Poultry

Avian blood may contain various disease agents, including viruses, bacteria, rickettsiae, protozoa, microfilariae, and rarely fungi. These organisms can be identified by microscopic examination of wet mounts, buffy coat, or blood smears or by appropriate culturing and molecular techniques. Microscopically, some are within blood cells (Plasmodium, Haemoproteus, Leucocytozoon, Isospora , Hepatozoon, Babesia, Aegyptianella), whereas others are free in the plasma (Trypanosoma, microfilariae, bacteria, spirochetes). None live exclusively in the blood; most are found in tissues but are present in blood during part of their life cycle. Some, such as microfilariae and Plasmodium, have numbers or stages of parasites that vary with time.

Chicken anemia virus (CAV) has a world-wide distribution. Infection of young chickens causes anemia, decreased weight gain, transient immunosuppression, and increased mortality. Infection of chickens older than 3 or 4 weeks of age usually does not cause clinical signs, but can cause immunosuppression resulting in secondary infections or can result in economic losses even in the absence of evidence of any disease. There is no specific treatment, and control of disease is through vaccination or natural exposure of breeders. Infection can be diagnosed by reduced hematocrit and detection of CAV nucleic acids in blood lymphocytes by PCR, or postmortem by thymic atrophy, lymphoblast depletion of the thymic cortex, pale bone marrow, and detection of CAV DNA or antigens in tissues.

Inclusion body hepatitis and hepatitis hydropericardium syndrome are diseases of young broilers caused by fowl adenoviruses. Clinical signs are nonspecific but often include a sudden increase in mortality. Gross lesions include a swollen liver containing multiple pale or hemorrhagic foci and hydropericardium. Definitive diagnosis is usually made by histopathology or PCR. There is no treatment, but prevention is achieved by vaccination.

Dissecting aneurysm is a fatal disease of turkeys. It is characterized by sudden death of rapidly growing birds with massive internal hemorrhage. The hemorrhage results from rupture of aneurysms formed in various parts of the vascular system. The frequency with which the posterior aorta is affected has given rise to the term “aortic rupture.” The disease has been reported in North America, Europe, and Israel. Most breeds of turkeys are susceptible, and the largest and most rapidly growing males, 8–24 wk old, are affected most often; females are also affected but at a lower incidence.

Hemorrhagic vasculopathy is a noninfectious cardiovascular disorder of rapidly growing male turkeys, although it occasionally affects other species. The predominant sign is sudden death. Diagnosis is based on the history and on finding typical lesions at necropsy. There is no specific treatment, but reducing stress and limiting feed intake during the rapid growth phase may reduce incidence.

Spontaneous cardiomyopathy of young turkeys is characterized by sudden death due to cardiac arrest and is not related to other cardiomyopathies of poultry.

Candidiasis is a mycotic disease of the digestive tract of various avian species, including chickens, turkeys, and quail caused by Candida albicans. It commonly develops after use of therapeutic levels of various antibiotics or when using unsanitary drinking facilities. Lesions are most frequently found in the crop and consist of thickened mucosa and whitish, raised pseudomembranes. The same lesions may be seen in the mouth and esophagus. Occasionally, shallow ulcers and sloughing of necrotic epithelium may be present. Listlessness and inappetence may be the only signs. A presumptive diagnosis may be made on observation of gross lesions. Diagnosis can be confirmed by demonstrating tissue invasion histologically and by culture of the organism. However, culture alone is not diagnostic of disease, because the yeast-like fungus is commonly isolated from clinically normal birds. Young chicks and poults are most susceptible.

Coccidiosis is caused by protozoa of the phylum Apicomplexa, family Eimeriidae. In poultry, most species belong to the genus Eimeria and infect various sites in the intestine. The infectious process is rapid (4–7 days) and is characterized by parasite replication in host cells with extensive damage to the intestinal mucosa. Poultry coccidia are generally host-specific, and the different species parasitize specific parts of the intestine. However, in game birds, including quail, the coccidia may parasitize the entire intestinal tract. Coccidia are distributed worldwide in poultry, game birds reared in captivity, and wild birds. (Also see Cryptosporidiosis.)

Cochlosoma anatis is a flagellated protozoan that infects ducks, turkeys, geese, and wild birds. C anatis can cause limited pathology in the gut of ducks and turkeys, leading to diarrhea, although the direct pathology is still debated. Microscopic evaluation of intestinal mucosal scrapings can be used to determine infection. There is no treatment or vaccine for this protozoan.

