Some 60 percent of all human diseases, and 75 percent of all emerging infectious diseases, are zoonotic (human-animal transmitted infectious diseases). In light of these staggering figures, the Nairobi-based International Livestock Research Institute (ILRI), recently released a report mapping the top 20 geographical hotspots of emerging zoonotic diseases and emerging disease outbreaks. Among the study's findings, the report reveals the heavy disease burden of zoonoses for one billion of the world's poor livestock holders, in addition to surprising new data on emerging diseases in industrialized countries, many of which have never been mapped.
The study identifies three classifications of high-priority zoonoses, the first of which, endemic zoonoses, causes the vast majority of illness and death in poor countries. Endemic zoonoses, such as brucellosis, are present in many places and are usually transmitted as food-borne illnesses. Given its widespread nature, the review suggests that endemic zoonoses are of greatest concern where the objective is reducing the burden of human illness and enhancing the profitability of livestock for poor small-scale livestock farmers in the developing world.
Other zoonotic diseases include epidemic zoonoses, such as anthrax and Rift Valley fever, which typically occur as outbreaks and are sporadic in temporal and geographical distribution.
And the report examines emerging zoonoses, which are relatively rare and are characterized by rapidly increasing rates of incidence or expanding geographic ranges. Emerging zoonoses, such as bird flu and HIV-AIDS, can spread to cause global cataclysms. While zoonotic diseases can be transmitted to humans by any animal, most human infections are transmitted from the world's 24 billion livestock.
From zoonotic gastrointestinal disease to rabies, zoonoses present a major threat to global health. "Zoonotic diseases are more important than people think," says Dr. John McDermott, director of CGIAR research program on agriculture for improved nutrition and health. According to McDermott, two thirds to three quarters of the pathogens causing the newest emerging disease events, like SARS, come from animals.
In total, the study examined 56 zoonoses, which combined are responsible for 2.5 billion cases of human illness and 2.7 million deaths annually. Of the 56 zoonoses, the report conducted an in depth review of the 13 zoonotic diseases that are responsible for the majority of the cases of human illness and death from zoonoses.
In identifying the hotspots for zoonoses, the report shows the clear relationship between the densities of animals to people as the greatest factor in determining the risk of zoonotic diseases. According to the study, India, China, and Bangladesh, as well as Ethiopia, Nigeria, and other African nations are the most affected by zoonotic diseases, in addition to being the countries with the least capacity to manage them.
Perhaps unsurprisingly, one of the study's many findings suggests a strong association between poverty, hunger, livestock keeping, and zoonoses. Consequently, those who are most affected by zoonoses tend to be poor livestock holders in the developing world. Given that three quarters of the world's poor living in rural areas, and one third of the world's urban poor, depend on livestock for food and income, the threat of zoonoses in the developing world is particularly hazardous.
But despite the danger of zoonoses, livestock ownership presents an opportunity for many poor livestock holders to escape poverty and hunger. For the world's 2.5 billion people living on less than two dollars a day, livestock provides these households with up to half of their income, and between 6 and 35 percent of their protein cosumption. But the widespread presence of zoonoses and lack of capacity to manage these diseases in the developing world presents seemingly insurmountable obstacles for alleviating hunger and advancing economic welfare for poor livestock holders.
"The burden of disease on poor people is pretty strongly held," says McDermott. "And this is important to quantify because often a lot of decisions for where to allocate resources for disease control is often misapplied and it is important to put them in the right places." Ultimately, McDermott hopes the report will help international aid agencies target their development assistance to help poor countries that currently face the greatest risk and burden of zoonotic diseases, and that could benefit the most from foreign aid and investment.
With greater investment, poor nations could increase their capacity to manage outbreaks of zoonotic diseases and better the economic and physical health of those in the developing world.
Are world leaders in global health and development up to the challenge?
Caitlin Aylward is a research intern with Nourishing the Planet