Echinococcus species in wildlife

Abstract

Transmission of Echinococcus spp. in life cycles that involve mainly wildlife is well recognized for those species with small mammals as intermediate hosts (e. g. E. multilocularis), as well as for E. felidis and the 'northern' genotypes of E. canadensis (G8 and G10). In contrast, the remaining taxa of E. granulosus sensu lato are best known for their domestic life cycles, and the numerous wild mammal species (mainly ungulates) that have been recorded with cystic echinococcosis in the past were mainly considered a result of spill-over from the dog-livestock transmission system. This view was challenged with the advent of molecular characterization, allowing discrimination of the metacestodes, although the contribution of wild mammals to various Echinococcus life cycles has remained uncertain for scarcity of wildlife studies. Numerous records of cysts in wild ungulates date back to the 20th century, but cannot with certainty be allocated to the Echinococcus species and genotypes that are recognized today. This means that our current knowledge is largely restricted to studies of the past two decades that kept adding gradually to our concepts of transmission in various geographic regions. In particular, new insights were gathered in the past years on E. granulosus s.l. in wildlife of sub-Saharan Africa, but also on transmission patterns of E. multilocularis in previously neglected regions, e. g. North America. Here, an update is provided on the current state of knowledge on wild mammals as hosts for all Echinococcus species, listing >150 species of wild hosts with references, as well as estimates on their epidemiological impact and our current gaps of knowledge.

Keywords: Definitive host; Echinococcus spp.; Intermediate host; Life cycles; Wildlife.

Graphical abstract

Fig. 1

Dingos (Canis lupus dingo) are the only definitive hosts that are relevant for the secondary silvatic life cycle of E. granulosus s.s. in Australia, while a number of different macropod marsupial species act as intermediate hosts (here: Macropus giganteus). Photos: T. Romig, Kosciuszko NP, Australia, 2016).

Fig. 2

Suitable (foreground) and non-suitable (background) intermediate hosts for Echinococcus spp. in the Etosha NP, Namibia. In this particular location, 33 of 40 examined plains zebras (Equus quagga burchellii) had cysts of E. equinus (Wassermann et al., 2015; Aschenborn et al., 2023a), while no Echinococcus cyst has ever been found in elephants (Loxodonta africana), despite parasitological examinations of >2000 animals from different parts of sub-Saharan Africa (Graber et al., 1969; Young, 1975). Photo: T. Romig, 2012.

Fig. 3

Black-backed jackals (Lupulella mesomelas) are specialized scavengers of large herbivore carcasses, e. g. at kills of large predators, and are frequent in wildlife areas in eastern and southern Africa. In Namibia they are definitive hosts for E. equinus, E. ortleppi and E. canadensis G6/7. By feeding on cysts left over by the predators and scavenging on carcasses of ungulates that had died from other causes, they may contribute significantly to the parasites' transmission in wildlife areas and even assume the role of principal definitive hosts on livestock or game farmland, where large predators are absent. Photo: T. Romig, Etosha NP, Namibia, 2012.

Fig. 4

Cheetahs (Acinonyx jubatus) were only recently recognized as competent hosts of Echinococcus. In the central Namibian farming area, they contribute to a possible silvatic transmission of E. canadensis G6/7, that also involves jackals and oryx antelopes. Exemplifying the interface of domestic and silvatic life cycles, this photo shows two cheetahs having killed a calf of Maasai cattle inside Amboseli National Park in Kenya. Photo: T. Romig, 2023.