Cryptosporidium sp are ubiquitous protozoal organisms that persist in the environment for various durations depending on temperature and humidity. Infection leads to respiratory and/or gastrointestinal disease in birds. Diagnosis is by fecal float or microscopic examination of tissues. There are no known effective treatments for Cryptosporidium; good biosecurity and sanitation are the most important steps to minimize transmission.

Duck viral enteritis (DVE) is an acute and often severe disease of both wild and domestic waterfowl induced by Anatid alphaherpesvirus 1. Lesions include generalized hemorrhages and necrosis of the GI mucosa and liver.  Prevention includes biosecurity and avoiding contact with captive waterfowl with wild birds. Some producers in the USA, Canada, and Europe use attenuated-virus vaccines to immunize breeders and ducklings.

Hexamitiasis is a protozoal infection of turkeys, pheasants, and related species that causes acute enteritis. Diagnosis is made by identifying the organism microscopically in intestinal scrapings. There is no effective treatment or vaccine.

Necrotic enteritis is an acute enterotoxemia. The clinical illness is usually very short, and often the only signs are a severe depression followed quickly by a sudden increase in flock mortality. The disease primarily affects broiler chickens (2–5 wk old) and turkeys (7–12 wk old) raised on litter but can also affect commercial layer pullets raised in cages. Early mortality is often related to coccidiosis vaccination programs, with Eimeria cycling in these flocks.

Trichomonosis is caused by flagellated protozoal parasites, leading to caseous necrosis of the oral cavity and potentially orbital, brain, and liver lesions. Diagnostic testing includes observing gross lesions, as well as wet mounts with saline or culture of the parasite in media. Treatment of birds can be attempted with several compounds, including carnidazole and metronidazole.

Ulcerative enteritis is caused by infection with Clostridium colinum. It primarily affects bobwhite quail, but several other bird species can also be infected. Clinical signs include sudden death and hemorrhagic enteritis but are less severe in chickens and game birds other than quail. Diagnosis is by histopathology, bacterial culture, and PCR. Streptomycin and furazolidone are effective treatments, and bacitracin in feed can be used as a preventive.

Infection of the intestinal tract with Campylobacter jejuni and other Campylobacter spp is common in poultry and waterfowl, but most species do not cause clinical disease. Poultry are a common source of human infection.

Avian chlamydiosis is a systemic, bacterial infection caused by Chlamydia psittaci. Among poultry, turkeys and ducks are more susceptible than chickens. The disease varies from asymptomatic to high morbidity and mortality. Clinical signs are nonspecific and include anorexia, apathy, drop in egg production, diarrhea, ocular discharge, and respiratory disease. Diagnosis is achieved using serology, culture, and/or PCR. Treatment is with antibiotics such as tetracyclines. It is a zoonosis referred to as psittacosis, parrot fever, or ornithosis, which can cause serious health problems in humans (eg, pneumonia).

Avian nephritis viral infections are contagious and are characterized by renal damage, visceral urate deposits, growth retardation, and limited mortality. They are seen mainly in chickens <7 days old, but also occur in ducks and geese. Subclinical infections have been reported in turkeys. Diagnosis is by PCR. No treatment or vaccines are available, so prevention is by improved husbandry.

Avian spirochetosis is an acute bacterial infection transmitted by tick to a wide range of birds. Clinical signs are highly variable and generally nonspecific. Diagnosis requires identifying the infective spirochete. Several antibiotics are effective treatments. Control methods include elimination of infected ticks or vaccination.

Colibacillosis is caused by infection with a pathogenic strain of Escherichia coli. Signs vary and can include acute fatal septicemia, airsacculitis, pericarditis, perihepatitis, and lymphocytic depletion of the bursa and thymus. Diagnosis is made by isolation of a pure culture of E coli. Most bacterial isolates are resistant to multiple antibiotics, so prevention of exposure through good management is recommended.

Duck viral hepatitis is an acute infectious disease affecting young ducklings. It is associated with high mortality and characteristic liver lesions. Diagnosis is by viral isolation or PCR. Vaccination and biosecurity controls can be used for prevention, as there is no specific treatment for infected ducks.

