Infectious Laryngotracheitis (ILT)

Infectious laryngotracheitis (ILT) is a highly contagious, acute, and economically significant viral respiratory disease of chickens, pheasants, and occasionally other avian species, caused by Gallid herpesvirus 1 (GaHV-1), a member of the family Herpesviridae, subfamily Alphaherpesvirinae, genus Iltovirus. The disease is characterized by severe dyspnea, gasping, coughing, expectoration of bloody mucus, and pronounced inflammation of the larynx and trachea, often with the formation of diphtheritic membranes and caseous plugs that can obstruct the airway. ILT is distributed worldwide and poses a major threat to commercial poultry operations, particularly in intensive broiler, layer, and breeder flocks, where it can cause high morbidity (up to 90-100%) and variable mortality (ranging from 5% to 70% depending on strain virulence, host immunity, and management). The disease is a notifiable entity in many countries due to its potential for rapid spread and severe economic impact, including decreased egg production, reduced weight gain, increased feed conversion ratio (FCR), and mortality. ILT is primarily a disease of the upper respiratory tract, but systemic involvement can occur, especially in severe outbreaks. The virus establishes latency in the trigeminal ganglion and can reactivate under stress, leading to intermittent shedding and perpetuation of infection within flocks. Control relies on strict biosecurity, vaccination with live attenuated or recombinant vaccines, and in some cases, depopulation and stamping-out policies. In turkeys, ILT is generally less severe, but natural infections have been reported. Ducks and geese are considered resistant. Backyard poultry flocks are often reservoirs and can introduce the virus to commercial operations. The disease is of significant concern to the poultry industry due to its high morbidity, mortality, and trade restrictions.

The causative agent of infectious laryngotracheitis is Gallid herpesvirus 1 (GaHV-1), also known as Infectious Laryngotracheitis Virus (ILTV). It is a double-stranded DNA virus belonging to the family Herpesviridae, subfamily Alphaherpesvirinae, genus Iltovirus. The virion is enveloped, icosahedral, and approximately 195-250 nm in diameter. The genome is linear, approximately 150-155 kbp, encoding over 70 open reading frames. Key viral proteins include glycoproteins involved in attachment and entry, such as gB, gC, gD, gH, and gL, which are targets for neutralizing antibodies. The virus is relatively fragile in the environment, being inactivated by lipid solvents, detergents, and common disinfectants, but it can survive for weeks in organic matter, such as tracheal exudates, at cool temperatures. There are multiple strains of ILTV that vary in virulence, ranging from highly pathogenic strains causing severe clinical disease and high mortality to mild or vaccine-related strains that produce subclinical or mild respiratory signs. Live attenuated vaccines, such as the chicken embryo origin (CEO) and tissue culture origin (TCO) vaccines, are derived from virulent strains and can revert to virulence upon bird-to-bird passage. Recombinant vaccines, such as those based on fowlpox virus or herpesvirus of turkeys (HVT) vectors expressing ILTV glycoproteins, are also available and are safer but may require different administration routes. The virus has a predilection for the epithelial cells of the larynx and trachea, where it replicates and causes necrosis and inflammation. Latency is established in the trigeminal ganglion and possibly other neural tissues, and reactivation can occur under stress, leading to virus shedding and transmission.

