Research reveals value of large animals in fighting disease

Don’t let their cute names fool you: the Mearns’ pouch mouse and the delicate mouse can be dangerous.

These and other rodents commonly harbor pathogens that can be deadly to humans. According to new research by Stanford scientists, populations of pathogen-carrying rodents can explode when larger animals die off in an ecosystem, leading to a doubling in the risk of potentially fatal diseases spreading to humans.

“It has tremendous consequences for us,” said co-author Rodolfo Dirzo, a Stanford professor of environmental science and senior fellow at theStanford Woods Institute for the Environment. “Our data suggest that maintaining healthy populations of mega fauna helps us stay in good shape in terms of avoiding nasty bacteria.”

The study is published in the journal Proceedings of the National Academy of Sciences.

Around the world, large animal species are dying off rapidly in the face of hunting or poaching, or indirectly via deforestation and other human impacts. More than half of all mammal species, for example, are declining. Such human impact on fauna, however, is differential: As the numbers of large mammals are declining, the numbers of small mammals, such as rodents, are increasing.

To study the potential health impacts of these large animal population declines, the researchers fenced off multiple 2.5-acre (4-hectare) plots of savanna land in Kenya, preventing access by elephants, giraffes, zebras and other large animals. Over the course of two years, the number of rodents in the study areas doubled, most likely because of increased availability of food and cover, among other reasons.

With more rodents came more of the pathogen-infected fleas they carry and increased disease risk for people. The study specifically examined the prevalence of Bartonella, a group of bacteria found throughout the world that can cause long-term damage to the human heart, brain, lungs and spleen.

“This is an underappreciated and insidiously simple route by which human change can drive disease risk,” said study lead author, Hillary Young, who conducted the research as a biology graduate student at Stanford and is currently an assistant professor at the University of California, Santa Barbara.

More than 60 percent of all human disease originates with pathogens carried by animals. Flea-transmitted pathogens are found everywhere from suburban enclaves to tropical forests. In East Africa, where rodent-borne disease is common, typhus and even the plague can spread via human contact with infected rodents. Most health clinics in the region are unprepared to detect, let along treat, some of these diseases.

Dirzo, Young and their colleagues, including Stanford Woods Institute research associate Dan Salkeld and former Stanford biology graduate student Douglas McCauley, plan to expand the research to look more closely at the cascade effect of large animal decline on human health. Among other analyses, they intend to study how different types of land use affect the prevalence of a wide variety of rodent-borne pathogens and how the risk of disease from these pathogens matches up with actual disease prevalence in people.

The material in this press release comes from the originating research organization. Content may be edited for style and length. Want more? Sign up for our daily email.

28 thoughts on “Research reveals value of large animals in fighting disease”

  1. Instead of worrying about the number of pathogens rodents could carry, we should be focusing on how to find preventative medication or methods for humans. However the best way to prevent wasting all this time and money on finding cures if the pathogen was to break out, we should be using it on preventing the killing off of predators, and finding safe and humane ways to keep predators from killing our live stock so that the numbers do not decrease any further.

  2. It’s actually amazing to think that such small animals cause such an uproar in even today’s technologically advanced plaque control or pest control. Yes its true as most of the bloggers have stated that the diseased rodents outbreaks are to blame on humans but now that it has happened have do we plan to control this epidemic? One way that have personally seen to work is not with poison or traps or such methods but rather introducing natural predators to the environment and then making sure they stay and help with the population control. On a farm in the Free state near Bultfontein farmers ave erected “T-poles” in the middle of the crops as lookout posts for owls and hawks to give them a better chance at catching these rodents. These rodents do not sincerely carry any deseases but are also a problem in destroying crops and have to be managed. maybe this method could be used in prevented the out-breaks mentioned in the article?
    The other thing mentioned is that the cause of these out-breaks are that larger animals become exstinct or are merely killed of? maybe in some cases this might be the truth but as a guy who knows how it is on farm these ‘biiger’ animals are actually a bigger for the farmers as much of these predators also endanger the livestock of the farmers. This gives the farmer a uneasy choice, either remove the predator or lose his means of living? in my eyes thats a rather easy choice. given this information I don’t think people should look down on hunting, poaching of course but not hunting , we could actually use hunting . in the first place hunting is one of the biggest sources of income for SA and secondly it a method of population control, just a funny example would be to estimate the number of Impala that would be prouncing around if it were not for hunting? then we would have to resort to other methods like culling which I see to be a bit drastic not even the possible income lost from doing this.

