The role of invasive alien species in the emergence and spread of zoonoses

Strength of enemy release from parasitoids is context-dependent in the invasive African Fig Fly, Zaprionus indianus

Understanding the mechanisms underlying the success of biological invasions is essential to employ effective prediction and management strategies. Escape from natural enemies in invaded regions (enemy release hypothesis, ERH) and increased competitive ability are hallmarks of invasive species; however, these two processes are rarely studied within the same context. Here, we examined the effect of enemy release on the competition outcomes of a successful invasive insect pest in North America, the African fig fly (Zaprionus indianus). Parasitoid wasps such as Leptopilina heterotoma that parasitize drosophilid larvae may seek out established species with known host suitability over a novel species, so we hypothesized Z. indianus may have low susceptibility to parasitoids, giving them a competitive advantage over co-occurring drosophilids. We tested this hypothesis by comparing the adult emergence rates from Z. indianus larvae reared alone or in competition with Drosophila hydei or D. simulans larvae in the presence and absence of parasitoid wasps under low and high larval densities. At low larval densities, Z. indianus emerged at equal rates to D. hydei but outcompeted D. simulans, and these outcomes were not affected by parasitoids. However, at high densities, the addition of parasitoids shifted competition outcomes in favor of Z. indianus, suggesting enemy release provides a competitive advantage under some circumstances. These results indicate that the strength of enemy release in Z. indianus is widely dependent on contextual factors such as density and competitor species. This study emphasizes how a community approach to testing the ERH is vital as the overall interpretation of the presence and strength of enemy release differed between intraspecific and interspecific experiments. Further investigation of how these results apply to field environments could offer insight into how Z. indianus alters ecosystems and how productive biological control may limit the spread of Z. indianus.

Avoiding novel, unwanted interactions among species to decrease risk of zoonoses

Circumstances that precipitate interactions among species that have never interacted during their evolutionary histories create ideal conditions for the generation of zoonoses. Zoonotic diseases have caused some of the most devastating epidemics in human history. Contact among species that come from different ecosystems or regions creates the risk of zoonoses. In certain situations, humans are generating and promoting conditions that contribute to the creation of infectious diseases and zoonoses. These conditions lead to interactions between wildlife species that have hitherto not interacted under normal circumstances. I call for recognition of the zoonotic potential that novel and unwanted interactions have; identification of these new interactions that are occurring among wild animals, domestic animals, and humans; and efforts to stop these kinds of interactions because they can give rise to zoonotic outbreaks. Live animal markets, the exotic pet trade, illegal wildlife trade, human use and consumption of wild animals, invasive non-native species, releasing of exotic pets, and human encroachment in natural areas are among the activities that cause the most interactions among wild species, domestic species, and humans. These activities should not occur and must be controlled efficiently to prevent future epidemic zoonoses. Society must develop a keen ability to identify these unnatural interactions and prevent them. Controlling these interactions and efficiently addressing their causal factors will benefit human health and, in some cases, lead to positive environmental, ethical, and socioeconomic outcomes. Until these actions are taken, humanity will face future zoonoses and zoonotic pandemic.

Invasive mammalian wildlife and the risk of zoonotic parasites

Invasive wild mammals are present in all continents, with Europe, North America, and the Asian-Pacific region having the largest number of established species. In particular, Europe has been the continent with the highest number of zoonotic parasites associated with invasive wild mammals. These invasive species may represent a major threat for the conservation of native ecosystems and may enter in the transmission cycle of native parasites, or act as spreaders of exotic parasites. Here, we review the role of invasive wild mammals as spreaders of zoonotic parasites, presenting important examples from Europe, America, and the Asia-Pacific region. Finally, we emphasize the need for more research on these mammals and their parasites, especially in areas where their monitoring is scantily performed.

Infectious agents present in monk parakeet (Myiopsitta monachus) and rose-ringed parakeet (Psittacula krameri) invasive species in the parks of Madrid and Seville, Spain

Introduction

The introduction of invasive species into an ecosystem could result in biodiversity loss and the spread of infectious agents that could cause re-emergent or emergent zoonotic diseases. Monk parakeets (Myiopsitta monachus) and rose-ringed parakeets (Psittacula krameri) are considered widespread invasive exotic species in urban habitats from the Iberian Peninsula. The aim of this study was to assess the presence of relevant infectious agents in wild parakeets captured in urban parks in Madrid and Seville (Spain).

Methods

A total of 81 cloacal samples were collected and analysed using molecular techniques.

Results

The prevalence of infectious agents varied between parakeet species: 9.5% of monk parakeets and 15% of rose-ringed parakeets were positive for enteropathogenic E. coli (EPEC), 13.3% of rose-ringed parakeets for avian influenza virus (AIV), 3.3% of rose-ringed parakeets for Newcastle disease virus (NDV), and a 23.8% of monk parakeets for Chlamydia psittaci.

Discussion

All C. psittaci-identified isolates were classified as B, E, or E/B genotypes, indicating transmission from wild urban pigeons to parakeets. These results highlight the need for monitoring parakeet populations due to the implications for human and animal health.