Ecological and Evolutionary Challenges for Wildlife Vaccination

Abstract

Wildlife vaccination is of urgent interest to reduce disease-induced extinction and zoonotic spillover events. However, several challenges complicate its application to wildlife. For example, vaccines rarely provide perfect immunity. While some protection may seem better than none, imperfect vaccination can present epidemiological, ecological, and evolutionary challenges. While anti-infection and antitransmission vaccines reduce parasite transmission, antidisease vaccines may undermine herd immunity, select for increased virulence, or promote spillover. These imperfections interact with ecological and logistical constraints that are magnified in wildlife, such as poor control and substantial trait variation within and among species. Ultimately, we recommend approaches such as trait-based vaccination, modeling tools, and methods to assess community-and ecosystem-level vaccine safety to address these concerns and bolster wildlife vaccination campaigns. The Potential of Wildlife Vaccines Highlights Vaccines vary in their efficacy and can be categorized as conferring waning, binary, or partial immunity. Some imperfect vaccines may indirectly increase parasite transmission or virulence. Target vaccine coverage depends on wildlife disease control objectives, for example, spillover prevention or conservation.

Paradoxes and synergies: optimizing management of a deadly virus in an endangered carnivore

“…Importantly, our results suggest that studies assuming full protection from vaccination may significantly underestimate the level of vaccination needed for population protection-underestimates which may even make epidemics worse if only partial vaccine immunity can be achieved. (32). In the case of binary immunity, vaccine efficacy would be unlikely to prolong and worsen epidemics as we saw here.…”

Environmental persistence but not per capita transmission rates of a chytrid fungus determines infection prevalence

“…Further, we show that Bd decomposition is similar across water sources from neighboring sites; these results suggests that exposure of hosts to dead Bd and/or its metabolites, which may lead to acquired resistance, could be similar at small spatial scales. Increased attention towards the effects of local scale variability in pathogen mortality, decomposition, and per capita transmission may increase the efficacy of efforts to surveil and manage wildlife infectious diseases (Cunningham et al 2017, Barnett and Civitello 2020).…”

“…Strategies for the surveillance and management of wildlife infectious diseases are informed by a mechanistic understanding of the distribution and persistence of pathogens in host populations and the environment (Cunningham et al 2017, Barnett and Civitello 2020). Yet, characterizing these mechanisms remains immensely challenging because of the complexity and natural variability of host-pathogen systems and the environments in which they exist (Plowright et al 2008, Tompkins et al 2011, Gandon et al 2016).…”

Anti‐tick and pathogen transmission blocking vaccines

“…In addition, the immune response elicited in the wildlife reservoir will not only need to prevent reservoir infection and pathogen replication in the reservoir host, but ideally also induce pathogen neutralization in the tick vector in order to prevent pathogen reproduction and transmission. 121 The use of bait stations can protect bait from exposure to rain and snow, reducing mould growth. In addition, bait stations also reduce the likelihood of nontarget animal consumption, through either using small entrance ways for rodent-targeted vaccines or using elevation when targeting larger animals such as deer.…”

“…Ensuring stability of the antigen under sometimes harsh conditions is a crucial factor determining the success of a reservoir‐targeted vaccination approach. In addition, the immune response elicited in the wildlife reservoir will not only need to prevent reservoir infection and pathogen replication in the reservoir host, but ideally also induce pathogen neutralization in the tick vector in order to prevent pathogen reproduction and transmission 121 . The use of bait stations can protect bait from exposure to rain and snow, reducing mould growth.…”