  3. The love for animals has faded in most environments. Its high time to stand and alert people and communities about the role played by animals in our lives because some people doesn’t see their worth.Rhino poaching has become a crucial thing, its leading to its extinction. If the care for such animals isn’t there it means there will still be more of diseases being discovered. Things are going to get worse.

  4. Humans with their ignorance behaviour, don’t actually realise that their actions of killing large animals for personal benefits will actually affect them indirectly. Killing these animals will distort the ecosystem and the number of disease carrying, small animals will incline, since there will be no more large animals to maintain their population. This will result to more fatal borne diseases being contracted and have health risk to us as humans. I personally believe that the human population should be more educated about the ecosystem and how it functions before it is late for our health. The more we don’t respect the ecosystem, the more it will backfire on us and we will face the consequences. We should therefore stand against illegal poaching and hunting of large animals that are essential of getting rid of rodents and thus, decreasing the chances of contracting various fatal diseases as humans. The question we should ask ourselves is, are we prepared to risk other incurable diseases that will cause a huge decline to our population?

  5. I think it is a given that humans are one of the biggest destroyers of the environment and of the life that survives in it. Humans are the poachers, the people that remove forests for shopping malls, new developments or what ever else the land may be used for. We are the polluters of the oceans, land and atmosphere. Due to all of this ecosystems and food chains/webs are disrupted, leading to the increase or decrease of a species, a disruption in equilibrium.

    Based on this post, it is clear that if the disease infested rodents are not kept to a minimal, the dangers of something like the Bubonic Plaque or “Black Death” may erupt, and it would all be because of own selfishness. This is why we need to maintain an equilibrium between these rodents and their predators and animals they are in competition with.

    However, we cannot only blame the rodents for carrying diseases, many other animals do to, but it is because of the size of the rodent and the fact that if can pretty much crawl through any space, that we blame it.

  6. The impact that humans have on the environment has been a topic which has enjoyed a lot of attention, especially over the past few years. Once again another negative impact has been found. The problem is the fact that human population is increasing at a rapid rate and even though it can be argued that humans can be more efficient with land use, more and more land and natural resources is needed to satisfy the needs of humans. The first thing that comes to my mind is vaccines for these types of diseases. I know that this will cost a lot of money and therefore i think that part of these greedy businesses’ social responsibility must to contribute to a sort of campaign that create and provide these vaccines. So the industry that was established as a result of deforestation for example, will then put back into communities that are suffering. What i was also wondering is aren’t the numbers of small animals, such as the rodents, going to start decreasing because of the increased competition among the animals for existing resources? It is also important that we educate people about this problem so that can protect themselves against diseases they might have not known to exist. I really hope that mankind doesn’t cause its own destruction. At the moment it looks like this indeed is the case.

  7. Human impact affects the balance of nature more negatively than positive. It is suppose to be the other way around. Because of human impact towards poaching and hunting , large mammals decreases and small mammals increases in numbers and this destroys the balance of nature. The increase in small mammals means increase in pathogens that is deadly to humans. In an indirect way humans will be the cause of more unknown illnesses and deaths. More research should be done to prevent these illnesses and more awareness towards these problems should be done.

  8. It is clear that humans with their destructive behavior and materialistic views have a big impact on our ecosystem. If it wasn’t for deforestation , trophy hunting to name a few reasons, our ecosystem would be in an equilibrium, and there would be fewer
    pathogens that causes diseases resulting in death and harm. Before humankind
    destructed the environment, there were fewer plagues because there was balance in
    nature. With fewer predators and big mammals, the reproduction rate of specifically rodents that carry many diseases would increase dramatically and pose a much bigger threat to the human race.

  9. This study emphasises how important the maintenance of the ecological balance is. It is evident that man is the biggest cause for the imbalances in nature. Mankind’s actions by killing large animals or deforesting in the name of “development” will surely have an effect on the equilibrium that nature requires to keep all species in balance with each other.

