Infectious Laryngotracheitis (ILT)

Infectious laryngotracheitis is a highly contagious viral respiratory disease of chickens caused by gallid herpesvirus type 1, an alphaherpesvirus that specifically targets the respiratory tract of gallinaceous birds. This disease is characterized by severe respiratory distress, gasping, coughing, and expectoration of bloody mucus, making it one of the more dramatic and distressing respiratory conditions observed in poultry. The disease was first described in the United States in the 1920s and has since been recognized worldwide, causing significant economic losses in commercial poultry operations and occasional devastating outbreaks in backyard flocks.

Infectious laryngotracheitis primarily affects chickens, though pheasants, peafowl, and partridges can also become infected. Turkeys and waterfowl are considered resistant to natural infection. The disease occurs in poultry-producing regions throughout the world, with endemic areas existing in major poultry-producing countries on every continent. Birds of any age can be affected, though clinical disease is most commonly seen in birds over three weeks of age, with adults typically showing more severe signs than younger birds. The disease is most problematic in commercial layer operations and broiler breeder farms, where the combination of bird density and economic stakes creates significant challenges.

The economic impact of infectious laryngotracheitis can be devastating when it strikes a naive flock. Mortality rates in severe outbreaks can reach fifty percent or higher, though more commonly range from ten to thirty percent in acute outbreaks. Milder epizootic forms and endemic situations may produce lower mortality but still cause substantial production losses. In laying flocks, egg production may drop by ten to fifty percent and may take weeks to months to recover, if it ever returns to baseline levels. The costs of treatment, increased management, and vaccination in response to outbreaks add to the economic burden. The welfare impact on affected birds is considerable, as the respiratory distress and suffocation associated with severe cases cause significant suffering.

There is no specific antiviral treatment for infectious laryngotracheitis, and management focuses on supportive care, prevention of secondary bacterial infections, and controlling spread within and between flocks. Vaccination is the primary tool for prevention and is widely used in endemic areas, though the use of live vaccines carries risks of vaccine virus spread and reversion to virulence. Early detection and rapid implementation of control measures are essential for minimizing the impact of outbreaks. Because the virus establishes latent infections in recovered birds, carriers remain a source of infection indefinitely, complicating eradication efforts and making strict biosecurity essential.

The causative agent of infectious laryngotracheitis is gallid herpesvirus type 1, also known as infectious laryngotracheitis virus or ILTV. This is a double-stranded DNA virus belonging to the family Herpesviridae, subfamily Alphaherpesvirinae. Like other alphaherpesviruses, ILTV has the ability to establish latent infections in sensory nerve ganglia, particularly the trigeminal ganglia, from which it can reactivate periodically to cause viral shedding without necessarily producing clinical disease. The virus is relatively fragile in the environment compared to some other poultry pathogens, surviving for only days to weeks outside the host under most conditions, though it can persist longer in organic material at cool temperatures.

There is no true breed predisposition to infectious laryngotracheitis, as all chickens are susceptible to the virus. However, the severity of clinical disease can vary based on the virulence of the particular viral strain involved. Field strains of ILTV range from highly virulent, causing severe acute disease with high mortality, to relatively mild strains producing subclinical infection or mild respiratory signs. Live attenuated vaccine strains have been designed to produce immunity with minimal pathogenicity, but these can spread to unvaccinated birds and may regain virulence through passage in susceptible populations. Different genetic lines of chickens may show some variation in susceptibility or severity of disease, but no line has true resistance.

Environmental and management factors play crucial roles in the transmission and severity of infectious laryngotracheitis. The virus spreads primarily through respiratory aerosols and direct contact with respiratory secretions from infected birds. Contaminated equipment, clothing, and vehicles can mechanically transport the virus between flocks over short distances, though the virus's limited environmental survival restricts long-distance fomite transmission. High stocking density facilitates aerosol transmission within houses. Poor ventilation increases the concentration of viral particles in the air and predisposes birds to more severe respiratory disease. Dust and aerosols generated during catching and handling operations can spread the virus rapidly through a house.

Several risk factors increase the likelihood of infectious laryngotracheitis outbreaks and influence disease severity. The presence of carrier birds from previous infections or vaccination with live vaccines creates an ongoing reservoir of virus within the flock. Introduction of new birds, whether carrying the virus or naive and susceptible to infection from carriers already present, is a common trigger for outbreaks. Stressors such as moving birds, onset of lay, concurrent disease, and environmental extremes can trigger reactivation of latent virus in carrier birds, initiating new outbreaks. Multi-age operations and geographic areas with high poultry density face elevated risk due to the increased opportunities for virus transmission between flocks.