Infectious laryngotracheitis is a worldwide disease affecting primarily chickens, with pheasants also susceptible. It is most commonly seen in commercial layers, broiler breeders, and occasionally broilers, especially in areas with high poultry density and poor biosecurity. The disease can occur at any age, but clinical signs are more severe in growing and adult birds, particularly in layers and breeders, where egg production drops significantly. In broilers, ILT is often less severe but can still cause respiratory distress and increased mortality, especially in older birds. The incubation period is typically 6-12 days, depending on the strain and route of exposure. Transmission occurs horizontally via respiratory aerosols, direct contact with infected birds, or indirect contact with contaminated fomites, equipment, litter, and personnel. The virus can also be spread through the consumption of contaminated water or feed. Wild birds, rodents, and insects may act as mechanical vectors. The virus is shed in respiratory secretions and can be present in the environment for weeks, especially in cool, damp conditions. Morbidity in susceptible flocks can reach 90-100%, while mortality varies from 5% to 70%, with highly virulent strains causing higher mortality. In layers, egg production can drop by 10-50% or more, and recovery may take several weeks. The disease is often more severe in flocks with concurrent infections, such as Mycoplasma gallisepticum, Escherichia coli, or infectious bronchitis virus. Poor ventilation, high ammonia levels, high stocking density, and immunosuppression are important predisposing factors. The disease is endemic in many countries, and outbreaks are often associated with the introduction of new birds, vaccination failures, or the use of live vaccines that can spread and revert to virulence. In some regions, ILT is a reportable disease, and control measures include quarantine, depopulation, and vaccination. The economic impact includes mortality, reduced egg production, poor feed conversion, treatment costs, and trade restrictions.

The pathogenesis of infectious laryngotracheitis begins with the inhalation of infectious virus, which attaches to and replicates in the epithelial cells of the upper respiratory tract, particularly the larynx and trachea. The virus enters the cells via receptor-mediated endocytosis or direct fusion with the plasma membrane, mediated by viral glycoproteins. After replication, the virus causes cytolytic infection, leading to cell death and desquamation of the epithelial lining. This results in severe inflammation, characterized by edema, hyperemia, and infiltration of heterophils and mononuclear cells. The tracheal mucosa becomes thickened and necrotic, and the lumen may be filled with fibrinous exudate, blood, and cellular debris, forming diphtheritic membranes or caseous plugs that can obstruct the airway, causing asphyxiation. The virus also infects the conjunctival epithelium, causing conjunctivitis and sometimes keratitis. After primary replication, the virus enters the sensory nerve endings and travels via retrograde axonal transport to the trigeminal ganglion, where it establishes latency. Under stress (e.g., poor ventilation, handling, or immunosuppression), the virus can reactivate, travel back to the respiratory tract, and be shed, leading to new outbreaks. The systemic spread of the virus is limited, but viremia can occur, especially in severe cases, leading to involvement of the lungs, air sacs, and other organs. The immune response involves both humoral and cell-mediated immunity. Local IgA antibodies in the respiratory tract and systemic IgG antibodies are produced, but cell-mediated immunity is crucial for recovery and protection. The virus can cause immunosuppression by infecting and destroying lymphocytes, particularly in the thymus and bursa of Fabricius, which may predispose birds to secondary bacterial infections. The severity of the disease depends on the virulence of the strain, the immune status of the host, and the presence of concurrent infections. In vaccinated flocks, the disease may be milder, but vaccine strains can cause respiratory signs and spread to susceptible birds.

Several intrinsic and extrinsic factors predispose poultry flocks to infectious laryngotracheitis. Intrinsic factors include genetic susceptibility, age, immune status, and production stress. Chickens are the primary hosts, and certain breeds or lines may be more susceptible, although all commercial breeds are vulnerable. Young birds, especially those under 4 weeks of age, may show less severe clinical signs but can still become infected and shed the virus. Adult layers and breeders are more severely affected due to the stress of high egg production, which can suppress the immune system and increase susceptibility. Immunosuppression from other diseases, such as infectious bursal disease (IBD), Marek's disease, or mycotoxins, can exacerbate ILT. Extrinsic factors include poor biosecurity, which allows the introduction of the virus through contaminated equipment, vehicles, personnel, or live birds. High stocking density and poor ventilation lead to high ammonia levels and respiratory irritation, which can increase the severity of the disease. Wet litter and poor sanitation provide a favorable environment for virus survival. Vaccination failures, due to improper administration, incorrect vaccine strain, or immunosuppression, can leave flocks susceptible. The use of live vaccines, especially CEO vaccines, can lead to the spread of vaccine virus and potential reversion to virulence, causing outbreaks. Seasonal factors, such as cold weather, can increase the risk of respiratory disease due to reduced ventilation and increased bird density. Wild birds, rodents, and insects can act as mechanical vectors, introducing the virus into flocks. The presence of other respiratory pathogens, such as Mycoplasma gallisepticum, infectious bronchitis virus, and Escherichia coli, can synergistically increase the severity of ILT. Poor nutrition, particularly deficiencies in vitamins A and E, can impair mucosal immunity and increase susceptibility. Stress from handling, transport, or changes in feed or lighting can trigger reactivation of latent virus and precipitate outbreaks.

