Ixodida
Family: Ixodidae
Genera: Ixodes, Dermacentor, Haemaphysalis, Hyalomma
Species: I. ricinus. I. persculcatus, D. reticulatus, H. concinna, H. marginatum

The map on the right shows the reported presence of specific tick species in primary sources.

The data were collected in the VectorNet project, which covers a geographical scope extending across Europe and the Mediterranean basin. Refer directly to the Scientific Report and the VectorNet resources for further information on disease vectors, including expert opinion.

Visit the Vector control - ticks for further information on vector control.

*To consider an arthropod species as a vector for viruses, the following four criteria should be satisfied (World Health Organization, 1967): (1) the species should be repeatedly associated with the disease in the field (season and places); (2) the virus should be recovered from field-collected adult females that do not have a fresh blood meal in the abdomen; (3) the species should be able to become infected after oral infection; and (4) the species should be able to transmit the infection biologically. However, based on the literature finding, all these criteria could be satisfied for only very few arthropod species, which could then be called a vector in this strict sense. Furthermore, other vector species could be present which were never tested for this pathogen.

Vaccination

EFSA conducts regular systematic literature reviews covering all vaccine efficacy studies published in peer-reviewed literature in English since 1970, when evaluating vaccines approved for use in the European Union. The next update of the SLR for vaccines is scheduled to be carried out in 2024.

Data were collected from all studies that evaluated the performance of commercial vaccines. For those studies meeting the inclusion criteria, vaccines were classified into the following types:

Inactivated (dead)
Live attenuated
Live recombinant
Recombinant (subunit vaccines)
Other

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

The review was last updated in November 2024. The complete list of references is available for download here. If important references to primary studies are missing, contact animal-diseases@efsa.europa.eu. The full review protocol can be downloaded here.

Treatments

The panel to the right summarizes all evidence collected by EFSA from published treatment efficacy studies. When available, evidence was collected from two main types of studies:

those in which the animals were subjected to a specific pharmaceutical treatment, and the efficacy of the treatment in preventing infections in the treated group is reported in comparison to a control group;
and those in which a vector-control substance (insecticide) was used, and its effect in preventing infections in hosts is reported.

For both types of studies, the following metrics are reported (whenever available):

Treatment efficacy
Titer of neutralizing antibodies
Percentage of infected hosts
Host mortality

Please note that having a control group was one of the inclusion criteria for studies to be included in this literature review. The full review protocol can be downloaded here.

It is also important to note that studies reporting treatments in animal models, that is, animals used specifically to mimic and study treatments intended for humans or other animal species, were not included in the systematic literature reviews.

You can download all data collected through systematic literature review here. Data fields are explained in this read-me file.

Acknowledgments

The CoVetLab consortium has been responsible for the systematic literature reviews since 2015, and has delivered story maps to EFSA since 2021. Partners are: Swedish Veterinary Agency (SVA, Sweden); Wageningen Bioveterinary Research (WBVR, The Netherlands); Animal and Plant Health Agency (APHA; UK) and the University of Surrey (UK).

References

The list of references displayed in this storymap is available on the right panel.

You can also download the complete list of references for each of the seven specific knowledge domains for which EFSA carries out systematic literature reviews regularly (living reviews):

Experimental Infections (complete list of references, complete dataset, Read me file)
Pathogen Survival (complete list of references, complete dataset, Read me file)
Diagnostic Tests (complete list of references, complete dataset, Read me file)
Vaccines (complete list of references, complete dataset, Read me file)
Treatments (complete list of references, complete dataset, Read me file)
Vector Control (complete list of references, complete dataset, Read me file)
Geographical distribution (complete list of references, complete dataset, Read me file)