Enterococcosis has been reported in a variety of avian species worldwide. Enterococcus spp are normal microflora found in the intestinal tract of poultry and other bird species. Enterococcus infections usually occur secondary to another disease. However, in recent years, Enterococcus cecorum has become an emerging pathogen in poultry, especially broilers. These pathologic changes have resulted in increased mortality, poor production, and increased condemnation. Enterococcus infections can result in either an acute or subacute/chronic form. Diagnosis is confirmed by isolation of the organism.

Erysipelas is an infection caused by Erysipelothrix rhusiopathiae. Common clinical signs are sudden death, cutaneous lesions, and swollen hocks. Diagnosis is by impression smear, PCR, and/or isolation and identification. Treatment is generally with rapid-acting penicillin. Erysipelas is zoonotic.

Fatty liver hemorrhagic syndrome is a metabolic disorder of chickens. The presenting complaint is typically sudden death of birds fed high-energy diets with limited exercise. Diagnosis is based on finding liver hemorrhage and fat engorgement at necropsy. The disorder can be controlled by monitoring feed intake and body weight when birds are in a positive energy balance. Changing the balance of carbohydrates and fat in the diet and supplementing with selenium may also help.

Sudden death syndrome occurs in rapidly growing young broiler chickens. The etiology is uncertain, but it may be a metabolic disorder that predisposes birds to cardiac arrhythmia. Affected birds die suddenly and have no specific gross lesions. The diagnosis is based on the clinical presentation, lack of gross lesions, and supported by characteristic microscopic cardiac lesions. Reducing the growth rate, particularly during the first 3 weeks of life, can reduce the incidence.

Fowl cholera is a contagious, bacterial disease of birds caused by Pasteurella multocida. Acutely, it causes elevated mortality. Chronically, it causes lameness, swollen wattles (in chickens), pneumonia (in turkeys), and torticollis, but it can also be asymptomatic. Both attenuated live vaccines and adjuvanted bacterins are available to aid in prevention, and it is sensitive to some antibiotics.

Fowlpox is a worldwide viral infection of chickens and turkeys. Nodular lesions on unfeathered skin are common in the cutaneous form. In the diphtheritic form, which affects the upper GI and respiratory tracts, lesions occur from the mouth to the esophagus and on the trachea. Diagnosis is by observing characteristic gross and microscopic lesions and PCR. Vaccination can prevent the disease and limit spread in affected flocks.

Goose parvovirus infection is a highly contagious and fatal disease of goslings and Muscovy ducklings, often causing as much as 70%−100% mortality in goslings <4 wk old. Goose parvovirus has been reported from all the major goose-farming countries of Europe and the Far East, where the disease is of serious economic significance. Muscovy ducks and several hybrid duck breeds are also susceptible to another parvovirus that has been shown to be antigenically related to goose parvovirus. This so-called Muscovy duck parvovirus has been isolated from an outbreak among Muscovy ducks in California. Goose parvovirus has not been detected in the USA.

Helminthiasis is infection by members of the phylum Nematoda (roundworms) or the class Cestoda (tapeworms, flatworms). In rare cases, infected birds develop clinical signs such as apathy or diarrhea, and the influence on zootechnical parameters is usually negligible. Infections are diagnosed by the presence of worms in affected organs, mostly the intestines, or by detection of eggs in the feces. Increasingly fewer compounds are available for treatment of chickens and other food-producing poultry, and control relies on improvement of management and sanitation.

The hemorrhagic enteritis virus belongs to the family Adenoviridae, genus Siadenovirus, species turkey adenovirus 3 (TAdV3), and it is serologically indistinct from the marble spleen disease virus. Clinical signs include splenomegaly in both turkeys and chickens, bloody diarrhea in turkeys, and acute respiratory disease in chickens. Clinical signs and lesions may allow a provisional diagnosis, which is normally confirmed by molecular diagnostic tests. There is no direct treatment available, but live vaccines can be used for prevention and to control outbreaks. Hygiene measures should be implemented to reduce the risk of secondary infection as a consequence of virus-induced immunosuppression.

The protozoan Histomonas meleagridis infects a wide range of gallinaceous birds and causes histomoniasis (blackhead disease). Chickens are typically asymptomatic carriers, but mortality in turkeys is commonly 80%-100%. Clinical signs include drooping head and wings, prolonged standing, closed eyes, ruffled feathers, emaciation, and sulfur-colored droppings. Diagnosis is based on pathognomonic ulceration of the ceca and necrotic lesions in the liver. There are no approved treatments or vaccines.

