July 05, 2012
Animal-to-Human Disease Cycle Widening
Nearly two-and-a-half billion people become ill every year from diseases transmitted from animals. Most are in low- and middle-income countries. A new study lists the top geographical hotspots for these diseases, including the United States.
Of the billions infected every year, more than two million die from diseases called zoonoses.
“Zoonoses are diseases which are transmitted between animals and people. A majority of human diseases are actually zoonotic. More than 60 percent of human diseases are transmitted from other vertebrate animals,” said Delia Grace, a veterinary epidemiologist and food safety expert at the International Livestock Research Institute in Nairobi.
“Some of these diseases are pretty common. Some of the food- borne diseases and also diseases such as tuberculosis, leptospirosis are not uncommon. Others are quite rare. So it depends a little bit on the disease,” she said.
There are many different infection pathways.
“In terms of human infections, probably the most common transmission pathway is food. People getting sick from food they eat. But other transmission pathways include direct contact with animals. And also some of these can be transmitted via the water, through water, and others can be transmitted through the air,” she said.
Grace is the lead author of the report called "Mapping of Poverty and Likely Zoonosis Hotspots."
“Most of these diseases are of pretty low impact. Diseases like avian influenza or mad cow disease have actually killed very few people. But they are of interest because some of them have the potential to kill a lot of people – diseases like the Spanish flu after the First World War or HIV/AIDS, both of which were originally zoonosis,” she said.
The report includes information on both old and new diseases.
“So in terms of the hotspots of the zoonosis which are there all the time – not the new zoonosis, but what we call the endemic zoonosis – we identified three countries, which bear the greatest burden of these diseases. And those are India, Ethiopia and Nigeria. But in terms of the new diseases – the diseases which haven’t been there, but are emerging – the hotspots are very different. They appear to be western United States and Western Europe,” she said.
The report is based on an analysis of over 1,000 surveys. Grace describes the findings as alarming, creating major problems for both people and animals.
Also, things could get worse in the coming years as meat production sharply increases to feed a rapidly growing world population. The U.N. predicts a population of nine billion by 2050, up from the current level of seven billion. High production farms often raise animals in very tight quarters. That can allow diseases to spread quickly. Another potential problem is the use of antibiotics in animals that can mask disease symptoms.
“What our study found,” she said, “is that for the pigs and poultry, which are most rapidly increasing – because these are the systems which can quickly gear-up to meet the needs of rapidly expanding human populations – that they are associated with a far higher level of food-borne disease than the sheep and cattle and buffalos, the more kind of slowly growing systems. So the alarming thing here is that unless we better manage zoonosis we can expect to see a lot more food-borne diseases.”
Grace said the know-how exists to build barriers to reduce disease transmission to both people and wildlife. However, putting it into practice can be a challenge. Rather than increasing food inspections, the report recommends an “incentive-based” system to encourage safer methods of raising animals. One incentive is to provide training and branding for small farmers leading to official certification that their products are safe. Another is to develop home testing kits that would allow consumers to learn whether their food is contaminated.
Grace said poverty and disease are closely linked, adding preventing animal disease transmission can help alleviate poverty.