New diseases threatening wildlife

The recent covid-19 pandemic has brought emerging diseases to the attention of the world. Society is increasingly aware of the consequences of ecosystem degradation and biodiversity loss and how they affect us.

The interaction between animal species, the environment, and humans determines the persistence and spread of pathogens such as viruses, bacteria, fungi, and parasites.

Anthropogenic factors such as land use change, the globalization of trade, human migration and pressures on the natural environment accelerated by the global crisis have a direct impact on the distribution and size of animal populations. This affects the presence and risk of common pathogens. In addition, it has implications for the conservation of biodiversity and human and animal health. Therefore, it is necessary to better understand and monitor the health of wild animals.

Common pathogens

These common pathogens, capable of infecting more than one host species, are inspiring environmental medicine. This is the concept from which one health or One healthbelieves that human, animal and environmental health are interdependent and linked to the ecosystems in which they coexist.

Increased contact with wildlife and global mobility contribute to the international spread of known and emerging diseases that affect human and animal health, sometimes reaching pandemic levels.

This is a case of chytridiomycosis, a new disease caused by fungi that threatens the extinction of a large proportion of amphibian species worldwide. With over 40% of species threatened with extinction, amphibians have declined markedly and are already the most endangered group of vertebrates on the planet.

A paradigm example is the emergence of highly pathogenic avian influenza viruses (HPAI) in birds in recent decades. During 2022, successive outbreaks of HPAI resulted in a sharp decline in the breeding colonies of several endangered bird species.

Host diversity facilitates the circulation and spread of these viruses, showing that better health surveillance is needed in this era of accelerated global change.

However, mammals are the main actors in emerging diseases. For example, at least 25 wild Iberian mammal emergencies were known in the last century. It should be noted that 72% of new diseases in wild mammals have been discovered in the last three decades. This may be due to its greater frequency as well as better surveillance of wildlife health accompanied by new technological developments in animal health.

Some pathogens affecting mammals have a direct impact on their survival, such as canine distemper virus, chamois virus and rabbit hemorrhagic disease virus or sarcoptic mange mite.

Others are common with production species and have serious socio-economic consequences, such as animal tuberculosis or African swine fever. Many are also zoonoses of public health importance, such as leishmaniasis and Crimean-Congo hemorrhagic disease.

Hosts and interactions between pathogens

Therefore, knowing how pathogens persist and circulate in an ecosystem is extremely important. Many of the pathogens that cause the above diseases are of the multi-host type. They are especially persistent as they are able to use more than one species for maintenance, reproduction and distribution.

In some cases, a greater variety of hosts contributes to the persistence of the pathogen. In others, on the contrary, a greater variety of species will act against pathogens that preferentially breed in the dominant host species. This hypothesis is known as the dilution effect.

Host communities are complex. Its complexity is determined by the number of species susceptible to infection by a particular pathogen, the total species richness (susceptible or not), as well as the type and frequency of direct or indirect interactions between the species that make up the community. . In this context, there will be species more related to others that can serve as indicators of the circulation of certain pathogens.

In turn, pathogens do not persist in the environment in isolation, but rather separate hosts (co-infection) and communities (co-occurrence). In addition, they can promote each other (mites that facilitate the transmission of pathogens) or limit their transmission by competing for the same host (swine fever and tuberculosis in wild boars), or cause cross-protection through trained immunity.

ecosystem health

We need to better understand the relationship between ecosystem degradation and disease risk. An ecosystem is healthy if it is active, retains its organization and autonomy over time, and is resilient to environmental stresses. Healthy ecosystems ensure human well-being through ecosystem services.

Numerous indicators have been proposed to assess the health of ecosystems, based on the functionality of ecosystems rather than their degradation. For example, the presence, distribution or abundance of relevant species, or the composition of aquatic invertebrate communities.

However, indicators like these do not take into account health aspects. In the future, it will be convenient to supplement and integrate information on the diversity and abundance of animal communities with health indicators. This will improve understanding of complex natural systems and optimize health surveillance to contribute to the prevention and control of emerging diseases.

Cristian Gortazar, IREC Professor of Veterinary Medicine, Head of the SaBio Group, University of Castile-La Mancha, and Ignacio García Bocanegra, UCO Veterinary Professor. Team Leader GISAZ, University of Cordoba

This article was originally published on The Conversation. Read the original.

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