Conversations with Jason Rohr: Modern agriculture and its relationship with human diseases

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Jason Rohr’s research interests fall at the interface of ecotoxicology, conservation biology, and community, population, behavioral, and disease ecology. He is particularly interested in how anthropogenic changes, mainly pollution and climate change, affect wildlife populations, species interactions, and the spread of disease. He and his collaborators and have studied interactions among multiple natural and anthropogenic stressors and are making efforts to integrate our research across disciplines. The Rohr Laboratory of Ecology and Public Health goal is to understand, and develop solutions to, environmental problems to enhance the likelihood of a sustainable existence for both humans and wildlife.

SCIENTIFIC INQUIRER: At first glance, it’s difficult to see how diseases, particularly new emerging ones, are linked with current agricultural practices, yet they clearly are. Can you explain the relationship?

JASON ROHR: The connections are abundant and diverse. First, many emerging zoonotic diseases (those transferred from animals to humans) require human-animal contact. This is a by-product of agriculture, with cases such as swine and avian influenza deriving from ag and even diseases such as HIV, coming from bushmeat hunting. Agricultural impacts on land use can also alter human-animal contact. Changes to water use and aquatic habitats for agricultural purposes are well known to change disease. For instance, dams to produce reservoirs for irrigation have been well-documented to increase human schistosomiasis and mosquito-borne diseases, such as malaria. Other agricultural practices, such as filling wetlands, can reduce certain diseases and improved nutrition from ag. can facilitated immunity that can help fight disease.

SI: Now can you (explain) for in the world’s booming population and how that exacerbates the situation?

JR: An increased human population can exacerbate the agricultural-disease link in several ways. First, more people likely means more ag. to feed those people. Second, more people means more contact among people and between people and animals, both of which can facilitate the spread of disease. Third, more people means more movement of people and products, which can introduce diseases where they have not been previously. Fourth, an increase in the human populace might also exacerbate antibiotic resistance as more antibiotics will be needed, more fertilizer that can exacerbate some diseases, and more pesticides, many of which can be immunosuppressive. Fifth, an increase in people and ag. will likely mean more biodiversity loss, and biodiversity loss has repeatedly been shown to increase disease risk. Sixth, if there are more people and thus less food per person (there might not be if we increase food production), then many humans might have less resources to dedicate towards immunity to fight infections. These are just a handful of the mechanisms.

SI: Can you discuss your paper and what your objectives were?

JR: Our goal was to review both the beneficial and adverse effects of agricultural expansion and intensification on the transmission of human infectious diseases. We synthesized the pathways through which agricultural practices influence human infectious diseases, and vice versa, and identify opportunities to minimize the adverse consequences of agricultural growth while maximizing the human health benefits of agricultural development. We hope that by synthesizing the complex intersection of food production and human health, we have highlighted the value of increasing agricultural- and disease-related research, management and policy, maximizing the benefits of agricultural development while minimizing its adverse effects on human health and the environment, and preparing for the imminent changes driven by the 11 billion people expected to inhabit Earth by 2100.

SI: What were some of the key measures that need to be taken in order to begin addressing the problem of feeding the world’s population yet keeping diseases at bay?

JR: How much population will increase, what disease control measures will occur and where, and what are the most important ways that ag. is and will increase and decrease disease.

SI: Sometimes, arguments need concrete examples to drive home points. Can you discuss your research experiences with human schistosomiasis and how current agricultural practices are exacerbating the problem?

JR: Sure. Dams were built partly to facilitate irrigation for agricultural expansion. The increase in irrigation ditches increased habitat for freshwater snails, which transmit the schistosomiasis-causing pathogen to humans. The increase in ag. increases fertilizer and insecticide use that can increase snails. Fertilizers increase submerged vegetation, the habitat for snails, and algae, the food for snails. Low levels of insecticides kill snail predators, such as crayfish, prawns, and many aquatic insects. Additionally, a primary predator on snails in Africa is the prawn, which is essentially is a crayfish that migrates to estuaries to breed. Dams prevent these predators from reaching the estuaries thus essentially eliminating this snail predator from the landscape.

SI: A significant number of zoonotic diseases have historically come from food sources, whether it’s influenza from farms or HIV from bushmeat. How can this problem be addressed?

JR: It is a tough problem to address because people need to eat. We need to know what scenarios create the greatest risk and educate people on how to minimize that risk. This will require research to identify what are the most important ways that ag. is and will increase and decrease disease, how to mitigate that risk, and then how to successfully change human behavior so that risk can be reduced.

SI: In your honest opinion, how likely is it that the problem your paper points out is addressed adequately in the future? What needs to happen?

JR: It all depends on your definition of adequately addressed. Human disease and food production are both high priorities internationally. There are clearly trade-offs however. That is, increasing population density and food production could increase disease risk. The goal will be to identify win-win scenarios for food production and disease reduction where they exist and implement those solutions/innovations widely. If we can do that, I think we can keep disease low as global human population and food production increase, but it won’t be easy!

For more information about Jason Rohr, visit his labpage.

IMAGE SOURCE: Muhammad Mahdi Karim/Creative Commons

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