History

A 4-month-old female chicken with a 48-hour history of progressively worsening, unilateral ocular discharge and periocular swelling was submitted for necropsy. This hen was in a flock of 18 chickens that, at any given time, included 4 to 8 similarly affected chickens. The flock was treated for 1 month with oxytetracycline-medicated feed on the basis of the veterinarian's recommendations. The affected chickens' condition improved after treatment, but clinical signs never completely resolved. Within the 48-hour period prior to death of the hen, its left eye started to progressively swell. Three other hens in the flock reportedly had mild periocular erythema and mild ocular swelling.

Clinical and Gross Findings

At necropsy, the 1.1-kg (2.42-lb) hen was mildly autolyzed and thin (body condition score of 1/5) with severe atrophy of the appendicular and pectoral muscles. A fluctuant, approximately 1-cm-diameter mass expanded the left ventral periorbital area. Marked purulent discharge exuded from this infraorbital sinus after sectioning (Figure 1). The appearance of the right eye was unremarkable. The ventral quadrant of the left lung was green and friable, and the cranial air sacs were thickened and cloudy.

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Photograph of the head of a 4-month-old chicken with a 48-hour history of ocular discharge and periocular swelling of the left eye. A fluctuant, approximately 1-cm-diameter, left-sided infraorbital mass has been excised to reveal abundant, pale tan, purulent discharge.

Citation: Journal of the American Veterinary Medical Association 251, 9; 10.2460/javma.251.9.1021

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Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→

Histopathologic and Microbiological Findings

Samples from the eyelid, lungs, air sacs, small intestine, and various other tissues of the hen were fixed in neutral-buffered 10% formalin and routinely processed for microscopic evaluation. The conjunctival surface of the affected eyelid was ulcerated and covered by a serocellular crust (Figure 2). The conjunctival surfaces were largely effaced and infiltrated by heterophils, epithelioid macrophages, lymphocytes, plasma cells, and fibroblasts. The conjunctiva was multifocally expanded by numerous aggregates of multinucleated giant cells surrounding heterophilic and necrotic debris with colonies of short bacilli (Figure 3). Lymphoid follicles were hyperplastic, and adjacent glands contained fibrinonecrotic debris. Vascular endothelium was reactive with perivascular heterophilic infiltration.

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Photomicrograph of a section of the left eyelid from the chicken in Figure 1. Much of the conjunctival surface is denuded and replaced by a serocellular crust (asterisk). The inflammation is composed of degenerate heterophils, macrophages, and multinucleated giant cells. The propria (†) is expanded by fewer mixed inflammatory cells, and the feathered skin surface (‡) is relatively unaffected. H&E stain; bar = 500 μm.

Citation: Journal of the American Veterinary Medical Association 251, 9; 10.2460/javma.251.9.1021

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Photomicrograph of the debris overlying the left eyelid from the chicken in Figure 1. Extracellular (asterisk) and intracellular (†) coccobacilli are mixed in an exudate of degenerate heterophils and macrophages. H&E stain; bar = 20 μm.

Citation: Journal of the American Veterinary Medical Association 251, 9; 10.2460/javma.251.9.1021

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Other histopathologic findings included feed material and mixed populations of bacteria in the terminal bronchioles of the left lung and overlying air sacs with no associated inflammation. Within the small intestine, there were numerous nematode eggs and adult worms. The eggs were birefringent and embryonated with bipolar plugs. The adult worms were partially embedded in the submucosa and each had a smooth cuticle, coelomyarian to polymyarian musculature, a stichosome surrounding the esophagus, hypodermal bacillary bands, and a reproductive tract. Mild to moderate numbers of lymphocytes infiltrated the submucosa adjacent to the adult worms.

Aerobic bacterial and mycoplasmal cultures of a swab specimen of the infraorbital mass yielded moderate to heavy numbers of an aerobic bacterial species; the organisms were identified as Pasteurella multocida subsp multocida on the basis of plate growth morphology, biochemical characteristics as measured by use of a microbial identification micromethod system,^a and results of Gram staining. Mycoplasmal culture (including enrichment) failed to detect any organisms.

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: severe, chronic, focally extensive, granulomatous, and heterophilic infraorbital sinusitis and conjunctivitis with intralesional bacilli consistent with P multocida.