Infectious bursal disease (IBD) is seen in young domestic chickens worldwide and is caused by infectious bursal disease virus (IBDV). Signs can include depression, watery diarrhea, ruffled feathers, and dehydration. Morbidity is high and mortality is usually low, but some very virulent strains are capable of causing 60% or higher mortality. Macroscopic and microscopic lesions in the cloacal bursa and molecular identification of the viral genome are used to diagnosis the disease. Vaccination to induce maternal immunity in young chicks is initially used to control the disease. Vectored and live-attenuated vaccines can be used to induce active immunity in chicks as the maternal antibodies wane.

Listeriosis affects a wide range of bird species, but most infections do not cause clinical signs. Sporadic cases in backyard chickens may cause encephalitis or septicemia and sudden death. Diagnosis is confirmed by histochemical staining that identifies Listeria monocytogenes, the causative organism, in affected tissues. Several antibiotics can be effective treatment for the septicemic form of the disease. Prevention should focus on eliminating potential sources of infection. There is a significant risk of zoonotic transmission.

Malabsorption syndrome is characterized by stunted growth and lack of pigmentation in growing chickens. A viral cause is suspected but has not been confirmed. There are no confirmatory tests or effective treatments.

Mycoplasmas are bacteria that lack a cell wall, are small in size, and have the smallest genome among all independently replicating forms of life .Because of their small genome and the lack of many metabolic pathways, they are fastidious microorganisms. For isolation, they have complex nutritional requirements but will grow on specialized artificial medium containing serum. Growth in broth and on agar media is slow (5–21 days), and the small (0.1–1 mm diameter) colony morphology typically has a "fried egg" appearance under low magnification. Mycoplasmas do not survive for more than a few days outside the host and are vulnerable to common disinfectants.

Hundreds of mycotoxins affect poultry, with varying degrees of pathogenicity. They can have additive effects with other toxins, infectious agents, or nutritional deficiencies. Diagnosis requires detection and quantification of the specific toxin. Treatment includes removal of contaminated feed and supportive care. Prevention includes management practices that avoid mold growth during feed preparation, transport, and storage.

Depending on whether the etiologic agent is known, neoplasms of poultry are divided into two main categories: virus-induced neoplasms and neoplasms of unknown etiology. There are three economically important virus-induced neoplastic diseases of poultry: Marek disease, caused by a herpesvirus, and avian leukosis/sarcoma and reticuloendotheliosis, caused by retroviruses. Although these neoplastic diseases cause economic losses from tumor mortality and poor performance, some of them have served as highly suitable models to study neoplasia.

Newcastle disease is an infection of domestic poultry and other bird species with virulent Newcastle disease virus (NDV). It is a worldwide problem that presents primarily as an acute respiratory disease, but depression, nervous manifestations, or diarrhea may be the predominant clinical form. Severity depends on the virulence of the infecting virus and host susceptibility. Occurrence of the disease is reportable and may result in trade restrictions.

Omphalitis is a noncontagious infection of the navel and/or yolk sac in young poultry. It is more likely in unclean environments, which allow opportunistic bacterial infection. Signs include navel inflammation, anorexia, depression, reduced weight gain, and increased mortality in the first 2 weeks after hatching. Treatment of affected birds with antibiotics is often ineffective. Prevention is by improving sanitation and general husbandry.

Also see Toxicology Introduction et seq.

Infection with Riemerella anatipestifer is a contagious, widely distributed bacterial disease that primarily affects young ducks and less frequently turkeys and geese. Other waterfowl, chickens, and pheasants occasionally may be affected.

Salmonella infections are classified as nonmotile serotypes ( S enterica Pullorum and S enterica Gallinarum) and the many motile paratyphoidSalmonella. These Salmonella infections have a worldwide distribution. As a result of the institution of a testing and control program in the USA through the USDA-administered National Poultry Improvement Plan, the incidence of S enterica Pullorum or S enterica Gallinarum infection has decreased dramatically. Historically, S enterica Arizonae was placed in its own category, but it is now included with the paratyphoid Salmonella. S enterica Arizonae is an egg-transmitted disease primarily of young turkeys. In addition to the above nonmotile salmonellae, Salmonella paratyphoid infections in poultry are relatively common and have public health significance because of contaminated poultry product consumption.

