Research reveals value of large animals in fighting disease


May 2, 2014 |

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.

rodent

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.


28 Responses to Research reveals value of large animals in fighting disease

  1. u12176941 May 5, 2014 at 3:15 am #

    it is very interesting to aknowledge the contrubution of mammals in our lives,and we still treat them as if they are on of important to our lives,to put this in question does this mean some of the viruses that infect these mammals not harmfull to human lives?

  2. Alonzo (14126720) May 5, 2014 at 2:20 am #

    The article proposes that small rodents are carrying diseases that are harmful to humans, and with the decline in larger mammals to keep the balance humans are going to suffer the pathogens. The article shows that because of a few people in the world who see only to their well being(poachers) the rest of us will suffer. Small rodents go virtually unnoticed in a suburb or field, they go everywhere and carry their disease, without larger mammals to feed on them, we(humans) will be the next to get infected. The number of rodents need to be kept under control, but how can we do that?

  3. Tsundzuka (13405153) May 5, 2014 at 12:35 am #

    @u14029414 you just mentioned what i was about to say about this article. Is true nature controls mortality and the birth rate of the ecosystem even though men can conserve the ecosystem but nature take a big part. This is related to “charles darwin natural selection” i had read in the textbook of biology

  4. u14043892 May 4, 2014 at 11:34 pm #

    As we all know, the natural environment should be in absolute balance, rodents and all mamals that carry pathogenical virusses should actaully be minimum. The flow of our ecosystems must not be disturbd, otherwise there is space for all kinds of dangerous destructive kinds of virusses, virusses are searching for the best of best environments to multiply. That is why rodents are the best option for them, they can produce a large group of siblings, of witch the the virusses can interact. The planes in Kenya should be managed and be kept in balance, elephants shoud run free, poaching must be minimized, and rodent control must be in order to keep our virus lifeline to the minimum, and our higinic lifestyle to the maximum….

  5. u14029414 May 4, 2014 at 12:30 pm #

    Once again nature controls it self. The large animals living in the same habitat as the disease carrying rodents keeps this diseases under control. Keeping the numbers of large animals like buffalo and elephants high will control the disease and stop it from spreading. Therefore this problem can be contained by just conserving the natural ecosystem.

  6. Dylan Mackenzie (14049580) May 4, 2014 at 10:48 am #

    This article does not come as a surprise or source of new information to me however it does reiterate the idea of the value of not only large animals in an ecosystem but all animals in fact. These animals all play a vital role or niche as it were in the ecosystem in order to maintain the balance. This article is therefore a prime example of how human interference, as mentioned in the above comments, disrupts the sensitive balances within nature. this sparks the thought of whether or not humans played an integral part in the Bubonic plague as fleas of the rodents were also the carriers of the disease which has devastated many areas in the past. This once again emphasizes how nature works in cycles and complex systems in which we can only begin to fathom. To me, nature seems to be either a battle or cooperation of big versus small.

  7. Christie Nel (u14022852) May 4, 2014 at 10:22 am #

    Humans do not always fully understand the impact that they have on the natural world. They have the potential to make or break any ecosystem in the world by simply altering one aspect which might seem to them as insignificant at that stage. Humans, for some unknown reason, always want to neutralize big predators even though they do not always pose as a threat to them. By eliminating these bigger predators their prey have the opportunity to take over the ecosystem and then all kinds of new problems start to arise, like for instance more mice can carry more pathogens and cause more frequent outbreaks of diseases. This can cause devastation.

  8. Dylan Mackenzie (14049580) May 4, 2014 at 9:40 am #

    This article does not come as a surprise or a source of new information to me however it does reiterate the idea of the value of not only large animals in an ecosystem but all animals in fact. These animals all play a vital role or niche as it were in the ecosystem in order to maintain the balance. This article is therefore a prime example of how human interference, as mentioned in the above comments, disrupts the sensitive balances within nature. This sparks the thought of whether or not humans play in integral part in the Bubonic plague as fleas of the rodents are also carriers of the disease which has devastated many in the past. This once again emphasizes how nature works in cycles and complex systems in which we can only begin to imagine. To me nature seems to be a battle or cooperation of big versus small.

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