Use of an Area Index to Retrospectively Analyze the Elimination of Fox Rabies in European Countries

Abstract

Oral vaccination of foxes (OVF) is a powerful tool to combat rabies in wildlife, and large parts of western Europe have been freed from rabies using this tool. Nevertheless, the success of OVF, given with the number of campaigns needed to eliminate the disease, depends on many factors. This article for the first time focuses on and assesses difference in OVF with respect to the spatial setting of vaccinated areas with time. The size of the areas vaccinated with time and the size of the overlapping area of consecutively vaccinated areas are particularly considered. In order to integrate these two aspects into one single figure, an Area Index is proposed ranging between 0 and 1. A statistical analysis indicates that the number of campaigns needed for rabies elimination significantly decreases on condition that the total rabies endemic area is consecutively treated right from the beginning of oral vaccination. Hence, from an economical and environmental point of view, vaccination areas should be selected the way that guarantees an Area Index close to 1. The concept of an Area Index, as described here, is a useful tool not only in the context of OVF, but it could also be used for other control schemes against infectious diseases in wildlife.

The elimination of fox rabies from Europe: determinants of success and lessons for the future

“…Previous research suggested that rabies could be eliminated from a region within 10–12 campaigns, i.e. 5–6 years [41,53]. But countries that successfully eliminated rabies in Europe required substantially longer (figure 3), with a median of 28 campaigns (14 years, range: 5–26) to achieve elimination, and 17 for control.…”

“…The area index captures the comprehensiveness of ORV in terms of the extent and spatial overlap of consecutive ORV campaigns [41]. Among the 22 countries area indices varied considerably from 0.006 to 1 (table 1).…”

“…We considered the following variables as potential factors influencing the baseline hazard of effort required to control and eliminate fox rabies from a country: the size of the country (in km 2 ); the area and proportion of the territory that was ever vaccinated (area given in km 2 ); the length of borders to neighbouring rabies-infected (endemic) areas (in km); initial rabies incidence in the year prior to the implementation of ORV, expressed both as the number of detected cases and the number of detected cases per square kilometre; years of ORV experience prior to each country starting an ORV programme; and an index that captures the contiguity and overlap of consecutive ORV campaigns carried out in a country ([41]; table 2). Areas were log transformed, and proportions logit transformed, prior to statistical analysis.…”

“…The index is calculated from the area and overlap of consecutive campaigns t ( t > 1) according to the following equations:with V t , the size of the vaccinated area at campaign t , and d t is the intersection of successive campaigns V t and V t−1 . The index varies from zero to one, from campaigns that are entirely non-overlapping to those that entirely overlap and are equal in size to the maximum area ever vaccinated [41]. If ORV campaigns were interrupted for more than one year, subsequent ORV campaigns were considered new ORV programmes and the area index was re-calculated (table 1).…”

The field efficiency of oral rabies vaccination in the Lithuanian red fox population from 2006 to 2013

“…The three live rabies vaccine strains used (SAG1, SAD Bern and SAD B19) in a total of 900 000 baits were reported to be ineffective as an oral prevention of rabies in wildlife (Milius et al 2004). Although ORV programs should ideally cover the entire affected area (Selhorst et al 2005), initial programs in the Baltic countries failed to vaccinate the entire affected area (Cliquet et al 2012). Specifically, initial ORV attempts in Latvia and Lithuania failed to efficiently control rabies, and were interrupted owing to budget constraints.…”