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By Madeline McCurry-Schmidt
ASAS Scientific Communications Associate

The future of hunger: How animal science supports global food security

In Part 3 of “The future of hunger” we looked at how new research and technology related to animal breeding can make animal production more efficient. In Part 4, we look at how studying diseases that sicken food animals can increase food production and help keep humans healthy.

Getting into the swine facilities at the University of Illinois requires a sort of costume. Visitors are given disposable white jumpsuits and clear plastic boots. In the end, they look more like astronauts than farmers.

This odd get-up is a form of biosecurity. Biosecurity steps minimize the risk that swine will be exposed to disease. Other steps include building swine facilities away from roads where other animals are transported and building strong fences around facilities to keep wild animals out.

Preventing disease is a challenge in all animal species, not just swine. Drive by a poultry farm, and you’ll probably see a sign with stop-sign red lettering:

“Help us maintain flock health. PLEASE KEEP OUT.”   

The battle against livestock diseases is a worldwide concern. Travel outside the continental United States, and customs will ask if you “have been on a farm/ranch/pasture” during your trip.

Animal producers have good reason to be strict about biosecurity. In recent years, farmers have fought off diseases like foot and mouth disease (FMD), bovine tuberculosis and porcine reproductive and respiratory syndrome. Pathogens can evolve quickly, and global trade can spread emerging diseases to vulnerable animal populations. Each disease outbreak is a challenge to the world’s food supply.

Healthier animals produce more food for animal consumption. Healthy pigs grow faster and produce more meat. Healthy cows produce more milk, and healthy hens produce more eggs. Animal diseases also have the ability to spread to humans. By studying animal diseases, animal scientists can increase the world’s food supply and protect human health.

The threat to animals

Bluetongue virus is an ugly disease. Sheep with Bluetongue virus can get high fevers, they drool and their faces swell up. Some get lesions on their feet and resort to walking on their knees. A lack of oxygenated blood to the tongue can cause the trademark blue tongue, making it difficult for sheep to breathe or swallow. The sickest sheep die within a week of showing symptoms. Most sheep survive, but it can take several months for survivors to recover.

Bluetongue disease is spread from animal to animal by biting midges that live in warm climates, like Africa and Southern Europe. The disease affects sheep, goats, buffalo, deer, cattle, dromedaries and antelope.

Bluetongue is just one of many diseases that animal scientists face when they work to keep animals healthy. These diseases threaten food security around the world. Evidence shows that when animal scientists have the resources to prevent diseases, they can improve agriculture. In July 2011, Great Britain was officially declared “free” of Bluetongue.

To eradicate Bluetongue virus, scientists and producers vaccinate animals, quarantine the sick, and work to control the insect population. Government support and funding for these eradication efforts is also important.

Salmonella is another kind of pathogen that scientists are working to eradicate. Salmonella is a genus bacteria that live naturally in the environment, and scientists work hard to protect animals from the disease.

Bradley Bearson, a microbiologist with the USDA Agricultural Research Service, said Salmonella can colonize a variety of animals, not just swine. In many cases, Salmonella infections do not cause symptoms.

“Often, Salmonella can colonize swine without causing obvious signs of disease,” said Bearson.

On rare occasions, pigs infected with Salmonella will have diarrhea, dehydration, septicemia or even death. But even without obvious symptoms, there are two major reasons why scientists want to stop Salmonella infections in swine herds.

One reason is that even infections without noticeable symptoms, called “sub-clinical” infections, can hurt swine production. An infected animal may look normal, but fighting off an infection takes energy. Studies show that swine with subclinical infections do not gain body weight as quickly as uninfected swine. Lower body weight means less meat produced for human consumption.

Swine producers are particularly concerned with subclinical infections in newborn piglets. At the 7th International Congress on Farm Animal Endocrinology (ICFAE), in Bern, Switzerland last August, researcher Jeff Carroll explained that piglets face extra immune challenges because they are also at risk for hypothermia. Piglets get cold easily, and sick piglets have to divide their energy between fighting infection and staying warm.