The clinical signs of infectious laryngotracheitis vary depending on the virulence of the strain, the immune status of the flock, and the presence of concurrent infections. In peracute and acute forms, the onset is sudden, with high morbidity and mortality. Affected birds exhibit severe respiratory distress, including gasping, coughing, sneezing, and expectoration of bloody mucus. They may extend their heads and necks to breathe, and there is often a characteristic 'pump-handle' breathing. Birds may be depressed, huddle together, and have ruffled feathers. Cyanosis of the comb and wattles may be observed due to hypoxia. In layers, there is a rapid drop in egg production, often by 10-50% or more, and eggs may have abnormal shells (thin-shelled, rough, or misshapen). Mortality can be high, ranging from 5% to 70%, depending on the strain and management. In milder forms, which may occur in vaccinated flocks or with less virulent strains, clinical signs are limited to mild respiratory rales, conjunctivitis, and reduced feed and water intake. There may be a slight increase in mortality and a transient drop in egg production. In broilers, the disease may be less severe, but affected birds may show poor growth, increased FCR, and increased condemnations at processing due to tracheitis and airsacculitis. In some cases, the infection may be subclinical, with only seroconversion and no obvious clinical signs. The disease can also cause neurological signs, such as torticollis or paralysis, if the virus invades the central nervous system, although this is rare. The clinical course typically lasts 1-2 weeks, but recovery may be prolonged, especially if secondary bacterial infections occur. In laying flocks, egg production may take several weeks to return to normal, and some birds may never fully recover. The presence of bloody mucus on the beaks and feathers is a classic sign of ILT and should raise immediate suspicion.

Infectious laryngotracheitis must be differentiated from several other respiratory diseases of poultry. Key differentials include: 1) Avian influenza (AI) - highly pathogenic AI can cause similar respiratory signs, cyanosis, and high mortality, but also often presents with edema of the head, wattles, and combs, and neurological signs. AI is a reportable disease and requires immediate notification. 2) Newcastle disease (ND) - virulent ND can cause respiratory signs, but also often includes neurological signs (torticollis, paralysis), greenish diarrhea, and a drop in egg production. 3) Infectious bronchitis (IB) - IB causes respiratory signs, but is more common in young birds and often leads to renal disease and egg quality problems. 4) Infectious coryza - caused by Avibacterium paragallinarum, it causes facial edema, nasal discharge, and conjunctivitis, but is less severe and does not cause bloody mucus. 5) Mycoplasmosis (Mycoplasma gallisepticum) - causes chronic respiratory disease, with rales, coughing, and airsacculitis, but is usually less acute and has a slower onset. 6) Fowl cholera (Pasteurella multocida) - can cause acute respiratory signs and high mortality, but also often presents with septicemia and swollen wattles. 7) Avian metapneumovirus (turkey rhinotracheitis) - causes respiratory signs, especially in turkeys, but also affects chickens. 8) Vitamin A deficiency - can cause respiratory epithelial metaplasia and caseous exudates in the mouth and trachea, but is not contagious. 9) Aspergillosis - can cause respiratory distress and tracheal plugs, but is usually associated with poor ventilation and contaminated litter. 10) Gapeworm (Syngamus trachea) - causes gasping and coughing, but is more common in backyard flocks and can be diagnosed by finding worms in the trachea. To differentiate, a thorough history, clinical signs, necropsy findings, and laboratory tests are essential. The presence of bloody mucus and severe tracheitis with diphtheritic membranes is highly suggestive of ILT. Laboratory confirmation is via PCR, virus isolation, or serology.

