Biodiversity Loss Linked with the Rise of Infectious Diseases

Biodiversity and public health are among the most discussed issues in sustainable development. Yet, they are also usually considered far apart from each other when in reality, those two are closely linked. For instance, did you know that biodiversity loss and infectious diseases in humans are connected?

When the COVID-19 disease first appeared in Wuhan, people did not immediately associate it with biodiversity loss. We now know the disease is zoonotic, a term for any disease that is transmissible from animals to humans. Zoonotic diseases make up over 75% of known novel and re-emerging diseases. 

The COVID-19 is not the only one. HIV/AIDS, Ebola, and severe acute respiratory syndrome (SARS) also came from wildlife. In fact, over 70% of zoonotic diseases originate from wildlife. The question is, how did such diseases end up in humans and become deadly when they do?

Increased human and wildlife contact promotes disease transmission

When introduced to the human population, biodiversity acts as a source pool. A 2010 study stated that the emergence of zoonotic pathogens positively correlated with mammalian species richness. 

However, only a handful of activities, such as agriculture and wildlife hunting, further accelerate the prevalence of pathogens in humans. These activities increase the amount of contact between animals and humans, leading to a pathogen “spillover” effect. Nearly 50% of zoonotic diseases emerging since the 1940s occurred in areas where land use change, agriculture and husbandry, and bushmeat consumption were rampant.

This is shown in a 2024 study in Ghana on coronavirus (CoV) pathogens. The study discovered that the CoV prevalence and infection rates were higher in less diverse bat communities. The dominant bat species was reportedly a “competent host species” to the CoV pathogens and occurred in high abundance. This established a favorable site for the pathogens to replicate and multiply themselves. Furthermore, the bat caves were frequented by locals for religious, tourism, and socioeconomic reasons, in addition to being surrounded by land clearing for agriculture. The bat cave, which initially was a site for bat-to-bat transmission, became a site for bat-to-human transmission.

In the case of COVID-19, studies have associated the SARS-CoV-19 pathogen with the Chinese wildlife trade. Scientists suggest a spillover effect ensued in the wet markets, where human and wildlife contact occurred daily. That said, no study has determined the definitive source of the SARS-CoV-19 pathogen by the time of this article. 

Species diversity can dilute zoonotic infections & diseases

In principle, zoonotic pathogens evolve just like any other living being. Their behavior and characteristics may change as they progress further along the evolutionary and transmission pathways. Zoonotic pathogens transmit from animal to animal and may undergo evolutionary changes that can reduce their severity or resistance before being transmitted to humans. In some cases, pathogens may not be able to survive at all if the subsequent host is unsuitable. Therefore, the higher the host diversity, the less likely zoonotic diseases would impact humans. Scientists dub this the “dilution” effect.

This dilution effect is demonstrated in Lyme disease. A study on Lyme disease vector ixodid ticks in North America showed that Lyme disease cases were reportedly higher in states where its competent host, the white-footed mouse, was overwhelmingly dominant. By contrast, case numbers were significantly lower in states where the white-footed mouse was less dominant. The white-footed mouse was less dominant in states where forested landscapes were present as homes to less competent hosts such as chipmunks.

Biodiversity conservation is vital for public health–but it cannot act alone

Biodiversity conservation can generally inhibit the transmission of zoonotic diseases. However, successful disease management requires various approaches. Proper diet and exercise, sanitation, and habitat management are important for disease prevention, as drug discovery, medical procedures, and universal healthcare coverage are vital in the event of a disease infection.  

In cases such as the avian flu, poultry meat has become so integral to many cultures’ diets that farms and markets cannot be eradicated. Preventing deforestation and wildlife poaching could only work so far. Measures such as farm sanitization, minimizing contact between poultry and wild birds, as well as drug discovery become important to ensure the disease is maintained at a manageable rate.

Scientists understand that biodiversity loss contributes to changes in host-pathogen dynamics. The characteristics of a pathogen could change with the environment and the hosts. That said, biodiversity loss is inevitable where human development is concerned. 

Additionally, eradicating one disease does not reduce the likelihood of the next emerging disease. Therefore, it is unlikely that humans will ever be able to control or eradicate a pathogen species completely. What we could do is accept that we coexist with pathogens and manage them in a way that works for us as well as other species and the environment.

Editor: Nazalea Kusuma

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