Carroll, a research leader for the USDA Agricultural Research Service Livestock Issues Research Unit, conducted an experiment where piglets were given injections of Lipopolysaccharides as an immune “challenge.”

“The pigs that were maintained in the warm environment exhibited no visual signs of illness.” Carroll said. But the cold pigs “redirected any nutrients they had toward survival.”

Carroll said it is important to study how temperature affects immune response. Carroll has also found that cattle face immune challenges when subjects to high temperatures.

It is important for animal scientists to study the cases when subclinical infections affect growth. With healthier animals, producers can raise more food to feed the world.

Bearson said good Salmonella control measures should include a biosecurity program. He said it is also important to understand gut health in animals and the role of feed additives and vaccines in controlling infection.

“A single management strategy will not be sufficient to consistently reduce pathogen colonization,” Bearson said.

A second reason to study animal diseases is the need to protect human health. Pathogens like Salmonella can have devastating effects on human health.

“Whenever pathogen exposure occurs due to Salmonella being present in food, water, or the environment, there is a risk of spread to other animals as well as a potential risk of human disease,” Bearson said.

Animal producers work to prevent Salmonella in herds, and food producers take specific, government-mandated steps to keep meat, milk and eggs safe. But sometimes, contamination reaches the public. According to Centers for Disease Control statistics, Salmonella infections were the cause of 62 percent of hospitalizations due to food-borne illness in 2008. In 2008, 13 people in the United States died after contracting Salmonella.

Officials tell consumers to wash their hands and cook food thoroughly. Food safety experts agree, and many say it is important to take prevention a step further; to keep food production safe, scientists need to understand how diseases spread between animals and humans.

The human toll

As mentioned above, pathogens evolve. They look for new territory, new hosts.

And sometimes, those new hosts are humans.

Zoonotic diseases are pathogens that have jumped between humans and animals. Most of these come from wild animals. In 2001, a team of researchers from the University of Edinburgh found that of the 1415 species of infectious organisms “known to be pathogenic to humans,” 868 were zoonotic. Sometimes the name of a disease makes it obvious: cowpox virus, European bat lyssavirus 2, Baboon cytomegalovirus.

Zoonotic diseases are not a new phenomenon. Long before humans knew about viral diseases, they knew that mad dogs could pass on rabies. The bubonic plague was a zoonotic disease that was originally passed between rodents. And scientists have identified armadillos as a potential source of the bacterium that causes leprosy in humans. Recently emerged zoonotic diseases include SARS and H1N1.

“More than two new species of human virus are reported every year,” wrote researchers from the University of Edinburgh Centre for Infectious Diseases in a 2008 paper for the Proceedings of the Royal Society B. “Recently discovered viruses are even more likely to be associated with a non-human reservoir.”

Scientists tracking emerging diseases pay close attention to how pathogens are transmitted between individuals. A “Stage 1” pathogen is only passed between animals and does not affect human health. Bluetongue disease is an example of a stage 1 pathogen. After stage 1, epidemiologists get nervous. At stage 2, an animal pathogen can be transmitted from animal to human but does not have the ability to spread from human to human. At stage 3, an animal pathogen can be passed from human to human, but it does not last long in the human population. Ebola is a stage 3 pathogen. Ebola outbreaks originate in the non-human primate population and can cause devastating, but short-lived, outbreaks in human populations. Stage 4 pathogens are gung-ho for humans. Stage 4 diseases like yellow fever enter the human population from animals and cause extended outbreaks in humans.

“We do not pay much attention to Stage 1 pathogens until they become stage 2, 3 or 4,” said X. J. Meng, a professor of molecular virology at Virginia Tech.

That lack of attention is a problem if epidemiologists want to stop stage 1 pathogens from adapting to humans.

Meng spoke in March at the Farm Animal Integrated Research (FAIR) conference. The conference focused on the future of animal agriculture, and Meng argued that successful animal production requires disease control in animals and humans.

“Infectious disease is the second leading cause of death worldwide,” Meng said. He explained that the risk of zoonotic disease is greater in developing countries. “The veterinary services in those countries are usually very limited.”