The diagnostic algorithm for infectious laryngotracheitis involves a stepwise approach. Step 1: Flock history and clinical signs - sudden onset of severe respiratory distress, gasping, coughing, bloody mucus, and high morbidity/mortality, especially in layers or breeders, should raise suspicion. Step 2: Gross necropsy - examine the larynx and trachea for severe inflammation, hemorrhage, and diphtheritic membranes or caseous plugs. Other lesions may include conjunctivitis, sinusitis, and airsacculitis. Step 3: Histopathology - collect tracheal and laryngeal tissues in 10% neutral buffered formalin. Microscopic examination reveals necrosis of the epithelium, intranuclear inclusion bodies (Cowdry type A) in epithelial cells, and syncytia formation. Step 4: Virus isolation - inoculate tracheal exudate or tissue homogenates onto chicken embryo kidney cells or chorioallantoic membrane (CAM) of embryonated chicken eggs. ILTV produces characteristic pocks on the CAM. Step 5: Molecular detection - use PCR or real-time PCR on tracheal swabs or tissues to detect ILTV DNA. This is rapid and sensitive. Step 6: Serology - collect serum samples for ELISA or virus neutralization tests to detect antibodies. A four-fold rise in antibody titers between acute and convalescent samples indicates recent infection. Step 7: Differential diagnosis - rule out other respiratory diseases using appropriate tests, such as PCR for AI, ND, IB, and Mycoplasma. Step 8: Reporting - if the disease is notifiable, report to the relevant veterinary authorities. The diagnostic algorithm should be implemented promptly to enable rapid control measures, including quarantine, vaccination, or depopulation.

Laboratory findings in infectious laryngotracheitis include: 1) Serology: ELISA is commonly used to detect antibodies against ILTV. A positive result indicates exposure, but not necessarily active infection. A four-fold increase in antibody titers between paired serum samples (acute and convalescent) confirms recent infection. Virus neutralization (VN) and agar gel immunodiffusion (AGID) tests are also available but are less commonly used. 2) Molecular diagnostics: PCR and real-time PCR are highly sensitive and specific for detecting ILTV DNA in tracheal swabs, tissues, or exudates. These tests can differentiate vaccine strains from field strains using restriction fragment length polymorphism (RFLP) or sequencing. 3) Virus isolation: Isolation of ILTV in embryonated chicken eggs (CAM inoculation) or cell culture (chicken embryo kidney cells) is confirmatory. The virus produces characteristic pocks on the CAM within 4-6 days. 4) Histopathology: Microscopic examination of tracheal tissues reveals necrosis of the epithelium, intranuclear inclusion bodies (Cowdry type A), syncytia, and inflammatory cell infiltration. 5) Hematology: There may be leukocytosis and heterophilia in the acute phase. 6) Blood chemistry: No specific changes are typical, but there may be elevated levels of acute-phase proteins. 7) Microbiology: Bacterial culture of tracheal exudates may reveal secondary bacterial infections, such as Escherichia coli, which can complicate the disease. 8) Mycotoxin assays: If immunosuppression is suspected, feed samples can be tested for mycotoxins (e.g., aflatoxin, ochratoxin) using ELISA or HPLC. 9) Coccidiosis lesion scoring: If concurrent coccidiosis is suspected, intestinal lesions can be scored on a 0-4 scale according to Johnson and Reid. 10) Complete blood count (CBC): May show lymphopenia due to viral-induced immunosuppression. These laboratory findings, combined with clinical signs and necropsy, provide a definitive diagnosis.

Imaging modalities are not commonly used in the diagnosis of infectious laryngotracheitis in poultry, but they can be helpful in research or in cases where other diseases are suspected. Radiography (X-ray) can be used to assess the respiratory tract, but due to the small size of birds, it is not routinely performed. In severe cases, radiographs may show increased opacity in the tracheal region due to exudate or caseous plugs. Ultrasonography is not typically used for respiratory disease in poultry. However, gross necropsy photography is an essential imaging tool for documenting lesions. Photographs of the trachea showing severe inflammation, hemorrhage, and diphtheritic membranes are valuable for diagnostic records and educational purposes. In research settings, computed tomography (CT) or magnetic resonance imaging (MRI) could be used to visualize the upper respiratory tract, but these are not practical for field diagnosis. Therefore, imaging is limited to necropsy findings and photographic documentation.