Case summary: P multocida sinusitis in a chicken.

Comments

Avian pasteurellosis, also known as fowl cholera, is a contagious disease of chickens and many other species of birds including turkeys, geese, ducks, quail, canaries, and several wild and zoo birds. This disease is of major economic importance worldwide.¹ As in the chicken of the present report, pasteurellosis has been recognized as a problem in backyard poultry in the developed world,² village chickens in the developing world,³ and free-range layers.^4,5 This disease is caused by P multocida. Pasteurella multocida is a bipolar, gram-negative rod bacterium that varies greatly in its antigenic makeup, which prevents production of highly effective bacterins. In poultry, pasteurellosis is usually an acute septicemic disease that is associated with high morbidity and mortality rates; however, a chronic localized form can also develop. This chronic form is the most common form in chickens and may develop following an episode of the acute form or develop independently.⁶

In poultry with the acute form of pasteurellosis, clinical signs are usually only evident shortly before death. Typical clinical signs of the acute form of the disease are fever, ruffled feathers, mucous discharge from the mouth, diarrhea, and tachypnea.¹ Lesions may be absent when the disease is peracute.⁶ The chronic form of the disease may appear as localized infection of joints and sinuses. Typical clinical signs can include torticollis and rales; wattles, eyes, sinuses, joints, or footpads may become swollen because of the accumulation of a typically caseous to purulent (as in the chicken of the present report) exudate.¹ Although history, clinical signs, and lesions may be strongly suggestive of fowl cholera, isolation and identification of P multocida should be performed if diagnostic confirmation is necessary.⁶

The differential diagnoses for chronic infraorbital sinusitis and conjunctivitis in chickens include primarily other bacterial diseases such as infectious coryza (infection with Avibacterium paragallinarum) and mycoplasmosis (infection with Mycoplasma gallisepticum). Results of laboratory cultures are required to differentiate pasteurellosis, infectious coryza, and mycoplasmosis.¹

After birds have recovered from overt clinical signs of infection, they can remain infected throughout their lives and become a reservoir of P multocida.⁷ Similarly, wild birds, including pigeons and sparrows, may carry P multocida and spread the organisms among poultry flocks.^6,8 Swine, raccoons, and cats are also known carriers of P multocida strains that are pathogenic to poultry.^6,9 The organisms can also be readily transmitted on fomites such as crates, feed bags, shoes, and equipment. Transovarial transmission of P multocida does not occur in birds.⁶ Given the ubiquitous nature of this agent, it was difficult to determine how the chicken of the present report acquired this infection.

To control pasteurellosis in poultry flocks, young birds without clinical signs of fowl cholera must be obtained from isolated flocks that lack a history of fowl cholera and should be raised on disease-free premises away from possible carriers. In commercial settings, killed bacterins or live bacterium vaccines may also be used; live bacterium vaccines provide better immunity, although they have an increased risk of pathological sequelae.⁶

For the treatment of fowl cholera in affected birds, administration of various sulfa drugs and antimicrobials (including tetracyclines [eg, oxytetracycline, which was administered to the chicken of the present report]) can lower the mortality rate; however, deaths may resume once the treatment is stopped. Pasteurella multocida is killed easily by many disinfectants along with sunlight, heat, and drying. However, the organism can persist for months in decaying carcasses and moist soil making appropriate management and biosecurity practices of vital importance. Infection is more probable when birds are stressed by factors such as poor sanitation, parasitism, malnutrition, and concurrent diseases.⁶ Gastrointestinal parasites and a poor body condition (malnutrition) were identified in the bird of the present report, suggesting a potential contributory role in disease progression. Sanitation of the premises was not evaluated, and concurrent disease in the weeks prior to death of this bird cannot be ruled out as a contributing factor.

The changes identified in the left lung were likely due to agonal aspiration. The nematodes present in the small intestine were morphologically consistent with Capillaria sp, which can be associated with general unthriftiness, decreased egg production, and retarded growth. In low numbers, these nematodes have minimal effect, but in the chicken of the present report, the stress of intestinal parasitism on the immune system may have compounded the impact of the respiratory tract disease.