Many diseases do not spread to humans; our physiology and immune systems fight them off. But when animal pathogens do infect humans, certain groups are particularly vulnerable. Infants, pregnant women and the elderly are “immunocompromised,” meaning it is harder for them to fight off infections. People with HIV or AIDS or those undergoing cancer treatments are also vulnerable.

Proximity to wild animals is also a risk. According to Meng, wild animals are the sources of 75 percent of zoonotic diseases. That was the case in 1999, when a group of pig farmers in Malaysia fell ill with Nipah virus. Scientists eventually identified a population of cat-like palm civets as the likely source of that strain of Nipah virus. The disease probably spread from the civets to the pigs to the pig farmers. This case reveals another factor in catching zoonotic diseases: when a disease finds a way to hit humans, animal producers are often the first ones affected.

“They share their whole environment with farm animals,” Meng said.

Meng said advances in animal science can minimize future zoonotic disease outbreaks.

In his talk at FAIR, Meng talked about his experience studying the hepatitis E virus [HEV]. In 1997, Meng discovered that swine were one reservoir of a strain of HEV that can affect humans. Though HEV does not have a high mortality rate, it can cause acute, severe liver disease in some people, particularly in pregnant women.

Meng discovered that swine and human HEV were related by analyzing the strains genetically. Since the discovery of swine HEV, Meng has used blood tests to track the prevalence of the disease.

“In some herds, up to 80 percent of the pigs are infected with the Hep E virus,” Meng said.

When humans get the swine strain of HEV, it is usually through contaminated water or food. Like with Nipah virus, humans close to infected animals are at the greatest risk. Meng has found that HEV is common in swine veterinarians in the United States.

By tracking the spread of swine HEV through genetic analysis and blood tests, scientists have identified at-risk populations.

The treatment

Controlling the spread of zoonotic and animal diseases requires balance. Time and money go toward treating outbreaks as they emerge, but resources are also needed to prevent outbreaks before they happen.

Many scientists are working on vaccines for zoonotic diseases. In 2006, a team of researchers from the College of Veterinary Medicine at Iowa State University reported the development of a vaccine against avian HEV. Some are working to stop pests that spread disease. In Texas, animal scientists are working with entomologists to better treat cattle and deer infested with ticks that transmit deadly “cattle fever.”
Others are researching better ways to control animal waste and minimize water and food contamination.

“Microbial contamination of surface water can originate from both extensive [e.g. grazing] and intensive [e.g. feedlot] livestock production systems,” wrote Agriculture and Agri-Food Canada animal scientists Tim McAllister and Ed Topp in the April 2011 issue of the review magazine Animal Frontiers. “Proper water treatment measures are critical to ensuring that infection levels of viable pathogens do not enter the drinking water supply.”

Use of growth-promoting antibiotics is another way livestock producers keep animals healthy and meet the global demand for food. In 2002, Gary Cromwell, a professor of swine nutrition at the University of Kentucky, published a paper in Animal Biotechnology showing that antibiotics dramatically improved pig growth. Cromwell analyzed the results of more than 1,000 growth experiments in swine over a 25-year period. In young pigs, antibiotics improved the growth rate by an average of 16.4%.

“It’s really a health promotant,” said Rodney Preston, a retired animal scientist and member of the Federation of Animal Science Societies’ Committee on Food Safety.

But it can be a challenge to apply this research in commercial facilities.

“You have to talk to producers about changing their behavior and changing their management systems,” said Nancy Morgan, a liaison to the World Back and economist with the Food and Agriculture Organisation of the United Nations.

Morgan said many animal producers kill sick animals to stop the spread of disease, also called “culling,” when they do not have to.

“If you suddenly have an outbreak of avian influenza, the response is automatically to cull the animals and try to contain the disease,” Morgan said.

But culling, said Morgan, is a short-term solution. To keep animal agriculture viable in many areas, it more important to focus resources on preventing diseases before culling is needed.

“It’s about looking at where along the chain are the risks to animal health or to human health. The risks along the chain make a difference,” Morgan said.

Those risks might be gaps in biosecurity, poor water management or a lack of funding for veterinarians. Morgan said these “value chain assessments” are a long-term solution.

“That is the type of applied research that is very useful for policy makers,” Morgan said.

John Clifford, deputy administrator and chief veterinary officer for the USDA Animal and Plant Health Inspection Service Veterinary Services program, agrees with Morgan regarding culling.

“It is wasteful,” Clifford said in a talk at FAIR.

Clifford said what the world really needs is better diagnostic tools. Then, instead of culling potentially sick animals, producers can remove only the sick animals from the herd. He calls this technique “strategic depopulation.” Clifford said it is also vital for the animal health community to stockpile vaccines in areas where disease risk is greater.

According to Clifford, education is also important. For example, foot and mouth disease (FMD) is a dreaded disease in animal agriculture. Animals like cattle, goats and sheep with FMD suffer from high fevers and get painful blisters in their mouths and on their feet. Animal producers will cull entire herds to stop the spread of FMD. Yet, Clifford pointed out, many animals eventually recover, and meat from these animals is safe for human consumption. If people understood the disease better, they could prevent unnecessary culling.

Advances in animal agriculture can feed the growing world population by the year 2050. However, changing agricultural practices and global trade can also increase the risk of animal and zoonotic diseases. With better diagnoses and understanding of diseases, producers could increase improve food safety and feed the growing population

“Clearly, there’s a lot of work that needs to be done,” Meng said.

Coming up:

In part 5 of “the future of hunger,” we will wrap up the series by looking at how advances in animal agriculture could be implemented around the world.

References:

“Entomologist works to save cattle in Texas” by Madeline McCurry-Schmidt http://takingstock.asas.org/?p=1954

“Foodborne Disease Outbreaks Are Deadly Serious – What You Can Do to Avoid Them” from the Centers for Disease Control http://www.cdc.gov/features/dsFoodborneOutbreaks/

“Hepatitis E virus: a zoonosis adapting to humans” by Florian Bihl and Francesco Negro http://jac.oxfordjournals.org/content/65/5/817.short

“Origins of major human infectious diseases” by Nathan D. Wolfe, Claire Panosian Dunavan and Jared Diamond http://www.nature.com/nature/journal/v447/n7142/box/nature05775_BX1.html

“Reptiles, Amphibians, and Salmonella” from the Centers for Disease Control http://www.cdc.gov/Features/SalmonellaFrogTurtle/

“Researchers Endorse Global Early Warning System to Prevent Pandemics” by Sarah Anderson http://www.universityofcalifornia.edu/news/article/9217

“Risk factors for human disease emergence” by Taylor LH, Latham SM and Woolhouse ME.http://www.ncbi.nlm.nih.gov/pubmed/11516376

“Serious about Salmonella: A guide for pig producers” http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDUQFjAA&url=http%3A%2F%2Fwww.food.gov.uk%2Fmultimedia%2Fpdfs%2Fpublication%2Fsalmonellapig1207.pdf&ei=SCt6T9DzIMSJgwfnxrGLDw&usg=AFQjCNHIWa2mNB_dkzeOG-IhFUZ08e-WDA

“Temporal trends in the discovery of human viruses” by Mark E.J Woolhouse, Richard Howey, Eleanor Gaunt, Liam Reilly, Margo Chase-Topping and Nick Savill http://rspb.royalsocietypublishing.org/content/275/1647/2111.full

“The Bluetongue Triangle” from USDA-ARS http://www.ars.usda.gov/is/AR/archive/jul99/blue0799.htm

“Within-herd biosecurity and Salmonella seroprevalence in slaughter pigs: A simulation study” by A. Lurette, S. Touzeau, P. Ezanno, T. Hoch, H. Seegers, C. Fourichon and C. Belloc http://jas.fass.org/content/89/7/2210.full?sid=28f49bb2-0a7b-4a09-92e2-ef1cdb4b6880

“Why and how antibiotics are used in swine production” by Gary Cromwell http://www.ncbi.nlm.nih.gov/pubmed/12212945