The pathophysiology of infectious laryngotracheitis involves viral replication in the epithelial cells lining the respiratory tract, particularly the larynx, trachea, and conjunctiva. Following exposure, typically through inhalation of virus-containing aerosols or direct contact with infected secretions, the virus attaches to and enters respiratory epithelial cells. Viral replication causes cell death and sloughing of the epithelium, resulting in hemorrhage, inflammation, and accumulation of fibrinous and hemorrhagic exudate in the tracheal lumen. In severe cases, this exudate can form diphtheritic membranes that obstruct the airway, leading to suffocation. The incubation period ranges from six to fourteen days depending on the route of exposure, viral dose, and strain virulence. Following recovery from acute infection, the virus establishes latency in the trigeminal ganglia, where it persists for the lifetime of the bird.

Early warning signs of infectious laryngotracheitis may be subtle and easily missed, particularly in the early stages of an outbreak. Attentive producers may notice decreased activity and slight reduction in feed consumption in a small number of birds. Mild watery eyes or slight nasal discharge might be observed in initial cases. Some birds may show subtle changes in vocalization or slight respiratory effort. In laying flocks, a small decrease in egg production may precede more obvious clinical signs by a day or two. As the disease spreads through the flock, the number of affected birds increases rapidly over several days.

The classic symptoms of infectious laryngotracheitis are distinctive and often dramatic once the disease becomes established. Severe respiratory distress is the hallmark sign, with affected birds extending their necks and gasping for air in what is sometimes described as pump-handle breathing. Coughing is frequent and may produce bloody mucus or frank blood that can be seen splattered on walls, feeders, and other birds. Birds may make rattling, gurgling, or squeaking sounds as they breathe through partially obstructed airways. In severe cases, expectoration of diphtheritic material or blood clots may be observed. Mortality often results from suffocation as the airway becomes progressively obstructed by inflammatory exudate and hemorrhage.

Behavioral changes in birds with infectious laryngotracheitis reflect their respiratory distress and general debilitation. Affected birds are typically depressed and reluctant to move, often standing or sitting with their eyes closed and heads drawn in or extended depending on the severity of respiratory compromise. Appetite is markedly reduced, and birds gather near water sources as they become dehydrated. Social behavior changes as sick birds separate themselves from healthy flockmates. Laying hens cease production during the acute phase of illness. Vocalization is reduced, and any sounds produced may be abnormal due to laryngeal involvement.

Physical signs beyond respiratory distress include conjunctivitis with swelling and reddening of the conjunctival membranes and periorbital tissues. Watery to mucopurulent ocular discharge may be present, and in some cases the conjunctival form of the disease predominates, producing severe swelling around the eyes with relatively less tracheal involvement. Nasal discharge is typically present and may be clear, mucoid, or blood-tinged. Birds that survive the acute phase may develop swelling of the infraorbital sinuses. Cyanosis of the comb and wattles indicates severe respiratory compromise and impending death. Weight loss occurs rapidly in birds that are not eating, and dehydration is common.

The progression of symptoms in infectious laryngotracheitis follows a relatively predictable course. Clinical signs typically appear six to twelve days after exposure, with initial cases showing mild respiratory signs. Over the following days, disease spreads rapidly through the flock, with increasing numbers of birds showing increasingly severe signs. Peak mortality usually occurs seven to ten days after the first clinical signs appear, with most deaths occurring over a one to two week period. Survivors begin to recover after two to three weeks, though some may develop chronic respiratory signs or remain unthrifty. The flock mortality rate varies widely depending on viral strain virulence, ranging from near zero in mild outbreaks to over fifty percent in severe cases caused by highly virulent strains.

Emergency symptoms requiring immediate attention include severe dyspnea with open-mouth breathing and marked extension of the neck, indicating critical airway obstruction. Cyanosis of the comb and wattles signals imminent respiratory failure. Sudden spikes in mortality, particularly with multiple birds found dead with bloody discharge from the beak, warrant urgent veterinary investigation and implementation of emergency protocols. Hemorrhage from the oral cavity or nares is always cause for concern and may indicate a particularly virulent form of the disease or concurrent involvement of notifiable diseases. Because infectious laryngotracheitis can resemble highly pathogenic avian influenza or virulent Newcastle disease in some presentations, any severe respiratory outbreak with high mortality should prompt immediate consultation with veterinary authorities to rule out these reportable conditions.

