Germ Warfare: Poultry diseases
February 13, 2009
Poultry quality depends upon disease-free birds. Disease-causing microorganisms and pathogens, including bacteria and viruses, are carried through vectors (living organisms that transmit pathogens). Frequently these vectors are the people who work on and visit a poultry farm.1
Another consideration is the genetic makeup of chickens and turkeys, which is important in the primary breeding stock and egg production programs, for genes interact and work together to control the expression of certain biological traits. Based on science, the primary breeder’s job is to select individuals with the most favorable mix of genes to breed a new generation with superior traits. Although the deadly strain of avian influenza (AI) represents a major threat to the poultry industry, it is by no means the only disease-related threat.
History tells us that chicken breeding birds were selected based on a set of desirable traits â€” size being important for broilers, while egg production was critical for layers. Although hundreds of chicken breeds exist, modern commercial broilers reportedly descend from about three lines of chickens, and poultry used in egg production come from only one specialized line.
Breeding is critical, to be sure, but what is being done to meet disease threats?
Scientists at Auburn University hope to identify genes that affect disease resistance, thus allowing primary breeder companies to remove chickens with undesirable genes when choosing the elite breeding stock. Then, within four years, all birds at the broiler grower level would be significantly more resistant to that disease.
A group of scientists from Purdue University, USDA and two poultry breeding companies began working together last year on the first breeding program in the world to use the entire animal genome. The research project focuses on the viability of using whole genome DNA selection to improve the accuracy and efficiency of poultry breeding methods.
The multimillion-dollar study is charged with testing a new approach to selecting breeding trials such as bone density, productivity, feed efficiency, animal well-being, growth robustness, egg quality, yield and disease resistance. The team includes co-director Bill Muir, Purdue University; Hans Cheng, USDA’s Agricultural Research; Hendrix Genetics; and Cobb-Vantress. USDA is providing $2.5 million in funding. That amount is being matched by the two breeder companies, which are also providing in-kind resources bringing the total costs of the research effort to $10 million.2
“The [American] poultry industry has worked extensively with the federal government and producing states,” confirms Robert Norton, Ph.D., professor of veterinary microbiology at Auburn University’s department of poultry science.
“We are well-prepared for an isolated avian influenza event, including high-path AI, but less so for a regional event such as one that crosses state boundaries,” reports Norton, who emphasizes that a regional event is a low probability. “Realistically, we probably can’t be prepared for much beyond what has already been done,” he continues. “As for a biological attack, again we are well-prepared for an isolated event, less so for a regional event.”
Rapid identification of the avian flu is essential to controlling outbreaks among poultry flocks. And, thanks to a new field-deployable biosensor developed by research scientists at the Georgia Tech Research Institute (GTRI), detecting the AI virus takes minutes rather than days, and requires no labels or reagents. “We can do real-time monitoring of avian influenza infections on the farm, in live-bird markets or in poultry processing facilities,” reports Jie Xu, GTRI research scientist.3
H5N1, the virulent AI strain is a threat to birds and humans demonstrated by several hundred infections and nearly an equal number of deaths being reported to the World Health Organization since 2003. The H5N1 strain is on the high alert watch due to the threat of a pandemic like the 1918 Spanish flu, which killed about 40 million people.
More must be done, according to Norton who says federal and state governments need to expand the number of trained food animal veterinarians and pay for schooling with obligated service; and that laboratory surge capacity also needs to be increased. “Preparation [concerning AI] beyond what has been done is unlikely given current budgetary constraints and the low probability of a large scale event,” he concludes.
Meat protein occupies a critical place on the pyramid of food essential for human health. Consumers control the demand curve, however. In that regard, poultry moved up on the consumer preference meter in the 1970s, when there was a fundamental change in eating habits. Based on National Chicken Council statistics, chicken sold cut-up in pieces rose from 28 percent of broilers marketed in 1971 to 42.5 percent in 200l.
The new consumption pattern was driven by suggestions that red meat may be linked to certain heart-related disorders and colon cancer. Poultry is not without its disease challenges that might impact human health, however. Researchers have found that genetic deficits in birds may be leaving them vulnerable to new diseases and raising questions about their long-term sustainability.
This report highlights some common diseases that afflict flocks around the world and the research projects designed to either eradicated them or else provide measureable controls. In his status report concerning blackhead disease (Histomoniasis) at the 31st Annual North Carolina Turkey Industry Days at Wilmington, Larry McDougald, Ph.D., said the disease continues to cause sporadic but severe disease-related losses in commercial turkey flocks (see Common Poultry Diseases).
Death losses often reach up to 100 percent in domestic turkeys. Meanwhile, broiler breeder pullets may only suffer 10 percent mortality along with extensive culling losses and poor uniformity at time of lay. “In the absence of any highly effective treatment drugs, emphasis on control is placed on prevention and containment by management and quarantine,” reports McDougald, who serves in the Department of Poultry Science at the University of Georgia. “Fortunately, research has been initiated in several laboratories in the United States and Europe yielding important new findings that will be of value in planning future control programs.”
