Human migration is important in the international spread of exotic Salmonella serovars in animal and human populations

Abstract

The exposure of indigenous humans and native fauna in Australia and the Wallacea zoogeographical region of Indonesia to exotic Salmonella serovars commenced during the colonial period and has accelerated with urbanization and international travel. In this study, the distribution and prevalence of exotic Salmonella serovars are mapped to assess the extent to which introduced infections are invading native wildlife in areas of high natural biodiversity under threat from expanding human activity. The major exotic Salmonella serovars, Bovismorbificans, Derby, Javiana, Newport, Panama, Saintpaul and Typhimurium, isolated from wildlife on populated coastal islands in southern temperate areas of Western Australia, were mostly absent from reptiles and native mammals in less populated tropical areas of the state. They were also not recorded on the uninhabited Mitchell Plateau or islands of the Bonaparte Archipelago, adjacent to south-eastern Indonesia. Exotic serovars were, however, isolated in wildlife on 14/17 islands sampled in the Wallacea region of Indonesia and several islands off the west coast of Perth. Increases in international tourism, involving islands such as Bali, have resulted in the isolation of a high proportion of exotic serovar infections suggesting that densely populated island resorts in the Asian region are acting as staging posts for the interchange of Salmonella infections between tropical and temperate regions.

Fig. 1.

Sampling locations in the Wallacea region of Indonesia and north-western Australia and on offshore islands and the mainland in south-western Western Australia.

Fig. 2

[colour online]. Relationship of total serovar assemblages in various faunal groups from different geographical locations using non-metric multidimensional scaling derived from a Bray–Curtis similarity matrix. Significantly different assemblages, determined using the Simprof test in the Primer software package, are indicated by different symbols. Spheres define important levels of similarity between clusters. Serovar assemblages in humans (_H) from different locations are indicated along with those in wildlife (_WL) from the same locations or Wallacean islands (Wall), Kimberley Islands (KimbI), Barrow Island (Barr), Garden Island (Gard), Rottnest Island (Rotto) and Carnac Island (Carn), as well as the lizards (_L) on Penguin Island.

Fig. 3

[colour online]. Relationship of exotic serovar assemblages in various faunal groups from different geographical locations using non-metric multidimensional scaling derived from a Bray–Curtis similarity matrix. Significantly different assemblages, determined using the Simprof test in the Primer software package, are indicated by different symbols. Spheres define important levels of similarity between clusters. Locations and groups as described in Figure 2.

Fig. 4

[colour online]. Relationship of native serovar assemblages in various faunal groups from different geographical locations using non-metric multidimensional scaling derived from a Bray–Curtis similarity matrix. Significantly different assemblages, determined using the Simprof test in the Primer software package, are indicated by different symbols. Spheres define important levels of similarity between clusters. Locations and groups as described in Figure 2.

Fig. 5

[colour online]. Variation in the ratio of exotic to native (E:N) serovars from listed locations with data from (a) humans, (b) wildlife in the south-west of Western Australia, (c) wildlife in the north-west of Western Australia and islands from the Wallacea region of Indonesia. Statistical significance: * P < 0·05 and ** P < 0·01.