Several different normally present Staphylococcus spp can cause localized or systemic infection in poultry if skin or mucous membrane barriers are compromised. Clinical signs vary, depending on the location infected. Diagnosis is confirmed by culture of lesions. Antibiotic treatment of systemic infection is often successful, but localized lesions can be more difficult to treat.

Streptococcosis is caused by bacteria that are part of the normal flora of the intestinal tract, so infections are often thought to occur secondarily to other diseases. It has been reported in numerous bird species throughout the world. There are two forms of the disease, an acute septicemic form and a chronic form. Flock mortality can be as high as 50%. Diagnosis is confirmed with isolation of the organism via culture. Treatment has been effective for early acute infections, with efficacy decreasing as the disease becomes chronic.

Tuberculosis, caused by Mycobacterium avium, can affect all birds, although susceptibility varies by species. Infection is chronic, leading to emaciation, decreased egg production, granulomas in multiple tissues, and death. Diagnosis is best made through necropsy demonstration of the bacteria in tissue samples. Because of the risk of creating drug-resistant strains, treatment is not recommended. Contaminated premises should not be used to raise poultry. Although M avium can infect humans, serovars found in birds and people are typically different. Nonetheless, precautions to avoid human exposure should be taken with infected birds.

Turkey viral hepatitis (TVH) is a disease of young turkeys characterized by the presence of hepatitis with or without pancreatitis. The virus is shed in droppings and transmitted by both direct and indirect contact. Diagnosis is based on histopathology, virus isolation, or detection of viral RNA using reverse transcriptase PCR. No specific treatments or preventive measures are available.

Ascites is an accumulation of noninflammatory transudate in one or more of the peritoneal cavities or potential spaces. The fluid, which accumulates most frequently in the two ventral hepatic, peritoneal, or pericardial spaces, may contain yellow protein clots. Ascites may result from increased vascular hydraulic pressure, vascular damage, increased tissue oncotic pressure, or decreased vascular oncotic (usually colloidal) pressure, but is most commonly associated with venous hypertension resulting from right heart failure in response to increased pulmonary resistance.

Cimex lectularius (bedbug) is a common bloodsucking parasite of people, but it can also feed on many other warm-blooded animals, including poultry. Bedbugs spend most of their time off the host in cracks and crevices, traveling to the host to feed at night. Because of this life history, it is rare in modern caged-laying operations. Bedbugs require a more complex environment (eg, nestboxes) and may become problematic in furnished-cage or cage-free layer facilities, breeding houses, pigeon lofts, etc.

Gangrenous dermatitis is a disease of turkeys and chickens caused by Clostridium septicum, C perfringens type A, and Staphylococcus aureus, either singly or in combination. The condition is characterized by rapid onset of acute mortality. Birds succumbing to the infection have necrosis of the skin and subcutaneous tissue, usually involving the breast, abdomen, wing, or thigh.

Production characteristics of modern poultry lines (eg, body weight in broiler chickens, egg production in laying hens) place high demands on the skeletal system, and inadequacies in nutrition or husbandry often result in skeletal diseases. Skeletal disorders may be primarily infectious or noninfectious; both may be seen concurrently within a flock. Skeletal disorders cause lameness from biomechanical dysfunction and in broiler chickens result in poor growth, culled birds, increased mortality (caused by starvation and dehydration), and carcass condemnation and downgrading. Bone fractures in spent hens may be a welfare issue.

Exertional myopathy results from overly strenuous muscular exercise and can be precipitated by preexisting conditions such as selenium deficiency. Inadequate energy metabolism and/or mechanical stresses occurring during contraction are thought to be the cause of myofiber degeneration.

Viral arthritis is a term used to describe inflammation affecting leg joints and/or tendons in poultry species that is attributable to reovirus infection. In cases that present clinically, birds appear lame and may have ruptured tendons. Definitive diagnosis relies on isolation and/or identification of reovirus from the affected tissue using virus isolation or RT-PCR. There are no treatment options, other than general supportive care, for birds once clinically affected. Prevention of clinical signs relies on the generation of a protective, serotype-specific immune response.