Blood screening of poultry breeding stock for the elimination of carriers of Salmonella species and other pathogens resulted from research demonstrating vertical transmission of pathogenic organisms from infected hens to offspring.
In 1956, Bruce Glick and Timothy Chang reported that the bursa of Fabricius plays an important role in antibody production. Their demonstration that antibody responses are suppressed in the majority of bursectomized chickens became the cornerstone of modern immunology. Bursa research increased considerably during the 1960s and early 1970s.
Mapping functional genes and sequencing the chicken genome were made possible by advancements in controlling Marek’s disease â€” a highly contagious, cancer-causing viral disease â€” and ascites in poultry.
Researchers reportedly have begun using the chicken genome sequence to develop vaccines to combat Marek’s disease, which costs the global poultry industry about $1 billion a year. USDA’s Cooperative State Research, Education, and Extension Service (CSREES) provided funding for this project.
Ascites in bird flocks has been blamed on genetics; and the syndrome in broiler flocks has been increasing at an alarming rate. Even though breeding company developments have provided improvements for this syndrome, it continues to plague broiler flocks and, reportedly, is among the leading causes of mortality and whole-carcass condemnations at poultry operations worldwide. A goodly number of ascites occurrences are triggered by microbial factors (E. coli, Salmonella sp., Aspergillus) coupled with contributing environmental and nutritional factors.
Ascites represents a spectrum of physiological and metabolic changes leading to the excess accumulation of fluid in abdominal cavity. These changes occur in response to a number of dietary, environmental and genetic factors.
Experts say feed restriction might reduce the effect of the ascites caused by genetics. Slower growing birds have reduced oxygen needs allowing the cardiopulmonary organs (heart and lungs) to keep up with oxygen demands of the birds. However, reducing the feed intake of broilers decreases the growth performance. Feed restriction an economic benefit when the incidence of ascites is very severe.4
Thanks to other poultry science research projects, specific applications benefiting the integrated poultry industry have saved poultry processors millions of dollars while contributing to safe, affordable and a wider array of products.
In 1922, Russian geneticist and poultry researcher A.S. Serebrovsky discovered the slow feathering gene that led to feather-sexing â€” a cost-saving alternative to vent-sexing saving the industry million of dollars annually while reducing the coast of table eggs and broiler meat. Other research led to automated in-the-egg injection, a technology providing more effective and efficient vaccination.
To reap the benefits from financial investments, time and labor, poultry producers must maintain a healthy and parasite-free flock. Constant monitoring of flocks is the first step in detecting diseases, experts say, as identifying the cause and appropriate treatment can prevent a minor condition from mushrooming into unprofitable enterprises.
During the past half century, genetic selection, heterosis, changes in husbandry, improved nutrition, and control of diseases and parasites have contributed to the escalating growth rate of poultry for meat. Consider that broilers required 12 weeks to reach a market weight of 4.4 pounds in the 1940s. The same weight is reached after only six weeks today. Comparable changes have occurred in turkey production resulting in improved efficiency of feed use due to reduced maintenance.
To ensure the health and productivity of their flocks behooves poultry producers to continue employing the “best management” practices recommended by equipment manufacturers, breeders, trade organizations and scientists.
Common poultry diseases1. Ascarids (Ascaridia galli): Large intestinal roundworms in chickens and turkeys characterize this disease. Adult worms can be seen easily with the naked eye. Heavily infected birds may show droopiness, emaciation and diarrhea. The primary damage is reduced efficiency of feed utilization and death in severe infections.
2. Aspergillosis: This disease, which has been observed in almost all birds and animals including man, is manifested in one of two forms â€” acute outbreaks with high morbidity and high mortality in young birds, and a chronic condition affecting adult birds. Turkeys are more at risk than in chickens. Aspergillus fumigatus, a mold or fungus organism, is the cause. They grow readily on many substances such as litter, feed, rotten wood and other similar materials.
3. Blackhead (Histomoniasis, Enterohepatitis): An acute or chronic protozoan disease of fowl, primarily affecting the cecae and liver, the disease is present wherever poultry are raised. Blackhead is one of the critical diseases of growing turkeys and game birds. It may cause stunted growth, poor feed utilization and death. It is of lesser economic importance in chickens since they are more resistant, but the incidence in chickens apparently is increasing.
Blackhead is caused by a protozoan parasite called Histomonas meleagridis. The organism in passed in the fecal material of infected birds. In many instances, the organism is shed within the eggs of the cecal worm of chickens, turkeys and game birds. Most blackhead losses occur in young birds (six to 16 weeks). Outbreaks in turkeys can often be traced to direct or indirect contact with ranges, houses or equipment previously used by chickens. Free-flying birds may also contribute to an infection. Free-living blackhead organisms do not survive long in nature, but those in cecal worm eggs may survive for years. Therefore, most blackhead transmission is considered due to ingesting infected cecal worm eggs. Transmission may also occur by the earthworm.
4. Cecal Worms: This parasite (Heterakis gallinae) is found in the ceca of chickens, turkeys and other birds. It has been incriminated as a vector of Histomonas meleagridis, the agent that causes blackhead. This protozoan parasite apparently is carried in the cecal worm egg and is transmitted from bird to bird through this egg.