Gross necropsy lesions in infectious laryngotracheitis are primarily confined to the upper respiratory tract. The larynx and trachea show severe congestion, hemorrhage, and edema. The lumen may contain blood-tinged mucus, fibrinous exudate, or caseous plugs that can obstruct the airway. The tracheal mucosa is thickened and may have a diphtheritic membrane. In some cases, the inflammation extends to the bronchi and lungs, causing pneumonia and airsacculitis. Conjunctivitis and sinusitis may also be present. Microscopic histopathology reveals severe necrosis and desquamation of the tracheal epithelium, with infiltration of heterophils and mononuclear cells. The most characteristic finding is the presence of intranuclear inclusion bodies (Cowdry type A) in epithelial cells, which are large, eosinophilic, and often surrounded by a clear halo. Syncytia (multinucleated giant cells) may also be observed. The lamina propria is edematous and infiltrated with inflammatory cells. In severe cases, there is extensive hemorrhage and fibrin deposition. The virus can also cause necrosis in the conjunctival epithelium and in the lungs. In the trigeminal ganglion, latency is established without significant histopathological changes. Immunohistochemistry (IHC) can be used to detect viral antigens in tissue sections, which is useful for confirmation. Electron microscopy can demonstrate herpesvirus particles in infected cells. These histopathological findings are pathognomonic for ILT and are essential for definitive diagnosis.

There is no specific antiviral treatment for infectious laryngotracheitis. Management focuses on supportive care, control of secondary bacterial infections, and vaccination to prevent spread. In affected flocks, the following measures are recommended: 1) Supportive therapy: Provide adequate ventilation, reduce stocking density, and minimize stress. Ensure access to clean water and feed. Supplement with vitamins and electrolytes to support the immune system. 2) Antibiotics: To control secondary bacterial infections, administer broad-spectrum antibiotics in drinking water or feed. Commonly used antibiotics include oxytetracycline (10-20 mg/kg body weight, or 200-400 g/ton of feed), tylosin (25 mg/kg body weight, or 100-200 g/ton), amoxicillin (10-20 mg/kg body weight, or 100-200 g/ton), or enrofloxacin (10 mg/kg body weight, or 50-100 mg/L drinking water, where legal). The duration of treatment is typically 3-5 days. 3) Anti-inflammatory drugs: Non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin or flunixin meglumine may be used to reduce inflammation and fever, but should be used with caution. 4) Vaccination: In the face of an outbreak, emergency vaccination with live attenuated vaccines (CEO or TCO) can be administered via eye drop, spray, or drinking water to reduce clinical signs and mortality. However, vaccination of already infected flocks may exacerbate the disease, so it should be done only under veterinary guidance. 5) Biosecurity: Strict biosecurity measures should be implemented to prevent the spread of the virus, including quarantine of affected flocks, disinfection of equipment and facilities, and control of personnel movement. 6) Depopulation: In severe outbreaks or in cases where the disease is notifiable, depopulation and stamping-out may be required to eradicate the virus. 7) Supportive care: Provide a warm, dry environment and ensure adequate nutrition. Some producers use probiotics or immune stimulants to support gut health and immunity. It is important to note that antibiotics are not effective against the virus itself, and their use should be based on culture and sensitivity results if possible. Withdrawal times must be observed for meat and eggs.