Clinical examination provides strong presumptive evidence for infectious laryngotracheitis when characteristic signs are present. A veterinarian examining an affected flock will note the classic presentation of respiratory distress, gasping, and bloody tracheal exudate in multiple birds. Examination of individual birds reveals the extent of respiratory compromise, presence of conjunctival involvement, and overall condition. Opening the trachea of freshly dead birds often reveals the pathognomonic finding of hemorrhagic tracheitis with blood and fibrinous exudate in the tracheal lumen. The history of disease onset and progression, vaccination status, recent bird introductions, and any known exposure to infected flocks all provide important context for the clinical assessment.

Laboratory diagnosis is essential for confirming infectious laryngotracheitis and is particularly important because the clinical presentation can overlap with other serious respiratory diseases. Virus isolation from tracheal swabs, tracheal tissue, or conjunctival swabs of acutely affected birds provides definitive diagnosis. The virus grows in chicken embryos and produces characteristic pocks on the chorioallantoic membrane. Polymerase chain reaction testing has become the preferred diagnostic method in many laboratories, offering rapid and specific detection of viral DNA in clinical samples. PCR can also help differentiate between wild-type field virus and vaccine strains, which has important epidemiological implications. Histopathology of tracheal tissue reveals characteristic intranuclear inclusion bodies and syncytial cell formation in infected epithelial cells.

Differential diagnosis is critically important because several other conditions can cause severe respiratory signs in poultry, including notifiable diseases that require immediate regulatory notification. Newcastle disease, particularly the velogenic form, can produce respiratory distress, gasping, and tracheal hemorrhage similar to infectious laryngotracheitis. Highly pathogenic avian influenza can cause severe respiratory signs with high mortality. Infectious bronchitis virus infection may cause respiratory signs, though typically without the hemorrhagic tracheal component. Aspergillosis can cause respiratory distress but usually has a more chronic presentation and characteristic fungal plaques visible in the air sacs and airways. Fowl pox in the wet or diphtheritic form produces plaques in the oral cavity and upper respiratory tract that may be confused with ILT lesions.

Herd-level diagnostics and epidemiological investigation help determine the scope of an outbreak and guide control measures. Serological testing using enzyme-linked immunosorbent assay can detect antibodies to ILTV and help determine the infection status of flocks. However, serology cannot distinguish between antibodies from natural infection versus vaccination, limiting its utility in vaccinated populations. Necropsy examination of multiple affected birds provides a comprehensive picture of the pathology and helps rule out concurrent conditions. Sampling and testing of in-contact birds and birds in nearby houses or farms helps assess the extent of spread. Investigation of recent bird movements, equipment sharing, and personnel traffic helps identify likely sources of introduction and routes of transmission.

Emergency and immediate treatment for infectious laryngotracheitis focuses on reducing mortality and minimizing transmission within the affected flock. Because there is no antiviral drug effective against the virus, treatment is purely supportive and symptomatic. Upon recognition of an outbreak, affected birds should be isolated from those not yet showing clinical signs, though in practice the virus has often already spread throughout the house by the time clinical signs become apparent. Reducing stressors by avoiding unnecessary disturbance, maintaining optimal environmental temperature, and ensuring easy access to water helps support affected birds. Some producers practice emergency vaccination with live vaccine to induce rapid immunity in birds not yet infected, though this approach carries risks and requires careful consideration.

Medical management of infectious laryngotracheitis centers on controlling secondary bacterial infections and supporting birds through the acute phase of illness. Broad-spectrum antibiotics administered in drinking water can help prevent or treat secondary bacterial infections that commonly complicate viral respiratory disease. Commonly used antibiotics include tetracyclines, erythromycin, and sulfonamides, though selection should ideally be based on culture and sensitivity testing. It is essential to observe appropriate withdrawal times for any medications used in food-producing poultry. Vitamin supplementation, particularly vitamins A, D, and E, may support immune function and respiratory epithelial repair. Electrolyte solutions help combat dehydration in birds that are drinking poorly.

Surgical intervention has no role in the routine management of infectious laryngotracheitis. However, in cases of acute airway obstruction where valuable individual birds are at imminent risk of suffocation, emergency relief may occasionally be attempted. Gentle suctioning or swabbing of the trachea to remove obstructing exudate has been performed in some situations, though this requires expertise and appropriate restraint to avoid causing additional trauma or stress. Such interventions are rarely practical in commercial settings and are reserved for exceptional circumstances involving valuable breeding stock or exhibition birds.

