Tracking the Spatial and Functional Dispersion of Vaccine-Related Canine Distemper Virus Genotypes: Insights from a Global Scoping Review

Abstract

Canine morbillivirus (CDV), the cause of canine distemper, is a pathogen affecting many hosts. While modified live virus (MLV) vaccines are crucial for controlling the disease in dogs, cases of vaccine-related infections have been found in both domestic and wild animals. Specifically, the America-1 and Rockborn-like vaccine genotypes are concerning due to their spread and ability to transmit between different species. This study conducted a review and analysis of molecular detections of these strains in various carnivores (domestic, captive, synanthropic, and wild species). This study used a conceptual model considering host ecology and the domestic-wild interface to evaluate plausible transmission connections over time using Linear Directional Mean (LDM) and Weighted Mean Centre (WMC) methods. Statistical analyses examined the relationship between how likely a strain is to spread and factors like host type and vaccination status. The findings showed that the America-1 genotype spread in a more organised way, with domestic dogs being the main source and recipient, bridging different environments. Synanthropic mesocarnivores also played this same role, with less intensity. America-1 was most concentrated in the North Atlantic and Western Europe. In contrast, the Rockborn-like strain showed a more unpredictable and restricted spread, residual circulation from past use rather than ongoing spread. Species involved in vaccine-related infections often share characteristics like generalist behaviour, social living, and a preference for areas where domestic animals and wildlife interact. We did not find a general link between a host vaccination status and the likelihood of the strain spreading. The study emphasised the ongoing risk of vaccine-derived strains moving from domestic and synanthropic animals to vulnerable wild species, supporting the need for improved vaccination approaches. Mapping these plausible transmission routes can serve as a basis for targeted surveillance, not only of vaccine-derived strains, but of any other circulating genotype.

Keywords: America-1; CDV; Morbillivirus canis; Rockborn-like; multi-host pathogen; spillover; spread; surveillance; transmission; vaccine genotypes; vaccines.

Figure 2

CDV infection flows considered for the analysis of plausible temporal connections based on the initial assumptions and hypotheses.

Figure 1

Article selection flowchart. Layers of information used to analyse data from articles that met all inclusion criteria established in this systematic review.

Figure 3

Host species and associated ecological and epidemiological characteristics for the CDV isolates analysed. (A) Host species identified in each case, with bars coloured by detected CDV genotype: America-1 (blue) and Rockborn-like (orange). (B) Habitat type used by the species, with categories coded by colour: Close habitat (blue), Open habitat (orange), and Mixed habitat (yellow). (C) Degree of ecological adaptability, distinguishing generalist species (blue) from specialist species (orange). (D) Social behaviour of the host species: solitary (blue) and gregarious (orange). (E) Degree of interaction with human environments (epidemiological interface with domestic animals), distinguishing cases where this interaction is absent of or minimally relevance (blue) and those involving a domestic–wild interface (orange). (F) Vaccination status reported for each case: no vaccination (blue) and vaccination (orange).

Figure 4

Geographical and temporal distribution of the CDV isolates analysed in this study. (A) Distributional range of the host species classified as either restricted or global. (B) Number of cases reported by continent. (C) Temporal distribution of records by year of publication. (D) Number of cases by country. Bars are coloured according to the detected CDV genotype: America-1 (blue) and Rockborn-like (orange).

Figure 5

Boxplots showing the distribution of viral dispersion potential (ordinal scale: 1 = highest plausibility; 7 = lowest) across host functional groups, differentiated by genotype and host role. Panels (A,B) represent the functional group of the origin host for America-1 and the corresponding distributions for destination hosts, respectively. Similarly, panels (C,D) show these same distributions for Rockborn-like genotypes. The colour scheme is consistent across genotypes and roles: (1) domestic dog, (2) captive carnivore, (3) synanthropic mesocarnivore, and (4) wild non-synanthropic carnivores. Dots represent statistical outliers beyond 1.5 × IQR.

Figure 6

Heatmaps illustrate the number of vaccine-related CDV connections between host functional groups based on documented cases for each genotype. The matrices reflect the directionality of the transmission (origin → destination) and are colour-coded by frequency (see scale). The left panel corresponds to the America-1 genotype, and the right panel shows the Rockborn-like genotype. Domestic dogs are the main origin group in both datasets, with marked differences in transmission structure and diversity across the host functional group.

Figure 7

Spatial representation of directional vectors calculated for epidemiologically plausible CDV connections. The left column corresponds to the America-1 genotype and the right column to the Rockborn-like genotype. Each map shows all plausible connection lines in grey and overlaid directional vectors coloured by category. Rows represent stratification by (1) vaccination status of the origin host, (2) vaccination status of the destination host, (3) connection potentiality level (1 = most plausible, 7 = less plausible), (4) origin host functional group, (5) destination host functional group, (6) continent of origin, and (7) continent of destination. Each directional vector was generated using case fields corresponding to the categories indicated, representing the average azimuth and length of the subset of connection lines. Angular dispersion is not visualised but was calculated internally for each case.

Figure 8

Weighted mean centres of connection midpoints stratified by origin host attributes. Spatial distribution of mean centres calculated from the midpoints of each plausible CDV connection vector, weighted by the inverse of the potentiality level (weight = 8 − level) to prioritise the most plausible connections. The upper panel corresponds to the America-1 genotype and the lower panel to the Rockborn-like genotype. Points are grouped and symbolised according to three categorical variables associated with the origin host: geographical area (continent), host functional group (domestic dog, synanthropic mesocarnivore, captive carnivore, wild non-synanthropic carnivore), and vaccination status (0 = unvaccinated, 1 = vaccinated). Each coloured symbol represents the weighted spatial centre of the midpoints for all plausible connections in that category. Yellow dots represent documented CDV cases retrieved from the literature, which serve as the basis for generating plausible transmission routes, shown as grey connecting lines. Black dots correspond to the individual midpoints of those routes, and coloured centroids reflect the aggregated mean centre for each host category.