    All species on earth have a part to play in nature and even the smallest change may have catastrophic consequences which can eventually lead to the distinction of the human race.

    More should be done to educate people to respect nature’s balance. Studies like this is important as it will make people more aware of what can happen

  10. It’s quite obvious that us humans are the ones to blame for this situation. We should stop wanting to have all the best things for ourselves, not thinking about the environment and all. The problem with all the rodents is that the less large animals, the more rodents. We have to stop animal poaching and destroying the natural habitat of the animals. We simply have to restore the uneven environmental equilibrium. In the meantime, research can be done on some of the pathogens and diseases that the mice and rats carry around. New medicine can be developed and new discoveries can be made.

  11. based on the article it is very clear that rodents are dangerous and they feed on large animals,it is very important for human beings to stop hunting and poaching because this increases the number of rodents.

  12. Although large animals carry the most pathogens, all animals are important in any way, regardless of the size. Such an interesting note, since we as humans get most of the diseases from animals, we also have a great impact on the lives of those animals Animal extinction is caused by our careless activities as humans.

  13. it is clear that rodents are a danger to human life, and that the only solution we have is to make sure that there are enough mammals to harvest crops so that we have a manageable number of rodents. Rodents also bring deadly and dangerous bacteria along with them, this goes to show that they are a huge health risk. Now comes the question of who is supposed to deal with the rodent issue? And what is responsible for the rapid increase in rodent population?

  14. This as a whole only serves to strengthen the argument for the harsher implementation of anti-poaching laws on a global scale. The earth as an ecological system has remained in a state of “uneven environmental equilibrium” (as conflicting as that sounds) which has served to maintain a balance of life on earth. Continued human interference with environmental systems will prove not only to propagate disease through ecological imbalance and the dominance of a certain species but too promote other avenues of destruction with, as an example, the colonization of alien plant species becoming prominent as larger mammals become less available to clear areas of vegetation.The dangers of constant human interference with the natural world know no bounds with disease, economic implications and the extinction of various species (including ourselves) all at risk.

  15. Yet those small animals can also helps us in finding new and effective cure for both chronic and acute, The small animals must be maintained in quantity to suit the balance between them and the human population. Larger animals do not have that much contact as small animals does to people, so it will not be that reasonable for them to transfer diseases as much faster than small animals. As those animals are dangerous, they are the ones that we can study and manipulate easily, providing a suitable solution to the latest traits of viruses that are hard to manipulate. We highly need them but in a fixed manner without avoiding and poaching the bigger ones as they are there for a purpose.

  16. It is apparent that we need the larger mammals to avoid contracting and passing different diseases from the rodents. We should emphasize on the poaching control laws which might help in conserving larger mammals. This is better than the expense of finding cures and increasing number of health cares.

  17. It is interesting to note how sensitive our ecological balance is and how important it is to ensure the sustainability of all species on earth. An interesting question that comes to mind :
    what would happen to the rodent population if the human specie declined?

  18. This phenomenon is yet another negative result of our careless and selfish treatment of the environment. Rats and mice are notorious for carrying dangerous pathogens and causing terrible plagues even in ancient egyptian times they were feared. Along with larger animals competing with rodents for food they[the larger animals] are also resistant to the pathogens that are carried by the rodents and therefore they are able to co-exist with one another. Humans have relatively weak immune systems when compared to other organisms and therefore can not co exist with them. As a result humans have resorted to extermination which is not fair to any animal even rodents as we were the ones that created an environment within which they could breed to extreme levels. In order to rectify this problem predators or larger herbivores should be introduced to the environment so that a healthy ecosystem can be created and maintained.

  19. based on the information provided via the blog it is evident that large animal do play an important role in controling the ecosysytem and conserving wild rodents.we have to also take into consideration other enviromental effects like climate change, natural disasters that will influence the habitat of the rodents.

  20. If the rodents increase because of JUST the larger mammals that decreases would the owls, hawks and other bird life help to keep the numbers of rodents stable ? The jackal and lynx would also increase and won’t they also stabilize the number of rodents ?

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