Supportive care is the mainstay of treatment and can significantly influence outcomes. Maintaining optimal environmental conditions, including appropriate temperature, good ventilation, and low ammonia levels, reduces stress on the respiratory system. Reducing stocking density, if possible, decreases transmission pressure and gives affected birds more space and less competition for resources. Providing easily accessible water, potentially with added electrolytes, is essential because dehydration develops rapidly in birds with respiratory distress that are eating and drinking poorly. Reducing lighting intensity may calm birds and reduce activity levels, which can help those with respiratory compromise. In severe cases, humidity management may help, as extremely dry air can further irritate damaged respiratory epithelium.

Herd treatment protocols must balance the needs of individual birds with practical and economic realities. Mass medication with antibiotics to prevent secondary infections is commonly practiced, with the entire flock treated through drinking water. Environmental management, including improved ventilation, reduced dust, and optimal temperature, is applied house-wide. Some producers implement emergency vaccination during outbreaks, applying live vaccine via drinking water or eye drop to birds that have not yet shown clinical signs. This approach, called field vaccination or outbreak vaccination, aims to induce immunity before the virus reaches all birds, but it risks introducing vaccine virus to the flock and has produced variable results.

Treatment decisions in infectious laryngotracheitis must consider economic factors and the individual circumstances of each operation. The cost of treatment inputs must be weighed against potential recovery of bird value and production. Mortality is unavoidable in severe outbreaks, and producers must make difficult decisions about salvage slaughter of recovered birds versus retaining them for continued production. In some cases, depopulation of severely affected flocks followed by thorough cleaning and disinfection may be more economically sound than attempting to manage through the outbreak. These decisions should be made in consultation with a veterinarian who can assess the specific situation. Regardless of decisions about the current flock, attention must turn to preventing introduction to other flocks on the premises and preventing future outbreaks through vaccination and biosecurity improvements.

The recovery timeline for birds surviving infectious laryngotracheitis varies depending on the severity of infection and extent of tissue damage. Birds with mild infection may recover clinically within one to two weeks, while those severely affected may take three to four weeks or longer to return to normal. Resolution of respiratory signs typically begins seven to fourteen days after onset, with gradual improvement in breathing effort, decreased coughing, and clearing of tracheal exudate. Birds that survive the acute phase but have sustained significant damage to the tracheal epithelium may have prolonged recovery and may never fully return to normal respiratory function.

Post-treatment care and monitoring require attention to both individual bird recovery and flock-level management. Birds should be monitored for lingering respiratory signs, secondary infections, and general thrift. Feed and water consumption should be tracked as indicators of recovery. Any birds that fail to improve or that develop complications should be evaluated individually and may need to be culled for welfare reasons. Environmental management continues to be important during recovery, with good ventilation and minimal stress facilitating healing. Mortality records should be maintained to track the progression and resolution of the outbreak.

Prognosis for individual birds depends on the severity of their infection and the development of complications. Birds with mild disease generally recover fully and return to normal productivity. Those with severe tracheitis may survive but may have persistent respiratory abnormalities or reduced performance. Secondary bacterial infections, particularly airsacculitis, worsen the prognosis and may result in chronic unthriftiness or later mortality. Importantly, all birds that recover from infection, regardless of severity, become latent carriers of the virus. These carrier birds harbor the virus in their trigeminal ganglia for life and can shed virus intermittently, particularly during periods of stress. This carrier state has profound implications for flock management and biosecurity.

Return to production in laying flocks is typically delayed and may be incomplete. Egg production usually begins to recover two to four weeks after clinical recovery, depending on the severity of the outbreak and the extent of production loss during the acute phase. Full recovery of production may take several additional weeks, and production may never return to pre-outbreak levels in severely affected flocks. The quality of eggs may be affected during recovery, with increased shell abnormalities and reduced internal quality. In meat-type birds, weight gain resumes following recovery, but overall performance is typically reduced compared to unaffected flocks, with impacts on final weight, feed conversion, and uniformity. The economic recovery of affected flocks must be assessed on a case-by-case basis, considering production losses, treatment costs, and market implications.