Enteric viruses of poultry are common and pervasive. They are potentially as diverse as enteric bacteria and are responsible for production diseases resulting in substantial financial losses. Many of these viruses have RNA genomes that continually evolve, leading to multiple circulating strains of varying pathogenicity. They can be difficult to diagnose due to confounding issues, such as their presence in healthy birds, variable pathogenicity, age-related resistance, coinfection with other pathogens, and lack of convenient diagnostic tests. They are associated with complex syndromes, such as malabsorption syndrome of broiler chickens and poult enteritis mortality syndrome, but also of diseases outside the enteric system, such as tenosynovitis caused by avian orthoreovirus. Recent metagenomics studies are beginning to shed light on the causes of some complex production diseases, and some of the more prominent virus families are described in this chapter, including astroviruses, coronaviruses, parvoviruses, picornaviruses and rotaviruses.

Avian encephalomyelitis is a viral infection affecting the CNS of several species of birds. Signs include tremors, ataxia, and weakness that progresses to paralysis. In severe outbreaks, morbidity and mortality may exceed 50%. Diagnosis is based on history, clinical signs, histopathology, and isolation of the virus. A live vaccine is available to prevent transmission and reduce egg losses.

Botulism is a toxic disorder resulting from ingestion of the exotoxin produced by Clostridium botulinum. It affects a wide variety of birds and mammals. Clinical signs include leg weakness and paresis that progresses to paralysis. Diagnosis is based on clinical signs and identification of the toxin in serum or GI contents. Immunization with inactivated toxoid has been successful in pheasants but is not cost-effective in commercial chicken flocks.

Encephalitis in poultry and farm-reared gamebirds may be caused by several different arboviruses. These include Eastern equine encephalitis (EEE) virus, Western equine encephalitis (WEE) virus, Highlands J (HJ) virus, Israel turkey meningoencephalitis virus, and West Nile Virus (See also West Nile Virus Infection in Poultry). The term “arbovirus,” an abbreviation of arthropod-borne virus, is used to describe a virus that replicates in a hematophagous (bloodsucking) arthropod and is transmitted by bite to a vertebrate host.

Also see Equine Arboviral Encephalomyelitis.

Artificial insemination (AI) is widely used to overcome low fertility in commercial turkeys, which results from unsuccessful mating as a consequence of large, heavily muscled birds being unable to physically complete the mating process. This is a serious and costly problem in the production of commercial turkey hatching eggs.

Fluid accumulation in the vestigial right oviduct is a common finding in hens. The abdominal cyst is filled with clear fluid and is attached to the right side of the cloacal wall. The cyst may vary in size from barely perceptible to 15–20 cm in diameter. An increased incidence has been seen in flocks after infectious bronchitis virus outbreaks. Oviductal cysts are a necropsy finding that rarely, if ever, affect flock performance.

Egg drop syndrome ’76 (EDS ‘76) is an atadenovirus-induced disease characterized by the production of pale, soft-shelled, and shell-less eggs by apparently healthy laying hens. The disease in laying hens has commonly been called "egg drop syndrome," but the full name (egg drop syndrome ’76 [EDS ’76]) should be used to distinguish it from the recently recognized flaviviral disease of ducks, which has been called "egg drop syndrome in ducks," and "duck egg drop syndrome," creating potential for confusion.

Cytodites nudus is a small, cosmopolitan mite occasionally noticed as white spots on the bronchi, lungs, air sacs, and abdominal organs of chickens, turkeys, pheasants, pigeons, canaries, and mallards. These mites are readily transmissible between birds through coughing. They are rarely found in commercial industries. The 14- to 21-day life cycle involves a larval and two nymphal stages. Infestation densities vary, and clinical signs range from none to weakness, weight loss, pneumonia, peritonitis, pulmonary edema, and death. Euthanasia of infected birds is the best means of control. Other recommended treatments include ivermectin or inhalation by birds of an insecticidal dust.

Aspergillosis is most often a respiratory infection in chickens and turkeys. It less often affects a wide range of other domestic and wild birds. Sick birds may display respiratory distress, suppressed growth, and general unthriftiness. Diagnosis is made through observation of granulomas, most typically in the respiratory tissues, and can be confirmed through culture or histopathology. There is no treatment for aspergillosis.

Avian influenza is a viral infection found in domestic poultry and a wide range of other birds. Wild waterfowl and shorebirds are often asymptomatic carriers. In poultry, low pathogenicity strains typically cause respiratory signs. High pathogenicity strains may cause widespread organ failure and sudden, high mortality. Diagnosis is by viral isolation or detection of the viral genome or specific antibodies. Antibiotics may help control secondary bacterial infection in flocks affected by low pathogenicity strains. Antiviral drugs are not approved or recommended. Prevention is accomplished by biosecurity. Vaccines matched for antigenic type can reduce clinical signs and reduce viral shedding in infected flocks, but use in the USA requires regulatory approval, especially for H5 and H7 strains. Sporadically, human infections have occurred, usually as isolated, individual cases of the H5 or H7 strains, but other hemagglutinin subtypes have been reported.

