Case Analysis: Prevention and Control of Infectious Croup in Chickens

Release Date:

2021-12-24

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Infectious coryza (IC) is an acute respiratory disease of chickens caused by Haemophilus paragallinarum. The most significant losses due to infectious coryza are poor growth in pullets and a marked decline in egg production among laying hens, ranging from 10% to 40%. When combined with other diseases—such as mycoplasmosis, fowl pox, infectious laryngotracheitis, or avian influenza subtype H9—the condition becomes more severe, prolongs the course of illness, and increases mortality. In recent years, cases of infectious coryza have been reported nationwide, resulting in substantial economic losses for poultry farms. Here we present a case report from March this year, detailing diagnosis and treatment, analyzing the causes of the outbreak, and summarizing preventive and control measures for reference. **Incidence** At the end of March 2021, at an egg-laying farm in Xinyang, Henan Province, with a flock size of 30,000 birds aged approximately 180 days, an outbreak occurred. Feed intake decreased, and the egg production rate dropped from 96% to 80%. Affected chickens exhibited unilateral or bilateral facial swelling, edema around the eye sockets and infraorbital sinuses, and produced a snorting sound. They appeared depressed and passed yellow-green feces. Within one week of onset, 40 birds died. On the second day of illness, a preliminary diagnosis of infectious coryza was made, and a corresponding treatment protocol was initiated. Mortality ceased after five days, with gradual recovery; by day ten, egg production had returned to normal levels. **Post-Mortem Findings** Marked swelling was observed on one or both sides of the nasal wings and around the eye sockets. Dissection revealed milky-white purulent material filling the nasal cavities, along with erythematous inflammation of the nasal sinuses, infraorbital sinuses, and surrounding tissues. The upper trachea showed redness, with mucus present inside. Other organs were largely unaffected. **Laboratory Diagnosis** Two head samples were collected from affected chickens and sent to the Luoyang Zhongke Gene Testing and Diagnostic Center. PCR testing confirmed the presence of Haemophilus paragallinarum nucleic acid (Figure 1 and Figure 2), while serological analysis identified the pathogen as type B infectious coryza. **Zhongke Gene Infectious Coryza Test Report** PCR results for HPG **Diagnostic Conclusion** Based on clinical signs, post-mortem findings, and laboratory test results, the diagnosis was established as infectious coryza caused by Haemophilus paragallinarum. **Treatment Protocol and Outcomes** 1. Administer an injectable vaccine against infectious coryza together with ceftiofur injection, delivering 0.6 mL intramuscularly into the chest of each bird. Concurrently, give Shuanghuanglian oral solution orally. 2. Conduct daily aerosol disinfection of the entire flock for two weeks, alternating between different disinfectants every three to four days. 3. Supplement with multivitamins. 4. Strengthen environmental management within the chicken house, ensuring fresh air circulation and preventing direct exposure to cold drafts. 5. After five days of treatment, mortality ceased, no new cases emerged, and egg production normalized within ten days. **Analysis of Etiology** 1. Infectious coryza commonly occurs during autumn–winter transitions and winter–spring periods when rapid temperature fluctuations and large diurnal temperature differences, coupled with inadequate ventilation management, predispose flocks to chilling and subsequent disease outbreaks. 2. Chickens of all ages are susceptible, though young birds typically experience milder symptoms. Adult birds, especially high-producing layers, tend to have shorter incubation periods, more severe clinical manifestations, and prolonged courses of illness. 3. In this particular outbreak, the flock was at peak egg production. Fluctuating temperatures in March—high temperatures preceding the onset followed by excessive ventilation—resulted in chilling, ultimately triggering the disease. **Prevention and Control Measures** 1. Since recovered birds serve as major sources of infection, purchasing breeding roosters and pullets from unknown origins should be avoided. 2. Implement a "all-in, all-out" rearing system. Prior to introducing new flocks, thoroughly clean and disinfect housing facilities and equipment, allowing the premises to remain empty for two to three weeks. 3. Enhance husbandry practices, paying special attention to ventilation management during transitional seasons to prevent chilling of the flock. 4. Conduct vaccinations using a coryza vaccine capable of providing simultaneous protection against serotypes A, B, and C. 5. Develop a vaccination schedule: administering two doses spaced four weeks apart before the expected natural outbreak can yield optimal immunity. For laying hens, vaccinating twice at four-week intervals before 20 weeks of age produces better immune responses than a single dose.