Vaccination is the primary preventive tool for infectious laryngotracheitis in areas where the disease is endemic or poses significant risk. Both live attenuated and recombinant vectored vaccines are available. Live vaccines provide strong mucosal immunity and are administered by eye drop, drinking water, or spray, but they carry risks including potential spread to unvaccinated birds, reversion to virulence through passage, and causing mild vaccine reactions. Recombinant vaccines, typically using fowl pox virus or herpesvirus of turkey as vectors, are safer and cannot spread or revert but may provide less robust protection than live vaccines. Vaccination programs should be designed with veterinary input based on local disease pressure, flock type, and management system. In broiler production areas, only recombinant vaccines may be permitted due to concerns about live vaccine spread to nearby layer farms.

Biosecurity measures are essential for preventing introduction of infectious laryngotracheitis to naive flocks and for containing spread during outbreaks. Preventing introduction of infected birds is fundamental, requiring sourcing of replacement stock from known disease-free sources and implementing quarantine and testing protocols for any new additions. All-in, all-out management eliminates the mixing of age groups and the persistence of carrier birds from cycle to cycle. Physical barriers, including perimeter fencing, secure entry points, and restricted access to poultry houses, limit opportunities for virus introduction. Sanitation protocols for personnel, including dedicated footwear and clothing, handwashing, and shower-in procedures for higher-security facilities, reduce mechanical transmission risk.

Nutritional management supports immune function and helps birds resist infection. A complete and balanced diet meeting all nutritional requirements for the species and production stage provides the foundation for health. Adequate vitamin A is essential for maintaining the integrity of respiratory epithelium. Vitamin E and selenium support immune function. Avoiding feed contamination and mycotoxins prevents immunosuppression that could increase susceptibility. Fresh, clean water prevents the concentration of pathogens in drinking systems. Overall good nutrition helps birds mount effective immune responses to vaccination and recover more quickly if infection does occur.

Management practices that reduce stress and limit virus transmission are important components of prevention. Maintaining appropriate stocking density reduces transmission pressure and environmental contamination. Excellent ventilation dilutes airborne virus and maintains air quality. Minimizing disturbance and handling of birds reduces stress and the potential for virus shedding from carrier birds. Avoiding mixing of birds from different sources prevents exposure of naive birds to potential carriers. Scheduling management procedures to minimize stress during high-risk periods helps maintain flock health. Immediate isolation and investigation of any respiratory cases allows rapid response to potential outbreaks.

Quarantine and testing protocols provide additional protection for high-value flocks and disease-free areas. New birds entering a premises should be held in isolation facilities located away from production birds for at least three weeks. During quarantine, birds should be observed for clinical signs and may be tested serologically or by PCR for evidence of infection. Movement controls during outbreaks restrict traffic between affected and unaffected houses or farms. Testing of breeding flocks and documentation of disease-free status protect commercial and pedigree genetics. Surveillance programs that monitor for disease presence in a region help inform vaccination decisions and biosecurity postures.

Daily management and monitoring form the foundation of living with infectious laryngotracheitis risk in endemic areas. Trained personnel should conduct daily observations of all flocks, watching for early signs of respiratory disease including increased mortality, reduced feed consumption, decreased egg production, or any respiratory signs in individual birds. Documentation of daily mortality with investigation of causes helps identify disease emergence. Regular review of production parameters, including daily egg production in layers and growth rates in meat birds, provides sensitive indicators of flock health. Any deviations from expected performance should prompt further investigation before clinical disease becomes widespread.

Housing and environmental management significantly influence the risk of infectious laryngotracheitis outbreaks and their severity when they occur. Poultry houses should provide excellent ventilation to dilute airborne pathogens while maintaining appropriate temperature and humidity. Ammonia levels must be kept low, as ammonia damages respiratory epithelium and predisposes birds to infection. Dust control measures, including appropriate litter management and ventilation, reduce aerosol transmission. Clean water systems prevent concentration of pathogens and ensure adequate hydration. Environmental enrichment and low-stress management practices reduce stress that could trigger virus reactivation in carrier birds.

Herd health programs in endemic areas must incorporate infectious laryngotracheitis into their strategic planning. Vaccination programs should be developed with veterinary input, specifying vaccine types, timing, and administration routes appropriate for the production system and local disease pressure. Biosecurity protocols must be documented, implemented consistently, and regularly audited for compliance. Disease response plans should be in place before outbreaks occur, specifying actions to be taken when disease is suspected or confirmed. Regular veterinary reviews of flock health, production records, and management practices help identify opportunities for improvement and adjust strategies as needed.