The prognosis for infectious laryngotracheitis depends on several factors, including the virulence of the strain, the immune status of the flock, the presence of secondary infections, and the speed of intervention. In flocks with high immunity (e.g., previously vaccinated or recovered), the disease may be mild, with low mortality and a quick recovery. In susceptible flocks, especially layers and breeders, the prognosis is guarded, with mortality ranging from 5% to 70%. The short-term prognosis (first 1-2 weeks) is critical, as severe respiratory obstruction can lead to asphyxiation. With supportive care and control of secondary infections, many birds can recover, but egg production may take several weeks to return to normal, and some birds may have permanent respiratory damage. The medium-term prognosis (1-2 months) is generally good if the flock survives the acute phase, but there may be a prolonged drop in egg production and increased culling. The long-term prognosis is influenced by the establishment of latency, which can lead to recurrent outbreaks under stress. In some cases, the disease can become endemic in the flock, leading to periodic episodes. The economic impact can be significant, with increased mortality, reduced egg production, poor feed conversion, and increased treatment costs. In severe outbreaks, depopulation may be necessary, resulting in total loss of the flock. Therefore, the prognosis is variable and depends on prompt and effective management.

Follow-up after an infectious laryngotracheitis outbreak is crucial to ensure recovery and prevent recurrence. The following steps are recommended: 1) Monitor the flock daily for clinical signs, including respiratory distress, coughing, and mortality. Keep records of feed and water intake, egg production, and mortality. 2) Serological monitoring: Collect serum samples at 2-4 weeks post-outbreak and then periodically (e.g., every 3-6 months) to assess antibody titers. A decline in titers may indicate waning immunity and the need for booster vaccination. 3) Vaccination: Implement a vaccination program to protect the flock from future outbreaks. Live attenuated vaccines (CEO or TCO) can be administered via eye drop, spray, or drinking water. Recombinant vaccines (e.g., HVT-ILT) are also available and can be given in ovo or subcutaneously. The timing and route of vaccination should be based on the risk of exposure and the production stage. 4) Biosecurity: Review and enhance biosecurity protocols to prevent the introduction of the virus. This includes controlling visitor access, disinfecting vehicles and equipment, and preventing contact with wild birds. 5) Cleaning and disinfection: After the outbreak, thoroughly clean and disinfect the poultry house, including all equipment, feeders, drinkers, and ventilation systems. Use disinfectants effective against enveloped viruses, such as quaternary ammonium compounds, phenols, or bleach. Allow the house to remain empty for at least 2-4 weeks before restocking. 6) Litter management: Remove and properly dispose of contaminated litter. 7) Pullet rearing audits: If the flock is a layer or breeder, ensure that replacement pullets are vaccinated and raised in a biosecure environment. 8) Necropsy of any dead birds: Perform necropsies on any birds that die to monitor for secondary infections or recurrence. 9) Record keeping: Maintain detailed records of the outbreak, including dates, clinical signs, laboratory results, and treatments, for future reference. 10) Consultation: Work with a poultry veterinarian to develop a comprehensive health plan for the flock.

Clinical pearls: 1) The presence of bloody mucus on the beaks and feathers is a classic sign of ILT and should prompt immediate investigation. 2) On necropsy, the trachea often contains caseous plugs or diphtheritic membranes that can be easily visualized. 3) Intranuclear inclusion bodies (Cowdry type A) in tracheal epithelial cells are pathognomonic for ILT. 4) ILT is a herpesvirus, so it establishes latency; stress can reactivate the virus and cause new outbreaks. 5) Vaccination with live vaccines can cause disease if the vaccine virus spreads to susceptible birds, so it is important to vaccinate all birds in a flock simultaneously. 6) ILT can be confused with highly pathogenic avian influenza (HPAI) or Newcastle disease (ND), which are reportable diseases; always rule these out first. 7) In layers, a sudden drop in egg production with respiratory signs is highly suggestive of ILT. 8) Good biosecurity is the most effective way to prevent ILT. Pitfalls: 1) Failing to consider ILT in the differential diagnosis of respiratory disease can lead to delayed diagnosis and spread. 2) Using live vaccines in the face of an outbreak can exacerbate the disease if birds are already infected. 3) Relying solely on clinical signs without laboratory confirmation can lead to misdiagnosis. 4) Neglecting to control secondary bacterial infections can increase mortality. 5) Inadequate cleaning and disinfection can leave the virus in the environment, leading to recurrence. 6) Not implementing a vaccination program in endemic areas can leave flocks susceptible. 7) Overlooking the role of wild birds and rodents in transmitting the virus. 8) Failing to report notifiable cases can result in legal consequences and further spread.

Current drug protocols for infectious laryngotracheitis focus on supportive care and control of secondary bacterial infections. Antibiotics are not effective against the virus but are used to prevent or treat bacterial complications. Common protocols include: 1) Oxytetracycline: Administer in drinking water at 10-20 mg/kg body weight per day, or in feed at 200-400 g/ton for 3-5 days. Withdrawal time for meat is 3 days, for eggs is 2 days. 2) Tylosin: Administer in drinking water at 25 mg/kg body weight per day, or in feed at 100-200 g/ton for 3-5 days. Withdrawal time for meat is 1 day, for eggs is 2 days. 3) Amoxicillin: Administer in drinking water at 10-20 mg/kg body weight per day, or in feed at 100-200 g/ton for 3-5 days. Withdrawal time for meat is 1 day, for eggs is 2 days. 4) Enrofloxacin: Administer in drinking water at 10 mg/kg body weight per day for 3-5 days. Note: Enrofloxacin is not approved for use in poultry in some countries (e.g., the US) due to concerns about antibiotic resistance. Withdrawal time for meat is 3 days, for eggs is 4 days. 5) Florfenicol: Administer in drinking water at 20-30 mg/kg body weight per day for 3-5 days. Withdrawal time for meat is 6 days, for eggs is 7 days. 6) Supportive vitamins: Vitamin A (10,000-20,000 IU/kg feed), Vitamin E (100-200 IU/kg feed), Vitamin C (100-200 mg/kg feed) can be added to the diet to support immune function. 7) Electrolytes and glucose: Provide in drinking water to maintain hydration and energy. 8) Vaccines: Live attenuated vaccines (CEO or TCO) are administered via eye drop (one drop per bird), spray (coarse spray), or drinking water (reconstituted in water with skim milk powder as a stabilizer). The dose is typically 10^3-10^4 TCID50 per bird. Recombinant vaccines (HVT-ILT) are administered in ovo (0.05 ml per embryo) or subcutaneously (0.2 ml per chick) at hatch. The withdrawal time for vaccines is not applicable. It is important to follow label instructions and consult a veterinarian for specific protocols. Antibiotic use should be based on culture and sensitivity testing when possible, and withdrawal times must be observed to ensure food safety.

Infectious laryngotracheitis has been extensively studied in poultry medicine. Key findings from the literature include: 1) The disease is caused by Gallid herpesvirus 1, and its pathogenesis involves replication in the upper respiratory tract with latency in the trigeminal ganglion (Bagust et al., 2000). 2) Live attenuated vaccines, particularly CEO vaccines, are effective but can revert to virulence and cause outbreaks (Guy et al., 1991). Recombinant vaccines, such as HVT-ILT, are safer and provide good protection (Johnson et al., 2010). 3) PCR-based diagnostics are highly sensitive and can differentiate vaccine and field strains (Kirkpatrick et al., 2006). 4) Control measures include strict biosecurity, vaccination, and in some cases, depopulation (OIE Terrestrial Manual, 2018). 5) The economic impact of ILT is significant, with losses due to mortality, reduced egg production, and increased FCR (Dufour-Zavala, 2008). 6) Concurrent infections with Mycoplasma gallisepticum or Escherichia coli can exacerbate the disease (Kleven, 2008). 7) Stress factors, such as poor ventilation and high stocking density, increase the severity of the disease (Hughes et al., 2013). 8) The use of antimicrobials is not effective against the virus but is recommended for secondary bacterial infections (Plumb, 2015). 9) Vaccination programs should be tailored to the specific risk factors of the flock, including the prevalence of the disease in the area and the production type (Guy, 2013). 10) The AAAP and WVPA provide consensus guidelines for the diagnosis and control of ILT (AAAP, 2016). These evidence-based recommendations are essential for the effective management of ILT in commercial poultry operations.