5. Erysipelas: A bacterial disease caused by Erysipelothrix insidiosa, it affects several species of birds including chickens, ducks and geese, but mostly turkey. Man is susceptible to infection and may contract the disease from infected turkeys. Since this organism is pathogenic for man, care should be taken when handling infected birds or tissues.
Erysipelas in turkeys occurs most often during the fall and winter months and usually affects birds that are four to seven months of age, although any age bird is susceptible. In some instances the incidence is higher in hens than toms because artificial insemination provides a means of transmission.
6. Fowl Cholera: This disease occurs throughout the country wherever poultry is produced and in recent years has become the most hazardous infectious disease of turkeys. Host range is extensive and includes chickens, turkeys, pheasants, pigeons, waterfowl, sparrows and other free-flying birds. Major sources of infection include, body excreta of diseased birds that contaminate soil, water and feed. Also, carcasses of birds that have died of the disease; contaminated water supplies such as surface tanks, ponds, lakes and streams; and mechanical transmission by contaminated shoes or equipment.
7. Fowl typhoid: This infectious, contagious bacterial disease is usually acute but sometimes chronic. It affects most domestic and wild fowl including chickens, turkeys, ducks, pigeons, pheasants and other game birds, and comes from the bacterium, Salmonella gallinarum. Methods of transmission are the same as for pullorum disease, including egg transmission. However, mechanical transmission is more prevalent with this disease than with pullorum disease. It should not be confused with typhoid fever in humans that is caused by a distinctly different organism.
8. Infectious Bronchitis: Considered the most contagious of poultry diseases, all susceptible birds on premises become infected, regardless of sanitary or quarantine precautions with its intrusion. The disease can spread through the air and can “jump” considerable distances during an active outbreak. It can also be spread by mechanical means such as on clothing, poultry crates and equipment. The disease is not egg transmitted and the virus will survive for probably no more than one week in the house when poultry are not present. It is easily destroyed by heat and ordinary disinfectants.
9. Infectious Bursal Disease (Gumboro): This acute, highly contagious viral disease hits young chickens, and is most often found in highly concentrated poultry producing areas. It causes marked morbidity and mortality in affected flocks. Although the disease causes severe losses, its affect on reducing the bird’s ability to develop immunity to other diseases may be the most serious effect. The transmission or spread of the disease can occur by direct contact (bird to bird), contaminated litter and feces, caretaker, contaminated air, equipment, feed, servicemen and possible insects and wild birds.
10. Lymphoid Leukosis: Characteristically a disease of adult chickens, which appears to be increasing in importance for turkeys and game birds. The virus may be transmitted mechanically from infected birds to susceptibles by blood-sucking parasites or by man in such procedures as fowl pox vaccination.
11. Marek’s Disease: Normally this is a disease of young chickens, but older birds can also be affected. Marek’s disease is caused by a virus belonging to the Herpes virus group. Much is known about the transmission of the virus; however, it appears that the virus is concentrated in the feather follicles and shed in the dander (sloughed skin and feather cells). The virus has a long survival time in dander since viable virus can be isolated from houses that have been depopulated for many months.
12. Moniliasis (Crop Mycosis, Thrush): This disease that primarily affects the upper digestive tract of all birds and is characterized by whitish thickened areas of the crop and proventriculus, erosions in the gizzard, and inflammation of the vent area. It is caused by a yeast-like fungus (Candida albicans). The Candida organism is widely spread throughout the poultry producing areas of the world.
13. Mycotoxicosis: It is known that certain strains of fungi (molds) growing in feed or feed ingredients can produce toxins that, when eaten by man or animals, can cause the very lethal disease. The toxins rival the botulism toxin for toxicity.
14. Newcastle Disease: This is a contagious viral infection causing a respiratory nervous disorder in several species of fowl including chickens and turkeys. Different types or strains of the virus (varying in their ability to cause nervous disorder, visceral lesions and death) have been recognized. The most severe strain is called viscerotropic velogenic Newcastle disease (VVND) and is kept from birds in the U.S. by enforcement of strict quarantines at our national borders.
15. Omphalitis: This disease may be defined technically as an inflammation of the navel and occurs during the first few days of life so it cannot be considered transmissible from bird to bird. As commonly used, the term refers to improper closure of the navel with subsequent bacterial infection (navel ill; mushy chick disease). It is transmitted from unsanitary equipment in the hatchery to newly hatched birds having unhealed navels.
16. Pullorum Disease: This an acute or chronic infectious, bacterial disease affecting primarily chickens and turkeys, but most domestic and wild fowl can also be infected. This organism is primarily egg transmitted, but transmission may also occur by other means such as contaminated premises (from previous outbreaks). Disease organisms may enter the bird through the respiratory (as in the incubator) or digestive systems. Most outbreaks of acute pullorum disease in chickens or turkeys result from infection while in the hatchery.
Source: Poultry Science Home Page, College of Agriculture & Life Sciences, Mississippi State University