Record keeping and monitoring provide essential data for managing infectious laryngotracheitis. Vaccination records should document products used, administration dates, and any reactions observed. Health records should capture disease occurrences, diagnostic test results, and treatments administered with withdrawal periods noted. Mortality records allow trend analysis and early detection of problems. Biosecurity logs track visitor access, vehicle movements, and bird introductions. Production records provide baseline data against which deviations can be detected. These records support epidemiological investigations when outbreaks occur and provide evidence of due diligence for trading partners and regulators.

Economic considerations drive many management decisions regarding infectious laryngotracheitis. The cost of prevention, including vaccination and biosecurity measures, must be weighed against the potential losses from disease outbreaks. In endemic areas, vaccination is almost always economically justified for susceptible flocks. Decisions about whether to vaccinate with live versus recombinant vaccines involve tradeoffs between protection level, cost, and risks of vaccine virus spread. Insurance products may be available to help manage financial risk from disease outbreaks. Marketing considerations, including customer requirements and disease-free certification programs, may influence management decisions. Overall farm business planning should account for the ongoing threat of infectious laryngotracheitis and allocate appropriate resources for prevention and response.

All breeds and genetic lines of chickens are susceptible to infectious laryngotracheitis, as no genetic resistance to this viral disease has been identified. The severity of disease may vary somewhat between individuals and lines, reflecting general immunocompetence and overall health status rather than specific resistance to ILTV. Commercial layer strains may show more dramatic production impacts simply because their high baseline production makes losses more measurable. Commercial broiler strains kept for meat production are less commonly affected severely because their short lifespan may not allow sufficient time for virus introduction and disease development. Heritage breeds and backyard flock birds may be at higher risk if housed in multi-age settings or if biosecurity is lax.

Production type influences risk through management practices associated with different systems. Layer operations face the greatest overall risk and impact due to the longer lifespan of hens, multi-age management on some farms, and the significant production losses that occur during outbreaks. Broiler breeder operations share similar risks due to the extended lifespan of breeder birds and their high economic value. Commercial broiler growout operations are at relatively lower risk when practicing all-in, all-out management with short production cycles, though outbreaks can still occur and cause significant losses. Backyard flocks and small-farm poultry face variable risk depending on management practices, contact with other poultry, and vaccination status.

Genetic selection for resistance to infectious laryngotracheitis is not currently practiced, as all chickens are susceptible and no resistance genes have been identified. Selection for general disease resistance traits and robust immune function may provide some nonspecific benefit. When selecting breeding stock or replacement birds, producers should prioritize health status and known freedom from infectious laryngotracheitis over other traits if the disease is a concern. Testing of source flocks using serology or PCR helps identify flocks that may harbor the virus. In carrier-positive flocks, all birds should be considered potential sources of virus regardless of their individual test results, as intermittent shedding makes individual testing unreliable for identifying carriers.

Several conditions commonly co-occur with infectious laryngotracheitis or share similar clinical presentations. Secondary bacterial infections are extremely common complications, with Escherichia coli being the most frequent secondary invader. E. coli infection can cause airsacculitis, perihepatitis, and septicemia, significantly increasing mortality and prolonging recovery. Mycoplasma gallisepticum infection often occurs alongside or predisposes to ILT, worsening the clinical picture. Infectious bronchitis virus may occur concurrently, causing additional respiratory compromise. Concurrent immunosuppressive conditions such as infectious bursal disease or chicken anemia virus infection can exacerbate the severity of ILT outbreaks.

Conditions with similar symptoms must be differentiated from infectious laryngotracheitis to ensure appropriate management and to rule out notifiable diseases. Newcastle disease, particularly velogenic strains, can produce severe respiratory signs, gasping, and tracheal hemorrhage similar to ILT. Highly pathogenic avian influenza causes respiratory distress and high mortality and must be ruled out in any severe respiratory outbreak. Fowl pox in the diphtheritic form produces plaques in the respiratory tract that may resemble ILT lesions. Aspergillosis causes chronic respiratory distress and may be confused with milder forms of ILT. Avian adenovirus infections can cause respiratory signs and tracheitis. Laboratory testing is essential for definitive differentiation between these conditions.

Complications and sequelae of infectious laryngotracheitis extend beyond the acute phase of disease. Chronic respiratory disease may persist in birds that sustained significant damage to the tracheal epithelium. Secondary bacterial infections can become established during the immunocompromised period and persist after viral clearance. The latent carrier state is the most significant long-term consequence, as recovered birds harbor virus for life and can serve as sources of infection for naive flockmates. Stress-induced reactivation of latent virus can trigger new outbreaks in flocks that have been clinically normal for extended periods. Permanent reduction in egg production may occur in layer flocks severely affected by the disease.