Infectious coryza (IC) is an acute respiratory disease of chickens caused by Avibacterium paragallinarum. The most significant economic losses associated with infectious coryza include poor growth in growing birds and a marked decline in egg production in layers, ranging from 10% to 40%. When co‑infected with other pathogens—such as Mycoplasma, fowl pox, infectious laryngotracheitis, or the H9 subtype of avian influenza—the clinical course is exacerbated, the duration of illness is prolonged, and mortality increases. In recent years, cases of infectious coryza have been reported across the country, resulting in substantial economic losses for poultry farms. Here, we present a case report from March of this year, detailing the diagnosis and treatment of infectious coryza, analyzing the etiological factors, and summarizing preventive and control measures for reference.

Incidence situation

At the end of March 2021, at a layer farm in Xinyang, Henan Province, with a flock size of 30,000 hens aged 180 days, an outbreak occurred characterized by reduced feed intake and a decline in egg production from 96% to 80%. Affected birds exhibited unilateral or bilateral facial swelling, edema around the eye sockets and in the infraorbital sinuses, and produced a “gurgling” sound; they were depressed and passed yellow-green droppings. Within one week of onset, 40 birds died. On the second day of illness, a preliminary diagnosis of infectious coryza was made, and a treatment protocol for coryza was implemented. Mortality ceased after five days, with gradual recovery; by day ten, egg production had returned to normal.

Autopsy findings

Marked swelling is observed on one or both sides of the nasal alae and around the orbit. Upon dissection, the nasal cavity is found to be filled with a milky-white purulent exudate; the paranasal sinuses, infraorbital sinuses, and surrounding tissues are erythematous and edematous; the upper trachea exhibits hyperemia, with mucus present within the lumen; the remaining organs are essentially normal.

Laboratory Diagnostic Findings

Two samples were collected from the heads of diseased chickens and tested by the Luoyang Zhongke Gene Testing and Diagnostic Center. The results showed positive PCR for Haemophilus paragallinarum (Figures 1 and 2), and serological identification confirmed it as type B rhinotracheitis.

Zhongke Gene Rhinitis Test Report

HPG’s PCR test results

Diagnosis result

Based on clinical signs, postmortem findings, and laboratory diagnostic results, the diagnosis was confirmed as infectious coryza in chickens caused by Haemophilus paragallinarum (Haemophilus paragallinarum).

Treatment Plan and Outcomes

1. Administer an inactivated nasal vaccine formulated with an adjuvant, combined with an injection of ceftiofur sodium; inject 0.6 mL intramuscularly into the chest of each chicken. Concurrently, administer Shuanghuanglian oral liquid by mouth.

2. Conduct daily mist disinfection of the flock for two consecutive weeks, rotating between different disinfectants every 3–4 days.

3. Supplement with multiple vitamins.

4. Strengthen environmental control in the chicken house, ensure fresh air circulation, and avoid direct drafts blowing on the chickens.

5. After 5 days of treatment, mortality ceased and no new affected chickens were observed; by day 10, the egg production rate had returned to normal.

Analysis of the Causes of Onset

1. Infectious coryza in chickens commonly occurs during the transition from autumn to winter and from winter to spring, when temperatures fluctuate rapidly and diurnal temperature variations are significant. Inadequate ventilation management in poultry houses can easily expose flocks to cold stress, leading to disease onset.

2. Chickens of all ages are susceptible, but the disease is generally less severe in young birds. In adult chickens, particularly high‑producing layers, the incubation period is short, the clinical signs are severe, and the course of the illness tends to be prolonged.

3. The affected flock was at the peak of its laying period. In March, temperatures fluctuated sharply; prior to the onset of illness, temperatures were relatively high, ventilation was excessive, and the birds were exposed to cold, which contributed to the outbreak.

Prevention and control

1. Since recovered chickens are the primary source of infection, it is not recommended to purchase breeding roosters or first‑laying hens from unknown sources.

2. The poultry farm employs an all-in, all-out rearing system. Prior to introducing a new flock, the poultry house and equipment must be thoroughly cleaned and disinfected, after which the house should remain empty for 2–3 weeks.

3. Strengthen management of rearing practices; during the transitional periods between autumn and winter, and between winter and spring, pay particular attention to ventilation to prevent the flock from becoming chilled.

4. Immunization: Select a nasal vaccine that provides simultaneous protection against serotypes A, B, and C for vaccination.

5. Immunization protocol: Vaccination administered 2–3 weeks prior to the anticipated natural outbreak of this disease yields optimal immune protection. For laying hens, a two-dose vaccination schedule with a 4‑week interval before 20 weeks of age provides superior immunity compared to a single dose.

Diarrhea in the farrowing house—Huizhong’s “live + inactivated” approach to prevention and control.

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