The Spotlight for issue 54:3 is on wildlife diseases. This post is written by Samantha Rumschlag and Jeremy Cohen.

All five Spotlight papers are available to read here.

In an ever-changing world, the risk of disease emergence is on the rise. As the climate warms, ranges of parasites and disease vectors are predicted to shift, exposing naïve populations to new threats. Humans are put in closer contact with wildlife as urban development and agriculture expand, increasing the odds of parasites jumping from animals to humans in spillover events. And, as globalization increases, transportation of hosts and their parasites unintentionally spreads diseases around the world. The consequences of emerging infectious diseases are far-reaching in their scope, placing global economies, the persistence of biodiversity, and human public health at risk. Predicting how these threats are shaped over time will be critical for mitigating their effects. This issue’s Spotlight on wildlife diseases focuses on new research that contributes to our understanding of the ecology of wildlife hosts and their parasites. The body of research delivers key contributions to disease monitoring and prevention in humans and wildlife, highlighting community ecology and advancements in spatial analyses.

Waterfowl_Jeremy Cohen
Anseriformes (waterfowl) have especially high prevalence of Avian influenza A. Photo by Jeremy Cohen.

Community Context across Scales

Host-parasite interactions are one of many within the tangled web of complex community interactions. Studying patterns of community interactions involving hosts might point to ways to manipulate properties and structures of communities to decrease the likelihood of a disease outbreak. Although there is much theory relating community interactions to disease outcomes, there is little application of community ecology to disease prevention and treatment. Several papers in this issue work to address this gap.

Studying patterns of community interactions may lead to identification of hosts most likely to contribute to disease emergence—typically a major challenge for disease ecologists. In this issue, an approach by Bordes et al.  uses network analyses constructed from field data to understand how helminthes and microparasites are transmitted between multiple rodent species and humans in Thailand, Cambodia, and Laos. Their work identifies three specific species that are disproportionately likely to transmit Wenzhou virus to humans. Monitoring for emerging arenaviruses in southeast Asia could be improved by focusing on these rodent species. Similarly, Caron et al. highlights the need for consideration of community dynamics in a review of bird hosts of influenza A viruses. Their work summarizes available data on avian flu prevalence in 101,000 birds. The prevailing view in the field is that Anseriformes (waterfowl) and Charadriiformes (shorebirds) are the most commonly infected orders of birds, responsible for maintaining flu viruses in natural populations. The authors conclude that waterfowl are commonly infected, as predicted; however, eight other host orders are more commonly infected than shorebirds. The bias towards shorebirds in the literature is attributed to outsized sampling near large waterways. An unbiased sampling of bird species that carry infections could increase the accuracy of documenting transmission cycles. Thus, despite highly different approaches, these studies point to specific host species that pose risks to humans by considering community interactions among hosts.

Both studies highlight the need to rethink a basic concept in the field of disease ecology: the reservoir host. Classically, a reservoir host is a long-term, asymptomatic host for a parasite that may act as source of infection for susceptible hosts. Typhoid Mary, a cook in the early 20th century in New York City, who unwittingly carried typhoid and exposed those she fed, is one of the most widely recognized examples of a human reservoir. Can a single species play a disproportionate role in the spread of an infectious disease within a community? The persistence of a parasite may more accurately be maintained by groups of multiple host species, interacting and providing a means for a given parasite to reproduce and spread.

While the study of community interactions among hosts can be important for understanding the spread of diseases, the study of interactions among members of the microbial community is a developing frontier that can aid in management of disease emergence. Manipulation of natural microbial communities by the addition of bacterial probiotics is a promising management solution for the targeted treatment of infectious diseases in wildlife. For instance, a developing body of research has explored the use of probiotics harvested from amphibian skin as a treatment against chytrid fungal infections, implicated in worldwide declines of amphibian hosts.

Spring peeper_Jeremy Cohen
Spring peepers are a North American frog that can be infected with chytrid fungus in natural populations. Photo by Jeremy Cohen.

Using a similar technique, Cheng et al. present the first effective treatment against white-nose syndrome, a fungal disease affecting bats. White-nose syndrome has proven to be a formidable foe for bats in eastern and midwestern North America, causing severe population declines during winter and threatening some species with extinction. The authors tested a probiotic bacterium, harvested from a healthy bat microbiome, to treat bats afflicted with white-nose syndrome. They found that this probiotic treatment reduced disease severity and increased survival when applied at the time of fungal infection, adding to the growing body of literature demonstrating how the natural microbiome can be manipulated to treat disease.

Mapping and Management

The management of natural populations of wildlife for the treatment of infectious disease at times has lead to unintended, adverse consequences. One of the most well documented cases involved culling badgers in an effort to control bovine tuberculosis. Culling badgers profoundly altered spatial movement behavior, increasing transmission rates, and surprisingly caused an increase in tuberculosis risk for cattle in some areas. Fears within the management community suggest that vaccination of badgers with Bacillus Calmette Guerin might provoke similar behavioral changes and increase risk to cattle. Luckily, new advancements in high-resolution GPS allow for the quantification of badger ranging behavior. Woodroffe et al. followed individual badgers via GPS tracking to test if vaccination or live trapping alters badger movement. Neither vaccination nor trapping influenced movement of badgers, suggesting that vaccination is an acceptable method for treatment in the field.

Giraffe_Jeremy Cohen
A giraffe drinking water in Kruger National Park, South Africa. Photo by Jeremy Cohen.

Indeed, the spatial documentation of diseased hosts is an important consideration for accurate emergence predictions and effective management of disease spread. Muneza et al. provide spatially explicit estimates of giraffe skin disease prevalence in Tanzania’s Ruaha National Park over four months using photography to recognize and diagnose individuals with a visual infection. This non-invasive procedure may aid in the measurement of population parameters important for disease modeling for hosts with visible diseases that move across large spatial ranges. Visual disease may be documented in species of conservation concern allowing for parameters to be estimated over long periods of time without destructive sampling.

This issue of the Journal of Applied Ecology shines a light on some of the most recent advancements to the field of disease ecology, highlighting the application of community ecology and developments in spatial analyses. While the emergence of new diseases in wildlife and humans may be on rise, our creative uses of new technologies, development of analytic capabilities, and advancements in understanding of community ecology will lead to more effective and efficient management strategies for combating the next outbreak.

Drs. Rumschlag and Cohen are currently post-doctoral scholars at the University of South Florida studying the influence of anthropogenic disturbance on host-pathogen interactions with a focus on laboratory experiments and spatial analyses. Learn more about their research here.

Spotlight: Wildlife diseases
– articles available in the Journal of Applied Ecology: