Can Genes Control Poultry Diseases?

By Doug Ottinger

My grandmother, born in 1893, was one of eight siblings raised on a diversified family farm in the old township of Tevis, Kansas, just south of Topeka.

As I grew up, she used to tell me many humorous stories of her childhood days, and the antics that only siblings raised in the vast stretches of Kansas farmland could have concocted and taken part in.

Even though they lived on a farm quite far from town, they were fairly modern for the time. They had a telephone at home, when very few people had such a luxury. They were also a devoutly religious family who believed in health reform. Being modern and up to date, they had one modern medical contrivance that was so necessary for the health and well being of the entire family: the enema can.

On the farm was an old tom turkey who had become the children’s pet. One day the turkey became ill. He progressively got worse, until it appeared that there was no hope for him. Not wanting to lose their pet, my grandmother and her older sister, Lois (whom my grandmother often described as the “family nurse”), decided that something had to be done. Lois came up with the idea that maybe the turkey just needed a good enema. The two girls procured the can from the water closet. Lois mixed up a concoction that she figured should be about right. Then the two girls went to the barnyard to find their sick pet. One of the girls held the turkey, inserting the rubber hose into its south end. The other one held the can that was full of the solution. When the hose was firmly embedded, they let the solution flow.

Once that was done, they figured there was not much more that they could do for the gravely ill bird. He showed no signs of immediate improvement. They returned to the house, without much visible hope for his recovery. The next morning they went out, searching for their sick pet. When they found him, he was strutting around like he had never been sick a day in his life. According my grandmother, he lived quite a few more years after that.

Years later, not too long before she died, I was talking to her about that story. She laughed as we talked about it, and then paused and said, “You know, I don’t suppose us kids ever washed that thing off. I think we just put it back on the shelf the way it was …”

With that story told, I will move on, and talk about some of the searches for genetically-linked disease controls that keep both poultry and humans healthy.

The Search for Genetic Resistance to Disease

Since time immemorial, human beings have struggled to find ways to keep both themselves and their livestock healthy and disease-free. Whether it has been herbal compounds put together to fight disease, or high-tech experiments in well-equipped laboratories, or just two little farm girls in Kansas wielding an enema can, the fight against disease has been, and may well continue to be, a never-ending one.

Researchers in the 1920s and 1930s began wondering if there were certain genes that would give animals resistance to disease. There were numerous studies devised that gave researchers some answers to the questions they had. Fowl Typhoid, caused by Salmonella gallinarum, and Pullorum Disease, caused by Salmonella pullorum, were just two of several diseases that were causing devastating losses in the poultry industry. These diseases could decimate a family farm flock in very little time, and the bacteria could linger, infecting any replacement stock. It was observed that some birds seemed to have resistance to the diseases. Consequently, researchers began to look into whether genetically-resistant strains, or lines of birds, could be developed, which would be able to resist and fight-off these infectious pathogens.

Lymphomas, tumors and various leukosis complexes were also serious problems in some areas of the United States and other places in the world. In the 1930s, Cornell University became a leader in the research and eradication of lymphoma in poultry. Their research delved into many areas, some of it being genetically-linked research. Other universities were key, active players in research projects involving disease control. Over the past 80-plus years, many studies have been carried out to help us find ways to eradicate such diseases as pullorum, Newcastle’s disease and Marek’s disease. Many of these included trials in genetically-linked control possibilities.

Often, research for genetic control of disease yielded disappointing results for the researchers. While they were able to find birds in the studies that could survive and bounce-back from diseases, even those as deadly as Newcastle’s and Marek’s disease, the fact remained that most if not all of these surviving birds were carriers of the dreaded pathogens, and the disease was still passed on to the offspring, or from adult bird to adult bird in a flock. Rarely was actual resistance to the given disease procured as the researchers had hoped for.

One researcher, Nelson Waters, carried out studies from 1939 through 1960 on the transmission of certain types of viral-caused tumors in poultry. Later, the research work continued under the guidance of another researcher, Lyle Crittenden. While this sort of study may not seem very exciting to most people, the findings were very important to researchers in the fields of disease transmission and spread, or pathogenic etiology. Waters and Crittenden found that a number of these viruses could be passed from parents to offspring (this is called linear transmission), as well as passed from bird-to-bird in a flock (this is called horizontal transmission). These findings helped researchers understand how some viruses could be spread. Research rooted in some of their findings still continues today.

In the late 1970s and well into the 1980s, momentum increased in the areas of finding genetic factors that controlled immune system responsiveness in animals, and finding ways to fight and hopefully eradicate diseases through genetic control of immunological responses. In 1987, researchers C.M Warner, D.L. Meeker, and M.F. Rothschild first published their findings in this area.

In 2000, researchers, headed by L.D. Bacon, published findings from a 25-year study done at the U.S.D.A. Avian Disease and Oncology Laboratory, in East Lansing, Michigan. This study reported on the selection and inter-breeding of commercial chicken lines that appeared to be genetically resistant to Lymphoid Sarcomas.

In 2004, a paper was written on new research that had just concluded in France. Led by Dr. Rima Zoorab, the research team conducted one of the first comprehensive studies to locate and identify, “immunegenes” in poultry. Starting from scratch, the team began identifying and “mapping” actual genes that seemed to give individual birds resistance to disease. The three main diseases of concern in this study were Infectious Bursal Disease, Marek’s disease, and coccidiosis (caused by the protozoan parasite, Eimeria tenella). It was a very complex study, starting with the messenger RNA in the cells. Eventually, 30 genes were identified that could be considered “immune genes” or “partially-immune genes.”

Over the past few years, researchers have identified strands of DNA that are susceptible to Marek’s disease in certain strains of broiler chickens. This research is currently ongoing and does give, at this point, some possible hope for at least partial genetic control of certain diseases. One other example of research currently being done comes from South Korea. Scientists there are working to find possible genetic resistance to strains of avian flu viruses, including the A1 and H5N1 strains.

Bacteria and Viruses Also Have  a Genetic Code

For many years, genetic experiments in disease control only focused on the genetics of the animals being infected. Researchers hoped that genes could be found that in some way would render the animals resistant to various diseases. However, as research continued, it became very clear to a number of researchers that both bacteria and viruses have a genetic code of their own.

Just like the animals they infect, these organisms have genetic material within them that regulates how they reproduce and behave. Bacteria also have an immune system of their own and can also be infect-ed by viral pathogens, and their immune system must then go into action, much the same as the higher animal’s systems do.

I recently had the opportunity to speak with Dr. Matt Koci of the Prestage Poultry Science Department at North Carolina State University. Dr. Koci’s department is working on several areas of research involving both salmonella and campillobacter bacterial colonization in poultry.  One of the things that he pointed out to me was the fact that they are looking heavily at the immune systems of the bacteria, as much as they are looking at the actual birds in these studies.

To give just a brief example of the daunting work still ahead of researchers in these areas, there are at least 2,600 variants, or serotypes, of salmonella bacterium alone. There are at least one million identified viruses. We have fairly composite knowledge on only about 5,000 of them. Add to this the thousands and thousands of other types of bacteria, and you can see that there is an enormous amount of information that we will still be learning many decades from now.

Genetic Research and Food Safety

Every year many people get sick from eating poultry products, as well as other foods, that are handled improperly.  Under-cooking, improper temperatures during storage or mistakes made in the initial handling of the products are contributing factors to these myriads of cases. Cases of poisoning happen at both commercial and home preparation levels. Many are relatively minor, with only slight discomfort to those infected. Other cases are more severe and require more advanced medical care. Sadly, some of these cases become fatal.

One area that has perplexed researchers for years, is why many types and strains of poultry can maintain extremely high counts of bacteria, such as Salmonella Enteritidis, or variants of campillobacter in their bodies, while some of their flock-mates or hatch-mates have fairly low concentrations. None of the birds show any outward signs of illness, or of being carriers of the bacteria. Yet, if a human were to contract these bacterial pathogens, especially at the levels that some of the birds have them, it would be fatal for the person.

One answer to this perplexing problem was given to me by Dr. Matt Koci of North Carolina State University during my recent interview with him. North Carolina State University is not only a leader in poultry research, but is also at the forefront in food-safety research.

According to Dr. Koci, there are several different studies being conducted in this area. Due to the fact that much of the research is still ongoing, it is too early to make any large announcements of the findings. However, one issue has become very clear in these studies. The differences in body temperatures of human beings versus the body temperature of the chicken seems to be one of the main factors in the different responses each has to these infections. Humans maintain a normal body temperature of 37°C (98.6°F). Chickens have a body temperature of 41°C (105.8°F). One of the key facts found, so far, in this study, according to Dr. Koci, is that the Salmonella Enteritidis behaves as a completely different organism at different body temperatures.

Some of the original intent in this study was to search for genetic links in chicken macrophage development, and the bird’s seeming resistance to these bacteria. (Macrophages are those little white blood cells that gobble-up the diseasecausing organisms that infect us.) Those findings are not compiled yet, but as with most research, the findings can take some interesting turns, and the findings on bacteria acting as different organisms, at different temperatures, is certainly one of these.

Recent research in various areas of the world, including the United States, the European Union, Australia and Asia, has concentrated on finding and developing birds that seem to have genetic resistance to the build-up of large colonies of salmonella or campillobacter bacteria in their intestines. If we can eliminate some of these disease-causing bacteria from the poultry, we can hopefully eliminate many of the worldwide cases of food poisoning suffered by humans every year.

Some genetic links have been found in these areas, and we have the technology to transfer this genetic material, from one bird to another. Based on our current findings, bird-to-bird genetic material might even be available some day that could be transferred to home flocks. However, this is genetic modification, and many people are vehemently opposed to this in any way, shape or form. I personally believe that some of these procedures hold some promise, but I also understand the ethical question of, “Where does one draw the line?” The search for genetic resistance to disease will probably be going on for many years to come. I would be interested to find-out what other readers of Backyard Poultry think. Letters to the editor, anybody?

Sources:
The Genetics of Disease Resistance in Chickens; European Commission, Research and Innovation, ec.europa.eu/research/infocentre/export/success/article_693_en.html (Research led by Dr. Rima Zoorob, Centre de la Recherche Scientifique, France. Published 26-Feb-2004).

Hartmann, W., Evolution of “Major Genes” affecting disease resistance in poultry in respect to the potential for commercial breeding, Program for Clinical Biologic Research 1989; 307:221-31.

Zecharias, B., et al., Immunological basis of differences in disease resistance in the chicken,Veterinary Research, 2002, March-April, 33(2): 109-25.

Vallejo, Roger L., et al, Genetic Map-ping of Qualitative Trait Loci Affecting Susceptibility to Marek’s Disease Virus Induced Tumors in F2 Intercross Chickens, Genetics, January 1, 1998, vol. 148, no. 1, 349-360, the Genetics Society of America.

Warner C.M., Meeker D.L., and Rothschild, M.F., Genetic Control of Immune Responsiveness, A Review of It’s use as a Tool for Selection for Disease Resistance, 1987, American Society of Animal Science.

Functional Gene Discovery for Dis-eases Resistance in Chicken, International Livestock Research Institute (ILRI), post-2002, exact date of research paper not listed by ILRI in internet postings of research papers.

Bishop, Steven C., et al, Breeding for Disease Resistance in Farm Animals, Third Edition, CAB International, 2010.

Wigley, Paul, et al, Macrophages Isolated from Chickens Genetically Re-sistant or Susceptible to Systemic Salmo-nellosis Show Magnitudal and Temporal Differential Expression of Cytokines and Chemokines following Salmonella en-terica Challenge, American Society for Microbiology, Infection and Immunity, February 2006, Vol. 74, no. 2, 1425-1430.

Hu, Jinxin, et al, Resistance to Sal-monellosis in the Chicken is linked to NRAMP1 and TNC, Genome Research, Cold Spring Harbor Laboratory Press, 1997.7; 693-704.

Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.) www.poultry.crc.com.au/www.foodborneillnesses.com/campylobacter_food_poisoning/Calenge, Fanny and Beaumont, Catherine, Toward integrative study of genetic resistance to Salmonella and Campylo-bacter colonization in fowl; Frontiers in Genetics/Livestock Genomics, 14 December 2012.

Koci, Matt, Ph.D., Associate Professor, Prestage Poultry Science Department, North Carolina State University, interview and discussion with Dr. Koci,March, 2016.

Bacon, L.D., et al, A Review of the Chicken Lines to Resolve Genes De-termining Resistance to Diseases, U.S. Department of Agriculture, Agricultural Research Service, Avian Disease and Oncology Laboratory, East Lansing Michigan, Accepted for publication March 6, 2000. Poultry Science 79; 1082-1093.

wattagnet.com Genetic Markers Potential Tools in Controlling Marek’s Disease, June 19, 2012.

Muir, W. M. and Aggrey, S.E., Poultry Genetics, Breeding and Biotechnology, C.A.B. International, 2003.

United States Department of Agriculture, Research, Education and Economic Information System: Current and Sporadic Disease Problems in Poultry, run years 2016-2019. portal.nifa.usda.gov/…/0004227-current-and-sporad-ic-disease-problems-in-poultry

Originally published in the October/November 2016 issue of Backyard Poultry magazine and regularly vetted for accuracy.