Different subtypes of the avian metapneumovirus (AMPV A-D) have been isolated from commercial poultry and wild birds, which are considered natural reservoirs. These viruses were shown to not only induce respiratory disease (turkey rhinotracheitis, swollen head syndrome) but also reproductive disorders in different avian species. Molecular methods are used to detect and further characterize AMPV, although classic virus propagation from field samples is difficult. Currently, biosecurity in combination with vaccination is applied in the field to control infection and reduce the risk from secondary respiratory pathogens.

Avian bordetellosis is a highly infectious, acute disease of the upper respiratory tract of young turkeys. Bordetella avium was once the only known etiologic agent, but B hinzii is now also known to be a potential cause. Clinical signs include sneezing (snick), watery or foamy eyes, clear nasal discharge following gentle pressure to the nares, mouth breathing, dyspnea, tracheal rales, and altered vocalization. Diagnosis is based on clinical signs and lesions and isolation of B avium or B hinzii from the respiratory tract. Antimicrobial therapy is rarely effective but sound husbandry practices may reduce the impact of an outbreak.

Infectious bronchitis is an acute, highly contagious upper respiratory tract disease in chickens. In addition to respiratory signs, decreased egg production and egg quality are common, and nephritis can be caused by some strains. Attenuated live and killed vaccines are available, but different antigenic types of the avian coronavirus causing the disease do not cross-protect, complicating control efforts. Diagnostic tests include ELISA and HI testing for serum antibodies and virus detection by RT-PCR and virus isolation in embryonated eggs. Sequence analysis of the Spike gene is used to genetically type the virus.

Infectious coryza is an acute respiratory disease of chickens caused by the bacterium Avibacterium paragallinarum. Clinical signs include decreased activity, nasal discharge, sneezing, and facial swelling. Diagnosis is based on PCR assay, bacterial culture, or production of typical clinical signs in susceptible chickens following inoculation with nasal exudate from an infected bird. Early antibiotic treatment may help infected birds recover. Prevention is based on sound management practices, including appropriate biosecurity measures and vaccination with serovars present in the local population.

Infectious laryngotracheitis (ILT) is an economically important respiratory disease of poultry. This highly contagious disease is caused by Gallid alpha herpesvirus type 1 (GaHV-1), commonly known as infectious laryngotracheitis virus (ILTV). The virus can be easily transmitted by infected birds and fomites. Lax biosecurity, transportation of infected birds, and spread of contaminated litter facilitates spread of the virus. Clinical signs of respiratory disease are not pathognomonic. Diagnosis is by real-time PCR and histopathology . Implementation of biosecurity is necessary for prevention, but vaccination is commonly used for control of the disease in endemic regions worldwide.

Quail bronchitis is a naturally occurring, highly contagious, often fatal respiratory disease of bobwhite quail, seen both in the wild and in captivity. The disease is of major economic significance to gamebird breeders and has a worldwide distribution. It is a serious disease on certain farms where quail are pen-raised, and particularly when quail of different ages are maintained on the same premises.

Poultry convert feed into food products quickly, efficiently, and with relatively low environmental impact compared with other livestock. The high rate of productivity of poultry results in relatively high nutrient needs. Poultry require the presence of at least 38 dietary nutrients in appropriate concentrations and balance. The nutrient requirement figures published in Nutrient Requirements of Poultry (National Research Council, 1994) are the most recent available and should be viewed as minimal nutrient needs for poultry. They are derived from experimentally determined levels after an extensive review of the published data. Criteria used to determine the requirement for a given nutrient include growth, feed efficiency, egg production, prevention of deficiency symptoms, and quality of poultry product. These requirements assume the nutrients are in a highly bioavailable form, and they do not include a margin of safety. Consequently, adjustments should be made based on bioavailability of nutrients in various feedstuffs. A margin of safety should be added based on the length of time the diet will be stored before feeding, changes in rates of feed intake due to environmental temperature or dietary energy content, genetic strain, husbandry conditions (especially the level of sanitation), and the presence of stressors (such as diseases or mycotoxins).